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"));
}