还是直接看代码实现吧

首先定义一个实体

public class User {    private Integer id;    private String name;    private int age;    public User(Integer id, String name, int age) {        this.id = id;        this.name = name;        this.age = age;    }    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }}

在定义一个mapper接口

public interface UserMapper {    User getUserById(Integer id);}

然后自定义一个invacationHandle

public class MapperProxy implements InvocationHandler {    /**     * 利用Proxy.newProxyInstance 获取代理类     * @param clz  目标接口     * @param 
    
          * @return     */    @SuppressWarnings("unchecked")    public 
     
       T newInstance(Class
      
        clz) {        return (T) Proxy.newProxyInstance(clz.getClassLoader(), new Class[] { clz }, this);    }    @Override    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {        //判断method是否是Object类中定义的方法        //如 hashCode()、toString()、equals()        //如果是则将target 指向 this        //如果直接调用 method.invoke 会报空指针错误        if (Object.class.equals(method.getDeclaringClass())) {            try {                return method.invoke(this, args);            } catch (Throwable t) {            }        }        // 投鞭断流        //  mybatis mapper底层实现原理        return findUserById((Integer) args[0]);    }    private User findUserById(Integer id) {        return new User(id, "zhangsan", 18);    }}
      
     
    

测试

public static void main(String[] args) {    MapperProxy proxy = new MapperProxy();    //获取代理类    UserMapper mapper = proxy.newInstance(UserMapper.class);    User user = mapper.getUserById(1001);    System.out.println("ID:" + user.getId());    System.out.println("Name:" + user.getName());    System.out.println("Age:" + user.getAge());    System.out.println(mapper.toString());}

输出结果

mybatis底层源码就是这么实现的，看看mybatis是怎么写的吧

@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {  try {    if (Object.class.equals(method.getDeclaringClass())) {      return method.invoke(this, args);    } else if (isDefaultMethod(method)) {      return invokeDefaultMethod(proxy, method, args);    }  } catch (Throwable t) {    throw ExceptionUtil.unwrapThrowable(t);  }  final MapperMethod mapperMethod = cachedMapperMethod(method);  return mapperMethod.execute(sqlSession, args);}

是不是很像 除了最后的return