程序包 cn.taketoday.context.annotation

Annotation Interface PropertySource

@Target(TYPE) @Retention(RUNTIME) @Documented @Repeatable(PropertySources.class) public @interface PropertySource
Annotation providing a convenient and declarative mechanism for adding a PropertySource to Environment. To be used in conjunction with @Configuration classes.

Example usage

Given a file app.properties containing the key/value pair testbean.name=myTestBean, the following @Configuration class uses @PropertySource to contribute app.properties to the Environment's set of PropertySources. 

 @Configuration
 @PropertySource("classpath:/com/myco/app.properties")
 public class AppConfig {

     @Autowired
     Environment env;

     @Bean
     public TestBean testBean() {
         TestBean testBean = new TestBean();
         testBean.setName(env.getProperty("testbean.name"));
         return testBean;
     }
 }
Notice that the Environment object is @Autowired into the configuration class and then used when populating the TestBean object. Given the configuration above, a call to testBean.getName() will return "myTestBean".

Resolving ${...} placeholders in <bean> and @Value annotations

In order to resolve ${...} placeholders in <bean> definitions or @Value annotations using properties from a PropertySource, one must register a PropertySourcesPlaceholderConfigurer. This happens automatically when using <context:property-placeholder> in XML, but must be explicitly registered using a static @Component method when using @Configuration classes. See the "Working with externalized values" section of @Configuration's javadoc and "a note on BeanFactoryPostProcessor-returning @Component methods" of Component's javadoc for details and examples.

Resolving ${...} placeholders within @PropertySource resource locations

Any ${...} placeholders present in a @PropertySource resource location will be resolved against the set of property sources already registered against the environment. For example: 
 @Configuration
 @PropertySource("classpath:/com/${my.placeholder:default/path}/app.properties")
 public class AppConfig {

     @Autowired
     Environment env;

     @Bean
     public TestBean testBean() {
         TestBean testBean = new TestBean();
         testBean.setName(env.getProperty("testbean.name"));
         return testBean;
     }
 }
Assuming that "my.placeholder" is present in one of the property sources already registered, e.g. system properties or environment variables, the placeholder will be resolved to the corresponding value. If not, then "default/path" will be used as a default. Expressing a default value (delimited by colon ":") is optional. If no default is specified and a property cannot be resolved, an IllegalArgumentException will be thrown.

A note on property overriding with @PropertySource

In cases where a given property key exists in more than one .properties file, the last @PropertySource annotation processed will 'win' and override. For example, given two properties files a.properties and b.properties, consider the following two configuration classes that reference them with @PropertySource annotations: 
 @Configuration
 @PropertySource("classpath:/com/myco/a.properties")
 public class ConfigA { }

 @Configuration
 @PropertySource("classpath:/com/myco/b.properties")
 public class ConfigB { }
The override ordering depends on the order in which these classes are registered with the application context. 
 StandardApplicationContext ctx = new StandardApplicationContext();
 ctx.register(ConfigA.class);
 ctx.register(ConfigB.class);
 ctx.refresh();
In the scenario above, the properties in b.properties will override any duplicates that exist in a.properties, because ConfigB was registered last.

In certain situations, it may not be possible or practical to tightly control property source ordering when using @PropertySource annotations. For example, if the @Configuration classes above were registered via component-scanning, the ordering is difficult to predict. In such cases - and if overriding is important - it is recommended that the user fall back to using the programmatic PropertySource API. See ConfigurableEnvironment and PropertySources javadocs for details.

NOTE: This annotation is repeatable according to Java 8 conventions. However, all such @PropertySource annotations need to be declared at the same level: either directly on the configuration class or as meta-annotations within the same custom annotation. Mixing of direct annotations and meta-annotations is not recommended since direct annotations will effectively override meta-annotations.

从以下版本开始:
4.0
作者:
Chris Beams, Juergen Hoeller, Phillip Webb, TODAY 2021/10/28 17:24
另请参阅:

  • 必需元素概要

    所需元素
    修饰符和类型
    必需的元素
    说明
    String[]
    value
    Indicate the resource location(s) of the properties file to be loaded.

  • 可选元素概要

    可选元素
    修饰符和类型
    可选元素
    说明
    String
    encoding
    A specific character encoding for the given resources, e.g.
    Class<? extends cn.taketoday.core.io.PropertySourceFactory>
    factory
    Specify a custom PropertySourceFactory, if any.
    boolean
    ignoreResourceNotFound
    Indicate if failure to find the a property resource should be ignored.
    String
    name
    Indicate the name of this property source.

  • 元素详细资料

    • value

      String[] value
      Indicate the resource location(s) of the properties file to be loaded.

      Both traditional and XML-based properties file formats are supported — for example, "classpath:/com/myco/app.properties" or "file:/path/to/file.xml".

      Resource location wildcards (e.g. **/*.properties) are not permitted; each location must evaluate to exactly one .properties resource.

      ${...} placeholders will be resolved against any/all property sources already registered with the Environment. See above for examples.

      Each location will be added to the enclosing Environment as its own property source, and in the order declared.

    • name

      String name
      Indicate the name of this property source. If omitted, a name will be generated based on the description of the underlying resource.
      另请参阅:
      • PropertySource.getName()
      • Resource.toString()
      默认值:
      ""

    • ignoreResourceNotFound

      boolean ignoreResourceNotFound
      Indicate if failure to find the a property resource should be ignored.

      true is appropriate if the properties file is completely optional. Default is false.

      默认值:
      false

    • encoding

      String encoding
      A specific character encoding for the given resources, e.g. "UTF-8".
      默认值:
      ""

    • factory

      Class<? extends cn.taketoday.core.io.PropertySourceFactory> factory
      Specify a custom PropertySourceFactory, if any.

      By default, a default factory for standard resource files will be used.

      另请参阅:
      • DefaultPropertySourceFactory
      • ResourcePropertySource
      默认值:
      cn.taketoday.core.io.PropertySourceFactory.class