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  • java自定义ClassLoader加载指定的class文件

    继承ClassLoader并且重写findClass方法就可以自定义一个类加载器,具体什么是类加载器以及类加载器的加载过程与顺序下次再说,下面给出一个小demo

    首先定义一个类,比如MyTest,并且将其编译成class文件,然后放到一个指定的文件夹下面,其中文件夹的最后几层就是它的包名,这里我将这个编译好的类放到 : /Users/allen/Desktop/cn/lijie/bug .class

    package cn.lijie;
    public class bugnew {
        public void shownew() {
            System.out.println("shownew test!");
        }
    }
    

      

    package com.infosec.manager.controller.login;
    
    import java.lang.reflect.Method;
    import java.net.URI;
    import java.nio.file.Files;
    import java.nio.file.Path;
    import java.nio.file.Paths;
    
    public class bug extends ClassLoader {
    	public void show() {
    		System.out.println("show test!");
    	}
    
    	public void shows() {
    		String myPath = "file:///D:/infosec/netauth/accountsync/bugnew.class";
    		System.out.println(myPath);
    		byte[] cLassBytes = null;
    		Path path = null;
    		try {
    			path = Paths.get(new URI(myPath));
    			cLassBytes = Files.readAllBytes(path);
    		
    		Class clazz = defineClass("cn.lijie.bugnew", cLassBytes, 0, cLassBytes.length);
    		Object obj = clazz.newInstance();
    		Method method = clazz.getMethod("shownew");
    		method.invoke(obj);
    		}catch (Exception e) {
    		}
    	}
    }
    

      

    自定义的类加载器:

    package com.infosec.manager.controller.login;
    
    import java.io.IOException;
    import java.net.URI;
    import java.net.URISyntaxException;
    import java.nio.file.Files;
    import java.nio.file.Path;
    import java.nio.file.Paths;
    
    public class MyClassLoader extends ClassLoader {
    	
    	protected Class<?> findClass() {
    		String myPath = "file:///D:/infosec/netauth/accountsync/bug.class";
    		byte[] cLassBytes = null;
    		Path path = null;
    		try {
    			path = Paths.get(new URI(myPath));
    			cLassBytes = Files.readAllBytes(path);
    		} catch (IOException | URISyntaxException e) {
    			e.printStackTrace();
    		}
    		Class clazz = defineClass("com.infosec.manager.controller.login.bug", cLassBytes, 0, cLassBytes.length);
    		return clazz;
    	}
    }
    

      

    测试的主函数:

    package com.infosec.manager.controller.login;
    
    import java.lang.reflect.Method;
    
    public class TestController {
    	
    	 public static void main(String[] args) throws ClassNotFoundException {
    	        MyClassLoader loader = new MyClassLoader();
    	        Class<?> aClass = loader.findClass();
    	        try {
    	            Object obj = aClass.newInstance();
    	            Method method = aClass.getMethod("shows");
    	            method.invoke(obj);
    	        } catch (Exception e) {
    	            e.printStackTrace();
    	        }
    	    }
    }
    

      

    执行主函数,调用外部class的show方法:

    判断class<?>[] 是否包含某个元素 instanceof 

    	private boolean guessInterface(Object object) {
    		if (object instanceof SynchAccountApi) {
    			return true;
    		}
    		if (object instanceof SyncUsersFromAppInterface) {
    			return true;
    		}
    		Class<?>[] allInterfaces = ClassUtils.getAllInterfaces(object);
    		return Arrays.stream(allInterfaces).anyMatch(aClass -> aClass.getName().contains("SynchAccountApi"));
    	}
    

      

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  • 原文地址:https://www.cnblogs.com/cuijinlong/p/13329090.html
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