findClass
protected Class<?> findClass(String name)throws ClassNotFoundException

使用指定的二进制名称查找类。此方法应该被类加载器的实现重写，该实现按照委托模型来加载类。在通过父类加载器检查所请求的类后，此方法将被 loadClass 方法调用。默认实现抛出一个 ClassNotFoundException。

参数：
name - 类的二进制名称

返回：
得到的 Class 对象

抛出：
ClassNotFoundException - 如果无法找到类

从以下版本开始：
1.2

public class MyClassLoader extends ClassLoader {//类加载器名称private String name;//加载类的路径private String path = "D:/";private final String fileType = ".class";public MyClassLoader(String name){//让系统类加载器成为该 类加载器的父加载器super();this.name = name;}public MyClassLoader(ClassLoader parent, String name){//显示指定该类加载器的父加载器super(parent);this.name = name;}public String getPath() {return path;}public void setPath(String path) {this.path = path;}@Overridepublic String toString() {return this.name;}/**
     * 获取.class文件的字节数组
     * @param name
     * @return
     */private byte[] loaderClassData(String name){InputStream is = null;byte[] data = null;ByteArrayOutputStream baos = new ByteArrayOutputStream();this.name = this.name.replace(".", "/");try {is = new FileInputStream(new File(path + name + fileType));int c = 0;while(-1 != (c = is.read())){baos.write(c);}data = baos.toByteArray();} catch (Exception e) {e.printStackTrace();} finally{try {is.close();baos.close();} catch (IOException e) {e.printStackTrace();}}return data;}/**
     * 获取Class对象
     */@Overridepublic Class<?> findClass(String name){byte[] data = loaderClassData(name);return this.defineClass(name, data, 0, data.length);}public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException {//loader1的父加载器为系统类加载器MyClassLoader loader1 = new MyClassLoader("loader1");loader1.setPath("D:/lib1/");//loader2的父加载器为loader1MyClassLoader loader2 = new MyClassLoader(loader1, "loader2");loader2.setPath("D:/lib2/");//loader3的父加载器为根类加载器MyClassLoader loader3 = new MyClassLoader(null, "loader3");loader3.setPath("D:/lib3/");Class clazz = loader2.loadClass("Sample");Object object = clazz.newInstance();}
}

public class Sample {public Sample(){System.out.println("Sample is loaded by " + this.getClass().getClassLoader());new A();}
}

public class A {public A(){System.out.println("A is loaded by " + this.getClass().getClassLoader());}
}