mybatis映射文件mapper.xml的具体写法

湛蓝之海

在开发过程中，需要开发人员配置mapper映射文件，本文主要介绍了mybatis映射文件mapper.xml的具体写法，感兴趣的可以了解一下
Mapper映射文件是一个xml格式文件，必须遵循相应的dtd文件规范
在学习mybatis的时候我们通常会在映射文件这样写：

<?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.qbd.mapper.StudentMappers">
  <select id="findbyid" parameterType="Integer" resultMap="StudentResult">
    select *from student where id=#{id}
  </select>
  
  <select id="findbygradeid" parameterType="Integer" resultMap="StudentResult">
    select *from student where gid=#{gid}
  </select>
  
  <resultMap type="Student" id="StudentResult">
    <id property="id" column="id"/>
    <result property="name" column="name"/>
    <result property="age" column="age"/>
    <association property="address" column="addid" select="com.qbd.mapper.AddressMappers.findbyid">  
    </association>
    <association property="grade" column="gid" select="com.qbd.mapper.GradeMappers.findbyid">  
    </association>
  </resultMap>
</mapper>

然后再写dao的实现在写一个类，来实现dao的接口。但是这样在实现中需要这样写：

package com.qbd.service;
import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;
 
import com.qbd.mapper.StudentMappers;
import com.qbd.model.Student;
import com.qbd.util.SqlSessionFactoryUtil;
 
public class StudentService {
  private static Logger logge=Logger.getLogger(StudentService.class);
  public static void main(String[] args) {
    SqlSession sqlSession=SqlSessionFactoryUtil.getSqlSession();
    
    StudentMappers studentMappers=(StudentMappers)sqlSession.getMapper(StudentMappers.class);
    Student student=new Student();
    student.setName("22");
    student.setAge(2);
    int s=studentMappers.add(student);
    sqlSession.commit();
    if(s>0){
      logge.info("success");
      System.out.println("success");
    }
    
  }
}

来读取配置文件
另一种方法就是：
直接在mapper.xml中的这一部分写成dao<mapper namespace="com.qbd.mapper.StudentMappers">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="com.qbd.ssm.dao.UserDao">
  <!-- 定义缓存  一般是一级缓存，如果用同一个sqlsession 那么相同查询直接会从缓存中查找 
  <cache size="1024" flushInterval="60000" eviction="LRU" readOnly="false"></cache>
  -->
  <!-- 查找所有 -->
  <select id="find" parameterType="Map" resultMap="StudentResult">
    select * from user
    <where>
      <if test="uname!=null and uname!='' ">
        and uname like #{uname}
      </if>
    </where>
    <if test="start!=null and size!=null">
      limit #{start},#{size}
    </if>
  </select>
  
  <select id="getTotal" parameterType="Map" resultType="Long">
    select count(*) from user
    <where>
      <if test="uname!=null and uname!='' ">
        and uname like #{uname}
      </if>
    </where>
  </select>
  <!-- 按照用户名和密码查找 -->
  <select id="getUser" resultMap="StudentResult" parameterType="Map">
    select *from user where uname=#{uname} and upassword=#{upassword}
  </select>
  <!-- 删除 -->
  <delete id="delete" parameterType="Map">
    delete from user where uid=#{uid}
  </delete>
  <!-- 修改 -->
  <update id="update" parameterType="User">
    update user
    <set>
      <if test="uname!=null">
         uname=#{uname},
      </if>
      <if test="upassword!=null">
        upassword=#{upassword},
      </if>
      <if test="upower!=null">
        upower=#{upower},
      </if>
    </set>
    where uid=#{uid}
  </update>
  <!-- 增加 -->
  <insert id="add" parameterType="User">
    insert into user values(null,#{uname},#{upassword},#{upower})
  </insert>
  <resultMap type="User" id="StudentResult">
    <id property="uid" column="uid"/>
    <result property="uname" column="uname"/>
    <result property="upassword" column="upassword"/>
  </resultMap>
</mapper>

那么就不用写dao的实现在service中就能掉用       mybatis默认会把mapper.xml映射为dao的实现
那么下面dao就能这样写：

package com.qbd.ssm.dao;
 
import java.util.List;
import java.util.Map;
 
import org.apache.ibatis.annotations.Delete;
 
import com.qbd.ssm.model.User;
 
public interface UserDao {
 
  public List<User> getAll();
  public User getUser(User user);
  public int delete(User user);
  public int update(User user);
  public int add(User user);
  public List<User> find(Map<String,Object> map);
  public Long getTotal(Map<String,Object> map);
}

service这样写

package com.qbd.ssm.service;
import java.util.List;
import java.util.Map;
import com.qbd.ssm.model.User; 
public interface UserService {
 
  public List<User> getAll();
  public User getUser(User user);
  public int delete(User user);
  public int update(User user);
  public int add(User user);
  public List<User> find(Map<String,Object> map);
  public Long getTotal(Map<String,Object> map);
}

service的实现：

package com.qbd.ssm.serviceimpl;
import java.util.List;
import java.util.Map;
import javax.annotation.Resource; 
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.qbd.ssm.dao.UserDao;
import com.qbd.ssm.model.User;
import com.qbd.ssm.service.UserService;
 
@Service("userService")
public class UserServiceImpl implements UserService {
 
  private UserDao userDao;
  
  public UserDao getUserDao() {
    return userDao;
  }
 
  @Resource
  public void setUserDao(UserDao userDao) {
    this.userDao = userDao;
  }
 
  public List<User> getAll() {
    // TODO Auto-generated method stub
    return userDao.getAll();
  }
 
  public User getUser(User user) {
    // TODO Auto-generated method stub
    return userDao.getUser(user);
  }
 
  public int delete(User user) {
    // TODO Auto-generated method stub
    return userDao.delete(user);
  }
 
  public int update(User user) {
    // TODO Auto-generated method stub
    return userDao.update(user);
  }
 
  public int add(User user) {
    // TODO Auto-generated method stub
    return userDao.add(user);
  }
 
  public List<User> find(Map<String, Object> map) {
    // TODO Auto-generated method stub
    return userDao.find(map);
  }
 
  public Long getTotal(Map<String, Object> map) {
    // TODO Auto-generated method stub
    return userDao.getTotal(map);
  }
}

在这里面userDao不能写错，spring会按照name进行注入
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原文链接：https://blog.csdn.net/two_people/article/details/51759881