mybatis的HELLOWORD

1.需要的依赖,注意资源导出(非常容易遗漏)

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

    <groupId>com.yeahlam</groupId>
    <artifactId>mybatisStudy</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>mybatis-01</module>
    </modules>
    <dependencies>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.6</version>
        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>

    <!--在build中配置resources，来防止我们资源导出失败的问题-->
    <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>
</project>

2.准备DAO接口

package com.yeahlam.dao;

import com.yeahlam.pojo.users;

import java.util.List;

public interface IUsersDao {
    List<users> getUserList();
}

3.mybatis不需要实例化DAO层了,但始终需要一个SQL来执行数据库操作,那就是mapper.xml了

<?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.yeahlam.dao.IUsersDao">
    <select id="getUserList" resultType="com.yeahlam.pojo.users">
    select * from users;
  </select>
</mapper>

4.准备mybatis核心文件,核心文件说明使用的数据库,密码等,最重要的就是mapper映射

mybatis-config.xml

<?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/mybatis01"/>
                <property name="username" value="root"/>
                <property name="password" value="xxxx"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/yeahlam/dao/DaoMapper.xml"></mapper>
    </mappers>
</configuration>

5.写一个POJO实体类,数据库中的每条数据将实例化到一个对象

package com.yeahlam.pojo;

public class users {
    private int id;
    private String username;
    private String password;

    public users() {
    }


    public users(int id, String username, String password) {
        this.id = id;
        this.username = username;
        this.password = password;
    }

    public int getId() {
        return id;
    }

    public void setId(int 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;
    }

    @Override
    public String toString() {
        return "users{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

6.创建mybatis的工具类获取session对象,这个和JDBC中connection对象非常相似,通过session可以执行对于的dao接口方法

package com.yeahlam.utils;

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

public class mybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;
    static {
        String resource = "mybatis-config.xml";
        InputStream inputStream = null;
        try {
            inputStream = Resources.getResourceAsStream(resource);
        } catch (IOException e) {
            e.printStackTrace();
        }
         sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    }

    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

7.测试

package com.yeahlam.dao;

import com.yeahlam.pojo.users;
import com.yeahlam.utils.mybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class UserDaoTest {
    @Test
    public void test(){
        SqlSession sqlSession = mybatisUtils.getSqlSession();
        IUsersDao usersDao = sqlSession.getMapper(IUsersDao.class);
        List<users> userList = usersDao.getUserList();
        for (users users : userList) {
            System.out.println(users);
        }
        sqlSession.close();
    }
}