【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InvocationHandlerprivate 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;}@Overridepublic 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;}@Overridepublic Student query(int id) {daoTransaction.startTransaction();Student student=studentService.query(id);daoTransaction.endTransaction();return student;}
}

public class StudentServiceImpl implements StudentService {@Overridepublic 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");}
}