mybatis结果的组装

mybatis系列

• SpringBoot集成mybatis

• mybatis的statement的解析与加载

• mybatis如何根据mapper接口生成其实现类

• mybatis的mapper返回map结果集

• mybatis结果的组装

序

本文主要解答一个问题，即如果bean没有setter，而且属性不是public的，mybatis的自动组装是否可以赋值成功的问题。

查询调用过程

DefaultSqlSession.selectList -->SimpleExecutor.doQuery --> SimpleStatementHandler.query --> DefaultResultSetHandler.handleResultSets --> BeanWrapper.setBeanProperty --> MetaClass.getSetInvoker --> Reflector.getSetInvoker

关键方法

SimpleStatementHandler.query

public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
    String sql = boundSql.getSql();
    statement.execute(sql);
    return resultSetHandler.<E>handleResultSets(statement);
  }

DefaultResultSetHandler.handleResultSets

@Override
  public List<Object> handleResultSets(Statement stmt) throws SQLException {
    ErrorContext.instance().activity("handling results").object(mappedStatement.getId());
 
    final List<Object> multipleResults = new ArrayList<Object>();
 
    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);
      rsw = getNextResultSet(stmt);
      cleanUpAfterHandlingResultSet();
      resultSetCount++;
    }
 
    String[] resultSets = mappedStatement.getResulSets();
    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);
  }

DefaultResultSetHandler.handleResultSets

private void handleResultSet(ResultSetWrapper rsw, ResultMap resultMap, List<Object> multipleResults, ResultMapping parentMapping) throws SQLException {
    try {
      if (parentMapping != null) {
        handleRowValues(rsw, resultMap, null, RowBounds.DEFAULT, parentMapping);
      } else {
        if (resultHandler == null) {
          DefaultResultHandler defaultResultHandler = new DefaultResultHandler(objectFactory);
          handleRowValues(rsw, resultMap, defaultResultHandler, rowBounds, null);
          multipleResults.add(defaultResultHandler.getResultList());
        } else {
          handleRowValues(rsw, resultMap, resultHandler, rowBounds, null);
        }
      }
    } finally {
      // issue #228 (close resultsets)
      closeResultSet(rsw.getResultSet());
    }
  }

DefaultResultSetHandler.handleRowValues

private void handleRowValues(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler<?> resultHandler, RowBounds rowBounds, ResultMapping parentMapping) throws SQLException {
    if (resultMap.hasNestedResultMaps()) {
      ensureNoRowBounds();
      checkResultHandler();
      handleRowValuesForNestedResultMap(rsw, resultMap, resultHandler, rowBounds, parentMapping);
    } else {
      handleRowValuesForSimpleResultMap(rsw, resultMap, resultHandler, rowBounds, parentMapping);
    }
  }

DefaultResultSetHandler.handleRowValuesForSimpleResultMap

private void handleRowValuesForSimpleResultMap(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler<?> resultHandler, RowBounds rowBounds, ResultMapping parentMapping)
      throws SQLException {
    DefaultResultContext<Object> resultContext = new DefaultResultContext<Object>();
    skipRows(rsw.getResultSet(), rowBounds);
    while (shouldProcessMoreRows(resultContext, rowBounds) && rsw.getResultSet().next()) {
      ResultMap discriminatedResultMap = resolveDiscriminatedResultMap(rsw.getResultSet(), resultMap, null);
      Object rowValue = getRowValue(rsw, discriminatedResultMap);
      storeObject(resultHandler, resultContext, rowValue, parentMapping, rsw.getResultSet());
    }
  }

DefaultResultSetHandler.getRowValue

private Object getRowValue(ResultSetWrapper rsw, ResultMap resultMap) throws SQLException {
    final ResultLoaderMap lazyLoader = new ResultLoaderMap();
    Object resultObject = createResultObject(rsw, resultMap, lazyLoader, null);
    if (resultObject != null && !typeHandlerRegistry.hasTypeHandler(resultMap.getType())) {
      final MetaObject metaObject = configuration.newMetaObject(resultObject);
      boolean foundValues = !resultMap.getConstructorResultMappings().isEmpty();
      if (shouldApplyAutomaticMappings(resultMap, false)) {
        foundValues = applyAutomaticMappings(rsw, resultMap, metaObject, null) || foundValues;
      }
      foundValues = applyPropertyMappings(rsw, resultMap, metaObject, lazyLoader, null) || foundValues;
      foundValues = lazyLoader.size() > 0 || foundValues;
      resultObject = foundValues ? resultObject : null;
      return resultObject;
    }
    return resultObject;
  }

DefaultResultSetHandler.applyPropertyMappings

private boolean applyPropertyMappings(ResultSetWrapper rsw, ResultMap resultMap, MetaObject metaObject, ResultLoaderMap lazyLoader, String columnPrefix)
      throws SQLException {
    final List<String> mappedColumnNames = rsw.getMappedColumnNames(resultMap, columnPrefix);
    boolean foundValues = false;
    final List<ResultMapping> propertyMappings = resultMap.getPropertyResultMappings();
    for (ResultMapping propertyMapping : propertyMappings) {
      String column = prependPrefix(propertyMapping.getColumn(), columnPrefix);
      if (propertyMapping.getNestedResultMapId() != null) {
        // the user added a column attribute to a nested result map, ignore it
        column = null;
      }
      if (propertyMapping.isCompositeResult()
          || (column != null && mappedColumnNames.contains(column.toUpperCase(Locale.ENGLISH)))
          || propertyMapping.getResultSet() != null) {
        Object value = getPropertyMappingValue(rsw.getResultSet(), metaObject, propertyMapping, lazyLoader, columnPrefix);
        // issue #541 make property optional
        final String property = propertyMapping.getProperty();
        // issue #377, call setter on nulls
        if (value != DEFERED
            && property != null
            && (value != null || (configuration.isCallSettersOnNulls() && !metaObject.getSetterType(property).isPrimitive()))) {
          metaObject.setValue(property, value);
        }
        if (value != null || value == DEFERED) {
          foundValues = true;
        }
      }
    }
    return foundValues;
  }

MetaObject.setValue

public void setValue(String name, Object value) {
    PropertyTokenizer prop = new PropertyTokenizer(name);
    if (prop.hasNext()) {
      MetaObject metaValue = metaObjectForProperty(prop.getIndexedName());
      if (metaValue == SystemMetaObject.NULL_META_OBJECT) {
        if (value == null && prop.getChildren() != null) {
          // don't instantiate child path if value is null
          return;
        } else {
          metaValue = objectWrapper.instantiatePropertyValue(name, prop, objectFactory);
        }
      }
      metaValue.setValue(prop.getChildren(), value);
    } else {
      objectWrapper.set(prop, value);
    }
  }

BeanWrapper.set

@Override
  public void set(PropertyTokenizer prop, Object value) {
    if (prop.getIndex() != null) {
      Object collection = resolveCollection(prop, object);
      setCollectionValue(prop, collection, value);
    } else {
      setBeanProperty(prop, object, value);
    }
  }

BeanWrapper.setBeanProperty

private void setBeanProperty(PropertyTokenizer prop, Object object, Object value) {
    try {
      Invoker method = metaClass.getSetInvoker(prop.getName());
      Object[] params = {value};
      try {
        method.invoke(object, params);
      } catch (Throwable t) {
        throw ExceptionUtil.unwrapThrowable(t);
      }
    } catch (Throwable t) {
      throw new ReflectionException("Could not set property '" + prop.getName() + "' of '" + object.getClass() + "' with value '" + value + "' Cause: " + t.toString(), t);
    }
  }

MetaClass.getSetInovker

public Invoker getSetInvoker(String name) {
    return reflector.getSetInvoker(name);
  }

Reflector.getSetInvoker

public Invoker getSetInvoker(String propertyName) {
    Invoker method = setMethods.get(propertyName);
    if (method == null) {
      throw new ReflectionException("There is no setter for property named '" + propertyName + "' in '" + type + "'");
    }
    return method;
  }

setMethods的修改

有setter的话，走Reflector. resolveSetterConflicts

private void resolveSetterConflicts(Map<String, List<Method>> conflictingSetters) {
    for (String propName : conflictingSetters.keySet()) {
      List<Method> setters = conflictingSetters.get(propName);
      Method firstMethod = setters.get(0);
      if (setters.size() == 1) {
        addSetMethod(propName, firstMethod);
      } else {
        Class<?> expectedType = getTypes.get(propName);
        if (expectedType == null) {
          throw new ReflectionException("Illegal overloaded setter method with ambiguous type for property "
              + propName + " in class " + firstMethod.getDeclaringClass() + ".  This breaks the JavaBeans " +
              "specification and can cause unpredicatble results.");
        } else {
          Iterator<Method> methods = setters.iterator();
          Method setter = null;
          while (methods.hasNext()) {
            Method method = methods.next();
            if (method.getParameterTypes().length == 1
                && expectedType.equals(method.getParameterTypes()[0])) {
              setter = method;
              break;
            }
          }
          if (setter == null) {
            throw new ReflectionException("Illegal overloaded setter method with ambiguous type for property "
                + propName + " in class " + firstMethod.getDeclaringClass() + ".  This breaks the JavaBeans " +
                "specification and can cause unpredicatble results.");
          }
          addSetMethod(propName, setter);
        }
      }
    }
  }

private void addSetMethod(String name, Method method) {
    if (isValidPropertyName(name)) {
      setMethods.put(name, new MethodInvoker(method));
      setTypes.put(name, method.getParameterTypes()[0]);
    }
  }

没有setter的话，走Reflector. addSetField

private void addSetField(Field field) {
    if (isValidPropertyName(field.getName())) {
      setMethods.put(field.getName(), new SetFieldInvoker(field));
      setTypes.put(field.getName(), field.getType());
    }
  }

小结

即使bean的属性是私有的，没有setter，mybatis也会通过反射去设置值。

备注

本文的代码引用来自mybatis的3.3.0版本的源码