# Mybatis Sql执行过程

Posted 2021-07-16 MarlonBrando1998

SqlSessionFactory

​ 从SqlSessionFactory说起吧，org.apache.ibatis.session.SqlSessionFactory接口。通过openSession() 可以打开连接操作sql，里面的方法有如下：

Sql执行的过程

• 例如下面的测试代码，运行一个用注解方式执行的Sql，用xml方式配置执行测试代码可见博客：https://blog.csdn.net/qq_37248504/article/details/109861871

• 测试部分被代码，完整代码见提交记录https://gitee.com/Marlon_Brando/back/commit/83b5e69e30ea9238fe824a395ce951767d8a33bd

@Component
public class MybatisConfig {

    private static final Logger logger = LoggerFactory.getLogger(MybatisConfig.class);

    @Autowired
    private DataSource dataSource;

    @Bean
    public SqlSessionFactory sqlSessionFactory() {
        SqlSession sqlSession = null;
        try {
            // 采用Mybatis的JDBC事务方式
            TransactionFactory transactionFactory = new JdbcTransactionFactory();
            Environment environment = new Environment("myenverniement", transactionFactory, dataSource);
            // 创建Configuration对象
            Configuration configuration = new Configuration(environment);
            configuration.addMapper(TestMapper.class);
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
            sqlSession = sqlSessionFactory.openSession();
            TestMapper testMapper = sqlSession.getMapper(TestMapper.class);
            Map<String, Object> result = testMapper.testOne();
            logger.info("result:{}", result);
            logger.info(LogConstant.LOG_SUCCESS_PREFIX + "SqlSessionFactory配置完成");
            return sqlSessionFactory;
        } catch (Exception e) {
            logger.error(LogConstant.ERROR, e.getMessage());
            return null;
        } finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
        }
    }
}

定义事务提交方式

// 采用Mybatis的JDBC事务方式
TransactionFactory transactionFactory = new JdbcTransactionFactory();

初始化Mybatis Environment

• Environment.java源码如下：构造方法参数（事务、数据源）

public final class Environment {
    private final String id;
    // 事务
    private final TransactionFactory transactionFactory;
    // 数据源
    private final DataSource dataSource;
    
    public Environment(String id, TransactionFactory transactionFactory, DataSource dataSource) {
        if (id == null) {
            throw new IllegalArgumentException("Parameter 'id' must not be null");
        } else if (transactionFactory == null) {
            throw new IllegalArgumentException("Parameter 'transactionFactory' must not be null");
        } else {
            this.id = id;
            if (dataSource == null) {
                throw new IllegalArgumentException("Parameter 'dataSource' must not be null");
            } else {
                this.transactionFactory = transactionFactory;
                this.dataSource = dataSource;
            }
        }
    }
}

初始化Configuration

​ MyBatis所有的配置信息都保存在Configuration对象之中，配置文件中的大部分配置都会存储到该类中。构造方法参数是Environment，上面已经说过Environment了。

public Configuration(Environment environment) {
    this();
    this.environment = environment;
}

• 可以添加Mapper添加数据接收对象等等。
• Mybatis和SpringBoot集成之后，在启动服务的时候，会扫描xml文件、mapper中的接口，将所有的配置信息配置到 Configuration中，之后用dao层操作的时候，拿出相应的sql进行执行。

初始化SqlSessionFactory

// 得到SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);

• build()参数有如下种类，其实都是一样的道理，

得到操作Sql的接口

sqlSession = sqlSessionFactory.openSession();
TestMapper testMapper = sqlSession.getMapper(TestMapper.class);
Map<String, Object> result = testMapper.testOne();

• openSession()源码：

private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;

    DefaultSqlSession var8;
    try {
        Environment environment = this.configuration.getEnvironment();
        // 获取事务提交方式
        TransactionFactory transactionFactory = this.getTransactionFactoryFromEnvironment(environment);
        tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
        // 获取执行器
        Executor executor = this.configuration.newExecutor(tx, execType);
        // 返回调用dao 的session对象
        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();
    }
    return var8;
}

getMapper执行

TestMapper testMapper = sqlSession.getMapper(TestMapper.class);
Map<String, Object> result = testMapper.testOne();

• 源码：

// 从configuration中获得对应的接口
public <T> T getMapper(Class<T> type) {
    return this.configuration.getMapper(type, this);
}

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    return this.mapperRegistry.getMapper(type, sqlSession);
}

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    // mapper 代理
    MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory)this.knownMappers.get(type);
    if (mapperProxyFactory == null) {
        throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    } else {
        try {
            return mapperProxyFactory.newInstance(sqlSession);
        } catch (Exception var5) {
            throw new BindingException("Error getting mapper instance. Cause: " + var5, var5);
        }
    }
}

• 根据type类型，从MapperRegistry对象中的knownMappers获取到当前类型对应的代理工厂类，然后通过代理工厂类生成对应Mapper的代理类。
• 最终获取到我们接口对应的代理类TestMapper对象
  
• 实现InvocationHandler，使用JDK代理
  

mapperRegistry 中的属性加载时间

• 在初始化SqlSessionFactory对象的时候，解析xml文件，
  
• 解析的过程中会解析mapper中用注解标记的方法，解析xml映射文件，还会对Mapper接口中的方法进行解析，并将每个方法的全限定类名作为key存入存入Configuration中的mappedStatements属性。