MyBatis 源代码阅读笔记 2 基于"注解"方式的代码编写

源代码工程

https://github.com/Jason-Chen-2017/source-code-reading

代码详解:

package com.light.sword;

import org.apache.ibatis.datasource.DataSourceFactory;
import org.apache.ibatis.datasource.pooled.PooledDataSourceFactory;
import org.apache.ibatis.mapping.Environment;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.apache.ibatis.transaction.TransactionFactory;
import org.apache.ibatis.transaction.jdbc.JdbcTransactionFactory;

import javax.sql.DataSource;
import java.util.List;
import java.util.Properties;

public class MyBatisDemoAnno {

    public static void main(String[] args) {
        // 获取数据源
        DataSourceFactory dataSourceFactory = new PooledDataSourceFactory();
        Properties props = new Properties();
        props.setProperty("driver", "com.mysql.cj.jdbc.Driver");
        props.setProperty("url", "jdbc:mysql://127.0.0.1:3306/test");
        props.setProperty("username", "root");
        props.setProperty("password", "root");
        dataSourceFactory.setProperties(props);
        DataSource dataSource = dataSourceFactory.getDataSource();
        // 事务管理
        TransactionFactory transactionFactory = new JdbcTransactionFactory();
        Environment environment = new Environment("dev", transactionFactory, dataSource);
        // 配置对象
        Configuration configuration = new Configuration(environment);
        // add Mapper 接口类
        configuration.addMapper(ProductMapper.class);
        // open SqlSession
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        // 从SQL会话中获取 ProductMapper
        ProductMapper productMapper = sqlSession.getMapper(ProductMapper.class);
        List<Product> productList = productMapper.findAll();
        System.out.println(productList);
    }
}

其中, ProductMapper 如下:

package com.light.sword;

import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface ProductMapper {

    @Select("select * from product")
    List<Product> findAll();

}

运行输出:

[Product{id=1, name='Product1'}, Product{id=2, name='Product2'}]

对应到XML的配置则是:

<?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>
    <typeAliases>
        <typeAlias alias="Product" type="com.light.sword.Product"></typeAlias>
    </typeAliases>
    <environments default="dev">
        <environment id="dev">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://127.0.0.1:3306/test"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="mapper/ProductMapper.xml"></mapper>
    </mappers>

</configuration>

mapper/ProductMapper.xml

<?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">
<!-- namespace命名空间，做SQL隔离 -->
<mapper namespace="productMapper">
    <select id="listAll" resultType="Product">
        select *
        from product
    </select>
</mapper>

源码运行解析

DataSource

===CONFINGURATION==============================================
 jdbcDriver                     com.mysql.cj.jdbc.Driver
 jdbcUrl                        jdbc:mysql://127.0.0.1:3306/test
 jdbcUsername                   root
 jdbcPassword                   ************
 poolMaxActiveConnections       10
 poolMaxIdleConnections         5
 poolMaxCheckoutTime            20000
 poolTimeToWait                 20000
 poolPingEnabled                false
 poolPingQuery                  NO PING QUERY SET
 poolPingConnectionsNotUsedFor  0
 ---STATUS-----------------------------------------------------
 activeConnections              0
 idleConnections                0
 requestCount                   0
 averageRequestTime             0
 averageCheckoutTime            0
 claimedOverdue                 0
 averageOverdueCheckoutTime     0
 hadToWait                      0
 averageWaitTime                0
 badConnectionCount             0
===============================================================

我们使用的是

DataSourceFactory dataSourceFactory = new PooledDataSourceFactory();

  public PooledDataSource() {
    dataSource = new UnpooledDataSource();
  }

        // 获取数据源
        DataSourceFactory dataSourceFactory = new PooledDataSourceFactory();
        Properties props = new Properties();
        props.setProperty("driver", "com.mysql.cj.jdbc.Driver");
        props.setProperty("url", "jdbc:mysql://127.0.0.1:3306/test");
        props.setProperty("username", "root");
        props.setProperty("password", "root");
        dataSourceFactory.setProperties(props);
        DataSource dataSource = dataSourceFactory.getDataSource();

然后 事务管理器:

public class JdbcTransaction implements Transaction {

  private static final Log log = LogFactory.getLog(JdbcTransaction.class);

  protected Connection connection;
  protected DataSource dataSource;
  protected TransactionIsolationLevel level;
  protected boolean autoCommit;

  public JdbcTransaction(DataSource ds, TransactionIsolationLevel desiredLevel, boolean desiredAutoCommit) {
    dataSource = ds;
    level = desiredLevel;
    autoCommit = desiredAutoCommit;
  }

  public JdbcTransaction(Connection connection) {
    this.connection = connection;
  }

  @Override
  public Connection getConnection() throws SQLException {
    if (connection == null) {
      openConnection();
    }
    return connection;
  }

  @Override
  public void commit() throws SQLException {
    if (connection != null && !connection.getAutoCommit()) {
      if (log.isDebugEnabled()) {
        log.debug("Committing JDBC Connection [" + connection + "]");
      }
      connection.commit();
    }
  }

  @Override
  public void rollback() throws SQLException {
    if (connection != null && !connection.getAutoCommit()) {
      if (log.isDebugEnabled()) {
        log.debug("Rolling back JDBC Connection [" + connection + "]");
      }
      connection.rollback();
    }
  }

  @Override
  public void close() throws SQLException {
    if (connection != null) {
      resetAutoCommit();
      if (log.isDebugEnabled()) {
        log.debug("Closing JDBC Connection [" + connection + "]");
      }
      connection.close();
    }
  }

  protected void setDesiredAutoCommit(boolean desiredAutoCommit) {
    try {
      if (connection.getAutoCommit() != desiredAutoCommit) {
        if (log.isDebugEnabled()) {
          log.debug("Setting autocommit to " + desiredAutoCommit + " on JDBC Connection [" + connection + "]");
        }
        connection.setAutoCommit(desiredAutoCommit);
      }
    } catch (SQLException e) {
      // Only a very poorly implemented driver would fail here,
      // and there's not much we can do about that.
      throw new TransactionException("Error configuring AutoCommit.  "
          + "Your driver may not support getAutoCommit() or setAutoCommit(). "
          + "Requested setting: " + desiredAutoCommit + ".  Cause: " + e, e);
    }
  }

  protected void resetAutoCommit() {
    try {
      if (!connection.getAutoCommit()) {
        // MyBatis does not call commit/rollback on a connection if just selects were performed.
        // Some databases start transactions with select statements
        // and they mandate a commit/rollback before closing the connection.
        // A workaround is setting the autocommit to true before closing the connection.
        // Sybase throws an exception here.
        if (log.isDebugEnabled()) {
          log.debug("Resetting autocommit to true on JDBC Connection [" + connection + "]");
        }
        connection.setAutoCommit(true);
      }
    } catch (SQLException e) {
      if (log.isDebugEnabled()) {
        log.debug("Error resetting autocommit to true "
            + "before closing the connection.  Cause: " + e);
      }
    }
  }

  protected void openConnection() throws SQLException {
    if (log.isDebugEnabled()) {
      log.debug("Opening JDBC Connection");
    }
    connection = dataSource.getConnection();
    if (level != null) {
      connection.setTransactionIsolation(level.getLevel());
    }
    setDesiredAutoCommit(autoCommit);
  }

  @Override
  public Integer getTimeout() throws SQLException {
    return null;
  }

}

openSession

根据 configuration 构建 SqlSessionFactory, 然后使用 SqlSessionFactory 打开session :

        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        // 从SQL会话中获取 ProductMapper
        ProductMapper productMapper = sqlSession.getMapper(ProductMapper.class);
        List<Product> productList = productMapper.findAll();

通过 接口类型的 ProductMapper 创建出实例对象的代码:

  public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
    if (mapperProxyFactory == null) {
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    }
    try {
      return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }

MapperProxyFactory

package org.apache.ibatis.binding;

import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import org.apache.ibatis.session.SqlSession;

/**
 * @author Lasse Voss
 */
public class MapperProxyFactory<T> {

  private final Class<T> mapperInterface;
  private final Map<Method, MapperMethod> methodCache = new ConcurrentHashMap<>();

  public MapperProxyFactory(Class<T> mapperInterface) {
    this.mapperInterface = mapperInterface;
  }

  public Class<T> getMapperInterface() {
    return mapperInterface;
  }

  public Map<Method, MapperMethod> getMethodCache() {
    return methodCache;
  }

  @SuppressWarnings("unchecked")
  protected T newInstance(MapperProxy<T> mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }

  public T newInstance(SqlSession sqlSession) {
    final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }

}