spring-context中@PropertySources和@PropertySource的源码解析说明

spring版本为5.0.11

@PropertySource加载指定的属性文件（*.properties）到 Spring 的 Environment 中。

• @PropertySource 和 @Value 组合使用，可以将自定义属性文件中的属性变量值注入到当前类的使用@Value注解的成员变量中。
• @PropertySource 和 @ConfigurationProperties 组合使用，可以将属性文件与一个Java类绑定，将属性文件中的变量值注入到该Java类的成员变量中

@PropertySources注解就是@PropertySource的数组集合

@PropertySource源码

/**
 * Annotation providing a convenient and declarative mechanism for adding a
 * {@link org.springframework.core.env.PropertySource PropertySource} to Spring's
 * {@link org.springframework.core.env.Environment Environment}. To be used in
 * conjunction with @{@link Configuration} classes.
 *
 * <h3>Example usage</h3>
 *
 * <p>Given a file {@code app.properties} containing the key/value pair
 * {@code testbean.name=myTestBean}, the following {@code @Configuration} class
 * uses {@code @PropertySource} to contribute {@code app.properties} to the
 * {@code Environment}'s set of {@code PropertySources}.
 *
 * <pre class="code">
 * &#064;Configuration
 * &#064;PropertySource("classpath:/com/myco/app.properties")
 * public class AppConfig {
 *
 *     &#064;Autowired
 *     Environment env;
 *
 *     &#064;Bean
 *     public TestBean testBean() {
 *         TestBean testBean = new TestBean();
 *         testBean.setName(env.getProperty("testbean.name"));
 *         return testBean;
 *     }
 * }</pre>
 *
 * <p>Notice that the {@code Environment} object is
 * {@link org.springframework.beans.factory.annotation.Autowired @Autowired} into the
 * configuration class and then used when populating the {@code TestBean} object. Given
 * the configuration above, a call to {@code testBean.getName()} will return "myTestBean".
 *
 * <h3>Resolving <code>${...}</code> placeholders in {@code <bean>} and {@code @Value} annotations</h3>
 *
 * <p>In order to resolve ${...} placeholders in {@code <bean>} definitions or {@code @Value}
 * annotations using properties from a {@code PropertySource}, you must ensure that an
 * appropriate <em>embedded value resolver</em> is registered in the {@code BeanFactory}
 * used by the {@code ApplicationContext}. This happens automatically when using
 * {@code <context:property-placeholder>} in XML. When using {@code @Configuration} classes
 * this can be achieved by explicitly registering a {@code PropertySourcesPlaceholderConfigurer}
 * via a {@code static} {@code @Bean} method. Note, however, that explicit registration
 * of a {@code PropertySourcesPlaceholderConfigurer} via a {@code static} {@code @Bean}
 * method is typically only required if you need to customize configuration such as the
 * placeholder syntax, etc. See the "Working with externalized values" section of
 * {@link Configuration @Configuration}'s javadocs and "a note on
 * BeanFactoryPostProcessor-returning {@code @Bean} methods" of {@link Bean @Bean}'s
 * javadocs for details and examples.
 *
 * <h3>Resolving ${...} placeholders within {@code @PropertySource} resource locations</h3>
 *
 * <p>Any ${...} placeholders present in a {@code @PropertySource} {@linkplain #value()
 * resource location} will be resolved against the set of property sources already
 * registered against the environment. For example:
 *
 * <pre class="code">
 * &#064;Configuration
 * &#064;PropertySource("classpath:/com/${my.placeholder:default/path}/app.properties")
 * public class AppConfig {
 *
 *     &#064;Autowired
 *     Environment env;
 *
 *     &#064;Bean
 *     public TestBean testBean() {
 *         TestBean testBean = new TestBean();
 *         testBean.setName(env.getProperty("testbean.name"));
 *         return testBean;
 *     }
 * }</pre>
 *
 * <p>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 {@code
 * IllegalArgumentException} will be thrown.
 *
 * <h3>A note on property overriding with @PropertySource</h3>
 *
 * <p>In cases where a given property key exists in more than one {@code .properties}
 * file, the last {@code @PropertySource} annotation processed will 'win' and override.
 *
 * <p>For example, given two properties files {@code a.properties} and
 * {@code b.properties}, consider the following two configuration classes
 * that reference them with {@code @PropertySource} annotations:
 *
 * <pre class="code">
 * &#064;Configuration
 * &#064;PropertySource("classpath:/com/myco/a.properties")
 * public class ConfigA { }
 *
 * &#064;Configuration
 * &#064;PropertySource("classpath:/com/myco/b.properties")
 * public class ConfigB { }
 * </pre>
 *
 * <p>The override ordering depends on the order in which these classes are registered
 * with the application context.
 *
 * <pre class="code">
 * AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
 * ctx.register(ConfigA.class);
 * ctx.register(ConfigB.class);
 * ctx.refresh();
 * </pre>
 *
 * <p>In the scenario above, the properties in {@code b.properties} will override any
 * duplicates that exist in {@code a.properties}, because {@code ConfigB} was registered
 * last.
 *
 * <p>In certain situations, it may not be possible or practical to tightly control
 * property source ordering when using {@code @PropertySource} annotations. For example,
 * if the {@code @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 {@link org.springframework.core.env.ConfigurableEnvironment ConfigurableEnvironment}
 * and {@link org.springframework.core.env.MutablePropertySources MutablePropertySources}
 * javadocs for details.
 *
 * <p><b>NOTE: This annotation is repeatable according to Java 8 conventions.</b>
 * However, all such {@code @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.
 *
 * @author Chris Beams
 * @author Juergen Hoeller
 * @author Phillip Webb
 * @author Sam Brannen
 * @since 3.1
 * @see PropertySources
 * @see Configuration
 * @see org.springframework.core.env.PropertySource
 * @see org.springframework.core.env.ConfigurableEnvironment#getPropertySources()
 * @see org.springframework.core.env.MutablePropertySources
 */
@Target(ElementType.TYPE)//只能标注在类上
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Repeatable(PropertySources.class)
public @interface PropertySource {

    /**
     * Indicate the name of this property source. If omitted, a name will
     * be generated based on the description of the underlying resource.
     * @see org.springframework.core.env.PropertySource#getName()
     * @see org.springframework.core.io.Resource#getDescription()
     */
    String name() default "";

    /**
     * 指定资源地址
     * Indicate the resource location(s) of the properties file to be loaded.
     * <p>Both traditional and XML-based properties file formats are supported
     * &mdash; for example, {@code "classpath:/com/myco/app.properties"}
     * or {@code "file:/path/to/file.xml"}.
     * <p>Resource location wildcards (e.g. *&#42;/*.properties) are not permitted;
     * each location must evaluate to exactly one {@code .properties} resource.
     * <p>${...} placeholders will be resolved against any/all property sources already
     * registered with the {@code Environment}. See {@linkplain PropertySource above}
     * for examples.
     * <p>Each location will be added to the enclosing {@code Environment} as its own
     * property source, and in the order declared.
     */
    String[] value();

    /**
     * 表明如果没发现资源应当忽视，默认是false
     * Indicate if failure to find the a {@link #value() property resource} should be
     * ignored.
     * <p>{@code true} is appropriate if the properties file is completely optional.
     * Default is {@code false}.
     * @since 4.0
     */
    boolean ignoreResourceNotFound() default false;

    /**
     * 指定编码
     * A specific character encoding for the given resources, e.g. "UTF-8".
     * @since 4.3
     */
    String encoding() default "";

    /**
     * Specify a custom {@link PropertySourceFactory}, if any.
     * <p>By default, a default factory for standard resource files will be used.
     * @since 4.3
     * @see org.springframework.core.io.support.DefaultPropertySourceFactory
     * @see org.springframework.core.io.support.ResourcePropertySource
     */
    Class<? extends PropertySourceFactory> factory() default PropertySourceFactory.class;

}

@PropertySources源码

/**
 * Container annotation that aggregates several {@link PropertySource} annotations.
 * 聚合多个@PropertySource注解的容器注解
 * <p>Can be used natively, declaring several nested {@link PropertySource} annotations.
 * Can also be used in conjunction with Java 8's support for <em>repeatable annotations</em>,
 * where {@link PropertySource} can simply be declared several times on the same
 * {@linkplain ElementType#TYPE type}, implicitly generating this container annotation.
 *
 * @author Phillip Webb
 * @since 4.0
 * @see PropertySource
 */
@Target({ElementType.TYPE})//只能标注在类上
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface PropertySources {
    PropertySource[] value();
}

示例一：@PropertySource + @Value 

@PropertySource(value = {"classpath:/user1.properties"})
@Component
public class TestPropertySource {
    @Value("${user1.name}")
    private String name;
    @Value("${user1.age}")
    private int age;

    public User getUser(){
        User user=new User();
        user.setName(name);
        user.setAge(age);
        return user;
    }
}

示例二：@PropertySource 和 @ConfigurationProperties 

@Component
@PropertySource(value = {"classpath:/user1.properties"})
@ConfigurationProperties(prefix = "user1")
public class User1Properties {
    private String name;
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User1Properties{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

测试

    @Autowired
    private  TestPropertySource testPropertySource;
    @Test
    public void test2(){
        System.out.println(testPropertySource.getUser());
    }
    @Resource
    private User1Properties user1Properties;
    @Test
    public void test3(){
        System.out.println(user1Properties);
    }