初学Mybatis-第一个Mybatis程序及踩坑解决

Mybatis

项目完成步骤

1. 数据库

2. 新建项目

   Maven->Next->设置名称，存储位置->完成
   

   
   
   

3. 导入依赖
   

4. 创建模块

   新建->模块->Maven->输入信息->完成
   

5. 编写Mybatis的核心配置文件和Mybatis的工具类

   核心配置文件

   在Mybatis-01/src/main/resuorce下新建mybatis-config.xml文件，粘贴一下内容

   <?xml version="1.0" encoding="UTF8" ?>
           <!DOCTYPE configuration
                   PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
                   "http://mybatis.org/dtd/mybatis-3-config.dtd">
   <!--核心配置文件-->
   <configuration>
   <environments default="development">
       <environment id="development">
           <transactionManager type="JDBC"/>
           <dataSource type="POOLED">
               <property name="driver" value="${driver}"/>
               <property name="url" value="${url}"/>
               <property name="username" value="${username}"/>
               <property name="password" value="${password}"/>
           </dataSource>
       </environment>
   </environments>
   <!--每个Mapper.xml都需要注册-->
   <mappers>
       <mapper resource="top/yanggeol/dao/UserMapper.xml"></mapper>
   </mappers>
   </configuration>
   

   修改部分内容：数据库相关信息

   <?xml version="1.0" encoding="UTF8" ?>
           <!DOCTYPE configuration
                   PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
                   "http://mybatis.org/dtd/mybatis-3-config.dtd">
   <!--核心配置文件-->
   <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=UTF-8"/>
               <property name="username" value="root"/>
               <property name="password" value="123456"/>
           </dataSource>
       </environment>
   </environments>
   
   <!--每个Mapper.xml都需要注册-->
   <mappers>
       <mapper resource="top/yanggeol/dao/UserMapper.xml"></mapper>
   </mappers>
   
   </configuration>
   

   工具类

   java包创建包top.yanggeol.dao和top.yanggeol.utils，utils中创建MybatisUtils工具类

   package top.yanggeol.utils;
   
   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;
   
   
   //sqlSessionFactory --> sqlSession
   public class MybatisUtils {
       
       private static SqlSessionFactory sqlSessionFactory;
   
       static {
           try {
               String resource = "mybatis-config.xml";
               InputStream inputStream = Resources.getResourceAsStream(resource);
               sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
           } catch (IOException e){
               e.printStackTrace();
           }
       }
   
       // 既然有了 SqlSessionFactory，顾名思义，我们可以从中获得 SqlSession 的实例。SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。
       // 你可以通过 SqlSession 实例来直接执行已映射的 SQL 语句 
       public static SqlSession getSqlSession() {
           SqlSession sqlSession = sqlSessionFactory.openSession();
           return sqlSession;
       }
   }
   
   

6. 编写代码

   utils包同级下创建破击包，包下创建User实体类

   package top.yanggeol.pojo;
   
   //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 + '\'' +
                   '}';
       }
   }
   
   

   dao层新建接口UserDao.java

   package top.yanggeol.dao;
   
   import top.yanggeol.pojo.User;
   
   import java.util.List;
   
   public interface UserDao {
       List<User> getUserList();
   }
   
   

   dao层新建配置文件UserMapper.xml

   <?xml version="1.0" encoding="UTF8" ?>
   <!DOCTYPE mapper
           PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
           "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
   <!--绑定一个对应的Dao接口-->
   <mapper namespace="top.yanggeol.dao.UserDao">
       <!--查询 id对应接口中的方法-->
       <select id="getUserList" resultType="top.yanggeol.pojo.User">
           select * from mybatis.user
       </select>
   </mapper>
   

7. 测试

   在test/java新建top.yanggeo.dao包并编写UserDaoTest.java测试文件

   package top.yanggeol.dao;
   
   import org.apache.ibatis.session.SqlSession;
   import org.junit.Test;
   import top.yanggeol.pojo.User;
   import top.yanggeol.utils.MybatisUtils;
   
   import java.util.List;
   
   public class UserDaoTest {
   
       @Test
       public void test() {
   
           //  1. 获得SqlSession对象
           SqlSession sqlSession = MybatisUtils.getSqlSession();
   
           //  2. 方式1执行SQL
           //  UserDao userDao = sqlSession.getMapper(UserDao.class);
           //  List<User> userList = userDao.getUserList();
   
           // 方式2
           List<User> userList = sqlSession.selectList("top.yanggeol.dao.UserDao.getUserList");
   
           for (User user : userList) {
               System.out.println(user);
           }
   
           // 关闭SqlSession
           sqlSession.close();
       }
   }
   

8. 结果

踩坑

1. 在Maven配置中添加一下代码防止找不到Mapper的xml文件找不到

​ The error may exist in top/yanggeol/dao/UserMapper.xml

<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>

2. com.sun.org.apache.xerces.internal.impl.io.MalformedByteSequenceException: 1 字节的 UTF-8 序列的字节 1 无效。
   将xml文件的第一行的UTF-8改成UTF8

3. 版本类型不对(Error : java 不支持发行版本xxx )
   看在FIle->项目结构>module里面语言级别与当前java版本是不是一样的
   
   然后看setting->如下java版本是否与当前本地的一样
   

4. 然后基本是问题就能解决了，程序测试也可以运行出来了.