@JsonInclude(JsonInclude.Include.NON_NULL)作用

其作用是jackson 實體轉json 為NULL的字段不參加序列化（即不顯示）

如果在某字段前添加了此注解，如果此字段在輸出的時候為null時，系統將不顯示此字段。

一、沒加此注解時，執行一個簡單的查詢操作

1. User.java類內容如下：

package com.example.simple.model;
/*
* 用戶表
* */

import java.io.Serializable;
import java.sql.Blob;
import java.util.Date;
import java.util.List;

public class SysUser implements Serializable {

    private static final long serialVersionUID = 6320941908222932112L ;


    /*
    * 用戶ID
    * */
    private Long id;
    /*
    * 用戶
    * */
    private String userName;
    /*
    * 密碼
    * */
    private String userPassword;
    /*
    * 郵箱
    * */
    private  String userEmail;
    /*
    * 簡介
    * */
    private String userInfo;
    /*
    * 頭像
    * */
    private byte[] headImg;
    /*
    * 創建時間
    * */
    private Date createTime;
//一個用戶擁有一個角色 為實現自動映射一對一關系  因此需要加上SysRole字段
    private SysRole role;

    private List<SysRole> roleList;

    public List<SysRole> getRoleList() {
        return roleList;
    }

    public void setRoleList(List<SysRole> roleList) {
        this.roleList = roleList;
    }

    public SysRole getRole() {
        return role;
    }

    public void setRole(SysRole role) {
        this.role = role;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getUserPassword() {
        return userPassword;
    }

    public void setUserPassword(String userPassword) {
        this.userPassword = userPassword;
    }

    public String getUserEmail() {
        return userEmail;
    }

    public void setUserEmail(String userEmail) {
        this.userEmail = userEmail;
    }

    public String getUserInfo() {
        return userInfo;
    }

    public void setUserInfo(String userInfo) {
        this.userInfo = userInfo;
    }

    public byte[] getHeadImg() {
        return headImg;
    }

    public void setHeadImg(byte[] headImg) {
        this.headImg = headImg;
    }

    public Date getCreateTime() {
        return createTime;
    }

    public void setCreateTime(Date createTime) {
        this.createTime = createTime;
    }
}

測試代碼如下：

 @Test
    public void testSelectById(){
        //獲取會話
        SqlSession sqlSession = getSqlSession();
        try{
            //獲取UserMapper接口
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            SysUser user = userMapper.selectById(1020L);
            Assert.assertNotNull(user);
            Assert.assertEquals("test-selective",user.getUserName());
        }finally {
            sqlSession.close();
        }

    }

查詢結果如下：

DEBUG [main] - Cache Hit Ratio [com.example.simple.mapper.RoleMapper]: 0.0
DEBUG [main] - ==> Preparing: select * from sys_user where id = ?
DEBUG [main] - ==> Parameters: 1020(Long)
TRACE [main] - <== Columns: id, user_name, user_password, user_email, user_info, head_img, create_time
TRACE [main] - <== Row: 1020, test-selective, 123456, null, <<BLOB>>, <<BLOB>>, 2020-12-09 21:04:13
DEBUG [main] - <== Total: 1

二、如果加上此注解

1. User.java類內容如下：

package com.example.simple.model;
/*
* 用戶表
* */

import com.fasterxml.jackson.annotation.JsonInclude;

import java.io.Serializable;
import java.sql.Blob;
import java.util.Date;
import java.util.List;

public class SysUser implements Serializable {

    private static final long serialVersionUID = 6320941908222932112L ;


    /*
    * 用戶ID
    * */
    private Long id;
    /*
    * 用戶
    * */
    private String userName;
    /*
    * 密碼
    * */
    private String userPassword;
    /*
    * 郵箱
    * */
    @JsonInclude(JsonInclude.Include.NON_NULL)
    private  String userEmail;
    /*
    * 簡介
    * */
    private String userInfo;
    /*
    * 頭像
    * */
    private byte[] headImg;
    /*
    * 創建時間
    * */
    private Date createTime;
//一個用戶擁有一個角色 為實現自動映射一對一關系  因此需要加上SysRole字段
    private SysRole role;

    private List<SysRole> roleList;

    public List<SysRole> getRoleList() {
        return roleList;
    }

    public void setRoleList(List<SysRole> roleList) {
        this.roleList = roleList;
    }

    public SysRole getRole() {
        return role;
    }

    public void setRole(SysRole role) {
        this.role = role;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getUserPassword() {
        return userPassword;
    }

    public void setUserPassword(String userPassword) {
        this.userPassword = userPassword;
    }

    public String getUserEmail() {
        return userEmail;
    }

    public void setUserEmail(String userEmail) {
        this.userEmail = userEmail;
    }

    public String getUserInfo() {
        return userInfo;
    }

    public void setUserInfo(String userInfo) {
        this.userInfo = userInfo;
    }

    public byte[] getHeadImg() {
        return headImg;
    }

    public void setHeadImg(byte[] headImg) {
        this.headImg = headImg;
    }

    public Date getCreateTime() {
        return createTime;
    }

    public void setCreateTime(Date createTime) {
        this.createTime = createTime;
    }
}

測試代碼一樣，控制台執行結果也和上面一樣，只是在頁面上顯示時email為空的值不在頁面上顯示，這個部分暫時還沒實現，后面實現了再更新。