mybatis-notes：mybatis用接口实现数据交互

在写一个很简单的入门级mybatis demo中，是直接通过xml来绑定mapper，这里使用接口来实现。

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数据库仍使用之前的数据库

数据库结构

方法一：用约束来保证接口能够在XML中找到对应的SQL语句

在之前的demo项目下新建一个demo2.cyj包用于做接口的实现方式，最终项目结构如下：

最终目录结构

1. 将之前的mybatis_config.xml和Student.java拷到相应包下

2. 新建一个包dao，再新建接口StudentDao.java，

package demo2.cyj.dao;

import demo2.cyj.pojo.Student;

public interface StudentDao{

    public Student selectStuById(int id);

    public int insertStu(String stu_name,int stu_age);
    
    public int updateById(Map<String,Object> map);
    
}

3. 在mapper包下新建StudentMapper.xml，配置如下

<?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="demo2.cyj.dao.StudentDao">
    <select id="selectStuById" parameterType="int" resultType="demo2.cyj.pojo.Student">
        select * from student where id = #{id}
    </select>

    <insert id="insertStu">
        insert into student(stu_name,stu_age) values(#{0},#{1})
    </insert>
    
    <update id="updateById" parameterType="map">
        update student set stu_name = #{sname},stu_age=#{sage} where id=#{sid}
    </update>
</mapper>

需要注意的是，mapper名空间和StudentDao接口的路径要一致，id和方法名一致，否则会报错：Exception in thread "main" org.apache.ibatis.binding.BindingException: Type interface demo2.cyj.dao.StudentDao is not known to the MapperRegistry.

Exception in thread "main" org.apache.ibatis.binding.BindingException: Type interface demo2.cyj.dao.StudentDao is not known to the MapperRegistry.
    at org.apache.ibatis.binding.MapperRegistry.getMapper(MapperRegistry.java:47)
    at org.apache.ibatis.session.Configuration.getMapper(Configuration.java:717)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.getMapper(DefaultSqlSession.java:292)
    at demo2.cyj.MybatisTest2.main(MybatisTest2.java:28)

4. 新建MybatisTest2.java测试类进行测试

package demo2.cyj;

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 demo2.cyj.dao.StudentDao;
import demo2.cyj.pojo.Student;

public class MybatisTest2 {
    public static void main(String[] args) throws IOException {

        // mybatis的配置文件的路径
        String resource = "demo2/cyj/config/mybatis_config.xml";
        // 读取配置文件的路径
        InputStream inputStream = Resources.getResourceAsStream(resource);
        // 获取到sqlSession的构造工厂类
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        // 括号内加true，那么会自动提交，否则(括号内不传参)最后要手动提交
        SqlSession session = sqlSessionFactory.openSession(true);
        
        //通过session将StudentDao.java和StudentMapper.xml绑定起来，
        //注意此方式中，mapper的名空间要和接口的路径一致，mapper的id要和接口的方法名一致
        StudentDao studentDao = session.getMapper(StudentDao.class);
        //在dao中指定了返回的类型是obj还是list，所以就不用特别指定selectOne还是selectList
        //查找byId
        Student s1 = studentDao.selectStuById(1);
        System.out.println("select:"+s1);
        
        //插入，通过逐个值传的方式
        int i = studentDao.insertStu("拐", 50);
        System.out.println("insert:"+i);
        
        //修改，通过传递map的方式
        Map<String,Object> map = new HashMap<>();
        map.put("sname", "黑拐");
        map.put("sage", 42);
        map.put("sid", 8);
        int b = studentDao.updateById(map);
        System.out.println("update:"+b);

    }
}

在这种方式中，与之前不同的是要通过StudentDao studentDao = session.getMapper(StudentDao.class)，将mapper和接口绑定起来；
特别注意的一点是，这段代码中：
Student s1 = studentDao.selectStuById(1);
因为在dao中的接口方法声明上就指定了返回的类型是obj还是list，所以就不用特别指定selectOne还是selectList

运行结果： 运行结果

附其他部分代码：

mybatis_config.xml代码：

<?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>
  <!-- 配置默认开发环境，default中的值与下面的开发环境id对应 -->
  <environments default="development">
  <!-- 配置开发环境 -->
    <environment id="development">
    <!-- JDBC事务 -->
      <transactionManager type="JDBC"/>
      <!-- 连接池 -->
      <dataSource type="POOLED">
        <property name="driver" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&amp;characterEncoding=utf8"/>
        <property name="username" value="aaa"/>
        <property name="password" value="123"/>
      </dataSource>
    </environment>
  </environments>
 <mappers>
    <mapper resource="demo2/cyj/mapper/StudentMapper.xml"/>
  </mappers>
</configuration>

Student.java代码：

package demo2.cyj.pojo;

public class Student {
    private int id ; 
    private String stu_name ; 
    private int stu_age ;   
    public Student() {} 
    public Student(int id, String stu_name, int stu_age) {
        super();
        this.id = id;
        this.stu_name = stu_name;
        this.stu_age = stu_age;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getStu_name() {
        return stu_name;
    }
    public void setStu_name(String stu_name) {
        this.stu_name = stu_name;
    }
    public int getStu_age() {
        return stu_age;
    }
    public void setStu_age(int stu_age) {
        this.stu_age = stu_age;
    }
    @Override
    public String toString() {
        return "Student [id=" + id + ", stu_name=" + stu_name + ", stu_age=" + stu_age + "]";
    }
}

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方法二：通过接口+注解SQL方式来交互数据

在之前的demo项目下新建一个demo3.cyj包用于做接口的实现方式，最终项目结构如下：

最终目录结构

1. 将之前demo中的Student.java复制到相应包下

2. 在config包下新建mybatis_config.xml，并配置

<?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>
  <!-- 配置默认开发环境，default中的值与下面的开发环境id对应 -->
  <environments default="development">
  <!-- 配置开发环境 -->
    <environment id="development">
    <!-- JDBC事务 -->
      <transactionManager type="JDBC"/>
      <!-- 连接池 -->
      <dataSource type="POOLED">
        <property name="driver" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&amp;characterEncoding=utf8"/>
        <property name="username" value="aaa"/>
        <property name="password" value="123"/>
      </dataSource>
    </environment>
  </environments>
</configuration>

3. 在dao包下新建接口StudentDao.java，并通过注解配置sql语句：

package demo3.cyj.dao;

import org.apache.ibatis.annotations.Select;

import demo3.cyj.pojo.Student;

public interface StudentDao{
    @Select({"select * from student where id = #{id}" })
    public Student selectStuById(int id);   
}

此时在mybatis_confiig.xml中添加<mappers></mappers>的配置，全部代码如下：

<?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>
    <!-- 配置默认开发环境，default中的值与下面的开发环境id对应 -->
    <environments default="development">
        <!-- 配置开发环境 -->
        <environment id="development">
            <!-- JDBC事务 -->
            <transactionManager type="JDBC" />
            <!-- 连接池 -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver" />
                <property name="url"
                    value="jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&amp;characterEncoding=utf8" />
                <property name="username" value="aaa" />
                <property name="password" value="123" />
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper class="demo3/cyj/dao/StudentDao" />
    </mappers>
</configuration>

4. 新建MybatisTest3.java测试类进行测试

package demo3.cyj;

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 demo3.cyj.dao.StudentDao;
import demo3.cyj.pojo.Student;

public class MybatisTest3 {
    
    public static void main(String[] args) throws IOException {

        // mybatis的配置文件的路径
        String resource = "demo2/cyj/config/mybatis_config.xml";
        // 读取配置文件的路径
        InputStream inputStream = Resources.getResourceAsStream(resource);
        // 获取到sqlSession的构造工厂类
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        
        //在使用注解方式查询时需要注册mapper，相当于还是生成了一个mapper，只不过在开发时可以少写一点
        sqlSessionFactory.getConfiguration().addMapper(StudentDao.class);  
        // 括号内加true，那么会自动提交，否则(括号内不传参)最后要手动提交
        SqlSession session = sqlSessionFactory.openSession(true);
        
        StudentDao studentDao = session.getMapper(StudentDao.class);
        //在dao中指定了返回的类型是obj还是list，所以就不用特别指定selectOne还是selectList
        Student s3 = studentDao.selectStuById(1);
        System.out.println(s3);
    }
}

运行结果如下： 运行结果

在这种方式中，需要注意的一点是，因为省略了,mapper的xml文件，所以在使用前要注册mapper，具体代码是
sqlSessionFactory.getConfiguration().addMapper(StudentDao.class);
如果没写就会报错：
Exception in thread "main" org.apache.ibatis.binding.BindingException: Type interface demo3.cyj.dao.StudentDao is not known to the MapperRegistry.

Exception in thread "main" org.apache.ibatis.binding.BindingException: Type interface demo3.cyj.dao.StudentDao is not known to the MapperRegistry.
    at org.apache.ibatis.binding.MapperRegistry.getMapper(MapperRegistry.java:47)
    at org.apache.ibatis.session.Configuration.getMapper(Configuration.java:717)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.getMapper(DefaultSqlSession.java:292)
    at demo3.cyj.MybatisTest3.main(MybatisTest3.java:27)

附Student.java代码:

package demo3.cyj.pojo;

public class Student {

    private int id ; 
    private String stu_name ; 
    private int stu_age ;
    
    public Student() {} 
    public Student(int id, String stu_name, int stu_age) {
        super();
        this.id = id;
        this.stu_name = stu_name;
        this.stu_age = stu_age;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getStu_name() {
        return stu_name;
    }
    public void setStu_name(String stu_name) {
        this.stu_name = stu_name;
    }
    public int getStu_age() {
        return stu_age;
    }
    public void setStu_age(int stu_age) {
        this.stu_age = stu_age;
    }
    @Override
    public String toString() {
        return "Student [id=" + id + ", stu_name=" + stu_name + ", stu_age=" + stu_age + "]";
    }
}