Java 反射机制[Field反射]

jopen 10年前

1.  反射概念及功能

          反射就是把Java类中的各种成分映射成相应的Java类。例如一个Java类中用一个Class类的对象来表示。一个类中的组成部分分为成员变量,方法,构造方法,包等等。

          Java反射机制主要提供了以下功能: 判断在运行时任意一个对象所属的类;在运行时构造任意一个类的对象;判断在运行时任意一个类所具有的成员变量和方法;在运行时调用任意一个对象的方法;生成动态代理。

2.  Field反射

         以下代码将obj对象中的String类型的字段对应的Value中含有i的字符替换为abc。通过这个简单的案例进行初步分析Java的反射机制。

Java Code

/*    * System Abbrev :    * system Name  :    * Component No  :    * Component Name:    * File name     :ReflectTestMain.java    * Author        :Qiuzhenping    * Date          :2014-10-25    * Description   :  <description>    */         /* Updation record 1:     * Updation date        :  2014-10-25     * Updator          :  Qiuzhenping     * Trace No:  <Trace No>     * Updation No:  <Updation No>     * Updation Content:  <List all contents of updation and all methods updated.>     */    package com.qiuzhping.reflect.main;         import java.lang.reflect.Constructor;    import java.lang.reflect.Field;    import java.lang.reflect.Method;         /**     * <Description functions in a word>     * 反射就是把Java类中的各种成分映射成相应的Java类。     * <Detail description>     *     * @author  Qiuzhenping     * @version  [Version NO, 2014-10-25]     * @see  [Related classes/methods]     * @since  [product/module version]     */    public class ReflectTestMain {                  /** <default constructor>              */             public ReflectTestMain() {                       // TODO Auto-generated constructor stub             }                  /** <Description functions in a word>              * 2014-10-25              * <Detail description>              * @author  Qiuzhenping              * @param args [Parameters description]              * @return void [Return type description]              * @exception throws [Exception] [Exception description]              * @see [Related classes#Related methods#Related properties]              */             public static void main(String[] args) throws Exception{                       // TODO Auto-generated method stub                       //Constructor[] contructor = Person.class.getConstructors();                       //Method[] method = Person.class.getMethods();                       Person p = new Person(24, "Qiuzhping", "100001", "Qiuzhping");    //               Field [] field = p.getClass().getDeclaredFields();    //               for(Field f:field){    //                         f.setAccessible(true);    //                         System.out.println(f.getName());    //                         Object obj = f.get(p);    //                         System.out.println(obj);    //               }                       changeStringValue(p);                       System.out.println(p.toString());             }                  /** <Description functions in a word>              *  将obj对象中的String类型的字段对应的Value中含有i的字符替换为abc<BR>              *  2014-10-26              * <Detail description>              * @author  Qiuzhenping              * @param obj [Parameters description]              * @return void [Return type description]              * @exception throws [Exception] [Exception description]              * @see [Related classes#Related methods#Related properties]              */             private static void changeStringValue(Object obj) throws Exception {                       Field[] fields = obj.getClass().getDeclaredFields();                       for(Field f : fields){                                f.setAccessible(true);//暴力反射                                if(f.getType() == String.class){//字节码比较是用 ==                                         String oldValue = (String) f.get(obj);                                         String newValue = oldValue.replaceAll("i", "abc");//将所有的i替换为abc                                         f.set(obj, newValue);                                }                       }                                   }                          static class Person {                            public Person(int age, String name, String id, String pwd) {                                super();                                this.age = age;                                this.name = name;                                this.id = id;                                this.pwd = pwd;                       }                       @Override                       public String toString() {                                return "age = "+age +"\tname = "+name+"\tid = "+id+"\tpwd = "+pwd;                       }                       private int age;                       private String name;                       private String id;                       private String pwd;                       public int getAge() {                                return age;                       }                       public void setAge(int age) {                                this.age = age;                       }                       public String getName() {                                return name;                       }                       public void setName(String name) {                                this.name = name;                       }                       public String getId() {                                return id;                       }                       public void setId(String id) {                                this.id = id;                       }                       public String getPwd() {                                return pwd;                       }                       public void setPwd(String pwd) {                                this.pwd = pwd;                       }                       /** <default constructor>                        */                       public Person() {                                // TODO Auto-generated constructor stub                       }                  }    }