Mybatis系列十七：源码解析-SqlSession

素颜马尾好姑娘i 2022-02-13 07:19 242阅读 0赞

mybatis全局配置文件mybatis-config.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">
    <configuration>
    	<environments default="development">
    		<environment id="development">
    			<transactionManager type="JDBC" />
    			<dataSource type="POOLED">
    				<property name="driver" value="com.mysql.jdbc.Driver" />
    				<property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
    				<property name="username" value="root" />
    				<property name="password" value="root" />
    			</dataSource>
    		</environment>
    	</environments>
    	
    	<mappers>
    		<mapper resource="EmployeeMapper.xml" />
    	</mappers>
    </configuration>

mapper映射文件EmployeeMapper.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">
    <mapper namespace="com.atguigu.mybatis.dao.EmployeeMapper">
    
    
    	<select id="getEmpById" resultType="com.atguigu.mybatis.bean.Employee">
    		select id,last_name lastName,email,gender from tbl_employee where id = #{id}
    	</select>
    </mapper>

测试方法：

/**
    	 * 1、获取sqlSessionFactory对象
    	 * 		解析文件的每一个信息保存在Configuration中，然后返回包含Configuration的DefaultSqlSession。
    	 * 		MappedStatement：代表一个增删改查的详细信息。
    	 * 2、获取sqlSession对象
    	 * 		 返回一个SqlSession 的实现类DefaultSqlSession对象。
    	 * 		 这一步会创建Executor 对象。
    	 * 3、获取接口的代理对象
    	 * 4、执行增删改查方法
    	 * @throws IOException
    	 */
    	@Test
    	public void test() throws IOException {
    		//1、获取sqlSessionFactory对象
    		String resource = "mybatis-config.xml";
    		InputStream inputStream = Resources.getResourceAsStream(resource);
    		SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    		//2、获取sqlSession对象
    		SqlSession openSession = sqlSessionFactory.openSession();
    		try {
    			//3、获取接口的代理对象
    			EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
    			//4、执行增删改查方法
    			Employee employee = mapper.getEmpById(1);
    			System.out.println(mapper);
    			System.out.println(employee);
    		} finally {
    			openSession.close();
    		}
    	}

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源码解析：  
二、获取sqlSession对象

SqlSession openSession = sqlSessionFactory.openSession();

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpemhpcWlhbmcxMjE3_size_16_color_FFFFFF_t_70 1]  
1、DefaultSqlSessionFactory

public SqlSession openSession() {
            return this.openSessionFromDataSource(this.configuration.getDefaultExecutorType(), (TransactionIsolationLevel)null, false);
        }
        
    	private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
            Transaction tx = null;
    
            DefaultSqlSession var8;
            try {
                //获取一些信息，创建事务tx
                Environment environment = this.configuration.getEnvironment();
                TransactionFactory transactionFactory = this.getTransactionFactoryFromEnvironment(environment);
                tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
                //newExecutor创建执行器
                Executor executor = this.configuration.newExecutor(tx, execType);
                //把返回的executor 保存在DefaultSqlSession中。包含configuration和executor
                var8 = new DefaultSqlSession(this.configuration, executor, autoCommit);
            } catch (Exception var12) {
                this.closeTransaction(tx);
                throw ExceptionFactory.wrapException("Error opening session.  Cause: " + var12, var12);
            } finally {
                ErrorContext.instance().reset();
            }
    		//返回SqlSession 的实现类DefaultSqlSession对象。它里面包含了configuration和executor
            return var8;
        }

2、Configuration

//根据Executor在全局配置中的类型，创建出SimpleExecutor或ReuseExecutor或BatchExecutor
    	public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
            executorType = executorType == null ? this.defaultExecutorType : executorType;
            executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
            Object executor;
            if (ExecutorType.BATCH == executorType) {
                executor = new BatchExecutor(this, transaction);
            } else if (ExecutorType.REUSE == executorType) {
                executor = new ReuseExecutor(this, transaction);
            } else {
                executor = new SimpleExecutor(this, transaction);
            }
    		//根据全局配置是否开启二级缓存，创建CachingExecutor
            if (this.cacheEnabled) {
                executor = new CachingExecutor((Executor)executor);
            }
    		//使用每一个拦截器重新包装executor并返回
            Executor executor = (Executor)this.interceptorChain.pluginAll(executor);
            return executor;
        }

3、CachingExecutor

//查询前先去缓存里查找
    	public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
            BoundSql boundSql = ms.getBoundSql(parameterObject);
            CacheKey key = this.createCacheKey(ms, parameterObject, rowBounds, boundSql);
            return this.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
        }

4、InterceptorChain

public Object pluginAll(Object target) {
            Interceptor interceptor;
            for(Iterator i$ = this.interceptors.iterator(); i$.hasNext(); target = interceptor.plugin(target)) {
                interceptor = (Interceptor)i$.next();
            }
    
            return target;
        }

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