自定义Classloader实现类加载

1.test

package com.interview.javabasic.reflect;

public class ClassLoaderChecker {
    public static void main(String[] args) throws ClassNotFoundException, IllegalAccessException, InstantiationException {
        MyClassLoader m = new MyClassLoader("/Users/baidu/Desktop/", "myClassLoader");
        Class c = m.loadClass("Wali");
        System.out.println(c.getClassLoader());
        System.out.println(c.getClassLoader().getParent());
        System.out.println(c.getClassLoader().getParent().getParent());
        System.out.println(c.getClassLoader().getParent().getParent().getParent());
        c.newInstance();
    }
}


//wali
public class Wali{
   static{
      System.out.println("hello");
  }
}

2.自定义ClassLoader   MyClassLoader.java

package com.interview.javabasic.reflect;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;

public class MyClassLoader extends ClassLoader {
    private String path;
    private String classLoaderName;

    public MyClassLoader(String path, String classLoaderName) {
        this.path = path;
        this.classLoaderName = classLoaderName;
    }

    //用于寻找类文件
    @Override
    public Class findClass(String name) {
        byte[] b = loadClassData(name);
        return defineClass(name, b, 0, b.length);
    }

    //用于加载类文件
    private byte[] loadClassData(String name) {
        name = path + name + ".class";
        InputStream in = null;
        ByteArrayOutputStream out = null;
        try {
            in = new FileInputStream(new File(name));
            out = new ByteArrayOutputStream();
            int i = 0;
            while ((i = in.read()) != -1) {
                out.write(i);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                out.close();
                in.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return out.toByteArray();
    }
}