BeanUtils -- shallow copy -- example / principle

Original website ：BeanUtils-- Shallow copy -- example / principle _IT A blog with a sharp blade -CSDN Blog

brief introduction

explain

        This paper introduces BeanUtils Copy principle of .

summary

        BeanUtils Is a shallow copy .

         If the member to be copied is a basic data type , It copies the value of the member , Equivalent to data is independent . The basic data types here include basic type and packaging type , for example ：Integer、int、String、Long、long etc. ）

         If the member to be copied is not a basic data type , Just copy the reference address （ Use the same reference address （ That is to say ： Same object ））.

example

Code

Entity

User

package com.knife.entity;

import lombok.Data;

@Data
public class User {
    private Long id;

    private String userName;

    private UserDetail userDetail;
}

UserDetail

package com.knife.entity;

import lombok.Data;

@Data
public class UserDetail {
    private Long id;

    private String address;
}

Controller

package com.knife.controller;

import com.knife.entity.User;
import com.knife.entity.UserDetail;
import org.springframework.beans.BeanUtils;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

    @GetMapping("/test")
    public String test() {
        User user = new User();
        user.setId(1L);
        user.setUserName("Tony");

        UserDetail userDetail = new UserDetail();
        userDetail.setId(2L);
        userDetail.setAddress(" Shanghai ");
        user.setUserDetail(userDetail);

        User user1 = new User();
        BeanUtils.copyProperties(user, user1);

        return "test success";
    }
}

test

Breaking point ：

visit ：http://localhost:8080/test

result ：

You can see ,user and user1 Their userDetail Members are the same object ：{[email protected]}

Principle analysis

Breaking point

visit ：http://localhost:8080/test

Run to this place ：

BeanUtils#copyProperties(java.lang.Object, java.lang.Object, java.lang.Class<?>, java.lang.String...)

As shown in the figure below ：

You can see ,targetPds It contains all members of the target object , Deal with it in turn , Look at the code in the lower part ：

         You can find , It uses reflection , First call the getXxx Method gets value , Then call the... Of the target object setXxx Method to set the value .

        therefore , When the member is an object other than the basic type , it getXxx You will get the reference address ,setXxx Will set the reference address , So it will share the same object .