MyBatis之SqlSessionFactory

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范围和生命周期

SqlSessionFactory 一旦被创建就应该在应用的运行期间一直存在，没有任何理由对它进行清除或重建。使用 SqlSessionFactory 的最佳实践是在应用运行期间不要重复创建多次，多次重建 SqlSessionFactory 被视为一种代码“坏味道（bad smell）”。因此 SqlSessionFactory 的最佳范围是应用范围。有很多方法可以做到，最简单的就是使用单例模式或者静态单例模式。【摘自博文】

源码

package org.apache.ibatis.session;

import java.sql.Connection;
/**
 * Creates an {@link SqlSession} out of a connection or a DataSource
 * @author Clinton Begin
 */
public interface SqlSessionFactory {
  // 自动提交属性默认为false
  SqlSession openSession();
 // 自定义自动提交属性
  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();

}

实战

源码来自美团开源项目Leaf

package com.sankuai.inf.leaf.segment.dao.impl;

import com.sankuai.inf.leaf.segment.dao.IDAllocDao;
import com.sankuai.inf.leaf.segment.dao.IDAllocMapper;
import com.sankuai.inf.leaf.segment.model.LeafAlloc;
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;

public class IDAllocDaoImpl implements IDAllocDao {

    SqlSessionFactory sqlSessionFactory;

    public IDAllocDaoImpl(DataSource dataSource) {
        TransactionFactory transactionFactory = new JdbcTransactionFactory();
        Environment environment = new Environment("development", transactionFactory, dataSource);
        Configuration configuration = new Configuration(environment);
        configuration.addMapper(IDAllocMapper.class);
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
    }

    @Override
    public List<LeafAlloc> getAllLeafAllocs() {
        // 设置自动提交属性为false
        SqlSession sqlSession = sqlSessionFactory.openSession(false);
        try {
            // 查询不需要提交事务
            return sqlSession.selectList("com.sankuai.inf.leaf.segment.dao.IDAllocMapper.getAllLeafAllocs");
        } finally {
            // 关闭sqlSession
            sqlSession.close();
        }
    }

    @Override
    public LeafAlloc updateMaxIdAndGetLeafAlloc(String tag) {
        // 自动提交属性默认为false
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try {
            sqlSession.update("com.sankuai.inf.leaf.segment.dao.IDAllocMapper.updateMaxId", tag);
            LeafAlloc result = sqlSession.selectOne("com.sankuai.inf.leaf.segment.dao.IDAllocMapper.getLeafAlloc", tag);
            // 手动提交事务
            sqlSession.commit();
            return result;
        } finally {
            // 关闭sqlSession
            sqlSession.close();
        }
    }

    @Override
    public LeafAlloc updateMaxIdByCustomStepAndGetLeafAlloc(LeafAlloc leafAlloc) {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try {
            sqlSession.update("com.sankuai.inf.leaf.segment.dao.IDAllocMapper.updateMaxIdByCustomStep", leafAlloc);
            LeafAlloc result = sqlSession.selectOne("com.sankuai.inf.leaf.segment.dao.IDAllocMapper.getLeafAlloc", leafAlloc.getKey());
            sqlSession.commit();
            return result;
        } finally {
            sqlSession.close();
        }
    }

    @Override
    public List<String> getAllTags() {
        SqlSession sqlSession = sqlSessionFactory.openSession(false);
        try {
            return sqlSession.selectList("com.sankuai.inf.leaf.segment.dao.IDAllocMapper.getAllTags");
        } finally {
            sqlSession.close();
        }
    }
}