mybatis案例程序

前置工作

• 导包（mysql-connector-java、mybatis）
• 实体类

Mapper层

1.接口

public interface BookMapper {
    public Book getBookById(Integer bookID);
}

2.创建Mapper的映射文件

<?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">
<mapper namespace="com.ylzl.mapper.BookMapper">
    <select id="getBookById" resultType="com.ylzl.pojo.Book">
        select * from books where bookID=#{bookID}
    </select>
</mapper>

Service层

可以不使用Service层，使用其他方式包含以下核心代码也可以。

核心代码

static {
  String resource = "mybatis-config.xml";
  try {
    InputStream inputStream = Resources.getResourceAsStream(resource);
  } catch (IOException e) {
    e.printStackTrace();
  }
}

//1.读取xml配置文件，创建SqlSessionFactory对象
SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(inputStream);
//2.通过创建SqlSessionFactory对象获取SqlSession对象
SqlSession sqlSession = sqlSessionFactory.openSession();
//3.通过SqlSession对象获取代理对象mapper，传入接口class对象
BookMapper mapper=sqlSession.getMapper(BookMapper.class);
//4.通过mapper调用接口对应方法
mapper.getBookById(bookID);

以下为使用Service层实现的方式

1.接口

public interface BookService {
    Book getBookById(Integer bookID);
}

2.接口实现类（重点关注）

public class BookServiceImpl implements BookService{
    static InputStream inputStream = null;
    static {
        String resource = "mybatis-config.xml";
        try {
            inputStream = Resources.getResourceAsStream(resource);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    //1.读取xml配置文件，创建SqlSessionFactory对象
    private final SqlSessionFactory sqlSessionFactory
            = new SqlSessionFactoryBuilder().build(inputStream);

    @Override
    public Book getBookById(Integer bookID) {
        //2.通过创建SqlSessionFactory对象获取SqlSession对象
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //3.通过SqlSession对象获取代理对象mapper，传入接口class对象,
        BookMapper mapper = sqlSession.getMapper(BookMapper.class);
        //4.通过mapper调用接口对应方法
        return  mapper.getBookById(bookID);
    }
}

Mybatis配置文件mybatis-config.xml（重点关注）

<?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">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <!--配置数据源-->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/ssmbuild"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>

    <!--配置映射文件-->
    <mappers>
        <mapper resource="com/ylzl/mapper/BookMapper.xml"/>
    </mappers>
</configuration>

测试

BookService bookServicelmpl = new BookServiceImpl();
System.out.println(bookServicelmpl.getBookById(2));

遇到的问题

1.BookMapper.xml不放在resources下，加过滤

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

2.解决xml编码问题：1 字节的 UTF-8 序列的字节 1 无效：https://www.cnblogs.com/thetree/p/12991403.html