mybatis學習小結——使用配置文件的方式實現crud

1,新建一個maven項目，配置pom.xml,引入相關包

<dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.2.6</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.46</version>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
    </dependencies>

2，新建mybatis核心配置文件mybatis-config.xml,配置數據源。配置數據源可以有兩種配置方式：

方式一：將數據庫連接信息寫入另一個properties文件，然後在mybatis-config.xml中引用

方式二：直接在mybatis-config.xml中配置

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://127.0.0.1:3306/test
jdbc.username=root
jdbc.password=123456

<?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>

    <!--fatal: the different elements label in configuration have stable order-->

    <!--define datasoure method1: config in a properties file and import here-->
    <!--import database config file-->
    <properties resource="db.properties"></properties>

    <!--define nickname-->
    <typeAliases>
        <!--<typeAlias type="com.sohu.zzy.domain.User" alias="User"></typeAlias>-->
        <package name="com.sohu.zzy.domain"></package>
    </typeAliases>

    <!--define datasource-->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>

    <!--define datasoure method2: config in here directly-->
    <!--<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://127.0.0.1:3306/test"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>-->


    <!--define mapperxml file source ,package-->
    <mappers>
        <!--<package name="mybatis"></package>-->
        <mapper resource="mybatis/UserMapper.xml"></mapper>
    </mappers>

</configuration>

3，配置文件中的標籤說明：

A.<typealiases>

起別名，給某個類起個別名，如果不起別名的話，則一般我們調用、配置的時候需要寫包含包名的全路徑；配置別名之後，則可以直接使用類名即可調用。兩種配置方式：

（1）給單個類配置別名

（2）掃描整個包

B.<mappers>

配置mapper接口與sql的映射掃描，兩種方式配置：

（1）單個文件配置

（2）掃描整個包（沒有嘗試成功，尚未找到原因）

特別注意：

運行過程中可能遇到找不到usermapper方法的映射的報錯。

如果出現：

org.apache.ibatis.binding.BindingException: Invalid bound statement (not found)

一般的原因是Mapper interface和xml文件的定義對應不上，需要檢查包名，namespace，函數名稱等能否對應上，需要比較細緻的對比，我經常就是寫錯了一兩個字母搞的很長時間找不到錯誤

按以下步驟一一執行：

a：檢查xml文件所在的package名稱是否和interface對應的package名稱一一對應

b：檢查xml文件的namespace是否和xml文件的package名稱一一對應

c：檢查函數名稱能否對應上

d：去掉xml文件中的中文註釋

e：隨意在xml文件中加一個空格或者空行然後保存

一般來說到此就可以排除錯誤了，如果仍未解決，還有一種可能：就是xml編譯的問題，查看編譯後的文件是否含有UserMapper.xml文件，如果沒有那麼就是編譯的問題了

解決方法有兩種：

a、把*Mapper.xml文件放到resource文件夾下管理

b、pom配置一下編譯xml文件

<resource>
    <directory>src/main/java</directory>
    <includes>
        <include>**/*.xml</include>
    </includes>
</resource>

4，創建user.java對象類，數據庫建相應的表

5，創建UserMapper.java接口類，用於對數據庫進行操作的接口

package com.sohu.zzy.mybatis.mapper;

import com.sohu.zzy.domain.User;
import org.apache.ibatis.annotations.Param;

import java.util.List;
import java.util.Map;

/**
 * Created by zhuzhengyi on 2019/6/11.
 */
public interface UserMapper {

    User findById(Integer id);

    /**
     * 查詢所有用戶
     * @return
     */
    List<User> findAll();

    /**
     * multiple parameters :
    method1: use the parameter order number
    method2: use annotation in usermapper.java
    method3:
     */
    List<User> selectMulParam1(int offset,int pagenum);
    List<User> selectMulParam2(@Param(value = "offset") int offset,
                               @Param(value = "pagenum") int pagenum);
    List<User> selectMulParam3(Map<String,Object> map);


    /**
     * add user
     * @param user
     */
    public void saveUser(User user);

    /**
     * update user
     * @param user
     */
    public void updateUser(User user);

    /**
     * delete user by id
     * @param id
     */
    public void deleteById(int id);
}

6，爲接口類中的操作配置相應的sql映射，UserMapper.xml

​
<?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.sohu.zzy.mybatis.mapper.UserMapper">

    <resultMap id="userResultMap" type="User">

    </resultMap>

    <select id="findById" parameterType="Integer" resultType="User">
        select * from user where id = #{id}
    </select>

    <select id="findAll" resultMap="userResultMap">
        select * from user
    </select>

    <!--multiple parameters :
    method1: use the parameter order number
    method2: use annotation in usermapper.java
    method3:-->
    <select id="selectMulParam1" resultMap="userResultMap">
        SELECT * from user limit #{0},#{1}
    </select>
    <select id="selectMulParam2" resultMap="userResultMap">
        SELECT * from user limit #{offset},#{pagenum}
    </select>
    <select id="selectMulParam3" resultMap="userResultMap">
        SELECT * from user limit #{offset},#{pagenum}
    </select>

    <insert id="saveUser" parameterType="User" >
        insert into user(id,name,password,age,source)VALUES (#{id},#{name},#{password},#{age},#{source})
    </insert>

</mapper>

​

7,採用單例模式創建sqlsessionfactory，這樣沒次需要調用接口訪問數據庫的時候可直接從工廠類中獲得一個session。如果不是要該方式也可以，但是會導致每次調用接口的時候都需要創建一個session對象，比較麻煩，所以建議使用此方式。

package com.sohu.zzy.mybatis.utils;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.InputStream;

/**
 * Created by zhuzhengyi on 2019/6/11.
 */
public class MybatisUtils {
    /**
     * 單例模式創建sqlsessionfactory
     */

    //provide globel sqlsessionfactory
    private static SqlSessionFactory sqlSessionFactory;

    static {
        try {
            //get config file stream
            InputStream ins = Resources.getResourceAsStream("mybatis-config.xml");
            //create sqlsessionfactory object
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(ins);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public MybatisUtils() {
    }

    public static SqlSessionFactory getSqlSessionFactory() {
        return sqlSessionFactory;
    }

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

8，創建測試用例

package com.sohu.zzy.test;

import com.sohu.zzy.domain.User;
import com.sohu.zzy.mybatis.mapper.UserMapper;
import com.sohu.zzy.mybatis.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * Created by zhuzhengyi on 2019/6/11.
 */
public class UserMapperTest {

    /**
     * 使用接口userMapper,然後調用接口的方法
     */
    @Test
    public void testFindById(){
        //create sqlsession object access sqlsessionfactory
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //get interface object by sqlsession
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        //run method in proxy object
        User user = userMapper.findById(1);
        sqlSession.close();
        System.out.println(user.getName());

    }

    /**
     * 不使用接口userMapper,直接調用接口的方法
     */
    @Test
    public void testFindById2(){
        //create sqlsession object access sqlsessionfactory
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        //run method directly without interface
        User user = sqlSession.selectOne("com.sohu.zzy.mybatis.mapper.UserMapper.findById",1);

        sqlSession.close();
        System.out.println(user.getName());

    }

    /**
     * test findall
     */
    @Test
    public void findAll(){
        //create sqlsession object access sqlsessionfactory
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //get interface object by sqlsession
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        //run method in proxy object
        List<User> list = userMapper.findAll();
        sqlSession.close();
        for(User user : list){
            System.out.println(user);
            System.out.println(user.getName());
        }
    }

    /**
     * test multiple parameters method
     */
    @Test
    public void testSelectMulParam1(){
        //create sqlsession object access sqlsessionfactory
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //get interface object by sqlsession
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        //run method in proxy object
        List<User> list = userMapper.selectMulParam1(2,2);
        sqlSession.close();
        for(User user : list){
            System.out.println(user);
            System.out.println(user.getName());
        }
    }
    @Test
    public void testSelectMulParam2(){
        //create sqlsession object access sqlsessionfactory
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //get interface object by sqlsession
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        //run method in proxy object
        List<User> list = userMapper.selectMulParam2(2,2);
        sqlSession.close();
        for(User user : list){
            System.out.println(user);
            System.out.println(user.getName());
        }
    }
    @Test
    public void testSelectMulParam3(){
        //create sqlsession object access sqlsessionfactory
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //get interface object by sqlsession
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

        Map<String,Object> map = new HashMap<String, Object>();
        map.put("offset",2);
        map.put("pagenum",2);
        //run method in proxy object
        List<User> list = userMapper.selectMulParam3(map);
        sqlSession.close();
        for(User user : list){
            System.out.println(user);
            System.out.println(user.getName());
        }
    }

    @Test
    public void saveUser(){
        //create sqlsession object access sqlsessionfactory
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //get interface object by sqlsession
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

        User user = new User();
        user.setId(5);
        user.setName("xxxx");
        user.setPassword("asdfadf");
        user.setAge(23);
        user.setSource(2);

        userMapper.saveUser(user);
        sqlSession.commit();
        sqlSession.close();
    }

    @Test
    public void updateUser(){
        //create sqlsession object access sqlsessionfactory
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //get interface object by sqlsession
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

        User user = new User();
        user.setId(2);
        user.setName("xyyy");
        user.setPassword("asdfadf");
        user.setAge(23);
        user.setSource(2);

        userMapper.updateUser(user);
        sqlSession.commit();
        sqlSession.close();
    }

    @Test
    public void deleteUser(){
        //create sqlsession object access sqlsessionfactory
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //get interface object by sqlsession
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

        userMapper.deleteById(2);
        sqlSession.commit();
        sqlSession.close();
    }

}