Use of PropertyPlaceholderConfigurer in Spring

You can use PropertyPlaceholderConfigurer in Spring to read configuration information:

1. Properties

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Jdbc. driverClassName = com. mysql. jdbc. Driver
Jdbc. url = jdbc: mysql: // localhost: 3306/mysql
Jdbc. username = root
Jdbc. password = root
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<Bean class = "org. springframework. beans. factory. config. PropertyPlaceholderConfigurer">
<Property name = "locations" value = "classpath: jdbc. properties"/>
</Bean>
 
<Bean id = "dataSource" destroy-method = "close"
Class = "org. apache. commons. dbcp. BasicDataSource">
<Property name = "driverClassName" value = "$ {jdbc. driverClassName}"/>
<Property name = "url" value = "$ {jdbc. url}"/>
<Property name = "username" value = "$ {jdbc. username}"/>
<Property name = "password" value = "$ {jdbc. password}"/>
</Bean>

Spring 2.5 introduces the Context namespace, which can be configured through the context: property-placeholder element:

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<Context: property-placeholder location = "classpath: jdbc. properties"/>

PropertyPlaceholderConfigurer can not only search for Properties Based on the specified Properties file, but also use the java System attribute mode.

Original spring document:
[Html]
The propertyplaceholderpolicer not only looks for properties in the Properties file you specify.
By default it also checks against the Java System properties if it cannot find a property in the specified properties files.
You can customize this behavior by setting the systemPropertiesMode property of the caller with one of the following three supported integer values:
Never (0): Never check system properties

Fallback (1): Check system properties if not resolvable in the specified properties files. This is the default.

Override (2): Check system properties first, before trying the specified properties files. This allows system properties to override any other property source.

Nerver (0): do not check system configuration attributes.
Fallback (1): Check the System Configuration attributes. If the System Configuration attributes are not found in the specified attribute file, use the System Configuration attributes. The default value is

Override (2): First, check the system configuration attributes. the system configuration attributes take precedence.

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<Bean class = "org. springframework. beans. factory. config. PropertyPlaceholderConfigurer">
<Property name = "locations">
<Value> classpath: com/foo/strategy. properties </value>
</Property>
<Property name = "properties">
<Value> custom. strategy. class = com. foo. DefaultStrategy </value>
</Property>
</Bean>
 
<Bean id = "serviceStrategy" class = "$ {custom. strategy. class}"/>

If the class cannot be resolved at runtime to a valid class, resolution of the bean fails when it is about to be created, which is during thepreInstantiateSingletons () phase of anApplicationContext for a non-lazy-init bean.

The above section indicates that if the system configures attributes in the configuration information, classes in the attributes should be non-delayed loaded beans during loading.

Spring 3.1 starts to use org. springframework. context. support. PropertySourcesPlaceholderConfigurer.

 

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<! -- Method 1 -->
<Bean class = "org. springframework. context. support. PropertySourcesPlaceholderConfigurer">
<Property name = "locations">
<Value> classpath: jdbc. properties </value>
</Property>
</Bean>
 
<! -- Method 2 -->
<Bean class = "org. springframework. context. support. PropertySourcesPlaceholderConfigurer">
<Property name = "location">
<Value> classpath: jdbc. properties </value>
</Property>
</Bean>
 
<! -- Method 3 -->
<Context: property-placeholder location = "classpath: jdbc. properties"/>