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java自定义注解及其信息提取

转自：https://xuwenjin666.iteye.com/blog/1637247

1. 自定义注解

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.annotation.ElementType;
import java.lang.annotation.Documented;

@Documented
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Haha {
String author();
String desc();
String date();
String[] checkPoint();
}

 

2. 使用自定义注解

public class MyAnnotation {
    @Haha(author = "hahaAuthor1",
            desc = "hahaDesc",
            date="2019-03-01",
            checkPoint = {"1","2"}
    )
    public void useMyAnnotation1(){
        System.out.println("MyAnnotation.useMyAnnotation1");}

@Haha(author </span>= "hahaAuthor2"<span style="color: rgba(0, 0, 0, 1)">,
        desc </span>= "hahaDesc"<span style="color: rgba(0, 0, 0, 1)">,
        date</span>="2019-03-01"<span style="color: rgba(0, 0, 0, 1)">,
        checkPoint </span>= {"1","2"<span style="color: rgba(0, 0, 0, 1)">}
)
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> useMyAnnotation2(){
    System.out.println(</span>"MyAnnotation.useMyAnnotation2"<span style="color: rgba(0, 0, 0, 1)">);
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> notUseAnnotation(){
    System.out.println(</span>"MyAnnotation.notUseMyAnnotation"<span style="color: rgba(0, 0, 0, 1)">);

}



}

 

3. 信息提取

import java.lang.reflect.Method;
import java.lang.annotation.Annotation;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import com.google.gson.Gson;

public class GetMyAnnotatioinInfo {
public static GetMyAnnotatioinInfo info = null;


</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">static</span><span style="color: rgba(0, 0, 0, 1)"> GetMyAnnotatioinInfo getInstance(){
    </span><span style="color: rgba(0, 0, 255, 1)">if</span>(info == <span style="color: rgba(0, 0, 255, 1)">null</span>) info = <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> GetMyAnnotatioinInfo();
    </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> info;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span> Map&lt;String, String&gt; getAnnotationInfo(Class annotationClass, String annotationField, String className) <span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> Exception{
    Method[] methods </span>=<span style="color: rgba(0, 0, 0, 1)"> Class.forName(className).getDeclaredMethods();

    System.out.println(</span>"类中所有方法名"<span style="color: rgba(0, 0, 0, 1)">);
    </span><span style="color: rgba(0, 0, 255, 1)">for</span><span style="color: rgba(0, 0, 0, 1)">(Method m : methods) System.out.println(m.getName());

    System.out.println(</span>"目标注解名：" + annotationClass.getName() + " 类中使用了目标注解的方法有："<span style="color: rgba(0, 0, 0, 1)">);
    Map</span>&lt;String, String&gt; map = <span style="color: rgba(0, 0, 255, 1)">new</span> HashMap&lt;&gt;<span style="color: rgba(0, 0, 0, 1)">();
    Gson gson </span>= <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> Gson();
    </span><span style="color: rgba(0, 0, 255, 1)">for</span><span style="color: rgba(0, 0, 0, 1)"> (Method m : methods){
        </span><span style="color: rgba(0, 0, 255, 1)">if</span><span style="color: rgba(0, 0, 0, 1)">(m.isAnnotationPresent(annotationClass)){
            System.out.println(m.getName());
            Annotation an </span>=<span style="color: rgba(0, 0, 0, 1)"> m.getAnnotation(annotationClass);
            Method anMethod </span>= an.getClass().getDeclaredMethod(annotationField, <span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">);
            Object object </span>= anMethod.invoke(an, <span style="color: rgba(0, 0, 255, 1)">null</span><span style="color: rgba(0, 0, 0, 1)">);
            map.put(m.getName() </span>+ "." +<span style="color: rgba(0, 0, 0, 1)"> annotationField, gson.toJson(object));
        }
    }
    </span><span style="color: rgba(0, 0, 255, 1)">return</span><span style="color: rgba(0, 0, 0, 1)"> map;
}

</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">static</span> <span style="color: rgba(0, 0, 255, 1)">void</span> main(String[] args) <span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> Exception{
    GetMyAnnotatioinInfo anInfo </span>=<span style="color: rgba(0, 0, 0, 1)"> GetMyAnnotatioinInfo.getInstance();

    Map</span>&lt;String, String&gt; res = anInfo.getAnnotationInfo(Haha.<span style="color: rgba(0, 0, 255, 1)">class</span>, "author", MyAnnotation.<span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)">.getName());
    res.putAll(anInfo.getAnnotationInfo(Haha.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, "checkPoint", MyAnnotation.<span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)">.getName()));

    System.out.println(</span>"以上注释名及内容如下："<span style="color: rgba(0, 0, 0, 1)">);
    </span><span style="color: rgba(0, 0, 255, 1)">for</span>(Map.Entry&lt;String, String&gt;<span style="color: rgba(0, 0, 0, 1)"> entry : res.entrySet()){
        System.out.println(entry.getKey() </span>+ " = " +<span style="color: rgba(0, 0, 0, 1)"> entry.getValue());
    }
}



}

 

4. 执行结果

类中所有方法名
useMyAnnotation2
notUseAnnotation
useMyAnnotation1
目标注解名：Haha 类中使用了目标注解的方法有：
useMyAnnotation2
useMyAnnotation1
类中所有方法名
useMyAnnotation2
notUseAnnotation
useMyAnnotation1
目标注解名：Haha 类中使用了目标注解的方法有：
useMyAnnotation2
useMyAnnotation1
以上注释名及内容如下：
useMyAnnotation1.author = "hahaAuthor1"
useMyAnnotation2.author = "hahaAuthor2"
useMyAnnotation2.checkPoint = ["1","2"]
useMyAnnotation1.checkPoint = ["1","2"]

 

 5. 补充

5.1. 注解的定义：Java 文件叫做 Annotation，用 @interface 表示。

5.2. 元注解：@interface 上面按需要注解上一些东西，包括 @Retention、@Target、@Document、@Inherited 四种。

5.3. 注解的保留策略：

  • 　　@Retention(RetentionPolicy.SOURCE)   // 注解仅存在于源码中，在 class 字节码文件中不包含
  • 　　@Retention(RetentionPolicy.CLASS)     // 默认的保留策略，注解会在 class 字节码文件中存在，但运行时无法获得
  • 　　@Retention(RetentionPolicy.RUNTIME)  // 注解会在 class 字节码文件中存在，在运行时可以通过反射获取到

5.4. 注解的作用目标：

  • 　　@Target(ElementType.TYPE)                      // 接口、类、枚举、注解
  • 　　@Target(ElementType.FIELD)                     // 字段、枚举的常量
  • 　　@Target(ElementType.METHOD)                 // 方法
  • 　　@Target(ElementType.PARAMETER)            // 方法参数
  • 　　@Target(ElementType.CONSTRUCTOR)       // 构造函数
  • 　　@Target(ElementType.LOCAL_VARIABLE)   // 局部变量
  • 　　@Target(ElementType.ANNOTATION_TYPE) // 注解
  • 　　@Target(ElementType.PACKAGE)               // 包

5.5. 注解包含在 javadoc 中：

  • 　　@Documented

5.6. 注解可以被继承：

  • 　　@Inherited

5.7. 注解解析器：用来解析自定义注解。