Java 中类的加载器和反射

package org.lovian.reflection;

public class Person {
	private String name;
	int age;
	public String address;

	Person() {
		super();
	}

	public Person(String name, int age) {
		super();
		this.name = name;
		this.age = age;
	}

	private Person(String name, int age, String address) {
		super();
		this.name = name;
		this.age = age;
		this.address = address;
	}

	public void show() {
		System.out.println("name: " + name + " age: " + age);
	}

	@Override
	public String toString() {
		return "Person [name=" + name + ", age=" + age + ", address=" + address + "]";
	}
}

package org.lovian.reflection;

import java.lang.reflect.Constructor;

public class GetConstructorDemo {
	public static void main(String[] args) throws Exception {
		// 获取 Class 对象
		Class c = Class.forName("org.lovian.reflection.Person");

		// 获取所有公共构造方法
		Constructor[] cons = c.getConstructors();
		for (Constructor constructor : cons) {
			System.out.println(constructor);
		}
		System.out.println("=====================================");

		// 获取所有构造方法
		Constructor[] allCons = c.getDeclaredConstructors();
		for (Constructor constructor : allCons) {
			System.out.println(constructor);
		}
		System.out.println("=====================================");

		// 获取指定的公共构造方法
		Constructor constructor1 = c.getConstructor(String.class, int.class);
		Object obj1 = constructor1.newInstance("Xiaoming", 23);
		Person s1 = (Person) obj1;
		s1.show();
		System.out.println("=====================================");

		// 获取指定的任一构造方法，此处获取私有构造方法
		Constructor constructor2 = c.getDeclaredConstructor(String.class, int.class, String.class);
		constructor2.setAccessible(true);
		Object obj2 = constructor2.newInstance("Xiaohong", 20, "Pekin");
		Person s2 = (Person) obj2;
		s2.show();
	}
}

public org.lovian.reflection.Person(java.lang.String,int)
=====================================
private org.lovian.reflection.Person(java.lang.String,int,java.lang.String)
public org.lovian.reflection.Person(java.lang.String,int)
org.lovian.reflection.Person()
=====================================
name: Xiaoming age: 23
=====================================
name: Xiaohong age: 20

package org.lovian.reflection;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;

public class GetFieldDemo {
	public static void main(String[] args) throws Exception {
		// 获取字节码文件对象
		Class c = Class.forName("org.lovian.reflection.Person");

		// 获取所有公共的成员变量对象
		Field[] fields = c.getFields();
		for (Field field : fields) {
			System.out.println(field);
		}
		System.out.println("===========================");

		// 获取所有的成员变量对象
		Field[] allFields = c.getDeclaredFields();
		for (Field field : allFields) {
			System.out.println(field);
		}
		System.out.println("===========================");

		// 通过无参构造来创建对象
		Constructor con = c.getDeclaredConstructor();
		con.setAccessible(true);
		Object obj = con.newInstance();

		// 获取成员变量 address
		// 将指定对象变量上值设置为新值
		Field addressField = c.getField("address");
		addressField.set(obj, "Pekin"); // 给 obj 对象的 addressFiled 字段设置值为“Pekin”
		Field nameField = c.getDeclaredField("name");
		nameField.setAccessible(true);
		nameField.set(obj, "Xiaoming"); // 给 obj 对象的 nameFiled 字段设置值为“Xiaoming”
		Field ageField = c.getDeclaredField("age");
		ageField.setAccessible(true);
		ageField.set(obj, 20); // 给 obj 对象的 ageFiled 字段设置值为 20
		((Person) obj).show();
	}
}

package org.lovian.reflection;

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

public class GetMethodDemo {
	public static void main(String[] args) throws Exception{
		// 获取字节码文件对象
		Class c = Class.forName("org.lovian.reflection.Person");

		// 获取所有公共方法
		Method[] methods = c.getMethods();
		for (Method method : methods) {
			System.out.println(method);
		}
		System.out.println("==================================");

		// 获取所有方法
		Method[] allMethods = c.getDeclaredMethods();
		for (Method method : allMethods) {
			System.out.println(method);
		}
		System.out.println("==================================");

		// 通过反射创建对象
		Constructor con = c.getDeclaredConstructor();
		con.setAccessible(true);
		Object obj = con.newInstance();

		// 获取 show 方法并访问
		Method m1 = c.getMethod("show", null);
		m1.invoke(obj, null);
	}
}

// 读取 propeties 配置文件
// 注意： 在加载配置文件的时候，路径可以用绝对路径，也可以使用默认的项目下路径
// 还可以使用反射的方式： 当前类.class.getClassLoader.getResourceAsStream("config.properties") 来加载
InputStream is = new FileInputStream("config.properties");
Properties props = new Properties();
// 加载 inputstream
props.load(is);
ips.close();

// 获取配置的 className
String className = props.getProperty("className");
// 获取相应的 class 文件
Class c = Class.forName(className);
// 创建配置的 className 的实例对象
c.newInstance();

package org.lovian.reflection.proxy;

public interface UserDao {

	void add();

	void delete();

	void update();

	void find();
}


package org.lovian.reflection.proxy;

public class UserDaoImpl implements UserDao{

	@Override
	public void add() {
		System.out.println("add method");
	}

	@Override
	public void delete() {
		System.out.println("delete method");
	}

	@Override
	public void update() {
		System.out.println("update method");
	}

	@Override
	public void find() {
		System.out.println("find method");
	}

}

package org.lovian.reflection.proxy;

import java.lang.reflect.Proxy;

public class Test {
	public static void main(String[] args) {
		UserDao ud = new UserDaoImpl();
		System.out.println("-----original--");
		ud.add();
		ud.delete();
		ud.update();
		ud.find();
	}
}

package org.lovian.reflection.proxy;

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

public class MyInvocationHandler implements InvocationHandler {

	private Object target; //目标对象

	public MyInvocationHandler(Object target) {
		this.target = target;
	}

	@Override
	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

		// 添加权限校验功能
		System.out.println("Check privilege");
		Object result = method.invoke(target, args);
		// 添加日志记录功能
		System.out.println("Log Info");
		// 返回代理对象
		return result;
	}
}

package org.lovian.reflection.proxy;

import java.lang.reflect.Proxy;

public class Test {
	public static void main(String[] args) {
		UserDao ud = new UserDaoImpl();
		System.out.println("-----original--");
		ud.add();
		ud.delete();
		ud.update();
		ud.find();

		System.out.println();
		System.out.println("-------Proxy---");

		// 使用 Proxy 类来创建一个动态代理对象
		// public static Object newProxyInstance(ClassLoader loader,Class<?>[] interfaces,InvocationHandler h)
		// 创建一个 InvacationHandler 的实现类对象， 传入 ud 作为目标对象
		MyInvocationHandler handler = new MyInvocationHandler(ud);
		// 创建代理对象，返回一个对象
		Object proxyObj = Proxy.newProxyInstance(ud.getClass().getClassLoader(), ud.getClass().getInterfaces(), handler);
		// 这个返回的对象，其实和传入的对象是同一个类型
		UserDao proxyUd = (UserDao) proxyObj;

		proxyUd.add();
		proxyUd.delete();
		proxyUd.update();
		proxyUd.find();
	}
}