【笔记+代码】JDK动态代理理解

代码地址

https://github.com/cmdch2017/JDKproxy.git/

我的理解

我的理解是本身service-serviceImpl结构，新增一个代理对象proxy，代理对象去直接访问serviceImpl，在proxy进行事务的增强操作，所以代理对象实现了接口。如何实现动态呢？需要实现InovacationHandler接口，并用反射调用invoke方法，实现类似于泛型一样的效果。

CHATGPT回答

“JDK动态代理是通过Proxy类和InvocationHandler接口实现的。它允许在运行时生成代理类，无需事先定义代理类，从而在不修改原有代码的情况下对方法进行增强。通过实现InvocationHandler接口，我们可以在目标方法执行前后插入自定义逻辑，比如事务处理。动态代理的优势在于避免了手动创建大量代理类的繁琐工作，使代码更加简洁和易维护。”

核心代码

客户端

public class TestStudent {
    public static void main(String[] args) {
//        testQuery(1);
        testQueryObject(1);
    }
//这里是动态代理，多实现了一个InvocationHandler
    private static void testQueryObject(int id) {
        DaoTransaction transaction=new DaoTransaction();
        StudentServiceImpl studentService=new StudentServiceImpl();
        TransactionHandler transactionHandler=new TransactionHandler(studentService,transaction);
        StudentService proxyInstance=(StudentService)Proxy.newProxyInstance(StudentServiceImpl.class.getClassLoader(),StudentServiceImpl.class.getInterfaces(),transactionHandler);
        Student student=proxyInstance.query(id);
        System.out.println("id:"+student.getId()+",name:"+student.getName());
    }
//这里是静态代理
    private static void testQuery(int id) {
        DaoTransaction transaction=new DaoTransaction();
        StudentServiceImpl studentService=new StudentServiceImpl();
        ProxyStudent proxyStudent=new ProxyStudent(studentService,transaction);
        Student student=proxyStudent.query(id);
        System.out.println("id:"+student.getId()+",name:"+student.getName());
    }
}

动态代理学生

public class TransactionHandler implements InvocationHandler {
    private DaoTransaction daoTransaction;
    private Object object;

    public TransactionHandler(Object object, DaoTransaction daoTransaction) {
        this.object = object;
        this.daoTransaction = daoTransaction;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        return method.invoke(object,args);
    }
}

@Data
public class Student {
    private int id;
    private String name;
}

静态代理学生

public class ProxyStudent implements StudentService {
    private StudentServiceImpl studentService;
    private DaoTransaction daoTransaction;

    public ProxyStudent(StudentServiceImpl studentService, DaoTransaction daoTransaction) {
        this.studentService = studentService;
        this.daoTransaction = daoTransaction;
    }

    @Override
    public Student query(int id) {
        daoTransaction.startTransaction();
        Student student=studentService.query(id);
        daoTransaction.endTransaction();
        return student;
    }
}

public class StudentServiceImpl implements StudentService {

    @Override
    public Student query(int id) {
        System.out.println("执行查询");
        Student student=new Student();
        student.setId(id);
        student.setName("lst");
        return student;
    }
}

public interface StudentService {
    Student query(int id);
}

public class DaoTransaction {
    public void startTransaction() {
        System.out.println("开启事务");
    }

    public void endTransaction() {
        System.out.println("关闭事务");
    }
}