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## org.springframework.beans.factory.config
Class PropertyPlaceholderConfigurer

    java.lang.Object
      org.springframework.core.io.support.PropertiesLoaderSupport
          org.springframework.beans.factory.config.PropertyResourceConfigurer
              org.springframework.beans.factory.config.PropertyPlaceholderConfigurer

All Implemented Interfaces:
  BeanFactoryAware, BeanNameAware, BeanFactoryPostProcessor, Ordered, PriorityOrdered

Direct Known Subclasses:
  PreferencesPlaceholderConfigurer, ServletContextPropertyPlaceholderConfigurer

    public class PropertyPlaceholderConfigurer

extends PropertyResourceConfigurer
implements BeanNameAware, BeanFactoryAware

A property resource configurer that resolves placeholders in bean property values of context definitions. It pulls values from a properties file into bean definitions.

The default placeholder syntax follows the Ant / Log4J / JSP EL style:

    ${...}

Example XML context definition:

    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
       <property name="driverClassName"><value>${driver}</value></property>
       <property name="url"><value>jdbc:${dbname}</value></property>
     </bean>

Example properties file:

    driver=com.mysql.jdbc.Driver
     dbname=mysql:mydb

PropertyPlaceholderConfigurer checks simple property values, lists, maps, props, and bean names in bean references. Furthermore, placeholder values can also cross-reference other placeholders, like:

    rootPath=myrootdir
     subPath=${rootPath}/subdir

In contrast to PropertyOverrideConfigurer, this configurer allows to fill in explicit placeholders in context definitions. Therefore, the original definition cannot specify any default values for such bean properties, and the placeholder properties file is supposed to contain an entry for each defined placeholder.

If a configurer cannot resolve a placeholder, a BeanDefinitionStoreException will be thrown. If you want to check against multiple properties files, specify multiple resources via the "locations" setting. You can also define multiple PropertyPlaceholderConfigurers, each with its own placeholder syntax.

Default property values can be defined via "properties", to make overriding definitions in properties files optional. A configurer will also check against system properties (e.g. "user.dir") if it cannot resolve a placeholder with any of the specified properties. This can be customized via "systemPropertiesMode".

Note that the context definition is aware of being incomplete; this is immediately obvious to users when looking at the XML definition file. Hence, placeholders have to be resolved; any desired defaults have to be defined as placeholder values as well (for example in a default properties file).

Property values can be converted after reading them in, through overriding the `PropertyResourceConfigurer.convertPropertyValue(java.lang.String)` method. For example, encrypted values can be detected and decrypted accordingly before processing them.

Since:
  02.10.2003
Author:
  Juergen Hoeller
See Also:
  `PropertiesLoaderSupport.setLocations(org.springframework.core.io.Resource[])`, `PropertiesLoaderSupport.setProperties(java.util.Properties)`, `setPlaceholderPrefix(java.lang.String)`, `setPlaceholderSuffix(java.lang.String)`, `setSystemPropertiesModeName(java.lang.String)`, `System.getProperty(String)`, `PropertyResourceConfigurer.convertPropertyValue(java.lang.String)`, `PropertyOverrideConfigurer`

Field Summary
`static String` | `DEFAULT_PLACEHOLDER_PREFIX` Default placeholder prefix: "${"
`static String` | `DEFAULT_PLACEHOLDER_SUFFIX` Default placeholder suffix: "}"
`static int` | `SYSTEM_PROPERTIES_MODE_FALLBACK` Check system properties if not resolvable in the specified properties.
`static int` | `SYSTEM_PROPERTIES_MODE_NEVER` Never check system properties.
`static int` | `SYSTEM_PROPERTIES_MODE_OVERRIDE` Check system properties first, before trying the specified properties.

Fields inherited from class org.springframework.core.io.support.PropertiesLoaderSupport
`logger, XML_FILE_EXTENSION`

Fields inherited from interface org.springframework.core.Ordered
`HIGHEST_PRECEDENCE, LOWEST_PRECEDENCE`

Constructor Summary
`PropertyPlaceholderConfigurer()`

Method Summary
`protected String` | `parseStringValue(String strVal, Properties props, Set visitedPlaceholders)` Parse the given String value recursively, to be able to resolve nested placeholders (when resolved property values in turn contain placeholders again).
`protected void` | `processProperties(ConfigurableListableBeanFactory beanFactoryToProcess, Properties props)` Apply the given Properties to the given BeanFactory.
`protected String` | `resolvePlaceholder(String placeholder, Properties props)` Resolve the given placeholder using the given properties.
`protected String` | `resolvePlaceholder(String placeholder, Properties props, int systemPropertiesMode)` Resolve the given placeholder using the given properties, performing a system properties check according to the given mode.
`protected String` | `resolveSystemProperty(String key)` Resolve the given key as JVM system property, and optionally also as system environment variable if no matching system property has been found.
`void` | `setBeanFactory(BeanFactory beanFactory)` Only necessary to check that we're not parsing our own bean definition, to avoid failing on unresolvable placeholders in properties file locations.
`void` | `setBeanName(String beanName)` Only necessary to check that we're not parsing our own bean definition, to avoid failing on unresolvable placeholders in properties file locations.
`void` | `setIgnoreUnresolvablePlaceholders(boolean ignoreUnresolvablePlaceholders)` Set whether to ignore unresolvable placeholders.
`void` | `setNullValue(String nullValue)` Set a value that should be treated as `null` when resolved as a placeholder value: e.g. "" (empty String) or "null".
`void` | `setPlaceholderPrefix(String placeholderPrefix)` Set the prefix that a placeholder string starts with.
`void` | `setPlaceholderSuffix(String placeholderSuffix)` Set the suffix that a placeholder string ends with.
`void` | `setSearchSystemEnvironment(boolean searchSystemEnvironment)` Set whether to search for a matching system environment variable if no matching system property has been found.
`void` | `setSystemPropertiesMode(int systemPropertiesMode)` Set how to check system properties: as fallback, as override, or never.
`void` | `setSystemPropertiesModeName(String constantName)` Set the system property mode by the name of the corresponding constant, e.g.

Methods inherited from class org.springframework.beans.factory.config.PropertyResourceConfigurer
`convertProperties, convertPropertyValue, getOrder, postProcessBeanFactory, setOrder`

Methods inherited from class org.springframework.core.io.support.PropertiesLoaderSupport
`loadProperties, mergeProperties, setFileEncoding, setIgnoreResourceNotFound, setLocalOverride, setLocation, setLocations, setProperties, setPropertiesArray, setPropertiesPersister`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### DEFAULT_PLACEHOLDER_PREFIX

    public static final String DEFAULT_PLACEHOLDER_PREFIX

  Default placeholder prefix: "${"

  See Also:
    Constant Field Values

### DEFAULT_PLACEHOLDER_SUFFIX

    public static final String DEFAULT_PLACEHOLDER_SUFFIX

  Default placeholder suffix: "}"

  See Also:
    Constant Field Values

### SYSTEM_PROPERTIES_MODE_NEVER

    public static final int SYSTEM_PROPERTIES_MODE_NEVER

  Never check system properties.

  See Also:
    Constant Field Values

### SYSTEM_PROPERTIES_MODE_FALLBACK

    public static final int SYSTEM_PROPERTIES_MODE_FALLBACK

  Check system properties if not resolvable in the specified properties. This is the default.

  See Also:
    Constant Field Values

### SYSTEM_PROPERTIES_MODE_OVERRIDE

    public static final int SYSTEM_PROPERTIES_MODE_OVERRIDE

  Check system properties first, before trying the specified properties. This allows system properties to override any other property source.

  See Also:
    Constant Field Values

Constructor Detail

### PropertyPlaceholderConfigurer

    public PropertyPlaceholderConfigurer()

Method Detail

### setPlaceholderPrefix

    public void setPlaceholderPrefix(String placeholderPrefix)

  Set the prefix that a placeholder string starts with. The default is "${".

  See Also:
    `DEFAULT_PLACEHOLDER_PREFIX`

### setPlaceholderSuffix

    public void setPlaceholderSuffix(String placeholderSuffix)

  Set the suffix that a placeholder string ends with. The default is "}".

  See Also:
    `DEFAULT_PLACEHOLDER_SUFFIX`

### setSystemPropertiesModeName

    public void setSystemPropertiesModeName(String constantName)
                                     throws IllegalArgumentException

  Set the system property mode by the name of the corresponding constant, e.g. "SYSTEM_PROPERTIES_MODE_OVERRIDE".

  Parameters:
    `constantName` - name of the constant
  Throws:
    `IllegalArgumentException` - if an invalid constant was specified
  See Also:
    `setSystemPropertiesMode(int)`

### setSystemPropertiesMode

    public void setSystemPropertiesMode(int systemPropertiesMode)

  Set how to check system properties: as fallback, as override, or never. For example, will resolve ${user.dir} to the "user.dir" system property.

  The default is "fallback": If not being able to resolve a placeholder with the specified properties, a system property will be tried. "override" will check for a system property first, before trying the specified properties. "never" will not check system properties at all.

  See Also:
    `SYSTEM_PROPERTIES_MODE_NEVER`, `SYSTEM_PROPERTIES_MODE_FALLBACK`, `SYSTEM_PROPERTIES_MODE_OVERRIDE`, `setSystemPropertiesModeName(java.lang.String)`

### setSearchSystemEnvironment

    public void setSearchSystemEnvironment(boolean searchSystemEnvironment)

  Set whether to search for a matching system environment variable if no matching system property has been found. Only applied when "systemPropertyMode" is active (i.e. "fallback" or "override"), right after checking JVM system properties.

  Default is "true". Switch this setting off to never resolve placeholders against system environment variables. Note that it is generally recommended to pass external values in as JVM system properties: This can easily be achieved in a startup script, even for existing environment variables.

  NOTE: Access to environment variables does not work on the Sun VM 1.4, where the corresponding `System.getenv(java.lang.String)` support was disabled - before it eventually got re-enabled for the Sun VM 1.5. Please upgrade to 1.5 (or higher) if you intend to rely on the environment variable support.

  See Also:
    `setSystemPropertiesMode(int)`, `System.getProperty(String)`, `System.getenv(String)`

### setIgnoreUnresolvablePlaceholders

    public void setIgnoreUnresolvablePlaceholders(boolean ignoreUnresolvablePlaceholders)

  Set whether to ignore unresolvable placeholders. Default is "false": An exception will be thrown if a placeholder cannot be resolved.

### setNullValue

    public void setNullValue(String nullValue)

  Set a value that should be treated as `null` when resolved as a placeholder value: e.g. "" (empty String) or "null".

  Note that this will only apply to full property values, not to parts of concatenated values.

  By default, no such null value is defined. This means that there is no way to express `null` as a property value unless you explictly map a corresponding value here.

### setBeanName

    public void setBeanName(String beanName)

  Only necessary to check that we're not parsing our own bean definition, to avoid failing on unresolvable placeholders in properties file locations. The latter case can happen with placeholders for system properties in resource locations.

  Specified by:
    `setBeanName` in interface `BeanNameAware`
  Parameters:
    `beanName` - the name of the bean in the factory. Note that this name is the actual bean name used in the factory, which may differ from the originally specified name: in particular for inner bean names, the actual bean name might have been made unique through appending "#..." suffixes. Use the `BeanFactoryUtils.originalBeanName(String)` method to extract the original bean name (without suffix), if desired.
  See Also:
    `PropertiesLoaderSupport.setLocations(org.springframework.core.io.Resource[])`, `ResourceEditor`

### setBeanFactory

    public void setBeanFactory(BeanFactory beanFactory)

  Only necessary to check that we're not parsing our own bean definition, to avoid failing on unresolvable placeholders in properties file locations. The latter case can happen with placeholders for system properties in resource locations.

  Specified by:
    `setBeanFactory` in interface `BeanFactoryAware`
  Parameters:
    `beanFactory` - owning BeanFactory (never `null`). The bean can immediately call methods on the factory.
  See Also:
    `PropertiesLoaderSupport.setLocations(org.springframework.core.io.Resource[])`, `ResourceEditor`

### processProperties

    protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess,
                                     Properties props)
                              throws BeansException

  Description copied from class: `PropertyResourceConfigurer`
  Apply the given Properties to the given BeanFactory.

  Specified by:
    `processProperties` in class `PropertyResourceConfigurer`
  Parameters:
    `beanFactoryToProcess` - the BeanFactory used by the application context
    `props` - the Properties to apply
  Throws:
    `BeansException` - in case of errors

### parseStringValue

    protected String parseStringValue(String strVal,
                                      Properties props,
                                      Set visitedPlaceholders)
                               throws BeanDefinitionStoreException

  Parse the given String value recursively, to be able to resolve nested placeholders (when resolved property values in turn contain placeholders again).

  Parameters:
    `strVal` - the String value to parse
    `props` - the Properties to resolve placeholders against
    `visitedPlaceholders` - the placeholders that have already been visited during the current resolution attempt (used to detect circular references between placeholders). Only non-null if we're parsing a nested placeholder.
  Throws:
    `BeanDefinitionStoreException` - if invalid values are encountered
  See Also:
    `resolvePlaceholder(String, java.util.Properties, int)`

### resolvePlaceholder

    protected String resolvePlaceholder(String placeholder,
                                        Properties props,
                                        int systemPropertiesMode)

  Resolve the given placeholder using the given properties, performing a system properties check according to the given mode.

  Default implementation delegates to `resolvePlaceholder (placeholder, props)` before/after the system properties check.

  Subclasses can override this for custom resolution strategies, including customized points for the system properties check.

  Parameters:
    `placeholder` - the placeholder to resolve
    `props` - the merged properties of this configurer
    `systemPropertiesMode` - the system properties mode, according to the constants in this class
  Returns:
    the resolved value, of null if none
  See Also:
    `setSystemPropertiesMode(int)`, `System.getProperty(java.lang.String)`, `resolvePlaceholder(String, java.util.Properties)`

### resolvePlaceholder

    protected String resolvePlaceholder(String placeholder,
                                        Properties props)

  Resolve the given placeholder using the given properties. The default implementation simply checks for a corresponding property key.

  Subclasses can override this for customized placeholder-to-key mappings or custom resolution strategies, possibly just using the given properties as fallback.

  Note that system properties will still be checked before respectively after this method is invoked, according to the system properties mode.

  Parameters:
    `placeholder` - the placeholder to resolve
    `props` - the merged properties of this configurer
  Returns:
    the resolved value, of `null` if none
  See Also:
    `setSystemPropertiesMode(int)`

### resolveSystemProperty

    protected String resolveSystemProperty(String key)

  Resolve the given key as JVM system property, and optionally also as system environment variable if no matching system property has been found.

  Parameters:
    `key` - the placeholder to resolve as system property key
  Returns:
    the system property value, or `null` if not found
  See Also:
    `setSearchSystemEnvironment(boolean)`, `System.getProperty(String)`, `System.getenv(String)`

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