Java 反射机制[Field反射]

1. 反射概念及功能

反射就是把Java类中的各种成分映射成对应的Java类。比如一个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下面功能：推断在执行时随意一个对象所属的类；在执行时构造随意一个类的对象；推断在执行时随意一个类所具有的成员变量和方法；在执行时调用随意一个对象的方法。生成动态代理。

2. Field反射

下面代码将obj对象中的String类型的字段相应的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对应的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类型的字段相应的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){//字节码比較是用 ==

String oldValue = (String) f.get(obj);

String newValue = oldValue.replaceAll("i", "abc");//将全部的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 +" name = "+name+" id = "+id+" pwd = "+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

}