高级篇 KZ002.反射读取注解[未封装]

创建自定义注解

package com.hanpang.java;

/**

* 注解说明: 方法的文档注释

*

* @Author: 胖先生

* @Create: 2016-04-27 10:29

* @Home: http://www.cnblogs.com/pangxiansheng/

*/

import java.lang.annotation.Documented;

import java.lang.annotation.ElementType;

import java.lang.annotation.Inherited;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

@Documented

@Target(ElementType.METHOD)

@Inherited

@Retention(RetentionPolicy.RUNTIME)

public @interface MethodInfo{

String author() default "hanpang";

String date();

int revision() default 1;

String comments();

}

• 注解方法不能有参数。
• 注解方法的返回类型局限于原始类型，字符串，枚举，注解，或以上类型构成的数组。
• 注解方法可以包含默认值。
• 注解可以包含与其绑定的元注解，元注解为注解提供信息，有四种元注解类型：
  • @Documented – 表示使用该注解的元素应被javadoc或类似工具文档化，它应用于类型声明，类型声明的注解会影响客户端对注解元素的使用。如果一个类型声明添加了Documented注解，那么它的注解会成为被注解元素的公共API的一部分。
  • @Target – 表示支持注解的程序元素的种类，一些可能的值有TYPE, METHOD, CONSTRUCTOR, FIELD等等。如果Target元注解不存在，那么该注解就可以使用在任何程序元素之上。
  • @Inherited – 表示一个注解类型会被自动继承，如果用户在类声明的时候查询注解类型，同时类声明中也没有这个类型的注解，那么注解类型会自动查询该类的父类，这个过程将会不停地重复，直到该类型的注解被找到为止，或是到达类结构的顶层（Object）。
  • @Retention – 表示注解类型保留时间的长短，它接收RetentionPolicy参数，可能的值有SOURCE, CLASS, 以及RUNTIME。

复习一下:

package com.hanpang.java;

import java.io.FileNotFoundException;

import java.util.ArrayList;

import java.util.List;

/**

* 类说明: 完整点的示例

* @Author: 胖先生

* @Create: 2016-04-27 11:24

*/

public class AnnotationExample {

public static void main(String[] args) {

}

@Override //什么意思?

@MethodInfo(author = "wukong", comments = "重写了toString方法", date = "2016-04-27", revision = 1)

public String toString() {

return "Overriden toString method";

}

@Deprecated //什么意思?

@MethodInfo(comments = "该方法已经过时了,被放弃了", date = "2016-04-27")

public static void oldMethod() {

System.out.println("old method, don't use it.");

}

@SuppressWarnings({ "unchecked", "deprecation" }) //什么意思?

@MethodInfo(author = "bajie", comments = "这里方法里面有警告哟!", date = "2016-04-27", revision = 10)

public static void genericsTest() throws FileNotFoundException {

List l = new ArrayList();

l.add("abc");

oldMethod();

}

}

复习搞一段落,那么我们现在来学习关于注解的解析操作,如果有时间,我会写一个关于Excel的操作的工具

Java注解解析

我们将使用Java反射机制从一个类中解析注解，请记住，注解保持性策略应该是RUNTIME，否则它的信息在运行期无效，我们也不能从中获取任何数据。

类注解的解析

package com.hanpang.java;

import java.lang.annotation.*;

/**

* 类说明: 定义类的注解

*/

@Documented

@Retention(RetentionPolicy.RUNTIME)

@Target(ElementType.TYPE)

public @interface ClassInfo {

String value() default "";

String className();

}

package com.hanpang.java;

@ClassInfo(value = "标注在类上",className = "-->com.hanpang.java.AnnotationExample")

public class AnnotationExample {

public static void main(String[] args) {

}

}

类注解

你可以在运行期访问类，方法或者变量的注解信息，下是一个访问类注解的例子：

public class AnnotationParsing {

public static void main(String[] args) {

//1.获取Class

Class clz = AnnotationExample.class;

//2.获取类的所有注解

Annotation[] annotations = clz.getAnnotations();

//3.进行迭代

for (Annotation annotation : annotations) {

//4.判断获取的是否是我们自己写的注解

if (annotation instanceof ClassInfo) {

ClassInfo ci = (ClassInfo) annotation;

//5.获取属性值,并且进行测试

System.out.println("-->>hanpang<<--value值=" + ci.value() + "," + "当前类=AnnotationParsing.main()");

System.out.println("-->>hanpang<<--className值=" + ci.className() + "," + "当前类=AnnotationParsing.main()");

}

}

}

}

运行结果为:
-->>hanpang<<--value值=标注在类上,当前类=AnnotationParsing.main()

-->>hanpang<<--className值=-->com.hanpang.java.AnnotationExample,当前类=AnnotationParsing.main()

你还可以像下面这样指定访问一个类的注解：[如果你已经知道你要对哪个注解进行处理]

public class AnnotationParsing {

public static void main(String[] args) {

//1.获取Class

Class clz = AnnotationExample.class;

//2.获取你想要的注解

Annotation annotation = clz.getAnnotation(ClassInfo.class);

//3.判断是否匹配

if(annotation instanceof ClassInfo){

ClassInfo ci = (ClassInfo) annotation;

//获取属性值,并且进行测试

System.out.println("-->>hanpang<<--value值=" + ci.value() + "," + "当前类=AnnotationParsing.main()");

System.out.println("-->>hanpang<<--className值=" + ci.className() + "," + "当前类=AnnotationParsing.main()");

}

}

}

方法的注解解析,代码改造如下

package com.hanpang.java;

import java.io.FileNotFoundException;

import java.util.ArrayList;

import java.util.List;

@ClassInfo(value = "标注在类上",className = "-->com.hanpang.java.AnnotationExample")

public class AnnotationExample {

public static void main(String[] args) {

}

@Override

@MethodInfo(author = "wukong", comments = "Main method", date = "2016-04-27", revision = 1)

public String toString() {

return "Overriden toString method";

}

@Deprecated

@MethodInfo(comments = "deprecated method", date = "2016-04-27")

public static void oldMethod() {

System.out.println("old method, don't use it.");

}

@SuppressWarnings({ "unchecked", "deprecation" })

@MethodInfo(author = "bajie", comments = "Main method", date = "2016-04-27", revision = 10)

public static void genericsTest() throws FileNotFoundException {

List l = new ArrayList();

l.add("abc");

oldMethod();

}

}

方法注解,解析操作:

package com.hanpang.java;

import java.lang.annotation.Annotation;

import java.lang.reflect.Method;

public class AnnotationParsing {

public static void main(String[] args) throws NoSuchMethodException {

//1.实例化对象

AnnotationExample ae = new AnnotationExample();

//2.获取方法的对象--->>>这里写的有点简单类,如果是全部方法请使用数组

Method method = ae.getClass().getMethod("toString");//方法名

Annotation[] annotations = method.getAnnotations();

for (Annotation annotation : annotations) {

if(annotation instanceof MethodInfo){

MethodInfo mi = (MethodInfo)annotation;

System.out.println("-->>hanpang<<--author值=" + mi.author() + "," + "当前类=AnnotationParsing.main()");

System.out.println("-->>hanpang<<--commonts值=" + mi.comments() + "," + "当前类=AnnotationParsing.main()");

System.out.println("-->>hanpang<<--date值=" + mi.date() + "," + "当前类=AnnotationParsing.main()");

System.out.println("-->>hanpang<<--revision=" + mi.revision() + "," + "当前类=AnnotationParsing.main()");

}

}

}

}

运行结果为:
-->>hanpang<<--author值=wukong,当前类=AnnotationParsing.main()

-->>hanpang<<--commonts值=Main method,当前类=AnnotationParsing.main()

-->>hanpang<<--date值=2016-04-27,当前类=AnnotationParsing.main()

-->>hanpang<<--revision=1,当前类=AnnotationParsing.main()

另一种写法:

public class AnnotationParsing {

public static void main(String[] args) throws NoSuchMethodException {

//1.实例化对象

AnnotationExample ae = new AnnotationExample();

//2.获取方法的对象--->>>这里写的有点简单类,如果是全部方法请使用数组

Method method = ae.getClass().getMethod("toString");

Annotation annotation = method.getAnnotation(MethodInfo.class);

if(annotation instanceof MethodInfo){

MethodInfo mi = (MethodInfo)annotation;

System.out.println("-->>hanpang<<--author值=" + mi.author() + "," + "当前类=AnnotationParsing.main()");

System.out.println("-->>hanpang<<--commonts值=" + mi.comments() + "," + "当前类=AnnotationParsing.main()");

System.out.println("-->>hanpang<<--date值=" + mi.date() + "," + "当前类=AnnotationParsing.main()");

System.out.println("-->>hanpang<<--revision=" + mi.revision() + "," + "当前类=AnnotationParsing.main()");

}

}

}

参数注解解析:

package com.hanpang.java;

/**

* 新增参数注解

*/

import java.lang.annotation.*;

@Documented

@Target(ElementType.PARAMETER)

@Retention(RetentionPolicy.RUNTIME)

public @interface ParameterInfo {

String value() default "hanpang";

String desc();

}

//加大加粗为新增代码部分
package com.hanpang.java;

import java.io.FileNotFoundException;

import java.util.ArrayList;

import java.util.List;

@ClassInfo(value = "标注在类上",className = "-->com.hanpang.java.AnnotationExample")

public class AnnotationExample {

public static void main(String[] args) {

}

@Override

@MethodInfo(author = "wukong", comments = "Main method", date = "2016-04-27", revision = 1)

public String toString() {

return "Overriden toString method";

}

@Deprecated

@MethodInfo(comments = "deprecated method", date = "2016-04-27")

public static void oldMethod(@ParameterInfo(value = "刘文铭",desc = "测试参数注解解析") String user_name) {

System.out.println("old method, don't use it."+user_name);

}

@SuppressWarnings({ "unchecked", "deprecation" })

@MethodInfo(author = "bajie", comments = "Main method", date = "2016-04-27", revision = 10)

public static void genericsTest() throws FileNotFoundException {

List l = new ArrayList();

l.add("abc");

oldMethod("悟空");

}

}

package com.hanpang.java;

import java.lang.annotation.Annotation;

import java.lang.reflect.Method;

public class AnnotationParsing {

public static void main(String[] args) throws NoSuchMethodException {

//1.实例化对象

AnnotationExample ae = new AnnotationExample();

//2.获取方法对象

Method method = ae.getClass().getMethod("oldMethod",java.lang.String.class);

//3.获取参数的注解, 注意这里是二维数组

Annotation[][] parameterAnnotations = method.getParameterAnnotations();

//4.

Class[] parameterTypes = method.getParameterTypes();

for (int i = 0; i < parameterAnnotations.length; i++) {

Annotation[] annotations = parameterAnnotations[i];

Class parameterType = parameterTypes[i];

//继续迭代

for (Annotation annotation : annotations) {

if (annotation instanceof ParameterInfo){

ParameterInfo pi = (ParameterInfo)annotation;

System.out.println("-->>hanpang<<--数据类型值=" + parameterType.getName() + "," + "当前类=AnnotationParsing.main()");

System.out.println("-->>hanpang<<--pi.value()值=" + pi.value() + "," + "当前类=AnnotationParsing.main()");

System.out.println("-->>hanpang<<--pi.desc()值=" + pi.desc() + "," + "当前类=AnnotationParsing.main()");

}

}

}

}

}

运行结果:

-->>hanpang<<--数据类型值=java.lang.String,当前类=AnnotationParsing.main()

-->>hanpang<<--pi.value()值=刘文铭,当前类=AnnotationParsing.main()

-->>hanpang<<--pi.desc()值=测试参数注解解析,当前类=AnnotationParsing.main()

注意:需要注意的是 Method.getParameterAnnotations()方法返回一个注解类型的二维数组，每一个方法的参数包含一个注解数组

变量注解解析:

package com.hanpang.java;

import java.lang.annotation.*;

@Documented

@Target(ElementType.FIELD)

@Retention(RetentionPolicy.RUNTIME)

public @interface FieldInfo {

String value() default "hanpang";

String desc();

}

@ClassInfo(value = "标注在类上",className = "-->com.hanpang.java.AnnotationExample")

public class AnnotationExample {

//新增代码

@FieldInfo(value = "方位为属性和字段",desc = "不测试了,累挺!!")

public String account = null;

public static void main(String[] args) {

}

@Override

@MethodInfo(author = "wukong", comments = "Main method", date = "2016-04-27", revision = 1)

public String toString() {

return "Overriden toString method";

}

@Deprecated

@MethodInfo(comments = "deprecated method", date = "2016-04-27")

public static void oldMethod(@ParameterInfo(value = "刘文铭",desc = "测试参数注解解析") String user_name) {

System.out.println("old method, don't use it."+user_name);

}

@SuppressWarnings({ "unchecked", "deprecation" })

@MethodInfo(author = "bajie", comments = "Main method", date = "2016-04-27", revision = 10)

public static void genericsTest() throws FileNotFoundException {

List l = new ArrayList();

l.add("abc");

oldMethod("悟空");

}

}

package com.hanpang.java;

import java.lang.annotation.Annotation;

import java.lang.reflect.Field;

import java.lang.reflect.Method;

public class AnnotationParsing {

public static void main(String[] args) throws NoSuchMethodException, NoSuchFieldException {

//1.获取类

Class clz = AnnotationExample.class;

//2.获取属性对象

Field field = clz.getField("account");//clz.getDeclaredField() 没有测试

//3.获取注解数组

Annotation[] annotations = field.getAnnotations();

for (Annotation annotation : annotations) {

if(annotation instanceof FieldInfo){

FieldInfo fi = (FieldInfo)annotation;

System.out.println("-->>hanpang<<--fi.value()值=" + fi.value() + "," + "当前类=AnnotationParsing.main()");

System.out.println("-->>hanpang<<--fi.desc()值=" + fi.desc() + "," + "当前类=AnnotationParsing.main()");

}

}

}

}

运行结果:

-->>hanpang<<--fi.value()值=方位为属性和字段,当前类=AnnotationParsing.main()

-->>hanpang<<--fi.desc()值=不测试了,累挺!!,当前类=AnnotationParsing.main()

package com.hanpang.java;

import java.lang.annotation.Annotation;

import java.lang.reflect.Field;

import java.lang.reflect.Method;

public class AnnotationParsing {

public static void main(String[] args) throws NoSuchMethodException, NoSuchFieldException {

//1.获取类

Class clz = AnnotationExample.class;

//2.获取属性 注意一定是public的,如果set方法需要单独进行处理

Field field = clz.getField("account");//clz.getDeclaredField() 没有测试

//3.获取注解数组

Annotation annotation = field.getAnnotation(FieldInfo.class);

if(annotation instanceof FieldInfo){

FieldInfo fi = (FieldInfo)annotation;

System.out.println("-->>hanpang<<--fi.value()值=" + fi.value() + "," + "当前类=AnnotationParsing.main()");

System.out.println("-->>hanpang<<--fi.desc()值=" + fi.desc() + "," + "当前类=AnnotationParsing.main()");

}

}

}