ApplicationContextAware 接口作用

    public class SpringContextHolder implements ApplicationContextAware {
    private static ApplicationContext applicationContext = null;
     
    /**
    * 获取静态变量中的ApplicationContext.
    */
    public static ApplicationContext getApplicationContext() {
    assertContextInjected();
    return applicationContext;
    }
     
    /**
    * 从静态变量applicationContext中得到Bean, 自动转型为所赋值对象的类型.
    */
    @SuppressWarnings("unchecked")
    public static <T> T getBean(String name) {
    assertContextInjected();
    return (T) applicationContext.getBean(name);
    }
     
    /**
    * 从静态变量applicationContext中得到Bean, 自动转型为所赋值对象的类型.
    */
    public static <T> T getBean(Class<T> requiredType) {
    assertContextInjected();
    return applicationContext.getBean(requiredType);
    }
     
    /**
    * 清除SpringContextHolder中的ApplicationContext为Null.
    */
    public static void clearHolder() {
    applicationContext = null;
    }
     
    /**
    * 实现ApplicationContextAware接口, 注入Context到静态变量中.
    */
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) {
    SpringContextHolder.applicationContext = applicationContext;
    }
     
    /**
    * 检查ApplicationContext不为空.
    */
    private static void assertContextInjected() {
    Validate.validState(applicationContext != null,
    "applicaitonContext属性未注入, 请在applicationContext.xml中定义SpringContextHolder.");
    }
     
    }