MyBatis 原理

手写 MyBatis

纯 MyBatis 开发步骤

1. 读取 mybatis-config.xml 配置文件
2. 构建 SqlSessionFactory
3. 打开 SqlSession
4. 获取 Mapper 接口对象
5. 调用 Mapper 接口对象的方法操作数据库

源码流程

寻找入口 –> 断点跟踪 –> 先粗后细 –> 精略结合

目录结构

mapper

UUserInfoMapper 接口

// 接口定义执行数据库方法
List<MetaBasePO> selectOneLayer(
	@Param("parentId") Integer parentId, 
	@Param("types") List<String> types, 
	@Param("queryWord") String queryWord,
	@Param("deleted") Integer deleted, 
	@Param("status") Integer status, 
	@Param("containExtAttr") boolean containExtAttr
);

UUserInfoMapper.xml

<mapper namespace="com.mandalat.apolar.metadata.dao.mapper.MetaBaseMapper">
    <resultMap id="BaseResultMap" type="com.mandalat.apolar.common.biz.model.metadata.po.MetaBasePO">
        <result column="m_id" jdbcType="INTEGER" property="id" />
        <result column="m_parent_id" jdbcType="INTEGER" property="parentId" />
        <result column="m_group_id" jdbcType="INTEGER" property="groupId" />
        <result column="m_code" jdbcType="VARCHAR" property="code" />
        <result column="m_name" jdbcType="VARCHAR" property="name" />
        <result column="m_type" jdbcType="VARCHAR" property="type" />
        <result column="m_ext_attr" jdbcType="VARCHAR" property="extAttr" />
        <result column="m_owner" jdbcType="VARCHAR" property="owner" />
        <result column="m_post_to_db" jdbcType="TINYINT" property="postToDb" />
        <result column="m_is_deleted" jdbcType="TINYINT" property="isDeleted" />
        <result column="m_status" jdbcType="TINYINT" property="status" />
        <result column="m_sort_no" jdbcType="INTEGER" property="sortNo" />
        <result column="m_memo" jdbcType="VARCHAR" property="memo" />
        <result column="m_ctime" jdbcType="TIMESTAMP" property="ctime" />
        <result column="m_cuid" jdbcType="VARCHAR" property="cuid" />
        <result column="m_mtime" jdbcType="TIMESTAMP" property="mtime" />
        <result column="m_muid" jdbcType="VARCHAR" property="muid" />
    </resultMap>

    <select id="selectOneLayer" resultMap="BaseResultMap">
        select m_id, m_parent_id, m_group_id, m_code, m_name, m_type, m_owner,
            <if test="containExtAttr">
               m_ext_attr,
            </if>
            m_post_to_db, m_is_deleted, m_status, m_sort_no, m_memo, m_ctime, 
		m_cuid, m_mtime, m_muid from md_meta_base where m_parent_id=#{parentId}
            <if test="types != null and types.size()>0">
                and m_type in
                <foreach collection="types" item="type" open="(" close=")" separator=",">
                    #{type}
                </foreach>
            </if>
            <if test="queryWord != null and queryWord != ''">
                and (m_code like #{queryWord} or m_name like #{queryWord})
            </if>
            <if test="deleted != null">
                and m_deleted = #{deleted}
            </if>
            <if test="status != null">
                and m_status = #{status}
            </if>
        order by m_sort_no
    </select>

</mapper>

model

• 数据库对象类

mybatis

• mapping

MyConfiguration

public class MyConfiguration (){
  private MyEnviroment myEnviroment
  private Map<String, MapperStatement> mapperStatementMap
}

MyEnviroment

// 映射 mybatis-config.xml
public class MyEnviroment (){
  private String driver
  private String url
  private String username
  private String password
}

MapperStatement

// 映射 Mapper.xml
public class MapperStatement (){
  private String namesapce
  private String id
  private String parameterType
  private String resultType
  private String sql
}

• executor

MyExecutor

// 数据库初始化操作
public class MyExecutor {
  private DataSource datasource

  public MyExecutor (MyConfiguration myconfig){
    datasource = MyDataSource.getInstance(myconfig.getMyEnvironment())
  }

  public <T> T query (MapperStatement mapperStatement, Object parameter){
    Connection connection = null;
    PreparedStatement preparedState = null;
    ResultSet res = null;
    try{
      connection = datasource.getConnection()
      preparedState = connection.preparedStatement(mapperStatement.getSql())

      if (parameter instanceof Integer) {
        preparedState.setInt(1, (Integer) parameter)
      }

      res = preparedState.executeQuery()
      
      
    } catch (SQLException e) {
      e.printStackTrace();
    } final {
      if (null != res && null != preparedState) {
		try {
          res.close()
          preparedState.close()
        } catch (SQLException e) {
          e.printStackTrace();
        }
      }
      if (null != connection) {
		try {
          datasource.release(connection)
        } catch (SQLException e) {
          e.printStackTrace();
        }
      }
    }

    return res
  }
}

• session

MySqlSession

public class MySqlSession {
  private MyConfiguration myconfig
  private MyExecutor myexecutor

  public MySqlSession (MyConfiguration myconfig, MyExecutor myexecutor){
    this.myconfig = myconfig
    this.myexecutor = myexecutor
  }

  public <T> T getMapper(Class<T> clazz){
    // 动态代理对象
	MaperProxy maperProxy = new MaperProxy(this)

    // ClassLoader loader, Class<?>[] interfaces, InvocationHandler h
    return (T)Proxy.newProxyInstance(clazz.getClass().getClassLoader(),
                                          Class<?>[] {clazz},
                                          InvocationHandler h)
  }

  public <T> T doSomthing(int args, String statementKey){
    return myexecutor.query(myconfig.getMapperStatementMap().get(statementKey), args)
  }
}

MySqlSessionFactory

public class MySqlSessionFactory {
  private MyConfiguration myconfig

  public MySqlSessionFactory(MyConfiguration myconfig){
    this.myconfig = myconfig
  }

  public MySqlSession openSession(){
    MyExecutor myExecutor = new MyExecutor(myconfig)
    return new MySqlSession(myconfig, myExecutor)
  }
}

MySqlSessionFactoryBuild

public MySqlSessionFactory build(InputStream inputStream){
  // 解析 XML
  MyConfiguration myconfig = new XMLConfigBuilder(inputStream).parse()
  return new MySqlSessionFactory(MyConfiguration myconfig)
}

• proxy

MaperProxy

public class MaperProxy implements InvocationHandler (){
  private MySqlSession mySqlSession
  
  public MaperProxy(MySqlSession mySqlSession){
    this.mySqlSession = mySqlSession
  }

  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable{
	// 实现查询方法
    Class<?> clazz = method.getReturnType()
    // 返回类型是集合
    if (Collection.class.isAssignableForm(clazz)) {
      return mySqlSession.doSomthing(args)
    }
    // 返回类型是Map
    else if (Map.class.isAssignableForm(clazz)) {
      return mySqlSession.doSomthing(args)
    }
	// 返回对象
    else {
      String statementKey = method.getDeclaringClass().getName() + "." + method.getName()
      return mySqlSession.doSomthing(statementKey, args)
    }
    return null
  }
}

• parsing

XMLConfigBuilder

解析 XML 获取环境对象，Mapper 对象

• pool

MyDataSourceInterface

public interface MyDataSourceInterface extends DataSource{
  // 接口可以实现默认方法
}

MyDataSource

public class MyDataSource implements MyDataSourceInterface{
  // 实现部分方法即可
  // 数据库连接池
}

pom.xml

<dependencies>
  <dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java<artifactId>
  </dependency>
</dependencies>

main

// Resources <==> 类名.class.getClassLoder()
public class Application {
    public static void main(String[] args) {
      InputStream inputStream = Resources.getResourceAsStream('mybatis-config.xml')
      MySqlSessionFactory sqlsfactory = new MySqlSessionFactoryBuild().build(inputStream)
      MySqlSession session = sqlsfactory.openSession()
      UUserInfoMapper uuserInfoMapper = session.getMapper(UUserInfoMapper.class)
      UUserInfo uuserInfo = uuserInfoMapper.selectByPrimaryKey(1)
    }
}

mybatis-config.xml

environments -> dataSource
mappers

pom.xml 说明

1. 全局配置 project build

配置示例

<build>
  // 执行build任务时，没有指定目标，将使用默认值。当前配置相当于执行 mvn install
  <defaultGoal>install</defaultGoal>

  // build 目标文件的存放位置
  <directory>${basedir}/target</directory>

  // build 目标文件名称
  <finalName>${artifactId}-${version}</finalName>

  <filters>
    // 将属性值应用到支持 filter 的 resources 中
    // maven 的默认 filter 文件夹为 ${basedir}/src/main/filters
    <filter>filters/filter1.properties</filter>
  </filters>

  // 用于包含或者排除某些资源文件，描述与项目关联的文件是什么和在哪里
  <resources>
    <resource>
      // 指定 build 后的 resource 存放的文件夹，默认 basedir
      <targetPath>META-INF/plexus</targetPath>

      // filter 是否激活
      <filtering>false</filtering>

      // 定义 resource 文件所在文件夹
      <directory>${basedir}/src/main/plexus</directory>

      // 指定哪些文件将被匹配，以*作为通配符
      <includes>
        <include>configuration.xml</include>  
      </includes>

      // 指定哪些文件将被忽略
      <excludes>
        <exclude>**/*.properties</exclude>  
      </excludes>  
    </resource>  
  </resources>

  // 指定使用的插件
  <plugins>
    <plugin>  
      <groupId>org.apache.maven.plugins</groupId>  
      <artifactId>maven-jar-plugin</artifactId>  
      <version>2.0</version>

      <extensions>false</extensions>  
      <inherited>true</inherited>

      // 配置 plugin 期望得到的 properties 
      <configuration>  
        <classifier>test</classifier>  
      </configuration>

      // 作为 plugin 的依赖
      <dependencies>...</dependencies>  
      <executions>...</executions>  
    </plugin>  
  </plugins>  
</build>

pluginManagement <plugins> '子 pom' 直接使用 '父 pom' 定义的 plugin

2. 配置 profile build

<profiles>  
  <profile>  
    <build>…</build>  
  </profile>  
</profiles>