Java 反射

反射


动态加载类
//Class.forName通过类名返回一个类的元类型
Class clz = Class.forName("User");
实例化类

访问类的成员

Object obj = clz.newInstance();//调用默认的构造方法

Class objArgs[] = {int.class,String.class,int.class};
Constructor objCons = clz.getDeclaredConstructor(objArgs);//调用指定参数类型的构造方法
Object obj1 = objCons.newInstance(2,"Pang niu",26); 

--示例
--Bean类

public class User {
	
	private int id;
	private int age;
	private String name;
	public User(){}
	public User(int id,String name,int age){
		this.id = id;
		this.name = name;
		this.age = age;
	}
	public int getAge() {
		return age;
	}
	private void setAge(int age) {
		this.age = age;
	}
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	
	public String toString(){
		return "ID:"+this.id+" NAME:"+this.name+" Age:"+this.age;
	}
	
}


import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;


public class Main {

	/**
	 * @param args
	 * @throws ClassNotFoundException  类不存在的异常
	 * @throws IllegalAccessException  非法访问异常
	 * @throws InstantiationException  实例化异常,比如构造函数为PRIVATE
	 * @throws NoSuchMethodException 
	 * @throws SecurityException 
	 * @throws InvocationTargetException 
	 * @throws IllegalArgumentException 非法参数异常
	 */
	public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, SecurityException, NoSuchMethodException, IllegalArgumentException, InvocationTargetException {
		//动态加载类
		//Class.forName通过类名返回一个类的元类型
		Class clz = Class.forName("User");
		Object obj = clz.newInstance();//调用默认的构造方法		
		Method mSetId = clz.getMethod("setId", int.class);//必须指定方法的参数类型,得到唯一的方法。只能访问Public的方法
		mSetId.invoke(obj, 1);
		Method mSetName = clz.getMethod("setName", String.class);
		mSetName.invoke(obj, "Anker");
//		Method mSetAge = clz.getMethod("setAge", int.class);//方法为private,无法访问,只能访问public修饰
		Method mSetAge = clz.getDeclaredMethod("setAge", int.class);//
		mSetAge.setAccessible(true);//针对缺少可视性的方法,设置为可以访问
		mSetAge.invoke(obj, 27);
		System.out.println(obj.toString());		
		Class objArgs[] = {int.class,String.class,int.class};
		Constructor objCons = clz.getDeclaredConstructor(objArgs);
		Object obj1 = objCons.newInstance(2,"Pang niu",26);
		System.out.println(obj1);
	}

}

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;


public class Main2 {

	/**
	 * @param args
	 * @throws ClassNotFoundException  类不存在的异常
	 * @throws IllegalAccessException  非法访问异常
	 * @throws InstantiationException  实例化异常,比如构造函数为PRIVATE
	 * @throws NoSuchMethodException 
	 * @throws SecurityException 
	 * @throws InvocationTargetException 
	 * @throws IllegalArgumentException 非法参数异常
	 * @throws NoSuchFieldException 
	 */
	public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, SecurityException, NoSuchMethodException, IllegalArgumentException, InvocationTargetException, NoSuchFieldException {
		//动态加载类
		//Class.forName通过类名返回一个类的元类型
		Class clz = Class.forName("User");
		Object obj = clz.newInstance();
		
//		Field  fId = clz.getField("id"); //只能访问public的属性,否者报错Java.Lang.NoSuchFileException
//		Field  fName = clz.getField("name");		
		Field  fId1 = clz.getDeclaredField("id"); //只能访问public的属性,除非setAccessible来访问protected或者private的权限
		Field  fName1 = clz.getDeclaredField("setAge");
		fId1.setAccessible(true);
		fName1.setAccessible(true);
		fId1.set(obj, 1);
		fName1.set(obj, "Anker");
		System.out.println(obj);
	}

}


一些重要的反射API

public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException, SecurityException, NoSuchMethodException, IllegalArgumentException, InvocationTargetException, NoSuchFieldException {
	//动态加载类
	//Class.forName通过类名返回一个类的元类型
	Class clz = Class.forName("User");
	Method[] mthods = clz.getMethods();//获得所有的方法,包括从父类继承的方法
	for(Method m:mthods){
		if(m.getDeclaringClass() == clz){ //查询本类定义的方法
		System.out.println(m);
		if(Modifier.isStatic(m.getModifiers())){//判断方法是否是static
			System.out.println();//
		}
		System.out.println(m.getModifiers());//以整型代表方法的修饰符
		}
	}
}
反射与动态代码


Java 提供的动态代码的实现，为代理类与实现类继承同一个接口，针对接口要实现的方法可以实现动态代理。
package DymaticProxy;

public interface IWork {	
	public void run();
}


package DymaticProxy;
public class Worker implements IWork{
	
	public void run() {
		System.out.println("in work run");
		try {
			Thread.sleep(1000);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}

package DymaticProxy;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class LoggerProxy implements InvocationHandler {
	Object target = null;

	public Object newProxyInstance(Object targetObject) {
		target = targetObject;
		return Proxy.newProxyInstance(targetObject.getClass().getClassLoader(),
				target.getClass().getInterfaces(), this);
	}

	@Override
	public Object invoke(Object proxy, Method method, Object[] args)
			throws Throwable {
		System.out.println("start-->>" + method.getName());
		try {
			method.invoke(target, args);
			System.out.println("success-->" + method.getName());
		} catch (Exception ex) {
			ex.printStackTrace();
			System.out.println("error-->>" + method.getName());
			throw ex;
		}
		return null;
	}
}

JDK的动态代理机制只能代理实现了接口的类，而不能实现接口的类就不能实现JDK的动态代理，

CGlib 实现代理类与实现类可以不继承相同接口，通过创建继承代理类，来实现动态代理，

它的原理是对指定的目标类生成一个子类，并覆盖其中方法实现增强，
但因为采用的是继承，所以不能对final修饰的类进行代理。
具体查看附件。