一、编写自定义类加载器类

package com.mybatis.entity;

import java.io.ByteArrayOutputStream;

import java.io.File;

import java.io.FileInputStream;

import java.io.IOException;

import java.io.InputStream;

import java.net.MalformedURLException;

import java.net.URL;

import java.net.URLConnection;

/**

* 自定义类加载器

* @author dgw

*

*/

public class MyClassLoader extends ClassLoader{

public Class> getClass(String name) throws ClassNotFoundException {

byte[] data=null;

try {

data = this.loadNetClassFile(name);

} catch (Exception e) {

e.printStackTrace();

}

return super.defineClass(name, data, 0, data.length);

}

/**

* 从磁盘加载

* @param name

* @return

* @throws Exception

*/

public byte[] loadClassFile(String name) throws Exception{

String fileName = name.substring(name.lastIndexOf(".")+1)+".class";

String filePath = "D:"+File.separator+fileName;

File file=new File(filePath);

InputStream input=new FileInputStream(file);

ByteArrayOutputStream baos = inputStreamToBytes(input);

return baos.toByteArray();

}

/**

* 从网络加载

* @param name

* @return

* @throws Exception

*/

public byte[] loadNetClassFile(String name) throws Exception{

String fileName = name.substring(name.lastIndexOf(".")+1)+".class";

URL url=new URL("http://localhost:8080/"+fileName);

URLConnection openConnection = url.openConnection();

InputStream input=openConnection.getInputStream();

ByteArrayOutputStream baos = inputStreamToBytes(input);

return baos.toByteArray();

}

private ByteArrayOutputStream inputStreamToBytes(InputStream input) throws IOException {

ByteArrayOutputStream baos=new ByteArrayOutputStream();

//必须定义byte数组才能使用InputStream

byte[] data=new byte[1024];

int len=0;//读取的个数

while((len=input.read(data))!=-1){

baos.write(data,0,len);

}

input.close();

baos.close();

return baos;

}

}

二、编写测试类

package com.mybatis.entity;

/**

* 自定义类加载器测试类

* @author dgw

*

*/

public class TestMyClassLoader {

public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException {

MyClassLoader load=new MyClassLoader();

Class> clazz = load.getClass("com.love.mapper.User");

Object newInstance = clazz.newInstance();

System.out.println(newInstance);

}

}

三、需要加载的类User类

package com.love.mapper;

public class User {

private Integer id;

private String name;

private Integer age;

public Integer getId() {

return id;

}

public void setId(Integer id) {

this.id = id;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name == null ? null : name.trim();

}

public Integer getAge() {

return age;

}

public void setAge(Integer age) {

this.age = age;

}

@Override

public String toString() {

return "自定义类加载器加载类，User [id=" + id + ", name=" + name + ", age=" + age + "]";

}

}

四、把测试类放到本地磁盘D盘

五、把此时类User.class放到tomcat根目录root下面

六、测试效果图