MetaObject简介

MetaObject类相当于一个对象工具类，Mybatis在sql参数设置和结果集映射里经常使用到这个对象。

映射是指结果集中的列填充至JAVA Bean属性。这就必须用到反射，而Bean的属性 多种多样的有普通属性、对象、集合、Map都有可能。为了更加方便的操作Bean的属性，MyBatis提供了MeataObject 工具类，其简化了对象属性的操作。

/*** 对象元数据，提供了对象的属性值的获得和设置** @author Clinton Begin*/
public class MetaObject {/*** 原始 Object 对象*/private final Object originalObject;/*** 封装过的 Object 对象*/private final ObjectWrapper objectWrapper;private final ObjectFactory objectFactory;private final ObjectWrapperFactory objectWrapperFactory;private final ReflectorFactory reflectorFactory;private MetaObject(Object object, ObjectFactory objectFactory, ObjectWrapperFactory objectWrapperFactory, ReflectorFactory reflectorFactory) {this.originalObject = object;this.objectFactory = objectFactory;this.objectWrapperFactory = objectWrapperFactory;this.reflectorFactory = reflectorFactory;if (object instanceof ObjectWrapper) {this.objectWrapper = (ObjectWrapper) object;} else if (objectWrapperFactory.hasWrapperFor(object)) {// 创建 ObjectWrapper 对象this.objectWrapper = objectWrapperFactory.getWrapperFor(this, object);} else if (object instanceof Map) {// 创建 MapWrapper 对象this.objectWrapper = new MapWrapper(this, (Map) object);} else if (object instanceof Collection) {// 创建 CollectionWrapper 对象this.objectWrapper = new CollectionWrapper(this, (Collection) object);} else {// 创建 BeanWrapper 对象this.objectWrapper = new BeanWrapper(this, object);}}/*** 创建 MetaObject 对象** @param object 原始 Object 对象* @param objectFactory* @param objectWrapperFactory* @param reflectorFactory* @return MetaObject 对象*/public static MetaObject forObject(Object object, ObjectFactory objectFactory, ObjectWrapperFactory objectWrapperFactory, ReflectorFactory reflectorFactory) {if (object == null) {return SystemMetaObject.NULL_META_OBJECT;} else {return new MetaObject(object, objectFactory, objectWrapperFactory, reflectorFactory);}}public ObjectFactory getObjectFactory() {return objectFactory;}public ObjectWrapperFactory getObjectWrapperFactory() {return objectWrapperFactory;}public ReflectorFactory getReflectorFactory() {return reflectorFactory;}public Object getOriginalObject() {return originalObject;}/*** 1.查找对象中的属性，可以下划线转驼峰查找* @param propName* @param useCamelCaseMapping 下划线转驼峰查找* @return*/public String findProperty(String propName, boolean useCamelCaseMapping) {return objectWrapper.findProperty(propName, useCamelCaseMapping);}/*** 获取get方法属性名称和get方法去掉get后边的属性名称* getIds(){return id;} --> (id、ids)* @return*/public String[] getGetterNames() {return objectWrapper.getGetterNames();}/*** 获取set方法属性名称和set方法去掉set后边的属性名称* setIds(){return id;} --> (id、ids)* @return*/public String[] getSetterNames() {return objectWrapper.getSetterNames();}/*** 获取set方法后边属性的类型* @param name 这个name 要和setXXX方法中的XXX相同才能获取到，否则抛异常* @return*/public Class<?> getSetterType(String name) {return objectWrapper.getSetterType(name);}/*** 获取get方法后边属性的类型* @param name 这个name，要个getXXX方法中的XXX相同才能获取到，否则抛异常* @return*/public Class<?> getGetterType(String name) {return objectWrapper.getGetterType(name);}/*** 判断name是否是setXXX()方法中的XXX* @param name* @return*/public boolean hasSetter(String name) {return objectWrapper.hasSetter(name);}/*** 判断name是否是getXXX()方法中的XXX* @param name* @return*/public boolean hasGetter(String name) {return objectWrapper.hasGetter(name);}/*** 获取对象属性值，可以递归获取* @param name* @return*/public Object getValue(String name) {// 创建 PropertyTokenizer 对象，对 name 分词PropertyTokenizer prop = new PropertyTokenizer(name);// 有子表达式if (prop.hasNext()) {// 创建 MetaObject 对象MetaObject metaValue = metaObjectForProperty(prop.getIndexedName());// 递归判断子表达式 children ，获取值，metaValue == null，则返回nullif (metaValue == SystemMetaObject.NULL_META_OBJECT) {return null;} else {return metaValue.getValue(prop.getChildren());}// 无子表达式} else {// 获取值return objectWrapper.get(prop);}}/*** 给对象属性设置值，可以递归设置，基本类型，数组，对象，都可以自动创建* 但是ArrayList和数组需要手动创建* List必须创建对象，添加进list* @param name* @param value*/public void setValue(String name, Object value) {// 创建 PropertyTokenizer 对象，对 name 分词PropertyTokenizer prop = new PropertyTokenizer(name);// 有子表达式if (prop.hasNext()) {// 创建 MetaObject 对象MetaObject metaValue = metaObjectForProperty(prop.getIndexedName());// 递归判断子表达式 children ，设置值if (metaValue == SystemMetaObject.NULL_META_OBJECT) {if (value == null) {// don't instantiate child path if value is nullreturn;} else {// 创建值metaValue = objectWrapper.instantiatePropertyValue(name, prop, objectFactory);}}// 设置值metaValue.setValue(prop.getChildren(), value);// 无子表达式} else {// 设置值objectWrapper.set(prop, value);}}public MetaObject metaObjectForProperty(String name) {// 获得属性值Object value = getValue(name);// 创建 MetaObject 对象return MetaObject.forObject(value, objectFactory, objectWrapperFactory, reflectorFactory);}public ObjectWrapper getObjectWrapper() {return objectWrapper;}public boolean isCollection() {return objectWrapper.isCollection();}/*** 不支持add操作* @param element*/public void add(Object element) {objectWrapper.add(element);}/*** 不支持addAll操作* @param list* @param */public <E> void addAll(List<E> list) {objectWrapper.addAll(list);}}

测试：

public class MetaObjectTest {@Testpublic void test(){Role role = new Role();MetaObject metaObject = SystemMetaObject.forObject(role);//设置基本类型metaObject.setValue("name", "管理员");metaObject.setValue("role_id", 1);//设置List