高级篇 KZ002.反射读取注解[未封装]
2016-04-29 07:59
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创建自定义注解
复习一下:
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
方法的注解解析,代码改造如下
参数注解解析:
变量注解解析:
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。 |
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(); } } |
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()"); } } } |
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()"); } } } |
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 |
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()"); } } } |
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