/*
 * Copyright (c) 2005, 2022, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.jmx.mbeanserver;

import static com.sun.jmx.mbeanserver.Util.*;
import static com.sun.jmx.mbeanserver.MXBeanIntrospector.typeName;

import static javax.management.openmbean.SimpleType.*;

import com.sun.jmx.remote.util.EnvHelp;

import java.io.InvalidObjectException;
import java.lang.annotation.ElementType;
import java.lang.ref.WeakReference;
import java.lang.reflect.Array;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Proxy;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.BitSet;
import java.util.Collection;
import java.util.Comparator;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.SortedMap;
import java.util.SortedSet;
import java.util.TreeSet;
import java.util.WeakHashMap;

import javax.management.JMX;
import javax.management.ObjectName;
import javax.management.ConstructorParameters;
import javax.management.openmbean.ArrayType;
import javax.management.openmbean.CompositeData;
import javax.management.openmbean.CompositeDataInvocationHandler;
import javax.management.openmbean.CompositeDataSupport;
import javax.management.openmbean.CompositeDataView;
import javax.management.openmbean.CompositeType;
import javax.management.openmbean.OpenDataException;
import javax.management.openmbean.OpenType;
import javax.management.openmbean.SimpleType;
import javax.management.openmbean.TabularData;
import javax.management.openmbean.TabularDataSupport;
import javax.management.openmbean.TabularType;
import sun.reflect.misc.MethodUtil;
import sun.reflect.misc.ReflectUtil;

/**
 *   <p>A converter between Java types and the limited set of classes
 *   defined by Open MBeans.
 *
 *   <p>A Java type is an instance of java.lang.reflect.Type. For our
 *   purposes, it is either a Class, such as String.class or int.class;
 *   or a ParameterizedType, such as {@code List<String>} or
 *   {@code Map<Integer, String[]>}.
 *   On J2SE 1.4 and earlier, it can only be a Class.
 *
 *   <p>Each Type is associated with an DefaultMXBeanMappingFactory. The
 *   DefaultMXBeanMappingFactory defines an
 *   OpenType corresponding to the Type, plus a
 *   Java class corresponding to the OpenType. For example:
 *
 *   <pre>{@code
 *   Type                     Open class     OpenType
 *   ----                     ----------     --------
 *   Integer                  Integer        SimpleType.INTEGER
 *   int                      int            SimpleType.INTEGER
 *   Integer[]                Integer[]      ArrayType(1, SimpleType.INTEGER)
 *   int[]                    Integer[]      ArrayType(SimpleType.INTEGER, true)
 *   String[][]               String[][]     ArrayType(2, SimpleType.STRING)
 *   List<String>             String[]       ArrayType(1, SimpleType.STRING)
 *   ThreadState (an Enum)    String         SimpleType.STRING
 *   Map<Integer, String[]>   TabularData    TabularType(
 *                                           CompositeType(
 *                                             {"key", SimpleType.INTEGER},
 *                                             {"value",
 *                                               ArrayType(1,
 *                                                SimpleType.STRING)}),
 *                                           indexNames={"key"})
 *   }</pre>
 *
 *   <p>Apart from simple types, arrays, and collections, Java types are
 *   converted through introspection into CompositeType.  The Java type
 *   must have at least one getter (method such as "int getSize()" or
 *   "boolean isBig()"), and we must be able to deduce how to
 *   reconstruct an instance of the Java class from the values of the
 *   getters using one of various heuristics.
 *
 *  @since 1.6
 */
public class DefaultMXBeanMappingFactory extends MXBeanMappingFactory {
    abstract static class NonNullMXBeanMapping extends MXBeanMapping {
        NonNullMXBeanMapping(Type javaType, OpenType<?> openType) {
            super(javaType, openType);
        }

        @Override
        public final Object fromOpenValue(Object openValue)
        throws InvalidObjectException {
            if (openValue == null)
                return null;
            else
                return fromNonNullOpenValue(openValue);
        }

        @Override
        public final Object toOpenValue(Object javaValue) throws OpenDataException {
            if (javaValue == null)
                return null;
            else
                return toNonNullOpenValue(javaValue);
        }

        abstract Object fromNonNullOpenValue(Object openValue)
        throws InvalidObjectException;

        abstract Object toNonNullOpenValue(Object javaValue)
        throws OpenDataException;

        /**
         * True if and only if this MXBeanMapping's toOpenValue and
         * fromOpenValue methods are the identity function.
         */
        boolean isIdentity() {
            return false;
        }
    }

    static boolean isIdentity(MXBeanMapping mapping) {
        return (mapping instanceof NonNullMXBeanMapping &&
                ((NonNullMXBeanMapping) mapping).isIdentity());
    }

    private static final class Mappings
        extends WeakHashMap<Type, WeakReference<MXBeanMapping>> {}

    private static final Mappings mappings = new Mappings();

    /** Following List simply serves to keep a reference to predefined
        MXBeanMappings so they don't get garbage collected. */
    private static final List<MXBeanMapping> permanentMappings = newList();

    private static synchronized MXBeanMapping getMapping(Type type) {
        WeakReference<MXBeanMapping> wr = mappings.get(type);
        return (wr == null) ? null : wr.get();
    }

    private static synchronized void putMapping(Type type, MXBeanMapping mapping) {
        WeakReference<MXBeanMapping> wr = new WeakReference<>(mapping);
        mappings.put(type, wr);
    }

    private static synchronized void putPermanentMapping(
            Type type, MXBeanMapping mapping) {
        putMapping(type, mapping);
        permanentMappings.add(mapping);
    }

    static {
        /* Set up the mappings for Java types that map to SimpleType.  */

        final OpenType<?>[] simpleTypes = {
            BIGDECIMAL, BIGINTEGER, BOOLEAN, BYTE, CHARACTER, DATE,
            DOUBLE, FLOAT, INTEGER, LONG, OBJECTNAME, SHORT, STRING,
            VOID,
        };

        for (int i = 0; i < simpleTypes.length; i++) {
            final OpenType<?> t = simpleTypes[i];
            Class<?> c;
            try {
                c = Class.forName(t.getClassName(), false,
                                  ObjectName.class.getClassLoader());
            } catch (ClassNotFoundException e) {
                // the classes that these predefined types declare must exist!
                throw new Error(e);
            }
            final MXBeanMapping mapping = new IdentityMapping(c, t);
            putPermanentMapping(c, mapping);

            if (c.getName().startsWith("java.lang.")) {
                try {
                    final Field typeField = c.getField("TYPE");
                    final Class<?> primitiveType = (Class<?>) typeField.get(null);
                    final MXBeanMapping primitiveMapping =
                        new IdentityMapping(primitiveType, t);
                    putPermanentMapping(primitiveType, primitiveMapping);
                    if (primitiveType != void.class) {
                        final Class<?> primitiveArrayType =
                            Array.newInstance(primitiveType, 0).getClass();
                        final OpenType<?> primitiveArrayOpenType =
                            ArrayType.getPrimitiveArrayType(primitiveArrayType);
                        final MXBeanMapping primitiveArrayMapping =
                            new IdentityMapping(primitiveArrayType,
                                                primitiveArrayOpenType);
                        putPermanentMapping(primitiveArrayType,
                                            primitiveArrayMapping);
                    }
                } catch (NoSuchFieldException e) {
                    // OK: must not be a primitive wrapper
                } catch (IllegalAccessException e) {
                    // Should not reach here
                    assert(false);
                }
            }
        }
    }

    /** Get the converter for the given Java type, creating it if necessary. */
    @Override
    public synchronized MXBeanMapping mappingForType(Type objType,
                                                     MXBeanMappingFactory factory)
            throws OpenDataException {
        if (inProgress.containsKey(objType)) {
            throw new OpenDataException(
                    "Recursive data structure, including " + typeName(objType));
        }

        MXBeanMapping mapping;

        mapping = getMapping(objType);
        if (mapping != null)
            return mapping;

        inProgress.put(objType, objType);
        try {
            mapping = makeMapping(objType, factory);
        } catch (OpenDataException e) {
            throw openDataException("Cannot convert type: " + typeName(objType), e);
        } finally {
            inProgress.remove(objType);
        }

        putMapping(objType, mapping);
        return mapping;
    }

    private MXBeanMapping makeMapping(Type objType, MXBeanMappingFactory factory)
    throws OpenDataException {

        /* It's not yet worth formalizing these tests by having for example
           an array of factory classes, each of which says whether it
           recognizes the Type (Chain of Responsibility pattern).  */
        if (objType instanceof GenericArrayType) {
            Type componentType =
                ((GenericArrayType) objType).getGenericComponentType();
            return makeArrayOrCollectionMapping(objType, componentType, factory);
        } else if (objType instanceof Class<?>) {
            Class<?> objClass = (Class<?>) objType;
            if (objClass.isEnum()) {
                // Huge hack to avoid compiler warnings here.  The ElementType
                // parameter is ignored but allows us to obtain a type variable
                // T that matches <T extends Enum<T>>.
                return makeEnumMapping((Class<?>) objClass, ElementType.class);
            } else if (objClass.isArray()) {
                Type componentType = objClass.getComponentType();
                return makeArrayOrCollectionMapping(objClass, componentType,
                        factory);
            } else if (JMX.isMXBeanInterface(objClass)) {
                return makeMXBeanRefMapping(objClass);
            } else {
                return makeCompositeMapping(objClass, factory);
            }
        } else if (objType instanceof ParameterizedType) {
            return makeParameterizedTypeMapping((ParameterizedType) objType,
                                                factory);
        } else
            throw new OpenDataException("Cannot map type: " + objType);
    }

    private static <T extends Enum<T>> MXBeanMapping
            makeEnumMapping(Class<?> enumClass, Class<T> fake) {
        ReflectUtil.checkPackageAccess(enumClass);
        return new EnumMapping<>(Util.<Class<T>>cast(enumClass));
    }

    /* Make the converter for an array type, or a collection such as
     * List<String> or Set<Integer>.  We never see one-dimensional
     * primitive arrays (e.g. int[]) here because they use the identity
     * converter and are registered as such in the static initializer.
     */
    private MXBeanMapping
        makeArrayOrCollectionMapping(Type collectionType, Type elementType,
                                     MXBeanMappingFactory factory)
            throws OpenDataException {

        final MXBeanMapping elementMapping = factory.mappingForType(elementType, factory);
        final OpenType<?> elementOpenType = elementMapping.getOpenType();
        final ArrayType<?> openType = ArrayType.getArrayType(elementOpenType);
        final Class<?> elementOpenClass = elementMapping.getOpenClass();

        final Class<?> openArrayClass;
        final String openArrayClassName;
        if (elementOpenClass.isArray())
            openArrayClassName = "[" + elementOpenClass.getName();
        else
            openArrayClassName = "[L" + elementOpenClass.getName() + ";";
        try {
            openArrayClass = Class.forName(openArrayClassName);
        } catch (ClassNotFoundException e) {
            throw openDataException("Cannot obtain array class", e);
        }

        if (collectionType instanceof ParameterizedType) {
            return new CollectionMapping(collectionType,
                                         openType, openArrayClass,
                                         elementMapping);
        } else {
            if (isIdentity(elementMapping)) {
                return new IdentityMapping(collectionType,
                                           openType);
            } else {
                return new ArrayMapping(collectionType,
                                          openType,
                                          openArrayClass,
                                          elementMapping);
            }
        }
    }

    private static final String[] keyArray = {"key"};
    private static final String[] keyValueArray = {"key", "value"};

    private MXBeanMapping
        makeTabularMapping(Type objType, boolean sortedMap,
                           Type keyType, Type valueType,
                           MXBeanMappingFactory factory)
            throws OpenDataException {

        final String objTypeName = typeName(objType);
        final MXBeanMapping keyMapping = factory.mappingForType(keyType, factory);
        final MXBeanMapping valueMapping = factory.mappingForType(valueType, factory);
        final OpenType<?> keyOpenType = keyMapping.getOpenType();
        final OpenType<?> valueOpenType = valueMapping.getOpenType();
        final CompositeType rowType =
            new CompositeType(objTypeName,
                              objTypeName,
                              keyValueArray,
                              keyValueArray,
                              new OpenType<?>[] {keyOpenType, valueOpenType});
        final TabularType tabularType =
            new TabularType(objTypeName, objTypeName, rowType, keyArray);
        return new TabularMapping(objType, sortedMap, tabularType,
                                    keyMapping, valueMapping);
    }

    /* We know how to translate List<E>, Set<E>, SortedSet<E>,
       Map<K,V>, SortedMap<K,V>, and that's it.  We don't accept
       subtypes of those because we wouldn't know how to deserialize
       them.  We don't accept Queue<E> because it is unlikely people
       would use that as a parameter or return type in an MBean.  */
    private MXBeanMapping
            makeParameterizedTypeMapping(ParameterizedType objType,
                                         MXBeanMappingFactory factory)
            throws OpenDataException {

        final Type rawType = objType.getRawType();

        if (rawType instanceof Class<?>) {
            Class<?> c = (Class<?>) rawType;
            if (c == List.class || c == Set.class || c == SortedSet.class) {
                Type[] actuals = objType.getActualTypeArguments();
                assert(actuals.length == 1);
                if (c == SortedSet.class)
                    mustBeComparable(c, actuals[0]);
                return makeArrayOrCollectionMapping(objType, actuals[0], factory);
            } else {
                boolean sortedMap = (c == SortedMap.class);
                if (c == Map.class || sortedMap) {
                    Type[] actuals = objType.getActualTypeArguments();
                    assert(actuals.length == 2);
                    if (sortedMap)
                        mustBeComparable(c, actuals[0]);
                    return makeTabularMapping(objType, sortedMap,
                            actuals[0], actuals[1], factory);
                }
            }
        }
        throw new OpenDataException("Cannot convert type: " + objType);
    }

    private static MXBeanMapping makeMXBeanRefMapping(Type t)
            throws OpenDataException {
        return new MXBeanRefMapping(t);
    }

    private MXBeanMapping makeCompositeMapping(Class<?> c,
                                               MXBeanMappingFactory factory)
            throws OpenDataException {

        // For historical reasons GcInfo implements CompositeData but we
        // shouldn't count its CompositeData.getCompositeType() field as
        // an item in the computed CompositeType.
        final boolean gcInfoHack =
            (c.getName().equals("com.sun.management.GcInfo") &&
                c.getClassLoader() == null);

        ReflectUtil.checkPackageAccess(c);
        final List<Method> methods =
                MBeanAnalyzer.eliminateCovariantMethods(Arrays.asList(c.getMethods()));
        final SortedMap<String,Method> getterMap = newSortedMap();

        /* Select public methods that look like "T getX()" or "boolean
           isX()", where T is not void and X is not the empty
           string.  Exclude "Class getClass()" inherited from Object.  */
        for (Method method : methods) {
            final String propertyName = propertyName(method);

            if (propertyName == null)
                continue;
            if (gcInfoHack && propertyName.equals("CompositeType"))
                continue;

            // Don't decapitalize if this is a record component name.
            // We only decapitalize for getXxxx(), isXxxx(), and setXxxx()
            String name = c.isRecord() && method.getName().equals(propertyName)
                    ? propertyName : decapitalize(propertyName);
            Method old = getterMap.put(name, method);
            if (old != null) {
                final String msg =
                    "Class " + c.getName() + " has method name clash: " +
                    old.getName() + ", " + method.getName();
                throw new OpenDataException(msg);
            }
        }

        final int nitems = getterMap.size();

        if (nitems == 0) {
            throw new OpenDataException("Can't map " + c.getName() +
                                        " to an open data type");
        }

        final Method[] getters = new Method[nitems];
        final String[] itemNames = new String[nitems];
        final OpenType<?>[] openTypes = new OpenType<?>[nitems];
        int i = 0;
        for (Map.Entry<String,Method> entry : getterMap.entrySet()) {
            itemNames[i] = entry.getKey();
            final Method getter = entry.getValue();
            getters[i] = getter;
            final Type retType = getter.getGenericReturnType();
            openTypes[i] = factory.mappingForType(retType, factory).getOpenType();
            i++;
        }

        CompositeType compositeType =
            new CompositeType(c.getName(),
                              c.getName(),
                              itemNames, // field names
                              itemNames, // field descriptions
                              openTypes);

        return new CompositeMapping(c,
                                    compositeType,
                                    itemNames,
                                    getters,
                                    factory);
    }

    /* Converter for classes where the open data is identical to the
       original data.  This is true for any of the SimpleType types,
       and for an any-dimension array of those.  It is also true for
       primitive types as of JMX 1.3, since an int[]
       can be directly represented by an ArrayType, and an int needs no mapping
       because reflection takes care of it.  */
    private static final class IdentityMapping extends NonNullMXBeanMapping {
        IdentityMapping(Type targetType, OpenType<?> openType) {
            super(targetType, openType);
        }

        boolean isIdentity() {
            return true;
        }

        @Override
        Object fromNonNullOpenValue(Object openValue)
        throws InvalidObjectException {
            return openValue;
        }

        @Override
        Object toNonNullOpenValue(Object javaValue) throws OpenDataException {
            return javaValue;
        }
    }

    private static final class EnumMapping<T extends Enum<T>>
            extends NonNullMXBeanMapping {

        EnumMapping(Class<T> enumClass) {
            super(enumClass, SimpleType.STRING);
            this.enumClass = enumClass;
        }

        @Override
        final Object toNonNullOpenValue(Object value) {
            return ((Enum<?>) value).name();
        }

        @Override
        final T fromNonNullOpenValue(Object value)
                throws InvalidObjectException {
            try {
                return Enum.valueOf(enumClass, (String) value);
            } catch (Exception e) {
                throw invalidObjectException("Cannot convert to enum: " +
                                             value, e);
            }
        }

        private final Class<T> enumClass;
    }

    private static final class ArrayMapping extends NonNullMXBeanMapping {
        ArrayMapping(Type targetType,
                     ArrayType<?> openArrayType, Class<?> openArrayClass,
                     MXBeanMapping elementMapping) {
            super(targetType, openArrayType);
            this.elementMapping = elementMapping;
        }

        @Override
        final Object toNonNullOpenValue(Object value)
                throws OpenDataException {
            Object[] valueArray = (Object[]) value;
            final int len = valueArray.length;
            final Object[] openArray = (Object[])
                Array.newInstance(getOpenClass().getComponentType(), len);
            for (int i = 0; i < len; i++)
                openArray[i] = elementMapping.toOpenValue(valueArray[i]);
            return openArray;
        }

        @Override
        final Object fromNonNullOpenValue(Object openValue)
                throws InvalidObjectException {
            final Object[] openArray = (Object[]) openValue;
            final Type javaType = getJavaType();
            final Object[] valueArray;
            final Type componentType;
            if (javaType instanceof GenericArrayType) {
                componentType =
                    ((GenericArrayType) javaType).getGenericComponentType();
            } else if (javaType instanceof Class<?> &&
                       ((Class<?>) javaType).isArray()) {
                componentType = ((Class<?>) javaType).getComponentType();
            } else {
                throw new IllegalArgumentException("Not an array: " +
                                                   javaType);
            }
            valueArray = (Object[]) Array.newInstance((Class<?>) componentType,
                                                      openArray.length);
            for (int i = 0; i < openArray.length; i++)
                valueArray[i] = elementMapping.fromOpenValue(openArray[i]);
            return valueArray;
        }

        public void checkReconstructible() throws InvalidObjectException {
            elementMapping.checkReconstructible();
        }

        /**
         * DefaultMXBeanMappingFactory for the elements of this array.  If this is an
         *          array of arrays, the converter converts the second-level arrays,
         *          not the deepest elements.
         */
        private final MXBeanMapping elementMapping;
    }

    private static final class CollectionMapping extends NonNullMXBeanMapping {
        CollectionMapping(Type targetType,
                          ArrayType<?> openArrayType,
                          Class<?> openArrayClass,
                          MXBeanMapping elementMapping) {
            super(targetType, openArrayType);
            this.elementMapping = elementMapping;

            /* Determine the concrete class to be used when converting
               back to this Java type.  We convert all Lists to ArrayList
               and all Sets to TreeSet.  (TreeSet because it is a SortedSet,
               so works for both Set and SortedSet.)  */
            Type raw = ((ParameterizedType) targetType).getRawType();
            Class<?> c = (Class<?>) raw;
            final Class<?> collC;
            if (c == List.class)
                collC = ArrayList.class;
            else if (c == Set.class)
                collC = HashSet.class;
            else if (c == SortedSet.class)
                collC = TreeSet.class;
            else { // can't happen
                assert(false);
                collC = null;
            }
            collectionClass = Util.cast(collC);
        }

        @Override
        final Object toNonNullOpenValue(Object value)
                throws OpenDataException {
            final Collection<?> valueCollection = (Collection<?>) value;
            if (valueCollection instanceof SortedSet<?>) {
                Comparator<?> comparator =
                    ((SortedSet<?>) valueCollection).comparator();
                if (comparator != null) {
                    final String msg =
                        "Cannot convert SortedSet with non-null comparator: " +
                        comparator;
                    throw openDataException(msg, new IllegalArgumentException(msg));
                }
            }
            final Object[] openArray = (Object[])
                Array.newInstance(getOpenClass().getComponentType(),
                                  valueCollection.size());
            int i = 0;
            for (Object o : valueCollection)
                openArray[i++] = elementMapping.toOpenValue(o);
            return openArray;
        }

        @Override
        final Object fromNonNullOpenValue(Object openValue)
                throws InvalidObjectException {
            final Object[] openArray = (Object[]) openValue;
            final Collection<Object> valueCollection;
            try {
                @SuppressWarnings("deprecation")
                Collection<?> tmp = collectionClass.newInstance();
                valueCollection = cast(tmp);
            } catch (Exception e) {
                throw invalidObjectException("Cannot create collection", e);
            }
            for (Object o : openArray) {
                Object value = elementMapping.fromOpenValue(o);
                if (!valueCollection.add(value)) {
                    final String msg =
                        "Could not add " + o + " to " +
                        collectionClass.getName() +
                        " (duplicate set element?)";
                    throw new InvalidObjectException(msg);
                }
            }
            return valueCollection;
        }

        public void checkReconstructible() throws InvalidObjectException {
            elementMapping.checkReconstructible();
        }

        private final Class<? extends Collection<?>> collectionClass;
        private final MXBeanMapping elementMapping;
    }

    private static final class MXBeanRefMapping extends NonNullMXBeanMapping {
        MXBeanRefMapping(Type intf) {
            super(intf, SimpleType.OBJECTNAME);
        }

        @Override
        final Object toNonNullOpenValue(Object javaValue)
                throws OpenDataException {
            MXBeanLookup lookup = lookupNotNull(OpenDataException.class);
            ObjectName name = lookup.mxbeanToObjectName(javaValue);
            if (name == null)
                throw new OpenDataException("No name for object: " + javaValue);
            return name;
        }

        @Override
        final Object fromNonNullOpenValue(Object openValue)
                throws InvalidObjectException {
            MXBeanLookup lookup = lookupNotNull(InvalidObjectException.class);
            ObjectName name = (ObjectName) openValue;
            Object mxbean =
                lookup.objectNameToMXBean(name, (Class<?>) getJavaType());
            if (mxbean == null) {
                final String msg =
                    "No MXBean for name: " + name;
                throw new InvalidObjectException(msg);
            }
            return mxbean;
        }

        private <T extends Exception> MXBeanLookup
            lookupNotNull(Class<T> excClass)
                throws T {
            MXBeanLookup lookup = MXBeanLookup.getLookup();
            if (lookup == null) {
                final String msg =
                    "Cannot convert MXBean interface in this context";
                T exc;
                try {
                    Constructor<T> con = excClass.getConstructor(String.class);
                    exc = con.newInstance(msg);
                } catch (Exception e) {
                    throw new RuntimeException(e);
                }
                throw exc;
            }
            return lookup;
        }
    }

    private static final class TabularMapping extends NonNullMXBeanMapping {
        TabularMapping(Type targetType,
                       boolean sortedMap,
                       TabularType tabularType,
                       MXBeanMapping keyConverter,
                       MXBeanMapping valueConverter) {
            super(targetType, tabularType);
            this.sortedMap = sortedMap;
            this.keyMapping = keyConverter;
            this.valueMapping = valueConverter;
        }

        @Override
        final Object toNonNullOpenValue(Object value) throws OpenDataException {
            final Map<Object, Object> valueMap = cast(value);
            if (valueMap instanceof SortedMap<?,?>) {
                Comparator<?> comparator = ((SortedMap<?,?>) valueMap).comparator();
                if (comparator != null) {
                    final String msg =
                        "Cannot convert SortedMap with non-null comparator: " +
                        comparator;
                    throw openDataException(msg, new IllegalArgumentException(msg));
                }
            }
            final TabularType tabularType = (TabularType) getOpenType();
            final TabularData table = new TabularDataSupport(tabularType);
            final CompositeType rowType = tabularType.getRowType();
            for (Map.Entry<Object, Object> entry : valueMap.entrySet()) {
                final Object openKey = keyMapping.toOpenValue(entry.getKey());
                final Object openValue = valueMapping.toOpenValue(entry.getValue());
                final CompositeData row;
                row =
                    new CompositeDataSupport(rowType, keyValueArray,
                                             new Object[] {openKey,
                                                           openValue});
                table.put(row);
            }
            return table;
        }

        @Override
        final Object fromNonNullOpenValue(Object openValue)
                throws InvalidObjectException {
            final TabularData table = (TabularData) openValue;
            final Collection<CompositeData> rows = cast(table.values());
            final Map<Object, Object> valueMap =
                sortedMap ? newSortedMap() : newInsertionOrderMap();
            for (CompositeData row : rows) {
                final Object key =
                    keyMapping.fromOpenValue(row.get("key"));
                final Object value =
                    valueMapping.fromOpenValue(row.get("value"));
                if (valueMap.put(key, value) != null) {
                    final String msg =
                        "Duplicate entry in TabularData: key=" + key;
                    throw new InvalidObjectException(msg);
                }
            }
            return valueMap;
        }

        @Override
        public void checkReconstructible() throws InvalidObjectException {
            keyMapping.checkReconstructible();
            valueMapping.checkReconstructible();
        }

        private final boolean sortedMap;
        private final MXBeanMapping keyMapping;
        private final MXBeanMapping valueMapping;
    }

    private static final class CompositeMapping extends NonNullMXBeanMapping {
        CompositeMapping(Class<?> targetClass,
                         CompositeType compositeType,
                         String[] itemNames,
                         Method[] getters,
                         MXBeanMappingFactory factory) throws OpenDataException {
            super(targetClass, compositeType);

            assert(itemNames.length == getters.length);

            this.itemNames = itemNames;
            this.getters = getters;
            this.getterMappings = new MXBeanMapping[getters.length];
            for (int i = 0; i < getters.length; i++) {
                Type retType = getters[i].getGenericReturnType();
                getterMappings[i] = factory.mappingForType(retType, factory);
            }
        }

        @Override
        final Object toNonNullOpenValue(Object value)
                throws OpenDataException {
            CompositeType ct = (CompositeType) getOpenType();
            if (value instanceof CompositeDataView)
                return ((CompositeDataView) value).toCompositeData(ct);
            if (value == null)
                return null;

            Object[] values = new Object[getters.length];
            for (int i = 0; i < getters.length; i++) {
                try {
                    Object got = MethodUtil.invoke(getters[i], value, (Object[]) null);
                    values[i] = getterMappings[i].toOpenValue(got);
                } catch (Exception e) {
                    throw openDataException("Error calling getter for " +
                                            itemNames[i] + ": " + e, e);
                }
            }
            return new CompositeDataSupport(ct, itemNames, values);
        }

        /** Determine how to convert back from the CompositeData into
            the original Java type.  For a type that is not reconstructible,
            this method will fail every time, and will throw the right
            exception. */
        private synchronized void makeCompositeBuilder()
                throws InvalidObjectException {
            if (compositeBuilder != null)
                return;

            Class<?> targetClass = (Class<?>) getJavaType();
            /* In this 2D array, each subarray is a set of builders where
               there is no point in consulting the ones after the first if
               the first refuses.  */
            CompositeBuilder[][] builders = {
                {
                    new CompositeBuilderViaFrom(targetClass, itemNames),
                },
                {
                    new RecordCompositeBuilder(targetClass, itemNames),
                },
                {
                    new CompositeBuilderViaConstructor(targetClass, itemNames),
                },
                {
                    new CompositeBuilderCheckGetters(targetClass, itemNames,
                                                     getterMappings),
                    new CompositeBuilderViaSetters(targetClass, itemNames),
                    new CompositeBuilderViaProxy(targetClass, itemNames),
                },
            };
            CompositeBuilder foundBuilder = null;
            /* We try to make a meaningful exception message by
               concatenating each Builder's explanation of why it
               isn't applicable.  */
            final StringBuilder whyNots = new StringBuilder();
            Throwable possibleCause = null;
        find:
            for (CompositeBuilder[] relatedBuilders : builders) {
                for (int i = 0; i < relatedBuilders.length; i++) {
                    CompositeBuilder builder = relatedBuilders[i];
                    String whyNot = builder.applicable(getters);
                    if (whyNot == null) {
                        foundBuilder = builder;
                        break find;
                    }
                    Throwable cause = builder.possibleCause();
                    if (cause != null)
                        possibleCause = cause;
                    if (whyNot.length() > 0) {
                        if (whyNots.length() > 0)
                            whyNots.append("; ");
                        whyNots.append(whyNot);
                        if (i == 0)
                           break; // skip other builders in this group
                    }
                }
            }
            if (foundBuilder == null) {
                String msg =
                    "Do not know how to make a " + targetClass.getName() +
                    " from a CompositeData: " + whyNots;
                if (possibleCause != null)
                    msg += ". Remaining exceptions show a POSSIBLE cause.";
                throw invalidObjectException(msg, possibleCause);
            }
            compositeBuilder = foundBuilder;
        }

        @Override
        public void checkReconstructible() throws InvalidObjectException {
            makeCompositeBuilder();
        }

        @Override
        final Object fromNonNullOpenValue(Object value)
                throws InvalidObjectException {
            makeCompositeBuilder();
            return compositeBuilder.fromCompositeData((CompositeData) value,
                                                      itemNames,
                                                      getterMappings);
        }

        private final String[] itemNames;
        private final Method[] getters;
        private final MXBeanMapping[] getterMappings;
        private CompositeBuilder compositeBuilder;
    }

    /** Converts from a CompositeData to an instance of the targetClass.  */
    private abstract static class CompositeBuilder {
        CompositeBuilder(Class<?> targetClass, String[] itemNames) {
            this.targetClass = targetClass;
            this.itemNames = itemNames;
        }

        Class<?> getTargetClass() {
            return targetClass;
        }

        String[] getItemNames() {
            return itemNames;
        }

        /** If the subclass is appropriate for targetClass, then the
            method returns null.  If the subclass is not appropriate,
            then the method returns an explanation of why not.  If the
            subclass should be appropriate but there is a problem,
            then the method throws InvalidObjectException.  */
        abstract String applicable(Method[] getters)
                throws InvalidObjectException;

        /** If the subclass returns an explanation of why it is not applicable,
            it can additionally indicate an exception with details.  This is
            potentially confusing, because the real problem could be that one
            of the other subclasses is supposed to be applicable but isn't.
            But the advantage of less information loss probably outweighs the
            disadvantage of possible confusion.  */
        Throwable possibleCause() {
            return null;
        }

        abstract Object fromCompositeData(CompositeData cd,
                                          String[] itemNames,
                                          MXBeanMapping[] converters)
                throws InvalidObjectException;

        private final Class<?> targetClass;
        private final String[] itemNames;
    }

    /** Builder for when the target class has a method "public static
        from(CompositeData)".  */
    private static final class CompositeBuilderViaFrom
            extends CompositeBuilder {

        CompositeBuilderViaFrom(Class<?> targetClass, String[] itemNames) {
            super(targetClass, itemNames);
        }

        String applicable(Method[] getters) throws InvalidObjectException {
            // See if it has a method "T from(CompositeData)"
            // as is conventional for a CompositeDataView
            Class<?> targetClass = getTargetClass();
            try {
                Method fromMethod =
                    targetClass.getMethod("from", CompositeData.class);

                if (!Modifier.isStatic(fromMethod.getModifiers())) {
                    final String msg =
                        "Method from(CompositeData) is not static";
                    throw new InvalidObjectException(msg);
                }

                if (fromMethod.getReturnType() != getTargetClass()) {
                    final String msg =
                        "Method from(CompositeData) returns " +
                        typeName(fromMethod.getReturnType()) +
                        " not " + typeName(targetClass);
                    throw new InvalidObjectException(msg);
                }

                this.fromMethod = fromMethod;
                return null; // success!
            } catch (InvalidObjectException e) {
                throw e;
            } catch (Exception e) {
                // OK: it doesn't have the method
                return "no method from(CompositeData)";
            }
        }

        final Object fromCompositeData(CompositeData cd,
                                       String[] itemNames,
                                       MXBeanMapping[] converters)
                throws InvalidObjectException {
            try {
                return MethodUtil.invoke(fromMethod, null, new Object[] {cd});
            } catch (Exception e) {
                final String msg = "Failed to invoke from(CompositeData)";
                throw invalidObjectException(msg, e);
            }
        }

        private Method fromMethod;
    }

    /** This builder never actually returns success.  It simply serves
        to check whether the other builders in the same group have any
        chance of success.  If any getter in the targetClass returns
        a type that we don't know how to reconstruct, then we will
        not be able to make a builder, and there is no point in repeating
        the error about the problematic getter as many times as there are
        candidate builders.  Instead, the "applicable" method will return
        an explanatory string, and the other builders will be skipped.
        If all the getters are OK, then the "applicable" method will return
        an empty string and the other builders will be tried.  */
    private static class CompositeBuilderCheckGetters extends CompositeBuilder {
        CompositeBuilderCheckGetters(Class<?> targetClass, String[] itemNames,
                                     MXBeanMapping[] getterConverters) {
            super(targetClass, itemNames);
            this.getterConverters = getterConverters;
        }

        String applicable(Method[] getters) {
            for (int i = 0; i < getters.length; i++) {
                try {
                    getterConverters[i].checkReconstructible();
                } catch (InvalidObjectException e) {
                    possibleCause = e;
                    return "method " + getters[i].getName() + " returns type " +
                        "that cannot be mapped back from OpenData";
                }
            }
            return "";
        }

        @Override
        Throwable possibleCause() {
            return possibleCause;
        }

        final Object fromCompositeData(CompositeData cd,
                                       String[] itemNames,
                                       MXBeanMapping[] converters) {
            throw new Error();
        }

        private final MXBeanMapping[] getterConverters;
        private Throwable possibleCause;
    }

    /** Builder for when the target class has a setter for every getter. */
    private static class CompositeBuilderViaSetters extends CompositeBuilder {

        CompositeBuilderViaSetters(Class<?> targetClass, String[] itemNames) {
            super(targetClass, itemNames);
        }

        String applicable(Method[] getters) {
            try {
                Constructor<?> c = getTargetClass().getConstructor();
            } catch (Exception e) {
                return "does not have a public no-arg constructor";
            }

            Method[] setters = new Method[getters.length];
            for (int i = 0; i < getters.length; i++) {
                Method getter = getters[i];
                Class<?> returnType = getter.getReturnType();
                String name = propertyName(getter);
                String setterName = "set" + name;
                Method setter;
                try {
                    setter = getTargetClass().getMethod(setterName, returnType);
                    if (setter.getReturnType() != void.class)
                        throw new Exception();
                } catch (Exception e) {
                    return "not all getters have corresponding setters " +
                           "(" + getter + ")";
                }
                setters[i] = setter;
            }
            this.setters = setters;
            return null;
        }

        Object fromCompositeData(CompositeData cd,
                                 String[] itemNames,
                                 MXBeanMapping[] converters)
                throws InvalidObjectException {
            Object o;
            try {
                final Class<?> targetClass = getTargetClass();
                ReflectUtil.checkPackageAccess(targetClass);
                @SuppressWarnings("deprecation")
                Object tmp = targetClass.newInstance();
                o = tmp;
                for (int i = 0; i < itemNames.length; i++) {
                    if (cd.containsKey(itemNames[i])) {
                        Object openItem = cd.get(itemNames[i]);
                        Object javaItem =
                            converters[i].fromOpenValue(openItem);
                        MethodUtil.invoke(setters[i], o, new Object[] {javaItem});
                    }
                }
            } catch (Exception e) {
                throw invalidObjectException(e);
            }
            return o;
        }

        private Method[] setters;
    }

    /** Builder for when the target class has a constructor that is
        annotated with {@linkplain ConstructorParameters &#64;ConstructorParameters}
        or {@code @ConstructorProperties} so we can see the correspondence to getters.  */
    private static class CompositeBuilderViaConstructor
            extends CompositeBuilder {

        CompositeBuilderViaConstructor(Class<?> targetClass, String[] itemNames) {
            super(targetClass, itemNames);
        }

        String[] getConstPropValues(Constructor<?> ctr) {
            // is constructor annotated by javax.management.ConstructorParameters ?
            ConstructorParameters ctrProps = ctr.getAnnotation(ConstructorParameters.class);
            if (ctrProps != null) {
                return ctrProps.value();
            } else {
                // try the legacy java.beans.ConstructorProperties annotation
                String[] vals = JavaBeansAccessor.getConstructorPropertiesValue(ctr);
                return vals;
            }
        }

        String applicable(Method[] getters) throws InvalidObjectException {
            Class<?> targetClass = getTargetClass();
            Constructor<?>[] constrs = targetClass.getConstructors();

            // Applicable if and only if there are any annotated constructors
            List<Constructor<?>> annotatedConstrList = newList();
            for (Constructor<?> constr : constrs) {
                if (Modifier.isPublic(constr.getModifiers())
                        && getConstPropValues(constr) != null)
                    annotatedConstrList.add(constr);
            }

            if (annotatedConstrList.isEmpty())
                return reportNoConstructor();

            annotatedConstructors = newList();

            // Now check that all the annotated constructors are valid
            // and throw an exception if not.

            // First link the itemNames to their getter indexes.
            Map<String, Integer> getterMap = newMap();
            String[] itemNames = getItemNames();
            for (int i = 0; i < itemNames.length; i++)
                getterMap.put(itemNames[i], i);

            // Run through the constructors making the checks in the spec.
            // For each constructor, remember the correspondence between its
            // parameters and the items.  The int[] for a constructor says
            // what parameter index should get what item.  For example,
            // if element 0 is 2 then that means that item 0 in the
            // CompositeData goes to parameter 2 of the constructor.  If an
            // element is -1, that item isn't given to the constructor.
            // Also remember the set of properties in that constructor
            // so we can test unambiguity.
            Set<BitSet> getterIndexSets = newSet();
            for (Constructor<?> constr : annotatedConstrList) {
                String matchingMechanism = matchingMechanism(constr);

                String[] propertyNames = getConstPropValues(constr);

                Type[] paramTypes = constr.getGenericParameterTypes();
                if (paramTypes.length != propertyNames.length) {
                    final String msg =
                        "Number of constructor params does not match " +
                                referenceMechannism(matchingMechanism) +": " + constr;
                    throw new InvalidObjectException(msg);
                }

                int[] paramIndexes = new int[getters.length];
                for (int i = 0; i < getters.length; i++)
                    paramIndexes[i] = -1;
                BitSet present = new BitSet();

                for (int i = 0; i < propertyNames.length; i++) {
                    String propertyName = propertyNames[i];
                    if (!getterMap.containsKey(propertyName)) {
                        String msg =
                            matchingMechanism + " includes name " + propertyName +
                            " which does not correspond to a property";
                        for (String getterName : getterMap.keySet()) {
                            if (getterName.equalsIgnoreCase(propertyName)) {
                                msg += " (differs only in case from property " +
                                        getterName + ")";
                            }
                        }
                        msg += ": " + constr;
                        throw new InvalidObjectException(msg);
                    }
                    int getterIndex = getterMap.get(propertyName);
                    paramIndexes[getterIndex] = i;
                    if (present.get(getterIndex)) {
                        final String msg =
                            matchingMechanism + " contains property " +
                            propertyName + " more than once: " + constr;
                        throw new InvalidObjectException(msg);
                    }
                    present.set(getterIndex);
                    Method getter = getters[getterIndex];
                    Type propertyType = getter.getGenericReturnType();
                    if (!propertyType.equals(paramTypes[i])) {
                        final String msg =
                            matchingMechanism + " gives property " + propertyName +
                            " of type " + propertyType + " for parameter " +
                            " of type " + paramTypes[i] + ": " + constr;
                        throw new InvalidObjectException(msg);
                    }
                }

                if (!getterIndexSets.add(present)) {
                    final String msg =
                            reportMultipleConstructorsFoundFor(propertyNames);
                    throw new InvalidObjectException(msg);
                }

                Constr c = new Constr(constr, paramIndexes, present);
                annotatedConstructors.add(c);
            }

            /* Check that no possible set of items could lead to an ambiguous
             * choice of constructor (spec requires this check).  For any
             * pair of constructors, their union would be the minimal
             * ambiguous set.  If this set itself corresponds to a constructor,
             * there is no ambiguity for that pair.  In the usual case, one
             * of the constructors is a superset of the other so the union is
             * just the bigger constructor.
             *
             * The algorithm here is quadratic in the number of constructors
             * with a @ConstructorParameters or @ConstructructorProperties annotation.
             * Typically this corresponds to the number of versions of the class
             * there have been.  Ten would already be a large number, so although
             * it's probably possible to have an O(n lg n) algorithm it wouldn't be
             * worth the complexity.
             */
            for (BitSet a : getterIndexSets) {
                boolean seen = false;
                for (BitSet b : getterIndexSets) {
                    if (a == b)
                        seen = true;
                    else if (seen) {
                        BitSet u = new BitSet();
                        u.or(a); u.or(b);
                        if (!getterIndexSets.contains(u)) {
                            Set<String> names = new TreeSet<>();
                            for (int i = u.nextSetBit(0); i >= 0;
                                 i = u.nextSetBit(i+1))
                                names.add(itemNames[i]);
                            final String msg =
                                    reportConstructorsAmbiguousFor(names);
                            throw new InvalidObjectException(msg);
                        }
                    }
                }
            }

            return null; // success!
        }

        String reportNoConstructor() {
            return "no constructor has either @ConstructorParameters " +
                    "or @ConstructorProperties annotation";
        }

        String matchingMechanism(Constructor<?> constr) {
            return constr.isAnnotationPresent(ConstructorParameters.class) ?
                    "@ConstructorParameters" : "@ConstructorProperties";
        }

        String referenceMechannism(String matchingMechanism) {
            return matchingMechanism + " annotation";
        }

        String reportMultipleConstructorsFoundFor(String... propertyNames) {
            return "More than one constructor has " +
                    "@ConstructorParameters or @ConstructorProperties " +
                    "annotation with this set of names: " +
                    Arrays.toString(propertyNames);
        }

        String reportConstructorsAmbiguousFor(Set<String> names) {
            return "Constructors with @ConstructorParameters or " +
                    "@ConstructorProperties annotation " +
                    "would be ambiguous for these items: " +
                    names;
        }

        String reportNoConstructorFoundFor(Set<String> names) {
            return  "No constructor has either @ConstructorParameters " +
                    "or @ConstructorProperties annotation for this set of " +
                    "items: " + names;
        }

        Object fromCompositeData(CompositeData cd,
                                       String[] itemNames,
                                       MXBeanMapping[] mappings)
                throws InvalidObjectException {
            // The CompositeData might come from an earlier version where
            // not all the items were present.  We look for a constructor
            // that accepts just the items that are present.  Because of
            // the ambiguity check in applicable(), we know there must be
            // at most one maximally applicable constructor.
            CompositeType ct = cd.getCompositeType();
            BitSet present = new BitSet();
            for (int i = 0; i < itemNames.length; i++) {
                if (ct.getType(itemNames[i]) != null)
                    present.set(i);
            }

            Constr max = null;
            for (Constr constr : annotatedConstructors) {
                if (subset(constr.presentParams, present) &&
                        (max == null ||
                         subset(max.presentParams, constr.presentParams)))
                    max = constr;
            }

            if (max == null) {
                final String msg = reportNoConstructorFoundFor(ct.keySet());
                throw new InvalidObjectException(msg);
            }

            Object[] params = new Object[max.presentParams.cardinality()];
            for (int i = 0; i < itemNames.length; i++) {
                if (!max.presentParams.get(i))
                    continue;
                Object openItem = cd.get(itemNames[i]);
                Object javaItem = mappings[i].fromOpenValue(openItem);
                int index = max.paramIndexes[i];
                if (index >= 0)
                    params[index] = javaItem;
            }

            try {
                ReflectUtil.checkPackageAccess(max.constructor.getDeclaringClass());
                return max.constructor.newInstance(params);
            } catch (Exception e) {
                final String msg =
                    "Exception constructing " + getTargetClass().getName();
                throw invalidObjectException(msg, e);
            }
        }

        private static boolean subset(BitSet sub, BitSet sup) {
            BitSet subcopy = (BitSet) sub.clone();
            subcopy.andNot(sup);
            return subcopy.isEmpty();
        }

        private static class Constr {
            final Constructor<?> constructor;
            final int[] paramIndexes;
            final BitSet presentParams;
            Constr(Constructor<?> constructor, int[] paramIndexes,
                   BitSet presentParams) {
                this.constructor = constructor;
                this.paramIndexes = paramIndexes;
                this.presentParams = presentParams;
            }
        }

        private List<Constr> annotatedConstructors;
    }

    /** Builder for when the target class is a record */
    private static final class RecordCompositeBuilder
            extends CompositeBuilderViaConstructor {

        RecordCompositeBuilder(Class<?> targetClass, String[] itemNames) {
            super(targetClass, itemNames);
        }

        String[] getConstPropValues(Constructor<?> ctor) {
            var components = getTargetClass().getRecordComponents();
            var ptypes = ctor.getGenericParameterTypes();
            if (components.length != ptypes.length) {
                return super.getConstPropValues(ctor);
            }
            var len = components.length;
            String[] res = new String[len];
            for (int i=0; i < len ; i++) {
                if (!ptypes[i].equals(components[i].getGenericType())) {
                    return super.getConstPropValues(ctor);
                }
                res[i] = components[i].getName();
            }
            return res;
        }

        String applicable(Method[] getters) throws InvalidObjectException {
            Class<?> targetClass = getTargetClass();
            if (!targetClass.isRecord())
                return "class is not a record";

            return super.applicable(getters);
        }

        @Override
        Object fromCompositeData(CompositeData cd, String[] itemNames, MXBeanMapping[] mappings)
                throws InvalidObjectException {
            return super.fromCompositeData(cd, itemNames, mappings);
        }

        String reportNoConstructor() {
            return "canonical constructor for record not found";
        }

        String matchingMechanism(Constructor<?> constr) {
            return "canonical constructor";
        }

        String referenceMechannism(String matchingMechanism) {
            return matchingMechanism;
        }

        String reportMultipleConstructorsFoundFor(String... propertyNames) {
            return "More than one constructor has this set of names: " +
                    Arrays.toString(propertyNames);
        }

        String reportConstructorsAmbiguousFor(Set<String> names) {
            return "Constructors would be ambiguous for these items: " +
                    names;
        }

        String reportNoConstructorFoundFor(Set<String> names) {
            return  "No constructor has this set of " +
                    "items: " + names;
        }
    }

    /** Builder for when the target class is an interface and contains
        no methods other than getters.  Then we can make an instance
        using a dynamic proxy that forwards the getters to the source
        CompositeData.  */
    private static final class CompositeBuilderViaProxy
            extends CompositeBuilder {

        CompositeBuilderViaProxy(Class<?> targetClass, String[] itemNames) {
            super(targetClass, itemNames);
        }

        String applicable(Method[] getters) {
            Class<?> targetClass = getTargetClass();
            if (!targetClass.isInterface())
                return "not an interface";
            Set<Method> methods =
                newSet(Arrays.asList(targetClass.getMethods()));
            methods.removeAll(Arrays.asList(getters));
            /* If the interface has any methods left over, they better be
             * public methods that are already present in java.lang.Object.
             */
            String bad = null;
            for (Method m : methods) {
                String mname = m.getName();
                Class<?>[] mparams = m.getParameterTypes();
                try {
                    Method om = Object.class.getMethod(mname, mparams);
                    if (!Modifier.isPublic(om.getModifiers()))
                        bad = mname;
                } catch (NoSuchMethodException e) {
                    bad = mname;
                }
                /* We don't catch SecurityException since it shouldn't
                 * happen for a method in Object and if it does we would
                 * like to know about it rather than mysteriously complaining.
                 */
            }
            if (bad != null)
                return "contains methods other than getters (" + bad + ")";
            return null; // success!
        }

        final Object fromCompositeData(CompositeData cd,
                                       String[] itemNames,
                                       MXBeanMapping[] converters) {
            final Class<?> targetClass = getTargetClass();
            return
                Proxy.newProxyInstance(targetClass.getClassLoader(),
                                       new Class<?>[] {targetClass},
                                       new CompositeDataInvocationHandler(cd));
        }
    }

    static InvalidObjectException invalidObjectException(String msg,
                                                         Throwable cause) {
        return EnvHelp.initCause(new InvalidObjectException(msg), cause);
    }

    static InvalidObjectException invalidObjectException(Throwable cause) {
        return invalidObjectException(cause.getMessage(), cause);
    }

    static OpenDataException openDataException(String msg, Throwable cause) {
        return EnvHelp.initCause(new OpenDataException(msg), cause);
    }

    static OpenDataException openDataException(Throwable cause) {
        return openDataException(cause.getMessage(), cause);
    }

    static void mustBeComparable(Class<?> collection, Type element)
            throws OpenDataException {
        if (!(element instanceof Class<?>)
            || !Comparable.class.isAssignableFrom((Class<?>) element)) {
            final String msg =
                "Parameter class " + element + " of " +
                collection.getName() + " does not implement " +
                Comparable.class.getName();
            throw new OpenDataException(msg);
        }
    }

    /**
     * Utility method to take a string and convert it to normal Java variable
     * name capitalization.  This normally means converting the first
     * character from upper case to lower case, but in the (unusual) special
     * case when there is more than one character and both the first and
     * second characters are upper case, we leave it alone.
     * <p>
     * Thus "FooBah" becomes "fooBah" and "X" becomes "x", but "URL" stays
     * as "URL".
     *
     * @param  name The string to be decapitalized.
     * @return  The decapitalized version of the string.
     */
    public static String decapitalize(String name) {
        if (name == null || name.length() == 0) {
            return name;
        }
        int offset1 = Character.offsetByCodePoints(name, 0, 1);
        // Should be name.offsetByCodePoints but 6242664 makes this fail
        if (offset1 < name.length() &&
                Character.isUpperCase(name.codePointAt(offset1)))
            return name;
        return name.substring(0, offset1).toLowerCase() +
               name.substring(offset1);
    }

    /**
     * Reverse operation for java.beans.Introspector.decapitalize.  For any s,
     * capitalize(decapitalize(s)).equals(s).  The reverse is not true:
     * e.g. capitalize("uRL") produces "URL" which is unchanged by
     * decapitalize.
     */
    static String capitalize(String name) {
        if (name == null || name.length() == 0)
            return name;
        int offset1 = name.offsetByCodePoints(0, 1);
        return name.substring(0, offset1).toUpperCase() +
               name.substring(offset1);
    }

    public static String propertyName(Method m) {
        String rest = null;
        String name = m.getName();
        var c = m.getDeclaringClass();
        if (c.isRecord()) {
            for (var rc : c.getRecordComponents()) {
                if (name.equals(rc.getName())
                        && m.getReturnType() == rc.getType()) {
                    rest = name;
                    break;
                }
            }
        } else if (name.startsWith("get"))
            rest = name.substring(3);
        else if (name.startsWith("is") && m.getReturnType() == boolean.class)
            rest = name.substring(2);
        if (rest == null || rest.length() == 0
            || m.getParameterTypes().length > 0
            || m.getReturnType() == void.class
            || name.equals("getClass"))
            return null;
        return rest;
    }

    private static final Map<Type, Type> inProgress = newIdentityHashMap();
    // really an IdentityHashSet but that doesn't exist
}
