Mybatis 映射器接口实现类的方式 运行过程debug分析

查询一张表的所有数据。

环境：

使用工具IntelliJ IDEA 2018.2版本。

创建Maven工程不用骨架

 <?xml version="1.0" encoding="UTF-8"?>

 <project xmlns="http://maven.apache.org/POM/4.0.0"

          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

          xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

     <modelVersion>4.0.0</modelVersion>

     <groupId>com.jxjdemo</groupId>

     <artifactId>day34_mybatis1_curd_dao</artifactId>

     <version>1.0-SNAPSHOT</version>

     <properties><!--锁定编译版本与字符集-->

         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

         <maven.compiler.source>1.8</maven.compiler.source>

         <maven.compiler.target>1.8</maven.compiler.target>

     </properties>

     <dependencies>

         <dependency><!--导入mysql依赖-->

             <groupId>mysql</groupId>

             <artifactId>mysql-connector-java</artifactId>

             <version>5.1.47</version>

         </dependency>

         <dependency> <!--导入mybatis依赖-->

             <groupId>org.mybatis</groupId>

             <artifactId>mybatis</artifactId>

             <version>3.5.2</version>

         </dependency>

         <dependency> <!--导入日志依赖-->

             <groupId>log4j</groupId>

             <artifactId>log4j</artifactId>

             <version>1.2.17</version>

         </dependency>

         <dependency>

             <groupId>junit</groupId>

             <artifactId>junit</artifactId>

             <version>4.12</version>

         </dependency>

     </dependencies>

 </project>

1. 表User

 package com.jxjdemo.domain;

 import java.util.Date;

 public class User {

     private Integer id;

     private String username;

     private Date birthday; //框架会帮我们自动转

     private String sex;

     private String address;

     @Override

     public String toString() {

         return "User{" +

                 "id=" + id +

                 ", username='" + username + '\'' +

                 ", birthday=" + birthday +

                 ", sex='" + sex + '\'' +

                 ", address='" + address + '\'' +

                 '}';

     }

 //省略Get与Set方法

2.映射器XML

 <?xml version="1.0" encoding="utf-8"?><!--引入约束-->

 <!DOCTYPE mapper

         PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"

         "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

         <mapper namespace="com.jxjdemo.dao.UserDao"><!--mapper：映射器配置/namespace：映射器的全限定类名-->

         <select id="queryAll" resultType="com.jxjdemo.domain.User"><!--查询所有-->

                 select * from user

         </select>

3.映射器配置文件

<?xml version="1.0" encoding="utf-8"?><!--引入约束-->

<!DOCTYPE mapper

        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"

        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

        <mapper namespace="com.jxjdemo.dao.UserDao"><!--mapper：映射器配置/namespace：映射器的全限定类名-->

        <select id="queryAll" resultType="com.jxjdemo.domain.User">

                select * from user

        </select>

        </mapper>

4.实现类

 package com.jxjdemo.dao.impl;

 import com.jxjdemo.dao.UserDao;

 import com.jxjdemo.domain.User;

 import org.apache.ibatis.session.SqlSession;

 import org.apache.ibatis.session.SqlSessionFactory;

 import java.util.List;

 public class UserDaoImpl implements UserDao {//执行SQL语句用实现类做，不用代理对象。

     //从工厂里面获取sqlsession对象

     private SqlSessionFactory factory;//以后由sping整合sping创建，现在去测试类里面创建

     public UserDaoImpl(SqlSessionFactory factory) {

         this.factory = factory;

     }

     @Override

     public List<User> queryAll() {

         SqlSession session = factory.openSession();

         List<User> list = session.selectList("com.jxjdemo.dao.UserDao.queryAll");//返回的是Object但实际得到的是(UserDao)

         session.close();//session关闭流，释放资源

         return list;

     }

5.测试类

 package com.jxjtest.test;

 import com.jxjdemo.dao.UserDao;

 import com.jxjdemo.dao.impl.UserDaoImpl;

 import com.jxjdemo.domain.User;

 import org.apache.ibatis.io.Resources;

 import org.apache.ibatis.session.SqlSessionFactory;

 import org.apache.ibatis.session.SqlSessionFactoryBuilder;

 import org.junit.After;

 import org.junit.Before;

 import org.junit.Test;

 import java.io.IOException;

 import java.io.InputStream;

 import java.util.Date;

 import java.util.List;

 public class MybatisCurdTest {

     private SqlSessionFactory factory;

     private InputStream is;

     private UserDao userDao;

     @Test

     public void testQueryAll(){ //查询全部

         //读取配置文件，获取sqlsession对象工厂，获取映射器提取

         List<User> userList = userDao.queryAll();

         for (User user : userList){

             System.out.println(user);

         }

     }

 @Before

     public void init() throws IOException { //重复执行的代码，单独提取出来

         is = Resources.getResourceAsStream("sqlMapConfig.xml");//提取成员变量后

         // SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(is); //获取sqlsession对象,通过工厂构建一个，提取成员变量

         factory = new SqlSessionFactoryBuilder().build(is);

         userDao = new UserDaoImpl(factory);//提取成员变量

     }

     @After

     public void destroy() throws IOException {  //关流

         is.close();

     }

 }

6.数据库核心配置文件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">

 <!--mybatis的核心配置文件，主要配置数据库连接信息-->

 <configuration><!--根标签-->

     <!--enxironments 可以配置多个数据库环境-->

     <environments default="mysql"><!--default 默认使用的数据库-->

         <environment id="mysql"><!--environment每一个数据库连接(配置)信息-->

             <transactionManager type="JDBC" /><!--事物管理方式-->

             <dataSource type="POOLED"><!--数据源。不使用UN连接池POOLED，POOLED使用连接池,JNDI查找数据源配置文件-->

                 <property name="driver" value="com.mysql.jdbc.Driver" />

                 <property name="url" value="jdbc:mysql://localhost:端口号/库名"/>

                 <property name="username" value="账号"/>

                 <property name="password" value="密码"/>

             </dataSource>

         </environment>

     </environments>

     <mappers>

         <mapper resource="com/jxjdemo/dao/UserDao.xml" />

     </mappers>

 </configuration>

　　7.省略log4j日志配置文件，目录结构。

8.在测试类打断点，开始deBug跟踪，从这里开始。

相册里面有步骤截图，可以配合一起看。

 List<User> userList = userDao.queryAll();

9.到实现类，获取session

 SqlSession session = factory.openSession();

10.跟踪这行代码做了什么事情，进入这个方法。

 List<User> list = session.selectList("com.jxjdemo.dao.UserDao.queryAll");

11.到了DefaultSqlSession.java类里面，在selectList调了selectList，方法的重载。

 @Override

   public <E> List<E> selectList(String statement) {

     return this.selectList(statement, null);

   }

   @Override

   public <E> List<E> selectList(String statement, Object parameter) {

     return this.selectList(statement, parameter, RowBounds.DEFAULT);

   }

12.到了ms，获取数据库，配置文件信息，与SQL类型。关键在于executor.query执行查询。

 public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {

     try {

       MappedStatement ms = configuration.getMappedStatement(statement);

       return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);

     } catch (Exception e) {

       throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);

     } finally {

       ErrorContext.instance().reset();

     }

   }

13.先对wrspCollection(parameter)包装一下。回到12.

 if (object instanceof Collection) {这里省略}

14.进入CachingExecutor.java.这个类自己不执行。

  @Override

   public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {

     BoundSql boundSql = ms.getBoundSql(parameterObject);

15.这里第一步，从ms.getBoundSql获取到了绑定的SQL语句。

CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);//缓存相关忽略

16.继续调query方法重载。

return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);

17.到了query方法。

 @Override

   public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)

       throws SQLException {

     Cache cache = ms.getCache();

18.找缓存。

 if (cache != null) {

19.缓存里面没有，CachingExecutor.java.这个类自己不执行，就调了delegate委托者。

 return delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);

20.CachingExecutor.java.这个类是从父类继承的，所以到了BaseExecutor.java.

@Override

  public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {

    ErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId());

21.往下走。

if (closed) {//1.

if (queryStack == 0 && ms.isFlushCacheRequired()) {//2.

queryStack++;//3.

list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;//4.

if (list != null) {//5.

22.到了queryFromDatabase开始到库里面查询。

list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);

23.BaseExecutor.java.执行了doQuery方法

localCache.putObject(key, EXECUTION_PLACEHOLDER);//

list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);//2.

24.进入doQuery查看，到了SimpleExecutor.java

 public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {

     Statement stmt = null;//

 Configuration configuration = ms.getConfiguration();//2.configuration所有的配置信息

 StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);//3.

 stmt = prepareStatement(handler, ms.getStatementLog());//4.准备得到一个

 return handler.query(stmt, resultHandler);//5.handler.query开始真正执行了

25.进入query到了RoutingStatementHandler.java

return delegate.query(statement, resultHandler);//调了delegate

26.调了delegate到了PreparedStatementHandler.java

 public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {

     PreparedStatement ps = (PreparedStatement) statement;PreparedStatement预编译对象

     ps.execute();//2.获取预编译对象，执行任意语句

     return resultSetHandler.handleResultSets(ps);//

   }

到了这里就是最终的结果，剩余处理结果集，封装的事情了。

结果：Mybatis封装的再深底层还是JDBC。