Java注解Annotation与自定义注解详解

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.SOURCE)
public @interface Override {

}

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Documented {

}

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Target {
  /**
   * Returns an array of the kinds of elements an annotation type
   * can be applied to.
   * @return an array of the kinds of elements an annotation type
   * can be applied to
   */
  ElementType[] value();
}

public enum ElementType {
  /** Class, interface (including annotation type), or enum declaration */
  TYPE,

  /** Field declaration (includes enum constants) */
  FIELD,

  /** Method declaration */
  METHOD,

  /** Formal parameter declaration */
  PARAMETER,

  /** Constructor declaration */
  CONSTRUCTOR,

  /** Local variable declaration */
  LOCAL_VARIABLE,

  /** Annotation type declaration */
  ANNOTATION_TYPE,

  /** Package declaration */
  PACKAGE,

  /** Type parameter declaration */
  TYPE_PARAMETER,

  /** Use of a type */
  TYPE_USE
}

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Inherited {

}

@Documented
@Target({ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface Constraint {
  Class<? extends ConstraintValidator<?, ?>>[] validatedBy();
}

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Retention {
  /**
   * Returns the retention policy.
   * @return the retention policy
   */
  RetentionPolicy value();
}

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Mapping
public @interface RequestMapping {
  String name() default "";

  @AliasFor("path")
  String[] value() default {};

  @AliasFor("value")
  String[] path() default {};

  RequestMethod[] method() default {};
  String[] params() default {};
  String[] headers() default {};
  String[] consumes() default {};
  String[] produces() default {};
}

@RequestMapping(value = "/list", 
        method = RequestMethod.POST, 
        produces = {"application/json;charset=UTF-8;"})
public String list(){

}

// 获取某个类型的注解
public <A extends Annotation> A getAnnotation(Class<A> annotationClass);
// 获取所有注解(包括父类中被Inherited修饰的注解)
public Annotation[] getAnnotations(); 
// 获取声明的注解(但是不包括父类中被Inherited修饰的注解)
public Annotation[] getDeclaredAnnotations();
// 判断某个对象上是否被某个注解进行标注
public boolean isAnnotationPresent(Class<? extends Annotation> annotationClass)

// 获取某个类声明的所有字段
public Field[] getDeclaredFields() throws SecurityException;
// 获取某个方法
public Method getMethod(String name, Class<?>... parameterTypes);

@Documented
@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface RequiresLogin {

}

@Controller
@RequestMapping("/user")
public class UserController {
  @RequiresLogin
  @RequestMapping(value = "/list", produces = {"application/json;charset=UTF-8;"})
  public String getUserList(){

    System.out.println("--------------");
    return "[{'id': 1, 'username':'zhangsan'}]";
  }
}

public class LoginAdvices {
  public void before(JoinPoint joinPoint) throws Exception{

    Object target = joinPoint.getTarget();
    String methodName = joinPoint.getSignature().getName();

    System.out.println(target + "-------" + methodName);
    Method method = target.getClass().getMethod(methodName);
    boolean annotationPresent = method.isAnnotationPresent(RequiresLogin.class);
    if (annotationPresent) {
      // 用户必须登录
      boolean isLogin = false;
      if (!isLogin) {
        throw new Exception("访问该接口必须先登录");
      } else {
        System.out.println("已登录...");
      }
    }
  }
}

<bean id="loginAdvices" class="com.mengdee.manager.aop.LoginAdvices"/>
  <!-- aop配置 -->
  <aop:config proxy-target-class="true">
    <!--切面 -->
    <aop:aspect ref="loginAdvices">
      <!-- 切点 -->
      <aop:pointcut id="pointcut1" expression="execution(* com.mengdee.manager.controller.*.*(..))"/>
      <!--连接通知方法与切点 -->
      <aop:before method="before" pointcut-ref="pointcut1"/>
    </aop:aspect>
  </aop:config>

public class ShiroException extends RuntimeException {
  public ShiroException() {
  }

  public ShiroException(String message) {
    super(message);
  }

  public ShiroException(Throwable cause) {
    super(cause);
  }

  public ShiroException(String message, Throwable cause) {
    super(message, cause);
  }
}