Mybatis（上）

1、实现mybatis

官方文档：https://mybatis.org/mybatis-3/zh/getting-started.html

MyBatis 是一款优秀的持久层框架，免除了几乎所有的 JDBC 代码以及设置参数和获取结果集的工作。MyBatis 可以通过简单的 XML 或注解来配置和映射原始类型、接口和实体类为数据库中的记录。

创建数据库

CREATE DATABASE `mybatis`;

USE `mybatis`;

CREATE TABLE `user` (
  `id` INT(20) NOT NULL AUTO_INCREMENT COMMENT '用户编号',	--非空，自增，注释
  `name` VARCHAR(30) NOT NULL COMMENT '用户名称',
  `pwd` VARCHAR(30) NOT NULL COMMENT '用户密码',
  PRIMARY KEY  (`id`)	--设置主键
) ENGINE=INNODB DEFAULT CHARSET=utf8

INSERT INTO `user`(`name`,`pwd`)  VALUE	('a','123'),('b','123')

项目架构如图：

1.1、导入依赖

pom.xml

<!-- MySQL驱动 -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.47</version>
</dependency>
<!-- Mybatis -->
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.4</version>
</dependency>
<!-- 单元测试 -->
<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.11</version>
    <scope>test</scope>
</dependency>

1.2、编写实体类

@Data		//使用lombok插件可见不写有参无参构造和get,set方法
public class User {
    
    
    private int id;
    private String name;
    private String pwd;
}

1.3、编写核心配置文件

mybatis-config.xml

<?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">
<!--核心配置文件-->
<configuration>
    <!--识别JavaBean，如果没有这个，mapper.xml中的传参和返回参数类型要写完整实体类路径-->
    <typeAliases>
        <package name="pojo"/>
    </typeAliases>
    <!--配置环境-->
    <environments default="development">
        <environment id="development">
            <!--事务管理-->
            <transactionManager type="JDBC"/>
            <!--数据库属性，一般另外写一个properties文件存放-->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useUnicode=true&amp;useSSL=true"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <!--绑定接口-->
    <mappers>
        <mapper resource="dao/UserMapper.xml"/>
    </mappers>
</configuration>

1.4、编写接口

public interface UserMapper {
    
    
    List<User> select();
    User getUserById(int id);
    int insert(User user);
    int delete(int id);
    int update(User user);
}

1.5、编写xml

Mapper.xml

#{}和${}的区别：#{}可以防止SQL注入

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--绑定对应的mapper接口，命名空间必须是完整路径-->
<mapper namespace="dao.UserMapper">
    <!--id 绑定对应接口方法名称，resultType 写对应返回类型-->
    <!--如果mybatis-config.cml没有配置<typeAliases>，resultType 写完整路径-->
    <select id="select" resultType="User">
        select * from user;
    </select>
    <!--parameterType 写传参类型-->
    <select id="getUserById" parameterType="int" resultType="User">
        <!--#{}内的字段要和接口参数相同-->
        select * from mybatis.user where id=#{id};
    </select>
    <insert id="insert" parameterType="User">
        insert into `user`(`name`,`pwd`) value (#{name},#{pwd})
    </insert>
    <delete id="delete" parameterType="int">
        delete from `user` where `id`=#{id}
    </delete>
    <update id="update" parameterType="User">
        update `user` set `name`=#{name} where `id`=#{id}
    </update>
</mapper>

1.6、包装工具类

public class MybatisUtils {
    
    
    //获取sqlSession对象
    public static SqlSession getSqlSession() throws IOException {
    
    
        //添加mybatis配置文件
        String resource = "mybatis-config.xml";
        //创建字符输入流
        InputStream inputStream = Resources.getResourceAsStream(resource);
        //创建SqlSession工厂
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        //通过SqlSession工厂获得sqlSession对象
        return sqlSessionFactory.openSession(true);
    }
}

1.7、测试

public class MyTest {
    
    
    @Test
    public void test() throws IOException{
    
    
        //获取session
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //获取mapper
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        //查询
        List<User> userList = mapper.select();
        for (User u : userList) {
    
    
            System.out.println(u);
        }
        //根据ID查询
        User user = mapper.getUserById(1);
        System.out.println(user);
        //openSession()不为true需要事务提交
        //sqlSession.commit();
        //关闭资源
        sqlSession.close();
    }
}

注：如运行不通过考虑maven静态资源过滤问题，在pom.xml添加

<build>
    <resources>
        <resource>
            <directory>src/main/java</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>false</filtering>
        </resource>
        <resource>
            <directory>src/main/resources</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>false</filtering>
        </resource>
    </resources>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <configuration>
                <source>8</source>
                <target>8</target>
            </configuration>
        </plugin>
    </plugins>
</build>

2、Map

parameterType 传参类型可以是map，有很多字段但只需要传少量参数的时候使用。

2.1、编写接口

public interface UserMapper {
    
    
    //import java.util.Map;
    int addUser(Map map);
}

2.2、编写xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--绑定对应的mapper接口-->
<mapper namespace="com.lin.dao.UserMapper">
    <insert id="addUser" parameterType="Map">
        insert into mybatis.user(name, pwd) value (#{username},#{password})
    </insert>
</mapper>

2.3、测试

public class MyTest {
    
    
    @Test
    public void test(){
    
    
        SqlSession sqlSession = null;
        try {
    
    
            sqlSession = MybatisUtils.getSqlSession();
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            HashMap<String, Object> map = new HashMap<>();
            map.put("username","hhh");
            map.put("password","123456");
            mapper.addUser(map);
        } catch (IOException e) {
    
    
            e.printStackTrace();
        } finally {
    
    
            sqlSession.close();
        }
    }
}

3、模糊查找

<select id="getUserByName" resultType="User">
    select * from mybatis.user where name like "%"#{name}"%";
</select>

4、优化

注意：mybatis-config的属性配置有规定顺序

configuration（配置）
	properties（属性）
	settings（设置）
	typeAliases（类型别名）
	typeHandlers（类型处理器）
	objectFactory（对象工厂）
	plugins（插件）
	environments（环境配置）
		environment（环境变量）
			transactionManager（事务管理器）
			dataSource（数据源）
	databaseIdProvider（数据库厂商标识）
	mappers（映射器）

4.1、属性优化

1、db.properties

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis?useUnicode=true&useSSL=true
username=root
password=123456

2、mybatis-config.xml

<!--这句写在最上面-->
<properties resource="db.properties"/>

<dataSource type="POOLED">
    <!--改变的地方-->
    <property name="driver" value="${driver}"/>
    <property name="url" value="${url}"/>
    <property name="username" value="${username}"/>
    <property name="password" value="${password}"/>
</dataSource>

4.2、别名优化

<typeAliases>
    <!--绑定别名-->
    <typeAlias type="pojo.User" alias="User"/>
    <!--
  扫描包，识别到的类型是类名开头小写（也可以是大写）
  <package name="pojo"/>
  -->
</typeAliases>

4.3、设置优化

<settings>
    <!--缓存-->
    <setting name="cacheEnabled" value="true"/>
    <!--懒加载-->
    <setting name="lazyLoadingEnabled" value="false"/>
    <!--驼峰命名-->
    <setting name="mapUnderscoreToCamelCase" value="false"/>
    <!--日志-->
    <setting name="logImpl" value="STDOUT_LOGGING"/>
</settings>

4.4、映射器

1、通过xml注册mapper

<mappers>
    <mapper resource="com/lin/dao/UserMapper.xml"/>
</mappers>

2、通过类注册

<mappers>
    <mapper class="com.lin.dao.UserMapper"/>
</mappers>

3、扫描包

<mappers>
    <package name="com.lin.dao"/>
</mappers>

方式2和3需注意：

1、接口和Mapper配置文件必须同名。

2、接口和Mapper配置文件必须在同一包下

5、ResultMap

结果集映射，解决表的字段与实体类的属性名不一致问题，在mapper.xml中的返回类型使用resultMap。

//实体类
public class User {
    
    
    private int id;
    private String name;
    private String password;
}

--表
CREATE TABLE `user` (
  `id` INT(20) NOT NULL AUTO_INCREMENT COMMENT '用户编号',	--非空，自增，注释
  `name` VARCHAR(30) NOT NULL COMMENT '用户名称',
  `pwd` VARCHAR(30) NOT NULL COMMENT '用户密码',
  PRIMARY KEY  (`id`)	--设置主键
) ENGINE=INNODB DEFAULT CHARSET=utf8

<!--mapper.xml-->
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.lin.dao.UserMapper">
    <resultMap id="UserMap" type="User">
        <!--column对应表的字段名 property对应实体类的属性名-->
        <!--可以只映射不相同的部分-->
        <!--<result column="id" property="id"/>
        <result column="name" property="name"/>-->
        <result column="pwd" property="password"/>
    </resultMap>
    <select id="select" resultMap="UserMap">
        select * from user;
    </select>
</mapper>

一般建议名称相同或使用驼峰命名。

6、日志

6.1、标准日志输出

<settings>
    <setting name="logImpl" value="STDOUT_LOGGING"/>
</settings>

6.2、LOG4J

可以控制输出的位置如：控制台，日志文件等

1、导包

<dependency>
    <groupId>log4j</groupId>
    <artifactId>log4j</artifactId>
    <version>1.2.17</version>
</dependency>

2、配置mybatis-config.xml

<settings>
    <setting name="logImpl" value="LOG4J"/>
</settings>

2、配置log4j.properties

### 设置###
log4j.rootLogger = debug,stdout,D,E

### 输出信息到控制抬 ###
log4j.appender.stdout = org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target = System.out
log4j.appender.stdout.layout = org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern = [%-5p] %d{yyyy-MM-dd HH:mm:ss,SSS} method:%l%n%m%n

### 输出DEBUG 级别以上的日志到=E://logs/error.log ###
log4j.appender.D = org.apache.log4j.DailyRollingFileAppender
log4j.appender.D.File = E://logs/log.log
log4j.appender.D.Append = true
log4j.appender.D.Threshold = DEBUG 
log4j.appender.D.layout = org.apache.log4j.PatternLayout
log4j.appender.D.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss}  [ %t:%r ] - [ %p ]  %m%n

### 输出ERROR 级别以上的日志到=E://logs/error.log ###
log4j.appender.E = org.apache.log4j.DailyRollingFileAppender
log4j.appender.E.File =E://logs/error.log 
log4j.appender.E.Append = true
log4j.appender.E.Threshold = ERROR 
log4j.appender.E.layout = org.apache.log4j.PatternLayout
log4j.appender.E.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss}  [ %t:%r ] - [ %p ]  %m%n

3、测试

private static Logger logger = Logger.getLogger(Test.class);

@Test
public  void Test2() {
    
    
    // System.out.println("This is println message.");

    // 记录debug级别的信息
    logger.debug("This is debug message.");
    // 记录info级别的信息
    logger.info("This is info message.");
    // 记录error级别的信息
    logger.error("This is error message.");
}

7、分页

7.1、分页的使用

1、接口

public interface UserMapper {
    
    
    List<User> queryAllUser(Map<String,Integer> map);
}

2、xml

<select id="queryAllUser" resultType="User">
    select * from mybatis.user limit #{si},#{ps}
</select>

3、测试

public void Test1() throws IOException {
    
    
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    Map<String,Integer> map=new HashMap<>();
    map.put("si",0);
    map.put("ps",10);
    List<User> userList = mapper.queryAllUser(map);
    for (User u : userList) {
    
    
        System.out.println(u);
    }
}

7.2、RowBounds

@Test
public void Test1() throws IOException {
    
    
    RowBounds rowBounds = new RowBounds(0, 10);
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    List<User> list = sqlSession.selectList("dao.UserMapper.queryAllUser",null,rowBounds);
    for (User user:list
        ) {
    
    
        System.out.println(user);
    }
    sqlSession.close();
}

8、注解开发

1、编写接口

public interface UserMapper {
    
    
    @Select("select * from user")
    List<User> queryAllUser();

    @Select("select * from user where id=#{id}")
    User queryUserById(@Param("id") int uid);

    @Insert("insert into user(name,pwd) value (#{name},#{pwd})")
    int addUser(User user);

    @Update("update user set name=#{name} where id=#{id}")
    int updateUser(User user);

    @Delete("delete from user where id=#{id}")
    int deleteUser(@Param("id") int id);
}

2、绑定接口

<mappers>
    <mapper class="dao.UserMapper"/>
</mappers>

3、测试

@Test
public void Test() throws IOException {
    
    
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    List<User> list = mapper.queryAllUser();
    for (User user:list) {
    
    System.out.println(user);}
    System.out.println(mapper.queryUserById(1));
    mapper.addUser(new User(125,"asd","123456"));
    mapper.updateUser(new User(1,"asd","123456"));
    mapper.deleteUser(50);
    sqlSession.close();
}