本章要点

• MapperProxy的创建
• SQL的执行（insert）

1.MapperProxy的创建

• 根据mapper的class类获取configuration中之前缓存的mapper

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

• mapperRegistry中获取

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

• 最终从knownMappers缓存中获取对应的mapper

  public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    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);
    }
  }

• 创建mapperProxy 对象

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

• 通过JDK生成代理对象

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

2.SQL执行

• 执行代理的invoke方法

  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if (Object.class.equals(method.getDeclaringClass())) {
      try {
        return method.invoke(this, args);
      } catch (Throwable t) {
        throw ExceptionUtil.unwrapThrowable(t);
      }
    }
    final MapperMethod mapperMethod = cachedMapperMethod(method);//缓存MapperMethod,并返回
    return mapperMethod.execute(sqlSession, args);
  }

• 缓存MapperMethod,并返回

  private MapperMethod cachedMapperMethod(Method method) {
    MapperMethod mapperMethod = methodCache.get(method);
    if (mapperMethod == null) {
      mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
      methodCache.put(method, mapperMethod);//缓存
    }
    return mapperMethod;
  }

• 执行execute方法，根据不同的sql（select，update，insert，delete）语句，执行不同的方法

 public Object execute(SqlSession sqlSession, Object[] args) {
    Object result;
    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;
      }
      case SELECT:
        if (method.returnsVoid() && method.hasResultHandler()) {
          executeWithResultHandler(sqlSession, args);
          result = null;
        } else if (method.returnsMany()) {
          result = executeForMany(sqlSession, args);
        } else if (method.returnsMap()) {
          result = executeForMap(sqlSession, args);
        } else if (method.returnsCursor()) {
          result = executeForCursor(sqlSession, args);
        } else {
          Object param = method.convertArgsToSqlCommandParam(args);
          result = sqlSession.selectOne(command.getName(), param);
        }
        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;
  }

• 接下来先看插入方法

 public int insert(String statement) {
    return insert(statement, null);
  }

  @Override
  public int insert(String statement, Object parameter) {
    return update(statement, parameter);//可见插入方法调用的其实是update方法
  }

  @Override
  public int update(String statement) {
    return update(statement, null);
  }

  public MappedStatement getMappedStatement(String id) {
    return this.getMappedStatement(id, true);
  }

  public MappedStatement getMappedStatement(String id, boolean validateIncompleteStatements) {
    if (validateIncompleteStatements) {
      buildAllStatements();//解析一些标签
    }
    return mappedStatements.get(id);//从缓存中拿数据，id就是全类名+方法名，如：com.zhaosc.mybatis.mapper.UserMapper.insert
  }

• 解析参数里面有没有集合或数组

 private Object wrapCollection(final Object object) {
    if (object instanceof Collection) {
      StrictMap<Object> map = new StrictMap<Object>();
      map.put("collection", object);
      if (object instanceof List) {
        map.put("list", object);
      }
      return map;
    } else if (object != null && object.getClass().isArray()) {
      StrictMap<Object> map = new StrictMap<Object>();
      map.put("array", object);
      return map;
    }
    return object;
  }

• 接下来到了真正执行方法的时候了

  public int update(MappedStatement ms, Object parameterObject) throws SQLException {
    flushCacheIfRequired(ms);
    return delegate.update(ms, parameterObject);
  }

org.apache.ibatis.executor.BaseExecutor.update(MappedStatement, Object)

  public int update(MappedStatement ms, Object parameter) throws SQLException {
    ErrorContext.instance().resource(ms.getResource()).activity("executing an update").object(ms.getId());
    if (closed) {
      throw new ExecutorException("Executor was closed.");
    }
    clearLocalCache();//清理本地缓存
    return doUpdate(ms, parameter);
  }

• 执行update：org.apache.ibatis.executor.SimpleExecutor.doUpdate(MappedStatement, Object)

  public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
    Statement stmt = null;
    try {
      Configuration configuration = ms.getConfiguration();//拿取配置信息
      StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
      stmt = prepareStatement(handler, ms.getStatementLog());//生成Statement 
      return handler.update(stmt);//处理执行JDBC
    } finally {
      closeStatement(stmt);//关闭
    }
  }

得到StatementHandler:

  public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);//构造函数比较重要
    statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
    return statementHandler;
  }

• 构造函数，根据不同的StatementType拿到不同的StatementHandler

  public RoutingStatementHandler(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {

    switch (ms.getStatementType()) {
      case STATEMENT:
        delegate = new SimpleStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
        break;
      case PREPARED:
        delegate = new PreparedStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
        break;
      case CALLABLE:
        delegate = new CallableStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);//存储过程
        break;
      default:
        throw new ExecutorException("Unknown statement type: " + ms.getStatementType());
    }

  }