用.class文件创建对象-优快云博客

本文链接：https://blog.youkuaiyun.com/iteye_5649/article/details/82601684

本文介绍了一个自定义的Java ClassLoader实现过程，展示了如何通过继承ClassLoader并重写方法来加载指定路径下的类文件，并实例化该类。此外还提供了加载类文件的具体步骤，包括读取字节码文件到内存。

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package com.loadClasses;

import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.lang.reflect.Method;

public class ClassLoaderOne extends ClassLoader{
	public static void main(String[] args) {
		try {
			ClassLoaderOne loader =
 new ClassLoaderOne(
    "D:\\WorkspacesShangHai\\myJava\\src\\lib\\Tool.class"
 );
			Class<?> clazz = null;
			try {
				clazz = loader.loadClass("com.loadClasses.Tool");
			} catch (ClassNotFoundException e) {
				e.printStackTrace();
			}  
	        Object o = null;
			try {
				o = clazz.newInstance();
			} catch (InstantiationException e) {
				e.printStackTrace();
			} catch (IllegalAccessException e) {
				e.printStackTrace();
			}  
	        System.out.println(o.getClass().getClassLoader()); 
                //sun.misc.Launcher$AppClassLoader@6b97fd
	        //======================2
	        Method[] methods = clazz.getMethods();  
			for (int i = 0; i < methods.length; i++) {  
			    String name = methods[i].getName();  
			    System.out.println(name);  
			    Class<?>[] params = methods[i].getParameterTypes();  
			    for (int j = 0; j < params.length; j++) {  
			        System.out.println(params[j].toString());  
			    }  
			}
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
	
	private byte[] data;  
	  
    public ClassLoaderOne(String clazzPath) throws IOException {  
        data = loadClassFile(clazzPath);  
    } 
    
    /** 
     * 加载class文件 
     *  
     * @param clazzPath 
     *            class绝对文件路径 
     * @return 字节数组 
     * @throws IOException 
     */  
    private byte[] loadClassFile(String clazzPath) throws IOException {  
        FileInputStream fis = new FileInputStream(clazzPath);  
        BufferedInputStream bis = new BufferedInputStream(fis);  
        ByteArrayOutputStream baos = new ByteArrayOutputStream();  
  
        byte[] buffer = new byte[1024 * 256];  
        int ch = 0;  
        while ((ch = bis.read(buffer, 0, buffer.length)) != -1) {  
            baos.write(buffer, 0, ch);  
        }  
        return baos.toByteArray();  
    }  
  
    @Override  
    protected Class<?> loadClass(String name, boolean resolve)  
            throws ClassNotFoundException {  
        Class<?> c = findLoadedClass(name);  
        if (c == null) {  
        // 如果父加载器不为null,使用父类加载器加载(比如Object,HashMap等核心类)
        	 if (getParent() != null) {
        		 try {  
                     c = getParent().loadClass(name);  
                 } catch (Exception e) {  
                     // 父类可能没加载，则抛异常  
                 }
        	 }
        	// 如果父类加载器没有加载,再使用自定义加载器加载  
             if (c == null) {  
                 c = defineClass(name, data, 0, data.length);  
             }
        }  
        return c;  
    } 
}

原文参考：http://wlh0706-163-com.iteye.com/blog/2098619