关于JAVA类加载器。

问题描述

public static <T> T classLoader(String className) throws Exception {ClassLoader myClassLoader = new ClassLoader() { @Override protected Class<?> findClass(String name) throws ClassNotFoundException {try { //获取类文件名 String fileName = name.substring(name.lastIndexOf('.') + 1) + '.class'; InputStream inputStream = getClass().getResourceAsStream(fileName); if (inputStream == null) {return super.findClass(fileName); } byte[] bytes = new byte[inputStream.available()]; inputStream.close(); return defineClass(name, bytes, 0, bytes.length);} catch (IOException e) { throw new ClassNotFoundException();} }};return (T) myClassLoader.loadClass(className).newInstance(); }public static void main(String[] args) throws Exception {//测试1Object obj2 = classLoader('com.myweb.reflect.classloader.ClassLoaderTest');System.out.println(obj2.getClass());System.out.println(obj2 instanceof com.myweb.reflect.classloader.ClassLoaderTest);//测试2ClassLoader myClassLoader = new ClassLoader() { @Override protected Class<?> findClass(String name) throws ClassNotFoundException {try { //获取类文件名 String fileName = name.substring(name.lastIndexOf('.') + 1) + '.class'; InputStream inputStream = getClass().getResourceAsStream(fileName); if (inputStream == null) {return super.findClass(fileName); } byte[] bytes = new byte[inputStream.available()]; inputStream.close(); return defineClass(name, bytes, 0, bytes.length);} catch (IOException e) { throw new ClassNotFoundException();} }};Object obj3 = myClassLoader.loadClass('com.myweb.reflect.classloader.ClassLoaderTest');System.out.println(obj3.getClass());System.out.println(obj3 instanceof com.myweb.reflect.classloader.ClassLoaderTest);}

输出：class com.myweb.reflect.classloader.ClassLoaderTesttrueclass java.lang.Classfalse

为什么两段相同的代码，只是一个单独提取出来，输出就不一样了呢？

问题解答

你确定是两段相同的代码吗？第一个代码段里面有多一句return (T) myClassLoader.loadClass(className).newInstance();