mybatis源码(二) mapper代理生成,sqlsession生成

回顾

上一篇讲了DefaultSqlSessionFactory类的生成,主要讲的就是maybatis配置文件的解析,mapper的解析,然后根据Configuration生成SqlSessionFactory;
这一篇我们讲前面提到的SqlSession.和mapper的生成.

SqlSession的生成

还是前面的小例子,前面创建了SqlSessionFactory,SqlSessionFactory有个方法openSession返回SqlSession;
我们看DefaultSqlSessionFactory的openSession方法:

再看具体方法:

/**
   * execType执行器类型,默认是ExecutorType.simple
   *
   * level 事务隔离级别,默认null
   *
   * autoCommit是否自动提交,默认false
   *   protected ExecutorType defaultExecutorType = ExecutorType.SIMPLE;
   *   @Override
   *   public SqlSession openSession() {
   *     return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
   *   }
   *
   * @param execType
   * @param level
   * @param autoCommit
   * @return
   */
  private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
     
    Transaction tx = null;
    try {
     
      //获取环境信息
      final Environment environment = configuration.getEnvironment();
      //根据环境信息返回事务工厂,我们使用spring进行管理,返回的是SpringManagedTransactionFactory
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      //根据数据源,事务隔离级别,是否自动提交生成事务管理器,返回的是Spring的事物SpringManagedTransaction
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
      //根据事务和执行器类别生成执行器,二级缓存默认打开,这里的SimpleExecutor会被包装成CacheExecutor
      final Executor executor = configuration.newExecutor(tx, execType);
      //返回默认的sqlsession
      return new DefaultSqlSession(configuration, executor, autoCommit);
    } catch (Exception e) {
     
      closeTransaction(tx); // may have fetched a connection so lets call close()
      throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);
    } finally {
     
      ErrorContext.instance().reset();
    }
  }

生成执行器Executor方法

 public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
     
    //如果为null,则设置为默认的tyoe,就是ExecutorType.SIMPLE
    executorType = executorType == null ? defaultExecutorType : executorType;
    //如果还是为null,则手动设置为ExecutorType.SIMPLE
    executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
    Executor executor;
    if (ExecutorType.BATCH == executorType) {
     
      // batch开头的想必大家不陌生了,批量操作
      executor = new BatchExecutor(this, transaction);
    } else if (ExecutorType.REUSE == executorType) {
     
      //复用预处理语句
      executor = new ReuseExecutor(this, transaction);
    } else {
     
      //simple简单的执行器
      executor = new SimpleExecutor(this, transaction);
    }
    if (cacheEnabled) {
     
      //是否开启二级缓存,封装为CachingExecutor
      executor = new CachingExecutor(executor);
    }
    //执行一次所有拦截方法
    executor = (Executor) interceptorChain.pluginAll(executor);
    return executor;
  }

interceptorChain的实现也比较简单,就是将所有拦截器放到list里面,循环调用:

public class InterceptorChain {
     

  private final List<Interceptor> interceptors = new ArrayList<>();

  public Object pluginAll(Object target) {
     
    for (Interceptor interceptor : interceptors) {
     
      target = interceptor.plugin(target);
    }
    return target;
  }

  public void addInterceptor(Interceptor interceptor) {
     
    interceptors.add(interceptor);
  }

  public List<Interceptor> getInterceptors() {
     
    return Collections.unmodifiableList(interceptors);
  }

}

再看看SqlSession

前面openSession的时候,根据configuration,执行器,是否自动提交生成了默认的SqlSession:

      return new DefaultSqlSession(configuration, executor, autoCommit);

// 这是sqlSession的属性
public class DefaultSqlSession implements SqlSession {
     

//mybatis配置文件,mapper信息
  private final Configuration configuration;
  //执行器
  private final Executor executor;
//自动提交
  private final boolean autoCommit;
  //记录本次executor执行过程中是否有过更改操作
  private boolean dirty;
  //游标,,具体没研究
  private List<Cursor<?>> cursorList;

  public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {
     
    this.configuration = configuration;
    this.executor = executor;
    this.dirty = false;
    this.autoCommit = autoCommit;
  }

看一下sqlsession的方法,主要是增删改查,还有获取mapper方法:

getMapper方法

上篇文章其实大部分讲过了,因为getMapper方法走的是configuration的getMapper方法,前面解析mapper文件的时候,也是解析xml的namespace类,将类加到MapperRegistry里面:

通过属性knownMappers获取到对应的maooer代理工厂类,然后通过MapperProxyFactory类生成对应的mapper代理;Proxy.newProxyInstance是通过jdk动态代理生成代理类的,详情可以了解:https://blog.csdn.net/qq_38366063/article/details/105298512

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) {
     
    //根据mapperProxy生成代理,
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] {
      mapperInterface }, mapperProxy);
  }

  public T newInstance(SqlSession sqlSession) {
     
    //根据传入的sqlsession生成mapperProxy类,mapperProxy类必须实现InvocationHandler接口;
    final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }

}

而新建的MapperProxy类就是实现了InvocationHandler接口的具体执行方法的类;具体怎么执行,下次在讲,到这里,mapper代理就生成了;而通过spring结合mybatis的是通过往spring容器注入对应接口的方式,详见:
https://blog.csdn.net/qq_38366063/article/details/108120233