【面试题精讲】JVM-打破双亲委派机制-自定义类加载器

public class MyClassLoader extends ClassLoader {
    private String classPath;
    public MyClassLoader(String classPath, ClassLoader parent) {
        super(parent);
        this.classPath=classPath;
    }
    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        byte[] classData = getClassData(name);
        if (classData == null){
            throw new ClassNotFoundException();
        }
        else{
            return defineClass(name,classData,0,classData.length);
        }
    }
    private byte[] getClassData(String className){
        String path = classNameToPath(className);
        try{
            InputStream inputStream = new FileInputStream(path);
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            byte[] buffer = new byte[1024];
            int num = 0;
            while((num=inputStream.read(buffer))!=-1){
                baos.write(buffer,0,num);
            }
            inputStream.close();
            return baos.toByteArray();
        }
        catch(Exception e) {
            return null;
        }
    }
    private String classNameToPath(String className){
        return classPath + className.replace(".", "/") + ".class";
    }
}

public class Test {
    public static void main(String[] args) {
        String classPath = "F:/work/TestDemo/bin/";
        MyClassLoader classLoader1 = new MyClassLoader(classPath, ClassLoader.getSystemClassLoader().getParent());
        MyClassLoader classLoader2 = new MyClassLoader(classPath, ClassLoader.getSystemClassLoader().getParent());
        try {
            Class<?> class1 = classLoader1.loadClass("demo.bean.User");
            Class<?> class2 = classLoader2.loadClass("demo.bean.User");
            System.out.println(class1 == class2); // false,因为类加载器不一样
            Object obj1= class1.newInstance();
            Object obj2= class2.newInstance();
            Method method=class1.getMethod("setUname", String.class);
            method.invoke(obj1, "张三");
            method.invoke(obj2,"李四");
            Method method1=class1.getMethod("getUname");
            Method method2=class2.getMethod("getUname");
            System.out.println(method1.invoke(obj1).equals(method2.invoke(obj2)));
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }
    }
}