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

@Overridepublic 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

@Overridepublic 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。