参考文献

@Value

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// org.springframework.beans.factory.annotation.Value
@Target({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Value {

	/**
	 * The actual value expression such as <code>#{systemProperties.myProp}</code>
	 * or property placeholder such as <code>${my.app.myProp}</code>.
	 */
	String value();

}

@Value数据来源

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org.springframework.core.env.PropertySource
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/**
 * Return the value associated with the given name,
 * or {@code null} if not found.
 * @param name the property to find
 * @see PropertyResolver#getRequiredProperty(String)
 */
@Nullable
public abstract Object getProperty(String name);
  • 可以将其理解为一个配置源，里面包含了key->value的配置信息，可以通过这个类中提供的方法获取key对应的value信息
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public interface Environment extends PropertyResolver {

	String[] getActiveProfiles();

	String[] getDefaultProfiles();

	@Deprecated
	boolean acceptsProfiles(String... profiles);

	boolean acceptsProfiles(Profiles profiles);

  // 以下方法为PropertyResolver中的方法,此处展示,粘贴到此处
  
	boolean containsProperty(String key);

	@Nullable
	String getProperty(String key);

	String getProperty(String key, String defaultValue);

	@Nullable
	<T> T getProperty(String key, Class<T> targetType);

	<T> T getProperty(String key, Class<T> targetType, T defaultValue);

	String getRequiredProperty(String key) throws IllegalStateException;

	<T> T getRequiredProperty(String key, Class<T> targetType) throws IllegalStateException;

	/**
	 * Resolve ${...} placeholders in the given text, replacing them with corresponding
	 * property values as resolved by {@link #getProperty}. Unresolvable placeholders with
	 * no default value are ignored and passed through unchanged.
	 * @param text the String to resolve
	 * @return the resolved String (never {@code null})
	 * @throws IllegalArgumentException if given text is {@code null}
	 * @see #resolveRequiredPlaceholders
	 */
	String resolvePlaceholders(String text);

	/**
	 * Resolve ${...} placeholders in the given text, replacing them with corresponding
	 * property values as resolved by {@link #getProperty}. Unresolvable placeholders with
	 * no default value will cause an IllegalArgumentException to be thrown.
	 * @return the resolved String (never {@code null})
	 * @throws IllegalArgumentException if given text is {@code null}
	 * or if any placeholders are unresolvable
	 */
	String resolveRequiredPlaceholders(String text) throws IllegalArgumentException;

}
  • 用来表示环境配置信息,
  • resolvePlaceholders用来解析${text}的，@Value注解最后就是调用这个方法来解析的。

解析@Value的过程

  1. 将@Value注解的value参数值作为Environment#resolvePlaceholders方法参数进行解析
  2. Environment内部会访问MutablePropertySources来解析
  3. MutablePropertySources内部有多个PropertySource，此时会遍历PropertySource列表，调用PropertySource.getProperty方法来解析key对应的值