本文是作者原创,版权归作者所有.若要转载,请注明出处.本文以简单的select语句为例,只贴我觉得比较重要的源码,其他不重要非关键的就不贴了

 

主流程和insert语句差不多,这里主要讲不同的流程,前面配置解析就不看了

SqlSession sqlSession = sqlSessionFactory.openSession(); 
    //通过动态代理实现接口 ,用动态代理对象去帮我们执行SQL 
    //这里生成mapper实际类型是org.apache.ibatis.binding.MapperProxy 
    DemoMapper mapper = sqlSession.getMapper(DemoMapper.class); 
    //这里用生成的动态代理对象执行 
    String projId="0124569b738e405fb20b68bfef37f487"; 
    String sectionName="标段"; 
    List<ProjInfo> projInfos = mapper.selectAll(projId, sectionName); 
    System.out.println(projInfos); 
    //sqlSession.commit(); 
    sqlSession.close();

点进去,看下方法sqlSession.getMapper(DemoMapper.class),这个调到下面这个方法

public <T> T getMapper(Class<T> type, SqlSession sqlSession) { 
    //这里就是动态代理生成的代理对象 
    final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type); 
    if (mapperProxyFactory == null) { 
      throw new BindingException("Type " + type + " is not known to the MapperRegistry."); 
    } 
    try { 
      return mapperProxyFactory.newInstance(sqlSession); 
    } catch (Exception e) { 
      throw new BindingException("Error getting mapper instance. Cause: " + e, e); 
    } 
  }

我们看下mapperProxyFactory.newInstance(sqlSession)这个方法

public T newInstance(SqlSession sqlSession) { 
    final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache); 
    return newInstance(mapperProxy); 
  }

继续点进去看

protected T newInstance(MapperProxy<T> mapperProxy) { 
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy); 
  }

好,很明显了,这里用的jdk的动态代理,关于动态代理,这里就不赘述了,下次有机会在设计模式里专门讲一下.所以这里返回的是代理对象

继续往下看,我们看mapper.selectAll(projId, sectionName)这个方法debug进去,调的是jdk动态代理的invoke方法,里面就是具体的查询逻辑了

//这里method是接口DemoMapper的selectAll方法 
  @Override 
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { 
    try { 
      // 如果目标方法是Object类继承来的,直接调用目标方法 
      //method.getDeclaringClass()是接口DemoMapper的类对象,这里结果为false,跳过这一步 
      if (Object.class.equals(method.getDeclaringClass())) { 
        return method.invoke(this, args); 
        //这里method是接口DemoMapper的selectAll方法,所以结果也为false,跳过这一步 
      } else if (method.isDefault()) { 
        if (privateLookupInMethod == null) { 
          return invokeDefaultMethodJava8(proxy, method, args); 
        } else { 
          return invokeDefaultMethodJava9(proxy, method, args); 
        } 
      } 
    } catch (Throwable t) { 
      throw ExceptionUtil.unwrapThrowable(t); 
    } 
    //这里将method放入缓存 
    // 从缓存中获取MapperMethod 对象,如果没有就创建新的并添加 
    final MapperMethod mapperMethod = cachedMapperMethod(method); 
    //这是真正的执行方法 
    return mapperMethod.execute(sqlSession, args); 
  }
缓存的东西,我们下次再说,我们继续点进去看
//就是这个执行方法 
  public Object execute(SqlSession sqlSession, Object[] args) { 
    Object result; 
    //command.getType()此时是select 
    switch (command.getType()) { 
      case INSERT: { 
        Object param = method.convertArgsToSqlCommandParam(args); 
        result = rowCountResult(sqlSession.insert(command.getName(), param)); 
        break; 
      } 
      case UPDATE: { 
        Object param = method.convertArgsToSqlCommandParam(args); 
        result = rowCountResult(sqlSession.update(command.getName(), param)); 
        break; 
      } 
      case DELETE: { 
        Object param = method.convertArgsToSqlCommandParam(args); 
        result = rowCountResult(sqlSession.delete(command.getName(), param)); 
        break; 
      } 
      //进入这个分支 
      case SELECT: 
        //这里结果为false,不进这里 
        if (method.returnsVoid() && method.hasResultHandler()) { 
          executeWithResultHandler(sqlSession, args); 
          result = null; 
          //这里结果为真,进这里 
        } else if (method.returnsMany()) { 
          result = executeForMany(sqlSession, args); 
          //这里结果为false,不进这里 
        } else if (method.returnsMap()) { 
          result = executeForMap(sqlSession, args); 
          //这里结果为false,不进这里 
        } else if (method.returnsCursor()) { 
          result = executeForCursor(sqlSession, args); 
        } else { 
          // 
          Object param = method.convertArgsToSqlCommandParam(args); 
          //处理参数完成后后param是hashmap类型,key有两种,一种是#{}里面的参数名, 
          // 另一种是(param1, param2, ...),value只有一种,就是我们的实际参数 
          //这里执行sql得到查询结果result,跟进去看下 
          result = sqlSession.selectOne(command.getName(), param); 
          if (method.returnsOptional() 
              && (result == null || !method.getReturnType().equals(result.getClass()))) { 
            result = Optional.ofNullable(result); 
          } 
        } 
        break; 
      case FLUSH: 
        result = sqlSession.flushStatements(); 
        break; 
      default: 
        throw new BindingException("Unknown execution method for: " + command.getName()); 
    } 
    if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) { 
      throw new BindingException("Mapper method '" + command.getName() 
          + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ")."); 
    } 
    return result; 
  }

继续往下看

private <E> Object executeForMany(SqlSession sqlSession, Object[] args) {
List<E> result;
Object param = method.convertArgsToSqlCommandParam(args);
if (method.hasRowBounds()) {
RowBounds rowBounds = method.extractRowBounds(args);
result = sqlSession.selectList(command.getName(), param, rowBounds);
} else {
//进这里,点进去看
result = sqlSession.selectList(command.getName(), param);
}
// issue #510 Collections & arrays support
if (!method.getReturnType().isAssignableFrom(result.getClass())) {
if (method.getReturnType().isArray()) {
return convertToArray(result);
} else {
return convertToDeclaredCollection(sqlSession.getConfiguration(), result);
}
}
return result;
}

继续

//这个是真正的sql执行方法了,statement是具体的方法名com.lusaisai.dao.DemoMapper.selectOne 
  //parameter是参数名和真是的参数 
  @Override 
  public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) { 
    try { 
      //configuration对象根据statement,得到关于sql语句的相关信息 
      //这里得到的ms包含sql语句 
      MappedStatement ms = configuration.getMappedStatement(statement); 
      //这里就是执行sql语句 
      return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER); 
    } catch (Exception e) { 
      throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e); 
    } finally { 
      ErrorContext.instance().reset(); 
    } 
  }

继续跟

//执行语句这个方法,跟进去看下 
  @Override 
  public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException { 
    // 
    BoundSql boundSql = ms.getBoundSql(parameterObject); 
    CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql); 
    //这个跟进去看戏,应该是真正的jdbc操作了 
    return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); 
  }

继续

@Override 
  public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) 
      throws SQLException { 
    Cache cache = ms.getCache(); 
    if (cache != null) { 
      flushCacheIfRequired(ms); 
      if (ms.isUseCache() && resultHandler == null) { 
        ensureNoOutParams(ms, boundSql); 
        @SuppressWarnings("unchecked") 
        List<E> list = (List<E>) tcm.getObject(cache, key); 
        if (list == null) { 
          list = delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); 
          tcm.putObject(cache, key, list); // issue #578 and #116 
        } 
        return list; 
      } 
    } 
    //前面是缓存处理跟进去 
    return delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); 
  }

这里继续

@Override 
  public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException { 
    ErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId()); 
    if (closed) { 
      throw new ExecutorException("Executor was closed."); 
    } 
    if (queryStack == 0 && ms.isFlushCacheRequired()) { 
      clearLocalCache(); 
    } 
    List<E> list; 
    try { 
      queryStack++; 
      list = resultHandler == null ? (List<E>) localCache.getObject(key) : null; 
      if (list != null) { 
        handleLocallyCachedOutputParameters(ms, key, parameter, boundSql); 
      } else { 
        //进这里,继续跟 
        list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql); 
      } 
    } finally { 
      queryStack--; 
    } 
    if (queryStack == 0) { 
      for (DeferredLoad deferredLoad : deferredLoads) { 
        deferredLoad.load(); 
      } 
      // issue #601 
      deferredLoads.clear(); 
      if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) { 
        // issue #482 
        clearLocalCache(); 
      } 
    } 
    return list; 
  }

继续

private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException { 
    List<E> list; 
    //key值就是待执行的sql 
    localCache.putObject(key, EXECUTION_PLACEHOLDER); 
    try { 
      //跟进去 
      list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql); 
    } finally { 
      localCache.removeObject(key); 
    } 
    localCache.putObject(key, list); 
    if (ms.getStatementType() == StatementType.CALLABLE) { 
      localOutputParameterCache.putObject(key, parameter); 
    } 
    return list; 
  }

继续

@Override 
  public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException { 
    Statement stmt = null; 
    try { 
      Configuration configuration = ms.getConfiguration(); 
      StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql); 
      stmt = prepareStatement(handler, ms.getStatementLog()); 
      return handler.query(stmt, resultHandler); 
    } finally { 
      closeStatement(stmt); 
    } 
  }

跟一下return那行

@Override 
  public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException { 
    //这里强转成预编译对象PreparedStatement 
    PreparedStatement ps = (PreparedStatement) statement; 
    ps.execute(); 
    return resultSetHandler.handleResultSets(ps); 
  }

好,我们看到PreparedStatement对象了,继续

public List<Object> handleResultSets(Statement stmt) throws SQLException { 
    ErrorContext.instance().activity("handling results").object(mappedStatement.getId()); 
 
    final List<Object> multipleResults = new ArrayList<>(); 
 
    int resultSetCount = 0; 
    ResultSetWrapper rsw = getFirstResultSet(stmt); 
 
    List<ResultMap> resultMaps = mappedStatement.getResultMaps(); 
    int resultMapCount = resultMaps.size(); 
    validateResultMapsCount(rsw, resultMapCount); 
    while (rsw != null && resultMapCount > resultSetCount) { 
      ResultMap resultMap = resultMaps.get(resultSetCount); 
      handleResultSet(rsw, resultMap, multipleResults, null); 
      //这里已经执行完sql,生成结果集了 
      rsw = getNextResultSet(stmt); 
      cleanUpAfterHandlingResultSet(); 
      resultSetCount++; 
    } 
 
    String[] resultSets = mappedStatement.getResultSets(); 
    if (resultSets != null) { 
      while (rsw != null && resultSetCount < resultSets.length) { 
        ResultMapping parentMapping = nextResultMaps.get(resultSets[resultSetCount]); 
        if (parentMapping != null) { 
          String nestedResultMapId = parentMapping.getNestedResultMapId(); 
          ResultMap resultMap = configuration.getResultMap(nestedResultMapId); 
          handleResultSet(rsw, resultMap, null, parentMapping); 
        } 
        rsw = getNextResultSet(stmt); 
        cleanUpAfterHandlingResultSet(); 
        resultSetCount++; 
      } 
    } 
 
    return collapseSingleResultList(multipleResults); 
  }

继续跟我注释的那行

private ResultSetWrapper getNextResultSet(Statement stmt) { 
    // Making this method tolerant of bad JDBC drivers 
    try { 
      if (stmt.getConnection().getMetaData().supportsMultipleResultSets()) { 
        // Crazy Standard JDBC way of determining if there are more results 
        //这里的stmt已经包含可执行的sql了 
        if (!(!stmt.getMoreResults() && stmt.getUpdateCount() == -1)) { 
          ResultSet rs = stmt.getResultSet(); 
          if (rs == null) { 
            return getNextResultSet(stmt); 
          } else { 
            return new ResultSetWrapper(rs, configuration); 
          } 
        } 
      } 
    } catch (Exception e) { 
      // Intentionally ignored. 
    } 
    return null; 
  }

 

最后再贴张网上找的图

 

 

好,到这里我们已经看完执行流程,其实封装了很多层,并没有全都要搞懂的必要,这里的重点是用了动态代理,底层肯定是jdbc操作,当然它还加了很多缓存和各种验证的代码.关于缓存的源码,有机会下次再看吧.

 

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(2)一起来看下使用mybatis框架的insert语句的源码执行流程吧讲解
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