学习MyBatis之简单入门HelloWorld

转：https://blog.csdn.net/gaomb_1990/article/details/78299784

一、准备

Eclipse：Luna Service Release 1 (4.4.1)
MyBatis：org.mybatis.mybatis-3.2.8
JDK：1.7.0_79

二、步骤

♦搭建一个Maven工程MyBatisDemo

♦POM文件导入相关依赖

<span style="font-family:'KaiTi_GB2312';"><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.queen.mybatis</groupId>
    <artifactId>MyBatisDemo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>war</packaging>
    <dependencies>
        <!-- 单元测试 -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.10</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.2.8</version>
        </dependency>
        <!-- MySql -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.32</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.6.4</version>
        </dependency>
    </dependencies>
</project></span>

♦配置MyBatis的核心文件mybatis-config.xml

<span style="font-family:'KaiTi_GB2312';"><?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/mybatis" />
                <property name="username" value="root" />
                <property name="password" value="root" />
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="UserMapper.xml" />
    </mappers>
</configuration></span>

注意：该文件中主要是连接数据库的信息，驱动，url，用户名，密码以及映射文件，将我们写好的sql映射文件（UserMapper.xml）一定要注册到全局配置文件（mybatis-config.xml）中 。

♦配置log4j.properties

<span style="font-family:'KaiTi_GB2312';">log4j.rootLogger=DEBUG,A1
log4j.logger.com.queen = DEBUG
log4j.logger.org.mybatis = DEBUG

log4j.appender.A1=org.apache.log4j.ConsoleAppender
log4j.appender.A1.layout=org.apache.log4j.PatternLayout
log4j.appender.A1.layout.ConversionPattern=%-d{yyyy-MM-dd HH:mm:ss,SSS} [%t] [%c]-[%p] %m%n</span>

主要记录MyBatis运行过程中产生的一些日志信息。

♦编写接口类UserMapper

<span style="font-family:'KaiTi_GB2312';">/**
 * @since 2017-07-15
 * @author queen
 * 定义一个UserMapper接口
 *
 */
public interface UserMapper {
    /**
     * 根据ID查找用户
     * @param id
     * @return
     */
    public User findUserById(int id);
}</span>

♦编写接口映射文件UserMapper.xml

<span style="font-family:'KaiTi_GB2312';"><?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.queen.mybatis.mapper.UserMapper">
    <select id="findUserById" resultType="com.queen.mybatis.bean.User">
        select id, loginId, userName, role, note from t_user where id = #{id}
    </select>
</mapper></span>

♦编写JavaBean类User

<span style="font-family:'KaiTi_GB2312';">/**
 * @since 2017-07-15
 * @author queen
 * 定义一个Java类
 *
 */
public class User {
    // ID，唯一性
    private String id;
    // 登录ID
    private String loginId;
    // 用户名
    private String userName;
    // 角色
    private String role;
    // 备注
    private String note;

    public String getId() {
        return id;
    }

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

    public String getLoginId() {
        return loginId;
    }

    public void setLoginId(String loginId) {
        this.loginId = loginId;
    }

    public String getUserName() {
        return userName;
    }

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

    public String getRole() {
        return role;
    }

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

    public String getNote() {
        return note;
    }

    public void setNote(String note) {
        this.note = note;
    }

    @Override
    public String toString() {
        return "User [id=" + id + ", loginId=" + loginId + ", userName="
                + userName + ", role=" + role + ", note=" + note + "]";
    }

}</span>

♦最后编写测试类

<span style="font-family:'KaiTi_GB2312';">/**
 * @since 2017-07-15
 * @author queen
 * 编写测试Java类
 *
 */
public class MyBatisTest {
    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(inputStream);
    }

    @Test
    public void test() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        SqlSession openSession = sqlSessionFactory.openSession();
        try {
            User user = openSession.selectOne(
                    "com.queen.mybatis.mapper.UserMapper.findUserById", "1");
            System.out.println(user);
        } finally {
            openSession.close();
        }

    }

}</span>

♦测试运行一下，查找ID是1的数据，日志详细过程完美的打印在控制台

<span style="font-family:'KaiTi_GB2312';">2017-07-15 16:52:43,862 [main] [org.apache.ibatis.transaction.jdbc.JdbcTransaction]-[DEBUG] Opening JDBC Connection
2017-07-15 16:52:44,305 [main] [org.apache.ibatis.datasource.pooled.PooledDataSource]-[DEBUG] Created connection 706757729.
2017-07-15 16:52:44,305 [main] [org.apache.ibatis.transaction.jdbc.JdbcTransaction]-[DEBUG] Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@2a204461]
2017-07-15 16:52:44,309 [main] [com.queen.mybatis.mapper.UserMapper.findUserById]-[DEBUG] ==>  Preparing: select id, loginId, userName, role, note from t_user where id = ?
2017-07-15 16:52:44,372 [main] [com.queen.mybatis.mapper.UserMapper.findUserById]-[DEBUG] ==> Parameters: 1(String)
2017-07-15 16:52:44,419 [main] [com.queen.mybatis.mapper.UserMapper.findUserById]-[DEBUG] <==      Total: 1
User [id=1, loginId=Sabot, userName=萨博, role=革命军, note=革命军的二号人物，同艾斯一样，为蒙奇·D·路飞的哥哥（义兄）。]
2017-07-15 16:52:44,420 [main] [org.apache.ibatis.transaction.jdbc.JdbcTransaction]-[DEBUG] Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@2a204461]
2017-07-15 16:52:44,421 [main] [org.apache.ibatis.transaction.jdbc.JdbcTransaction]-[DEBUG] Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@2a204461]
2017-07-15 16:52:44,421 [main] [org.apache.ibatis.datasource.pooled.PooledDataSource]-[DEBUG] Returned connection 706757729 to pool.</span>

我们会很明显的发现这是一个完整的JDBC执行过程，打开连接，创建连接，将事务设置成false，准备SQL，SQL赋参数，执行SQL，事务提交，关闭连接，返回连接。其实MyBatis就是将这些动作封装，对于开发人员只需要关注SQL。

三、总结

MyBatis整个调用过程：
根据xml配置文件（全局配置文件）创建一个SqlSessionFactory对象有数据源一些运行环境信息
sql映射文件；配置了每一个sql，以及sql的封装规则等。
将sql映射文件注册在全局配置文件中
写代码：
①根据全局配置文件，SqlSessionFactoryBuilder得到SqlSessionFactory

<span style="font-family:'KaiTi_GB2312';">public SqlSessionFactory getSqlSessionFactory() throws IOException {
    String resource = "mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    return new SqlSessionFactoryBuilder().build(inputStream);
}</span>

②使用sqlSession工厂，获取到sqlSession对象使用他来执行增删改查

<span style="font-family:'KaiTi_GB2312';">SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();</span>

③一个sqlSession就是代表和数据库的一次会话，用完关闭
④使用sql的唯一标志来告诉MyBatis执行哪个sql，sql都是保存在sql映射文件中的。

至此，我们关于MyBatis教程之简单的入门介绍完毕。只做了简单的查询动作。