2017.12.27 sqlSessionFactory和sqlSession（to be continued）

参考来自：《深入浅出MyBatis技术原理与实践-第6章 》

1.SqlSessionFactory

SqlSessionFactory是一个接口，最重要的功能是提供SqlSession。

public interface SqlSessionFactory {

  SqlSession openSession();

  SqlSession openSession(boolean autoCommit);
  SqlSession openSession(Connection connection);
  SqlSession openSession(TransactionIsolationLevel level);

  SqlSession openSession(ExecutorType execType);
  SqlSession openSession(ExecutorType execType, boolean autoCommit);
  SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level);
  SqlSession openSession(ExecutorType execType, Connection connection);

  Configuration getConfiguration();

}

SqlSessionFactory有一个默认的实现类DefaultSqlSessionFactory。

package org.apache.ibatis.session.defaults;

import java.sql.Connection;
import java.sql.SQLException;

import org.apache.ibatis.exceptions.ExceptionFactory;
import org.apache.ibatis.executor.ErrorContext;
import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.mapping.Environment;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.ExecutorType;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.TransactionIsolationLevel;
import org.apache.ibatis.transaction.Transaction;
import org.apache.ibatis.transaction.TransactionFactory;
import org.apache.ibatis.transaction.managed.ManagedTransactionFactory;

/**
 * @author Clinton Begin
 */
public class DefaultSqlSessionFactory implements SqlSessionFactory {

  private final Configuration configuration;

  public DefaultSqlSessionFactory(Configuration configuration) {
    this.configuration = configuration;
  } 84 
  @Override
  public Configuration getConfiguration() {
    return configuration;
  }
 89   //其余略

}

在对SqlSessionFactory的构建中，直接使用构造方法去构建是有困难的，这样会将大量的逻辑放在构造方法中。因此采用的是builder模式，使用SqlSessionFactoryBuilder来构建。

SqlSessionFactory中提供了很多build方法，最终调用的都是下面两个中的一个，然后调用第三个build：生成一个defaultSqlSessionFactory(configuration config)。

Configuration类中则保存了配置相关的参数，全局唯一。

package org.apache.ibatis.session;

import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.util.Properties;

import org.apache.ibatis.builder.xml.XMLConfigBuilder;
import org.apache.ibatis.exceptions.ExceptionFactory;
import org.apache.ibatis.executor.ErrorContext;
import org.apache.ibatis.session.defaults.DefaultSqlSessionFactory;

public class SqlSessionFactoryBuilder {

  public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
      return build(parser.parse());
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    } finally {
      ErrorContext.instance().reset();
      try {
        reader.close();
      } catch (IOException e) {
        // Intentionally ignore. Prefer previous error.
      }
    }
  }

  public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
      return build(parser.parse());
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    } finally {
      ErrorContext.instance().reset();
      try {
        inputStream.close();
      } catch (IOException e) {
        // Intentionally ignore. Prefer previous error.
      }
    }
  }
    
  public SqlSessionFactory build(Configuration config) {
    return new DefaultSqlSessionFactory(config);
  }
  //其余略
}

综上所述，SqlSessionFactory的构建过程：

• mybatis通过SqlSessionFactoryBuilder去构建SqlSessionFactory。
• SqlSessionFactoryBuilder中提供了SqlXMLConfigBuilder读取XML配置文件中的信息，保存至Configuration类的单例中。
• 然后SqlSessionFactoryBuilder实例化DefaultSqlSessionFactory。