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PropertyPlaceholderConfigurer (Spring Framework API 2.0) - Spring Framework 2.0.5 API 文档英文版

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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

Direct Known Subclasses:

PreferencesPlaceholderConfigurer, ServletContextPropertyPlaceholderConfigurer

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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

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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 bean factory.
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	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

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DEFAULT_PLACEHOLDER_SUFFIX

public static final String DEFAULT_PLACEHOLDER_SUFFIX

Default placeholder suffix: "}"

See Also:

Constant Field Values

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SYSTEM_PROPERTIES_MODE_NEVER

public static final int SYSTEM_PROPERTIES_MODE_NEVER

Never check system properties.

See Also:

Constant Field Values

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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

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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

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setPlaceholderSuffix

public void setPlaceholderSuffix(String placeholderSuffix)

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

See Also:

DEFAULT_PLACEHOLDER_SUFFIX

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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)

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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)

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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)

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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.

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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

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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

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processProperties

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

Description copied from class: PropertyResourceConfigurer

Apply the given Properties to the bean factory.

Specified by:

processProperties in class PropertyResourceConfigurer

Parameters:

beanFactoryToProcess - the bean factory used by the application context

props - the Properties to apply

Throws:

BeansException - in case of errors

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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)

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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)

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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)

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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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