Java语言中的自定义类加载器实例解析

package com.lg.test;import java.io.ByteArrayOutputStream;import java.io.FileInputStream;import java.io.IOException;import java.io.InputStream;/** * Created by  on 2016/8/6. */public class FileClassLoader extends ClassLoader {	String rootDir=null;	public FileClassLoader(String rootDir) {		this.rootDir = rootDir;	}	@Override	  protected Class<?> findClass(String className) throws ClassNotFoundException {		//首先检查是否已经被加载了。		Class<?> c = findLoadedClass(className);		String path = rootDir + "/" + className.replace('.', '/') + ".class";		if (c != null) {			return c;		} else {			/*双亲委托模式*/			ClassLoader loaderParent = this.getParent();			c = loaderParent.loadClass(className);			if (c != null) {				return c;			} else {				/*如果再不行的话，就再进行加载。因为字节码的本质就是一个字节数组*/				InputStream is = null;				ByteArrayOutputStream outputStream = new ByteArrayOutputStream();				try {					is = new FileInputStream(path);					byte[] buffer = new byte[1024];					int len = 0;					while ((len = is.read(buffer)) != -1) {						outputStream.write(buffer, 0, len);					}					c = defineClass(className, buffer, 0, buffer.length);				}				catch (Exception e) {					e.printStackTrace();				}				finally {					if (is != null) {						try {							is.close();						}						catch (IOException e) {							e.printStackTrace();						}					}				}			}			return c;		}	}}

package com.lg.test;/** * Created by  on 2016/8/6. *//*相同的类加载器对同一个类进行加载，得到的hascode是相同的 * 不同的类加载器对同一类进行加载，得到的hascode是不一样的*/public class Demo {	public static void main(String[] args) {		FileClassLoader loader = new FileClassLoader("c://myjava");		FileClassLoader loader2=new FileClassLoader("c://myjava");		try {			Class<?> c = loader.findClass("com.lg.test.HelloWorld");			Class<?> c0=loader.findClass("com.lg.test.HelloWorld");			Class<?> c1=loader2.findClass("com.lg.test.HelloWorld");			Class<?> c2=loader.findClass("com.lg.test.Demo01");			Class<?> c3=loader.findClass("java.lang.String");			System.out.println(c.hashCode());			System.out.println(c.getClassLoader());			System.out.println(c0.hashCode());			System.out.println(c0.getClassLoader());			System.out.println(c1.hashCode());			System.out.println(c1.getClassLoader());			System.out.println(c2.hashCode());			System.out.println(c2.getClassLoader());			System.out.println(c3.hashCode());			System.out.println(c3.getClassLoader());		}		catch (ClassNotFoundException e) {			e.printStackTrace();		}	}}