一、MetaObject基本使用

public class User {private int id;private String name;private String phoneNumber;private User child;List<User> users;private List<String> likes;Map<String, String> labels;// get set
}

Object user = new User();
Configuration configuration = new Configuration();
MetaObject metaObject = configuration.newMetaObject(user);
// 直接属性赋值
metaObject.setValue("name", "zhangsan");
System.out.println(metaObject.getValue("name"));// 子属性赋值，对象为null会自动创建，并填充属性值
metaObject.setValue("child.name", "lisi");
System.out.println(metaObject.getValue("child.name"));// 查找驼峰属性 phoneNumber
System.out.println(metaObject.findProperty("phone_number", true));// 操作数组，基于索引操作数组
ArrayList<String> strings = new ArrayList<>();
strings.add("sing");
strings.add("run");
metaObject.setValue("likes", strings);
System.out.println(metaObject.getValue("likes"));
System.out.println(metaObject.getValue("likes[0]")); // 获取第一个// 操作Map
metaObject.setValue("labels", new HashMap<String, String>());
metaObject.setValue("labels[red]", "like");
metaObject.setValue("labels[blue]", "notLike");
System.out.println(metaObject.getValue("labels"));
System.out.println(metaObject.getValue("labels[red]"));

MetaObject是一个强大的反射工具类，
支持查找属性（忽略大小写、支持驼峰、支持子属性）、
查找子属性（“user.name”、"users[0].id"获取集合中子属性的值、"user[name]"获取map）、
支持设置子属性（自动创建子属性，必须带有空参构造方法且不能是集合）。

MetaObject工具类不止设置、查找属性值，还提供了获取set、get方法、查找属性值等反射常用方法。

二、关键类源码分析

1、MetaObject的构造方法

调用MetaObject 的forObject方法，可以将Object对象转换成BeanWrapper对象，最终调用了new BeanWrapper

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)) {this.objectWrapper = objectWrapperFactory.getWrapperFor(this, object);} else if (object instanceof Map) {this.objectWrapper = new MapWrapper(this, (Map) object);} else if (object instanceof Collection) {this.objectWrapper = new CollectionWrapper(this, (Collection) object);} else { // 普通类this.objectWrapper = new BeanWrapper(this, object);}
}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);}
}

2、PropertyTokenizer分词器

public class PropertyTokenizer implements Iterator<PropertyTokenizer> {private String name; // 属性名称private final String indexedName; // 带着索引的属性名称private String index; // 索引（如果有的话）private final String children; // 除了indexedName之外的剩余的表达式名称 // 构造方法，根据 . 来进行分词，分词完毕后会将以上四个属性初始化好public PropertyTokenizer(String fullname) {int delim = fullname.indexOf('.');if (delim > -1) {name = fullname.substring(0, delim);children = fullname.substring(delim + 1);} else {name = fullname;children = null;}indexedName = name;delim = name.indexOf('[');if (delim > -1) {index = name.substring(delim + 1, name.length() - 1);name = name.substring(0, delim);}}public String getName() {return name;}public String getIndex() {return index;}public String getIndexedName() {return indexedName;}public String getChildren() {return children;}// 判断是否有子节点@Overridepublic boolean hasNext() {return children != null;}// 创建子节点时，也是new一个PropertyTokenizer分词器，重复操作@Overridepublic PropertyTokenizer next() {return new PropertyTokenizer(children);}@Overridepublic void remove() {throw new UnsupportedOperationException("Remove is not supported, as it has no meaning in the context of properties.");}
}

3、BeanWrapper

BeanWrapper的构造方法，将原始对象和metaObject对象进行存储，并调用MetaClass的forClass方法，解析Object原始对象的基本数据。

BeanWrapper中提供了获取Object原始对象的 设置值、获取值、获取getset方法、获取属性、获取setget类型等等一系列核心操作方法，最终都是委派给MetaClass 来实现的。

public class BeanWrapper extends BaseWrapper {private final Object object;private final MetaClass metaClass;public BeanWrapper(MetaObject metaObject, Object object) {super(metaObject);this.object = object;this.metaClass = MetaClass.forClass(object.getClass(), metaObject.getReflectorFactory());}@Overridepublic Object get(PropertyTokenizer prop) {if (prop.getIndex() != null) {Object collection = resolveCollection(prop, object);return getCollectionValue(prop, collection);} else {return getBeanProperty(prop, object);}}@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);}}@Overridepublic String findProperty(String name, boolean useCamelCaseMapping) {return metaClass.findProperty(name, useCamelCaseMapping);}@Overridepublic String[] getGetterNames() {return metaClass.getGetterNames();}@Overridepublic String[] getSetterNames() {return metaClass.getSetterNames();}@Overridepublic Class<?> getSetterType(String name) {PropertyTokenizer prop = new PropertyTokenizer(name);if (prop.hasNext()) {MetaObject metaValue = metaObject.metaObjectForProperty(prop.getIndexedName());if (metaValue == SystemMetaObject.NULL_META_OBJECT) {return metaClass.getSetterType(name);} else {return metaValue.getSetterType(prop.getChildren());}} else {return metaClass.getSetterType(name);}}@Overridepublic Class<?> getGetterType(String name) {PropertyTokenizer prop = new PropertyTokenizer(name);if (prop.hasNext()) {MetaObject metaValue = metaObject.metaObjectForProperty(prop.getIndexedName());if (metaValue == SystemMetaObject.NULL_META_OBJECT) {return metaClass.getGetterType(name);} else {return metaValue.getGetterType(prop.getChildren());}} else {return metaClass.getGetterType(name);}}@Overridepublic boolean hasSetter(String name) {PropertyTokenizer prop = new PropertyTokenizer(name);if (prop.hasNext()) {if (metaClass.hasSetter(prop.getIndexedName())) {MetaObject metaValue = metaObject.metaObjectForProperty(prop.getIndexedName());if (metaValue == SystemMetaObject.NULL_META_OBJECT) {return metaClass.hasSetter(name);} else {return metaValue.hasSetter(prop.getChildren());}} else {return false;}} else {return metaClass.hasSetter(name);}}@Overridepublic boolean hasGetter(String name) {PropertyTokenizer prop = new PropertyTokenizer(name);if (prop.hasNext()) {if (metaClass.hasGetter(prop.getIndexedName())) {MetaObject metaValue = metaObject.metaObjectForProperty(prop.getIndexedName());if (metaValue == SystemMetaObject.NULL_META_OBJECT) {return metaClass.hasGetter(name);} else {return metaValue.hasGetter(prop.getChildren());}} else {return false;}} else {return metaClass.hasGetter(name);}}@Overridepublic MetaObject instantiatePropertyValue(String name, PropertyTokenizer prop, ObjectFactory objectFactory) {MetaObject metaValue;Class<?> type = getSetterType(prop.getName());try {Object newObject = objectFactory.create(type);metaValue = MetaObject.forObject(newObject, metaObject.getObjectFactory(), metaObject.getObjectWrapperFactory(), metaObject.getReflectorFactory());set(prop, newObject);} catch (Exception e) {throw new ReflectionException("Cannot set value of property '" + name + "' because '" + name + "' is null and cannot be instantiated on instance of " + type.getName() + ". Cause:" + e.toString(), e);}return metaValue;}private Object getBeanProperty(PropertyTokenizer prop, Object object) {try {Invoker method = metaClass.getGetInvoker(prop.getName());try {return method.invoke(object, NO_ARGUMENTS);} catch (Throwable t) {throw ExceptionUtil.unwrapThrowable(t);}} catch (RuntimeException e) {throw e;} catch (Throwable t) {throw new ReflectionException("Could not get property '" + prop.getName() + "' from " + object.getClass() + ".  Cause: " + t.toString(), t);}}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);}}@Overridepublic boolean isCollection() {return false;}@Overridepublic void add(Object element) {throw new UnsupportedOperationException();}@Overridepublic <E> void addAll(List<E> list) {throw new UnsupportedOperationException();}}

4、MetaClass

在MetaClass的构造方法中，通过ReflectorFactory反射工厂的findForClass，将原始的Object进行解析，最终将解析的结果存放到Reflector成员变量中。

在MetaClass的核心方法，大多数操作的底层都是操作Reflector来进行实现的。

public class MetaClass {private final ReflectorFactory reflectorFactory;private final Reflector reflector;private MetaClass(Class<?> type, ReflectorFactory reflectorFactory) {this.reflectorFactory = reflectorFactory;this.reflector = reflectorFactory.findForClass(type);}public static MetaClass forClass(Class<?> type, ReflectorFactory reflectorFactory) {return new MetaClass(type, reflectorFactory);}public MetaClass metaClassForProperty(String name) {Class<?> propType = reflector.getGetterType(name);return MetaClass.forClass(propType, reflectorFactory);}public String findProperty(String name) {StringBuilder prop = buildProperty(name, new StringBuilder());return prop.length() > 0 ? prop.toString() : null;}public String findProperty(String name, boolean useCamelCaseMapping) {if (useCamelCaseMapping) {name = name.replace("_", "");}return findProperty(name);}public String[] getGetterNames() {return reflector.getGetablePropertyNames();}public String[] getSetterNames() {return reflector.getSetablePropertyNames();}public Class<?> getSetterType(String name) {PropertyTokenizer prop = new PropertyTokenizer(name);if (prop.hasNext()) {MetaClass metaProp = metaClassForProperty(prop.getName());return metaProp.getSetterType(prop.getChildren());} else {return reflector.getSetterType(prop.getName());}}public Class<?> getGetterType(String name) {PropertyTokenizer prop = new PropertyTokenizer(name);if (prop.hasNext()) {MetaClass metaProp = metaClassForProperty(prop);return metaProp.getGetterType(prop.getChildren());}// issue #506. Resolve the type inside a Collection Objectreturn getGetterType(prop);}private MetaClass metaClassForProperty(PropertyTokenizer prop) {Class<?> propType = getGetterType(prop);return MetaClass.forClass(propType, reflectorFactory);}private Class<?> getGetterType(PropertyTokenizer prop) {Class<?> type = reflector.getGetterType(prop.getName());if (prop.getIndex() != null && Collection.class.isAssignableFrom(type)) {Type returnType = getGenericGetterType(prop.getName());if (returnType instanceof ParameterizedType) {Type[] actualTypeArguments = ((ParameterizedType) returnType).getActualTypeArguments();if (actualTypeArguments != null && actualTypeArguments.length == 1) {returnType = actualTypeArguments[0];if (returnType instanceof Class) {type = (Class<?>) returnType;} else if (returnType instanceof ParameterizedType) {type = (Class<?>) ((ParameterizedType) returnType).getRawType();}}}}return type;}private Type getGenericGetterType(String propertyName) {try {Invoker invoker = reflector.getGetInvoker(propertyName);if (invoker instanceof MethodInvoker) {Field declaredMethod = MethodInvoker.class.getDeclaredField("method");declaredMethod.setAccessible(true);Method method = (Method) declaredMethod.get(invoker);return TypeParameterResolver.resolveReturnType(method, reflector.getType());} else if (invoker instanceof GetFieldInvoker) {Field declaredField = GetFieldInvoker.class.getDeclaredField("field");declaredField.setAccessible(true);Field field = (Field) declaredField.get(invoker);return TypeParameterResolver.resolveFieldType(field, reflector.getType());}} catch (NoSuchFieldException | IllegalAccessException e) {// Ignored}return null;}public boolean hasSetter(String name) {PropertyTokenizer prop = new PropertyTokenizer(name);if (prop.hasNext()) {if (reflector.hasSetter(prop.getName())) {MetaClass metaProp = metaClassForProperty(prop.getName());return metaProp.hasSetter(prop.getChildren());} else {return false;}} else {return reflector.hasSetter(prop.getName());}}public boolean hasGetter(String name) {PropertyTokenizer prop = new PropertyTokenizer(name);if (prop.hasNext()) {if (reflector.hasGetter(prop.getName())) {MetaClass metaProp = metaClassForProperty(prop);return metaProp.hasGetter(prop.getChildren());} else {return false;}} else {return reflector.hasGetter(prop.getName());}}public Invoker getGetInvoker(String name) {return reflector.getGetInvoker(name);}public Invoker getSetInvoker(String name) {return reflector.getSetInvoker(name);}private StringBuilder buildProperty(String name, StringBuilder builder) {PropertyTokenizer prop = new PropertyTokenizer(name);if (prop.hasNext()) {String propertyName = reflector.findPropertyName(prop.getName());if (propertyName != null) {builder.append(propertyName);builder.append(".");MetaClass metaProp = metaClassForProperty(propertyName);metaProp.buildProperty(prop.getChildren(), builder);}} else {String propertyName = reflector.findPropertyName(name);if (propertyName != null) {builder.append(propertyName);}}return builder;}public boolean hasDefaultConstructor() {return reflector.hasDefaultConstructor();}}

5、DefaultReflectorFactory

DefaultReflectorFactory实现了ReflectorFactory，用于生成Reflector

public class DefaultReflectorFactory implements ReflectorFactory {private boolean classCacheEnabled = true;private final ConcurrentMap<Class<?>, Reflector> reflectorMap = new ConcurrentHashMap<>();public DefaultReflectorFactory() {}@Overridepublic boolean isClassCacheEnabled() {return classCacheEnabled;}@Overridepublic void setClassCacheEnabled(boolean classCacheEnabled) {this.classCacheEnabled = classCacheEnabled;}@Overridepublic Reflector findForClass(Class<?> type) {if (classCacheEnabled) {// synchronized (type) removed see issue #461return MapUtil.computeIfAbsent(reflectorMap, type, Reflector::new);} else {return new Reflector(type);}}}

6、Reflector

这是MyBatis的反射最底层类，构造方法中将原始的对象Class进行解析，所有的方法、属性等等都存放到这里用于存储。

public class Reflector {private final Class<?> type;private final String[] readablePropertyNames;private final String[] writablePropertyNames;private final Map<String, Invoker> setMethods = new HashMap<>();private final Map<String, Invoker> getMethods = new HashMap<>();private final Map<String, Class<?>> setTypes = new HashMap<>();private final Map<String, Class<?>> getTypes = new HashMap<>();private Constructor<?> defaultConstructor;private Map<String, String> caseInsensitivePropertyMap = new HashMap<>();public Reflector(Class<?> clazz) {type = clazz;addDefaultConstructor(clazz);addGetMethods(clazz);addSetMethods(clazz);addFields(clazz);readablePropertyNames = getMethods.keySet().toArray(new String[0]);writablePropertyNames = setMethods.keySet().toArray(new String[0]);for (String propName : readablePropertyNames) {caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);}for (String propName : writablePropertyNames) {caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);}}private void addDefaultConstructor(Class<?> clazz) {Constructor<?>[] constructors = clazz.getDeclaredConstructors();Arrays.stream(constructors).filter(constructor -> constructor.getParameterTypes().length == 0).findAny().ifPresent(constructor -> this.defaultConstructor = constructor);}private void addGetMethods(Class<?> clazz) {Map<String, List<Method>> conflictingGetters = new HashMap<>();Method[] methods = getClassMethods(clazz);Arrays.stream(methods).filter(m -> m.getParameterTypes().length == 0 && PropertyNamer.isGetter(m.getName())).forEach(m -> addMethodConflict(conflictingGetters, PropertyNamer.methodToProperty(m.getName()), m));resolveGetterConflicts(conflictingGetters);}private void resolveGetterConflicts(Map<String, List<Method>> conflictingGetters) {for (Entry<String, List<Method>> entry : conflictingGetters.entrySet()) {Method winner = null;String propName = entry.getKey();boolean isAmbiguous = false;for (Method candidate : entry.getValue()) {if (winner == null) {winner = candidate;continue;}Class<?> winnerType = winner.getReturnType();Class<?> candidateType = candidate.getReturnType();if (candidateType.equals(winnerType)) {if (!boolean.class.equals(candidateType)) {isAmbiguous = true;break;} else if (candidate.getName().startsWith("is")) {winner = candidate;}} else if (candidateType.isAssignableFrom(winnerType)) {// OK getter type is descendant} else if (winnerType.isAssignableFrom(candidateType)) {winner = candidate;} else {isAmbiguous = true;break;}}addGetMethod(propName, winner, isAmbiguous);}}private void addGetMethod(String name, Method method, boolean isAmbiguous) {MethodInvoker invoker = isAmbiguous? new AmbiguousMethodInvoker(method, MessageFormat.format("Illegal overloaded getter method with ambiguous type for property ''{0}'' in class ''{1}''. This breaks the JavaBeans specification and can cause unpredictable results.",name, method.getDeclaringClass().getName())): new MethodInvoker(method);getMethods.put(name, invoker);Type returnType = TypeParameterResolver.resolveReturnType(method, type);getTypes.put(name, typeToClass(returnType));}private void addSetMethods(Class<?> clazz) {Map<String, List<Method>> conflictingSetters = new HashMap<>();Method[] methods = getClassMethods(clazz);Arrays.stream(methods).filter(m -> m.getParameterTypes().length == 1 && PropertyNamer.isSetter(m.getName())).forEach(m -> addMethodConflict(conflictingSetters, PropertyNamer.methodToProperty(m.getName()), m));resolveSetterConflicts(conflictingSetters);}private void addMethodConflict(Map<String, List<Method>> conflictingMethods, String name, Method method) {if (isValidPropertyName(name)) {List<Method> list = MapUtil.computeIfAbsent(conflictingMethods, name, k -> new ArrayList<>());list.add(method);}}private void resolveSetterConflicts(Map<String, List<Method>> conflictingSetters) {for (Entry<String, List<Method>> entry : conflictingSetters.entrySet()) {String propName = entry.getKey();List<Method> setters = entry.getValue();Class<?> getterType = getTypes.get(propName);boolean isGetterAmbiguous = getMethods.get(propName) instanceof AmbiguousMethodInvoker;boolean isSetterAmbiguous = false;Method match = null;for (Method setter : setters) {if (!isGetterAmbiguous && setter.getParameterTypes()[0].equals(getterType)) {// should be the best matchmatch = setter;break;}if (!isSetterAmbiguous) {match = pickBetterSetter(match, setter, propName);isSetterAmbiguous = match == null;}}if (match != null) {addSetMethod(propName, match);}}}private Method pickBetterSetter(Method setter1, Method setter2, String property) {if (setter1 == null) {return setter2;}Class<?> paramType1 = setter1.getParameterTypes()[0];Class<?> paramType2 = setter2.getParameterTypes()[0];if (paramType1.isAssignableFrom(paramType2)) {return setter2;} else if (paramType2.isAssignableFrom(paramType1)) {return setter1;}MethodInvoker invoker = new AmbiguousMethodInvoker(setter1,MessageFormat.format("Ambiguous setters defined for property ''{0}'' in class ''{1}'' with types ''{2}'' and ''{3}''.",property, setter2.getDeclaringClass().getName(), paramType1.getName(), paramType2.getName()));setMethods.put(property, invoker);Type[] paramTypes = TypeParameterResolver.resolveParamTypes(setter1, type);setTypes.put(property, typeToClass(paramTypes[0]));return null;}private void addSetMethod(String name, Method method) {MethodInvoker invoker = new MethodInvoker(method);setMethods.put(name, invoker);Type[] paramTypes = TypeParameterResolver.resolveParamTypes(method, type);setTypes.put(name, typeToClass(paramTypes[0]));}private Class<?> typeToClass(Type src) {Class<?> result = null;if (src instanceof Class) {result = (Class<?>) src;} else if (src instanceof ParameterizedType) {result = (Class<?>) ((ParameterizedType) src).getRawType();} else if (src instanceof GenericArrayType) {Type componentType = ((GenericArrayType) src).getGenericComponentType();if (componentType instanceof Class) {result = Array.newInstance((Class<?>) componentType, 0).getClass();} else {Class<?> componentClass = typeToClass(componentType);result = Array.newInstance(componentClass, 0).getClass();}}if (result == null) {result = Object.class;}return result;}private void addFields(Class<?> clazz) {Field[] fields = clazz.getDeclaredFields();for (Field field : fields) {if (!setMethods.containsKey(field.getName())) {// issue #379 - removed the check for final because JDK 1.5 allows// modification of final fields through reflection (JSR-133). (JGB)// pr #16 - final static can only be set by the classloaderint modifiers = field.getModifiers();if (!(Modifier.isFinal(modifiers) && Modifier.isStatic(modifiers))) {addSetField(field);}}if (!getMethods.containsKey(field.getName())) {addGetField(field);}}if (clazz.getSuperclass() != null) {addFields(clazz.getSuperclass());}}private void addSetField(Field field) {if (isValidPropertyName(field.getName())) {setMethods.put(field.getName(), new SetFieldInvoker(field));Type fieldType = TypeParameterResolver.resolveFieldType(field, type);setTypes.put(field.getName(), typeToClass(fieldType));}}private void addGetField(Field field) {if (isValidPropertyName(field.getName())) {getMethods.put(field.getName(), new GetFieldInvoker(field));Type fieldType = TypeParameterResolver.resolveFieldType(field, type);getTypes.put(field.getName(), typeToClass(fieldType));}}private boolean isValidPropertyName(String name) {return !(name.startsWith("$") || "serialVersionUID".equals(name) || "class".equals(name));}/*** This method returns an array containing all methods* declared in this class and any superclass.* We use this method, instead of the simpler <code>Class.getMethods()</code>,* because we want to look for private methods as well.** @param clazz The class* @return An array containing all methods in this class*/private Method[] getClassMethods(Class<?> clazz) {Map<String, Method> uniqueMethods = new HashMap<>();Class<?> currentClass = clazz;while (currentClass != null && currentClass != Object.class) {addUniqueMethods(uniqueMethods, currentClass.getDeclaredMethods());// we also need to look for interface methods -// because the class may be abstractClass<?>[] interfaces = currentClass.getInterfaces();for (Class<?> anInterface : interfaces) {addUniqueMethods(uniqueMethods, anInterface.getMethods());}currentClass = currentClass.getSuperclass();}Collection<Method> methods = uniqueMethods.values();return methods.toArray(new Method[0]);}private void addUniqueMethods(Map<String, Method> uniqueMethods, Method[] methods) {for (Method currentMethod : methods) {if (!currentMethod.isBridge()) {String signature = getSignature(currentMethod);// check to see if the method is already known// if it is known, then an extended class must have// overridden a methodif (!uniqueMethods.containsKey(signature)) {uniqueMethods.put(signature, currentMethod);}}}}private String getSignature(Method method) {StringBuilder sb = new StringBuilder();Class<?> returnType = method.getReturnType();if (returnType != null) {sb.append(returnType.getName()).append('#');}sb.append(method.getName());Class<?>[] parameters = method.getParameterTypes();for (int i = 0; i < parameters.length; i++) {sb.append(i == 0 ? ':' : ',').append(parameters[i].getName());}return sb.toString();}/*** Checks whether can control member accessible.** @return If can control member accessible, it return {@literal true}* @since 3.5.0*/public static boolean canControlMemberAccessible() {try {SecurityManager securityManager = System.getSecurityManager();if (null != securityManager) {securityManager.checkPermission(new ReflectPermission("suppressAccessChecks"));}} catch (SecurityException e) {return false;}return true;}/*** Gets the name of the class the instance provides information for.** @return The class name*/public Class<?> getType() {return type;}public Constructor<?> getDefaultConstructor() {if (defaultConstructor != null) {return defaultConstructor;} else {throw new ReflectionException("There is no default constructor for " + type);}}public boolean hasDefaultConstructor() {return defaultConstructor != null;}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;}public Invoker getGetInvoker(String propertyName) {Invoker method = getMethods.get(propertyName);if (method == null) {throw new ReflectionException("There is no getter for property named '" + propertyName + "' in '" + type + "'");}return method;}/*** Gets the type for a property setter.** @param propertyName - the name of the property* @return The Class of the property setter*/public Class<?> getSetterType(String propertyName) {Class<?> clazz = setTypes.get(propertyName);if (clazz == null) {throw new ReflectionException("There is no setter for property named '" + propertyName + "' in '" + type + "'");}return clazz;}/*** Gets the type for a property getter.** @param propertyName - the name of the property* @return The Class of the property getter*/public Class<?> getGetterType(String propertyName) {Class<?> clazz = getTypes.get(propertyName);if (clazz == null) {throw new ReflectionException("There is no getter for property named '" + propertyName + "' in '" + type + "'");}return clazz;}/*** Gets an array of the readable properties for an object.** @return The array*/public String[] getGetablePropertyNames() {return readablePropertyNames;}/*** Gets an array of the writable properties for an object.** @return The array*/public String[] getSetablePropertyNames() {return writablePropertyNames;}/*** Check to see if a class has a writable property by name.** @param propertyName - the name of the property to check* @return True if the object has a writable property by the name*/public boolean hasSetter(String propertyName) {return setMethods.containsKey(propertyName);}/*** Check to see if a class has a readable property by name.** @param propertyName - the name of the property to check* @return True if the object has a readable property by the name*/public boolean hasGetter(String propertyName) {return getMethods.containsKey(propertyName);}public String findPropertyName(String name) {return caseInsensitivePropertyMap.get(name.toUpperCase(Locale.ENGLISH));}
}

7、总结

MyBatis的MetaObject反射工具类，可以说是MyBatis的底层类，几乎不与MyBatis有耦合，如果项目中也需要这样一个工具类，可以“拿来即用”，或者稍加修改就可以拿来使用。非常强大。

（图片来自于鲁班大叔）

三、MetaObject的getValue源码分析

我们以这样一个表达式为例，进行源码分析：

// 获取对象中users的第一个元素中的child属性中的name属性
metaObject.getValue("users[0].child.name");

MetaObject的getValue核心源码：

// org.apache.ibatis.reflection.MetaObject#getValue
public Object getValue(String name) {// 创建属性分词器，将users[0].child.name，创建一个name=users;indexedName=users[0];index=0;children=child.name的分词器PropertyTokenizer prop = new PropertyTokenizer(name); if (prop.hasNext()) { // 是否有下一个子节点MetaObject metaValue = metaObjectForProperty(prop.getIndexedName());// 继续构造一个MetaObject，对象是users[0]if (metaValue == SystemMetaObject.NULL_META_OBJECT) { // 如果是null，直接返回return null;} else { // 如果不是null，就递归调用getValue方法，直到查找到最后一个属性return metaValue.getValue(prop.getChildren()); }} else { // 如果没有子节点，通过反射调用get方法获取属性return objectWrapper.get(prop);}
}

写在后面

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