第一个Mybatis程序

代码演示：

1、搭建数据库环境：

CREATE DATABASE mybatis;

USE mybatis;

DROP TABLE IF EXISTS user;

CREATE TABLE user (
  id int(20) NOT NULL,
  name varchar(30) DEFAULT NULL,
  pwd varchar(30) DEFAULT NULL,
  PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

insert  into user(id,name,pwd) values (1,'黑子','123456'),(2,'美琴','abcdef'),(3,'初春','987654');

---

2、导入MyBatis相关的包

<!--mybatis-->
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.2</version>
</dependency>
<!--mysql驱动-->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.47</version>
</dependency>

导入log4j测试包：

<dependency>
    <groupId>log4j</groupId>
    <artifactId>log4j</artifactId>
    <version>1.2.17</version>
</dependency>    

---

3、编写Mybatis核心配置文件

<?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/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=utf8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>


    <mappers>
        <mapper class="com.ttt.dao.UserMapper"/>
    </mappers>
</configuration>

---

4、编写Mybatis工具类

public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;

    static{
        String str = "mybatis_config.xml";
        InputStream inputStream = null;
        try {
            inputStream = Resources.getResourceAsStream(str);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

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

}

---

5、编写实体类

public class User {
    private int id;
    private String name;
    private String pwd;

    public User() {
    }

    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", pwd='" + pwd + '\'' +
                '}';
    }
}

---

6、编写mapper接口

public interface UserMapper {
    //获取全部用户
    List<User> selectUser();

    //根据id查询用户
    User getUserByID(int id);

    //insert一个用户
    int addUser(User user);

    //修改用户
    int updateUser(User user);

    //删除一个用户
    int deleteUser(int id);
}

---

7、编写mapper.xml配置文件

<?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.UserMapper">
    <select id="selectUser" resultType="com.ttt.pojo.User">
        select * from mybatis.user
    </select>
    
    <select id="getUserByID" parameterType="int" resultType="com.ttt.pojo.User">
        select * from mybatis.user where id=${id}
    </select>

    <insert id="addUser" parameterType="com.ttt.pojo.User">
        insert into user(id, name, pwd) values (#{id}, #{name}, #{pwd})
    </insert>

    <update id="updateUser" parameterType="com.ttt.pojo.User">
        update user set name = #{name}, pwd=#{pwd} where id=#{id};
    </update>

    <delete id="deleteUser" parameterType="int">
        delete from mybatis.user where id=#{id};
    </delete>
</mapper>

---

8、编写测试类：

• Junit 包测试(测试查询功能）

 @Test
    public void test01(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        List<User> users = userMapper.selectUser();

        for (User user : users) {
            System.out.println(user);
        }

        sqlSession.close();
   }

---

问题分析：

通过问题提示：Could not find resource com/ttt/dao/UserMapper.xml,而我的UserMapper接口与UserMapper配置文件都放在一起，在Mybatis的核心配置文件配置的mapper路径也没有问题。导致这个问题是由于Maven静态资源过滤，就是java文件中只能创建java文件，而配置文件被过滤出来没有创建，可以看target文件：

就是最终只有UserMapper.class文件。

解决方法：在局部或者全局的pom.xml添加：

<build>
    <resources>
        <resource>
            <directory>src/main/java</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>false</filtering>
        </resource>
        <resource>
            <directory>src/main/resources</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>false</filtering>
        </resource>
    </resources>
</build>