mybatis的使用－单独使用mybatis

一、单独使用mybatis

参照mybatis官方文档 https://mybatis.org/mybatis-3/zh/getting-started.html

整体代码结构：

 

 

 

1.使用eclipse新建一个maven项目，将项目的java编译器版本修改为1.8。

 或者通过修改pom.xml文件，增加以下内容将编译修改为1.8：

    <build>
        <finalName>income</finalName>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

 

 

2.在pom.xml文件中增加mybatis依赖和mysql依赖。

pom.xml文件内容：

<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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.test</groupId>
  <artifactId>mybatisdemo</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>mybatisdemo</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.5.7</version>
    </dependency>
    
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.49</version>
    </dependency>
    
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.20</version>
        <scope>provided</scope>
    </dependency>
    
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
  
    <build>
        <finalName>income</finalName>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

 

3.新建BootStrap.java类

package com.test.mybatisdemo;

import java.io.IOException;
import java.io.InputStream;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import com.test.mybatisdemo.entity.User;
import com.test.mybatisdemo.mapper.UserMapper;

public class BootStrap 
{
    public static void main( String[] args ) throws IOException
    {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory= new SqlSessionFactoryBuilder().build(inputStream);
        
        try(SqlSession session = sqlSessionFactory.openSession()) {
            
            //使用mybatis的API，旧版本mybatis中常见
            User user1 = session.selectOne("com.test.mybatisdemo.mapper.UserMapper.getUserById",1);
            System.out.println(user1.getId() + "," 
                    + user1.getUserName() + "," 
                    + user1.getPassword() + "," 
                    + user1.getCreateTime());
            
            //使用Mapper方法，代码结构更清晰，更容易理解
            UserMapper userMapper = session.getMapper(UserMapper.class);
            User user = userMapper.getUserById(1);
            
            System.out.println(user.getId() + "," 
                                + user.getUserName() + "," 
                                + user.getPassword() + "," 
                                + user.getCreateTime());
        }
    }
}

 

4.为了将配置文件和代码文件分开存放，新增一个sources资源目录，用于存放mybatis-config.xml

 

 

5.配置mybatis-config.xml文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
  <environments default="development">
    <environment id="development">
      <transactionManager type="JDBC"/>
      <dataSource type="POOLED">
        <property name="driver" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/test"/>
        <property name="username" value="root"/>
        <property name="password" value="111111"/>
      </dataSource>
    </environment>
  </environments>

  <mappers>
    <mapper resource="com/test/mybatisdemo/mapper/UserMapper.xml"/>
    <!-- <package name="com/test/mybatisdemo/mapper"/> -->
  </mappers>
</configuration>

使用了方便增加多个mapper，配置mapper时，可以使用package指定命名空间，减少mapper的配置。

 

6.创建user表并插入一条测试数据

create table user
(
    id int(10),
    user_name varchar(20),
    password varchar(32),
    create_time datetime,
    primary key(id)
)

insert into user values(1,'测试用户','123456','2021-10-01 08:08:08');

 

7.创建User.java实体类

package com.test.mybatisdemo.entity;

import java.util.Date;

public class User {
    private Integer id;
    private String userName;
    private String password;
    private Date createTime;
    
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getUserName() {
        return userName;
    }
    public void setUserName(String userName) {
        this.userName = userName;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public Date getCreateTime() {
        return createTime;
    }
    public void setCreateTime(Date createTime) {
        this.createTime = createTime;
    }
    
    
}

如果不想手工增加setter和getter方法，可以使用lombok。

 

8.创建mapper接口，即UserMapper.java接口

package com.test.mybatisdemo.mapper;

import com.test.mybatisdemo.entity.User;

public interface UserMapper {

    User getUserById(Integer id);
    
}

该接口不需要实现类，由mybatis自动生成该接口的代理类。

 

9.创建mapper的配置文件，即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.test.mybatisdemo.mapper.UserMapper">
    <resultMap type="com.test.mybatisdemo.entity.User" id="userMap">
        <id column="id" property="id"/>
        <result column="user_name" property="userName"/>
        <result column="password" property="password"/>
        <result column="create_time" property="createTime"/>
    </resultMap>
    
    <select id="getUserById" resultMap="userMap">
      select * from user where id = #{id}
    </select>
</mapper>

由于user表的字段名和User.java类属性名不一致，mybatis无法识别并进行映射，因此，需要配置resultMap进行结果映射。

 resultMap的属性，参照：https://mybatis.org/mybatis-3/zh/sqlmap-xml.html

• constructor - 用于在实例化类时，注入结果到构造方法中
  • idArg - ID 参数；标记出作为 ID 的结果可以帮助提高整体性能
  • arg - 将被注入到构造方法的一个普通结果
• id – 一个 ID 结果；标记出作为 ID 的结果可以帮助提高整体性能
• result – 注入到字段或 JavaBean 属性的普通结果
• association – 一个复杂类型的关联；许多结果将包装成这种类型
  • 嵌套结果映射 – 关联可以是 resultMap 元素，或是对其它结果映射的引用
• collection – 一个复杂类型的集合
  • 嵌套结果映射 – 集合可以是 resultMap 元素，或是对其它结果映射的引用
• discriminator – 使用结果值来决定使用哪个 resultMap
  • case – 基于某些值的结果映射
    • 嵌套结果映射 – case 也是一个结果映射，因此具有相同的结构和元素；或者引用其它的结果映
       

 链接：https://pan.baidu.com/s/13nCPX0RkEbfhHWBbU4YyOQ
提取码：i2x1