编写第一个Mybatis

创建数据库

 
CREATE DATABASE mybatis;
USE mybatis; 
CREATE TABLE USER ( id INT NOT NULL PRIMARY KEY,
 NAME VARCHAR(64) NOT NULL, 
 pwd VARCHAR(64) NOT NULL )
ENGINE=INNODB DEFAULT CHARSET=utf8; 
INSERT INTO USER (id,NAME,pwd)VALUE (1,'张三','123123');
INSERT INTO USER (id,NAME,pwd)VALUES (2,'小落','12341234'),(3,'李四','1231233');

创建项目

1.创建一个普通的Maven项目

2.删除src目录，形成父工程

3.导入需要的包

<!--mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <!--Mybatis-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.6</version>
        </dependency>
        <!--junit-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>

4.编辑包的结构

5.编写Mybatis.xml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"><!--可以创建多个环境-->
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/><!--加载驱动-->
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/><!--连接数据库-->
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <!--每一个Mapper.xml都需要在Mybatis的核心配置文件中注册-->
    <mappers>
        <mapper resource="com/Google/Dao/userMapper.xml"></mapper>
    </mappers>
 
</configuration>

5.1报错

### Error querying database.  Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
 
The last packet successfully received from the server was 449 milliseconds ago.  The last packet sent successfully to the server was 442 milliseconds ago.

这里的问题出在数据库，所以检查数据库连接。发现useSSL=true
要改为useSSL=false；

6.编写工具类（getSession）

package com.Google.units;
 
 
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 sqlSessionFactory {
    private static SqlSessionFactory sqlSessionFactory;
    static {
        try {
            String resource = "Mybatis.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    /*sqlsession完全包含了所有面向数据库执行sql语句的所有方法*/
    public static SqlSession getsqlSession(){
        return sqlSessionFactory.openSession();
    }
}

7.编写实体类

package com.Google.pojo;
 
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 + '\'' +
                '}';
    }
}

8.编写接口

package com.Google.Dao;
 
import com.Google.pojo.User;
 
import java.util.List;
 
public interface userMapper {
    /*定义一个获取user数据的接口*/
    List<User> getUserList();
}

9.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">
<!--namespace 用于绑定一个对应的Mapper接口-->
<mapper namespace="com.Google.Dao.userMapper">
    <!--id: 写接口中的方法-->
    <!--resultType: （返回结果的数据类型），这里要填写具体的实体类-->
    <select id="getUserList" resultType="com.Google.pojo.User">
        select * from user
    </select>
</mapper>

10测试

package com.Google.Dao;
 
import com.Google.pojo.User;
import com.Google.units.sqlSessionFactory;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
 
import java.util.List;
 
public class userDao {
    @Test
    public void test() throws Exception{
 
        SqlSession sqlSession = sqlSessionFactory.getsqlSession();
        userMapper md =sqlSession.getMapper(userMapper.class);
 
        List<User> userList = md.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }
 
    }
}

注意点

1.先把需要配置的再区写测试，防止测试类的名字和Dao一样，这样先写测试类，然后再去配置文件，可能会把测试类配置到Mybatis配置文件中，这样就会报这样的错

type class com.google.dao.usermapper is not known to the mapperregistry.

2.由于Maven中约定大于配置，所以我们配置的文件可能会被过滤掉，只需要加入这些代码，就可解决这样的问题

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

3.最常见的错误

org.apache.ibatis.binding.BindingException: Type interface com.Google.Dao.userMapper is not known to the MapperRegistry.

这里就是要在Mybatis.xml和Dao目录下的配置文件一起配置，具体如下

<!--每一个Mapper.xml都需要在Mybatis的核心配置文件中注册-->
    <mappers>
        <mapper resource="com/Google/Dao/userMapper.xml"></mapper>
    </mappers>

<!--namespace 用于绑定一个对应的Mapper接口-->
<mapper namespace="com.Google.Dao.userMapper">
    <!--id: 写接口中的方法-->
    <!--resultType: （返回结果的数据类型），这里要填写具体的实体类-->
    <select id="getUserList" resultType="com.Google.pojo.User">
        select * from user
    </select>
</mapper>