classLoader自定义类加载器

 下面是实现的案例，参考地址：https://www.cnblogs.com/szlbm/p/5504631.html

注意点：这个名称为class文件的全路径

 

package info.lumanman003;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.FileChannel;
import java.nio.channels.WritableByteChannel;

public class MyClassLoader extends ClassLoader
{
    public MyClassLoader()
    {
        
    }
    
    public MyClassLoader(ClassLoader parent)
    {
        super(parent);
    }
    
    protected Class<?> findClass(String name) throws ClassNotFoundException
    {
        File file = getClassFile(name);
        try
        {
            byte[] bytes = getClassBytes(file);
            Class<?> c = this.defineClass(name, bytes, 0, bytes.length);
            return c;
        } 
        catch (Exception e)
        {
            e.printStackTrace();
        }
        
        return super.findClass(name);
    }
    
    private File getClassFile(String name)
    {
        File file = new File("C:\\Users\\WM\\Desktop\\info\\lumanman003\\Person.class");
        return file;
    }
    
    private byte[] getClassBytes(File file) throws Exception
    {
        // 这里要读入.class的字节，因此要使用字节流
        FileInputStream fis = new FileInputStream(file);
        FileChannel fc = fis.getChannel();
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        WritableByteChannel wbc = Channels.newChannel(baos);
        ByteBuffer by = ByteBuffer.allocate(1024);
        
        while (true)
        {
            int i = fc.read(by);
            if (i == 0 || i == -1)
                break;
            by.flip();
            wbc.write(by);
            by.clear();
        }
        
        fis.close();
        
        return baos.toByteArray();
    }
}

package info.lumanman003;

public class Person
{
    private String name;
    
    public Person()
    {
        
    }
    
    public Person(String name)
    {
        this.name = name;
    }
    
    public String getName()
    {
        return name;
    }
    
    public void setName(String name)
    {
        this.name = name;
    }
    
    public String toString()
    {
    	System.out.println("被动态加载了");
        return "I am a person, my name is " + name;
    }
}

package info.lumanman003;

import java.lang.reflect.Method;

public class TestMyClassLoader
{
    public static void main(String[] args) throws Exception
    {
        MyClassLoader mcl = new MyClassLoader();        
        Class<?> findClass = mcl.findClass("info.lumanman003.Person");
        
        //Class<?> c1 = Class.forName("com.xrq.classloader.Person", true, mcl); 
        Object obj = findClass.newInstance();
        Method[] methods = findClass.getMethods();
        for(int i=0;i<methods.length;i++){
        	if(methods[i].getName().equals("toString")){
        		System.out.println("哈哈哈");
        		methods[i].invoke(obj);
        	}
        }
    }
}