三层类加载器、双亲委派模型--Java类加载器总结分析

package Q2;

import java.io.IOException;
import java.io.InputStream;

public class ClassLoaderTest {
    public static void main(String[] args) throws Exception {
        ClassLoader myLoader = new ClassLoader() {
            @Override
            public Class<?> loadClass(String name) throws ClassNotFoundException {
                try {
                    String fileName = name.substring(name.indexOf(".") + 1)+".class";
                    InputStream is = getClass().getResourceAsStream(fileName);
                    if (is == null) {
                        return super.loadClass(name);
                    }
                    byte[] b = new byte[is.available()];
                    is.read(b);
                    return defineClass(name,b,0,b.length);
                } catch (IOException e) {
                    throw new ClassNotFoundException(name);
                }
            }
        };

        Object obj = myLoader.loadClass("Q2.ClassLoaderTest").newInstance();

        System.out.println(obj.getClass());
        System.out.println(obj instanceof Q2.ClassLoaderTest);
    }
}

class Q2.ClassLoaderTest
false

protected synchronized Class<?> loadClass(String name,boolean resolve)
            throws ClassNotFoundException {
        //首先检查请求的类是否已经加载过
        Class c = findLoadedClass(name);
        if (c == null) {
            try {
                if (parent != null) {
                     c = parent.loadClass(name,false);  //父类加载器不为空，调用父类加载器
                }else {
                    c = findBootstrapClassOrNull(name); //父类加载器为空，则使用启动类加载器
                }
            }catch (ClassNotFoundException e) {
                //如果父类加载器抛出ClassNotFoundException
                //说明父类无法完成加载请求
            }
            if (c == null) {
                //在父类无法加载时，调用本身类加载器进行加载
                c = findClass(name);
            }
        }
        if (resolve) {
            resolveClass(c);
        }
        return c;
    }