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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