最简单易懂的用ideal springboot Mybatis写的第一个查询数据库实验

题记：前面介绍了怎么创建第一个hello world，现在写第一个查询数据库的实验。文章最后附上源码。

先创建好数据如下代码，数据名test1，表名test1

/*
MySQL Data Transfer
Source Host: localhost
Source Database: test1
Target Host: localhost
Target Database: test1
Date: 2019/12/2 17:14:00
*/

SET FOREIGN_KEY_CHECKS=0;
-- ----------------------------
-- Table structure for test1
-- ----------------------------
CREATE TABLE `test1` (
  `id` int(10) NOT NULL default '0',
  `password` varchar(50) default NULL,
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

-- ----------------------------
-- Records 
-- ----------------------------
INSERT INTO `test1` VALUES ('123', '123');
INSERT INTO `test1` VALUES ('234', 'root');

先看一看项目的目录把，需要这样把目录创建好，如图所示。

这个就项目的目录，包需要自己创建，然后有UserService，User，UserMapper.xml都可以通过文件自动生成。

自动生成的文件下载地址我放在了GitHub上边mybatisGenerator.zip就是自动生成文件的包

下载完成了包然后解压会看见如下图所示

红色下标的就是要用到的，generatorConfig.xml就是要修改的东西，而运行命令就是在修改好了generatorConfig后再命令界面直接运行，下面一步步来：

因为乱码的问题，可以打开新建文本文档.txt看，有注释，大概需要修改的如图所示：

如图红色下划线所示的，都是需要修改的，结合注释，很容易就改好了。

然后复制该段命令

java -jar mybatis-generator-core-1.3.7.jar -configfile generatorConfig.xml -overwrite

在generatorConfig.xml文件目录下，什么文件都不选择，按住shift再点鼠标右键进入powershell窗口，鼠标右键粘贴，enter运行，就可以看到项目中多了3个文件如图所示：

然后这样就生成好了固定的文件了。

再配置application.property如下：

server.port=8090  
#端口号

mybatis.mapper-locations=classpath:mapper/*.xml

spring.datasource.url=jdbc:mysql://127.0.0.1:3306/test1
#  你的数据库表，这里我在数据库里面有个叫test1的表
spring.datasource.username=root
#  你的数据库账号
spring.datasource.password=root
#  你的数据库密码
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
#  如果这里报错误可以把cj去掉试试

User类

package com.example.demo.entity;

public class User {
    private Integer id;

    private String password;

    public Integer getId() {
        return id;
    }

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

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password == null ? null : password.trim();
    }


}

UserService类

package com.example.demo.service;

import com.example.demo.entity.User;

import java.util.List;

public interface UserService {

    String hellow();

    public String hellowWorld();

    int deleteByPrimaryKey(Integer id);

    int insert(com.example.demo.entity.User record);

    int insertSelective(com.example.demo.entity.User record);

    com.example.demo.entity.User selectByPrimaryKey(Integer id);

    int updateByPrimaryKeySelective(com.example.demo.entity.User record);

    int updateByPrimaryKey(com.example.demo.entity.User record);

    List<User> selectAll();
}

UserServicelmp类

package com.example.demo.serviceImp;

import com.example.demo.dao.UserMapper;
import com.example.demo.entity.User;
import com.example.demo.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import java.beans.Transient;
import java.util.List;


@Service
@Transactional

public class UserServicelmp implements UserService{
        protected static Logger logger= LoggerFactory.getLogger(UserServicelmp.class);
    @Autowired(required = false)
    UserMapper userMapper;

    @Override
    public String hellow() {
        logger.info("调用了hello");
        return "Hello world";
    }

    @Override
    public String hellowWorld() {
        return null;
    }

    @Override
    public int deleteByPrimaryKey(Integer id) {
        return 0;
    }

    @Override
    public int insert(User record) {
        return 0;
    }

    @Override
    public int insertSelective(User record) {
        return 0;
    }

    @Override
    public User selectByPrimaryKey(Integer id) {
        return null;
    }

    @Override
    public int updateByPrimaryKeySelective(User record) {
        return 0;
    }

    @Override
    public int updateByPrimaryKey(User record) {
        return 0;
    }

    @Override
    public List<User> selectAll() {
        return userMapper.selectAll();
    }
}

这里说一下，你直接再UserServicelmp后面写implements，然后根据提示就会创建这些return 0 的东西了。

hellowWorld测试类

package com.example.demo.controller;

import com.example.demo.entity.User;
import com.example.demo.service.UserService;
import org.mybatis.spring.annotation.MapperScans;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@CrossOrigin
@RestController
@RequestMapping("/test")
public class hellowWorld {
@Autowired(required = false)
UserService userService;

    @GetMapping("/hellow")
    public String hellow() {
        return "hellow world";
    }
        @GetMapping("/getAll")
        public List<User> getAll(){
                return userService.selectAll();
        }



}

UserMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.demo.dao.UserMapper">
  <resultMap id="BaseResultMap" type="com.example.demo.entity.User">
    <id column="id" jdbcType="INTEGER" property="id" />
    <result column="password" jdbcType="VARCHAR" property="password" />
  </resultMap>
  <sql id="Base_Column_List">
    id, password
  </sql>
  <select id="selectAll" resultType="com.example.demo.entity.User">
        select *
        from test1
    </select>
  <select id="selectByPrimaryKey" parameterType="java.lang.Integer" resultMap="BaseResultMap">
    select
    <include refid="Base_Column_List" />
    from test1
    where id = #{id,jdbcType=INTEGER}
  </select>
  <delete id="deleteByPrimaryKey" parameterType="java.lang.Integer">
    delete from test1
    where id = #{id,jdbcType=INTEGER}
  </delete>
  <insert id="insert" parameterType="com.example.demo.entity.User">
    insert into test1 (id, password)
    values (#{id,jdbcType=INTEGER}, #{password,jdbcType=VARCHAR})
  </insert>
  <insert id="insertSelective" parameterType="com.example.demo.entity.User">
    insert into test1
    <trim prefix="(" suffix=")" suffixOverrides=",">
      <if test="id != null">
        id,
      </if>
      <if test="password != null">
        password,
      </if>
    </trim>
    <trim prefix="values (" suffix=")" suffixOverrides=",">
      <if test="id != null">
        #{id,jdbcType=INTEGER},
      </if>
      <if test="password != null">
        #{password,jdbcType=VARCHAR},
      </if>
    </trim>
  </insert>
  <update id="updateByPrimaryKeySelective" parameterType="com.example.demo.entity.User">
    update test1
    <set>
      <if test="password != null">
        password = #{password,jdbcType=VARCHAR},
      </if>
    </set>
    where id = #{id,jdbcType=INTEGER}
  </update>
  <update id="updateByPrimaryKey" parameterType="com.example.demo.entity.User">
    update test1
    set password = #{password,jdbcType=VARCHAR}
    where id = #{id,jdbcType=INTEGER}
  </update>
</mapper>

其实这里面就写了一句，其他的都是自动生成的

<select id="selectAll" resultType="com.example.demo.entity.User">
        select *
        from test1
    </select>

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.1.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.1.1</version>
        </dependency>

            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>5.1.37</version>
                <scope>runtime</scope>
            </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

这样就完成了，然后启动项目，在浏览器运行http://localhost:8090/test/getAll

如图所示：

这样就完成了简单数据的查询。

最后附上代码（源码，加sql文件）GitHub上可以直接下载实验下载地址