Mybatis框架基础支持层——反射工具箱之Reflector&ReflectorFactory（3）
说明：Reflector是Mybatis反射工具的基础，每个Reflector对应一个类，在Reflector中封装有该类的元信息，
以及基于类信息的一系列反射应用封装API
public class Reflector { private static final String[] EMPTY_STRING_ARRAY = new String[0]; /** * 对应的类Class对象 */ private Class<?> type; /** * 类中可读属性的集合，就是存在相应的getter方法的属性 */ private String[] readablePropertyNames = EMPTY_STRING_ARRAY; /** * 类中可写属性的集合，就是存在相应的setter方法的属性 */ private String[] writeablePropertyNames = EMPTY_STRING_ARRAY; /** * 记录了属性相应的setter方法，key是属性名称，value是invoker对象， * invoker是对setter方法对应Method对象的封装 */ private Map<String, Invoker> setMethods = new HashMap<String, Invoker>(); /** * 记录了属性相应的getter方法，key是属性名称，value是invoker对象， * invoker是对getter方法对应Method对象的封装 */ private Map<String, Invoker> getMethods = new HashMap<String, Invoker>(); /** * 记录了属性相应的setter方法的参数值类型，key是属性名称，value是setter方法的参数值类型 */ private Map<String, Class<?>> setTypes = new HashMap<String, Class<?>>(); /** * 记录了属性相应的getter方法的返回值类型，key是属性名称，value是getter方法的返回值类型 */ private Map<String, Class<?>> getTypes = new HashMap<String, Class<?>>(); /** * 记录了默认构造方法 */ private Constructor<?> defaultConstructor; /** * 记录了所有属性名称的集合 */ private Map<String, String> caseInsensitivePropertyMap = new HashMap<String, String>(); /** * 在Reflector构造方法中会指定某个类的Class对象，并填充上述集合 */ public Reflector(Class<?> clazz) { type = clazz; /** * 查找clazz的默认构造方法（无参构造） */ addDefaultConstructor(clazz); /** * 处理clazz中的getter方法，填充getMethods集合和getTypes集合 */ addGetMethods(clazz); /** * 处理clazz中的setter方法，填充setMethods集合和setTypes集合 */ addSetMethods(clazz); /** * 处理没有getter/setter方法的字段 */ addFields(clazz); /** * 根据getMethods、setMethods集合，初始化可读/写属性名称的集合 */ readablePropertyNames = getMethods.keySet().toArray(new String[getMethods.keySet().size()]); writeablePropertyNames = setMethods.keySet().toArray(new String[setMethods.keySet().size()]); /** * 初始化caseInsensitivePropertyMap，其中记录了所有大写格式的属性名称 */ for (String propName : readablePropertyNames) { caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName); } for (String propName : writeablePropertyNames) { caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName); } } private void addDefaultConstructor(Class<?> clazz) { /** * 返回类中声明的所有构造函数Constructor，包括public、protected、default、private声明 * 如果Class对象是一个接口、抽象类、数组类或void，则返回length=0的Constructor数组 */ Constructor<?>[] consts = clazz.getDeclaredConstructors(); for (Constructor<?> constructor : consts) { if (constructor.getParameterTypes().length == 0) { if (canAccessPrivateMethods()) { try { constructor.setAccessible(true); } catch (Exception e) { // Ignored. This is only a final precaution, nothing we can do. } } if (constructor.isAccessible()) { this.defaultConstructor = constructor; } } } } private void addGetMethods(Class<?> cls) { Map<String, List<Method>> conflictingGetters = new HashMap<String, List<Method>>(); /** * 获取当前类中所有的方法，包括自己、父类、父类的父类...,接口等 */ Method[] methods = getClassMethods(cls); for (Method method : methods) { String name = method.getName(); if (name.startsWith("get") && name.length() > 3) { if (method.getParameterTypes().length == 0) { /** * PropertyNamer： * setter、getter方法名=>属性名称转换,和属性getter、setter方法判断 */ name = PropertyNamer.methodToProperty(name); addMethodConflict(conflictingGetters, name, method); } } else if (name.startsWith("is") && name.length() > 2) { if (method.getParameterTypes().length == 0) { name = PropertyNamer.methodToProperty(name); addMethodConflict(conflictingGetters, name, method); } } } //填充getMethods和getTypes集合 resolveGetterConflicts(conflictingGetters); } private void resolveGetterConflicts(Map<String, List<Method>> conflictingGetters) { for (String propName : conflictingGetters.keySet()) { List<Method> getters = conflictingGetters.get(propName); Iterator<Method> iterator = getters.iterator(); Method firstMethod = iterator.next(); if (getters.size() == 1) { addGetMethod(propName, firstMethod); } else { Method getter = firstMethod; Class<?> getterType = firstMethod.getReturnType(); while (iterator.hasNext()) { Method method = iterator.next(); Class<?> methodType = method.getReturnType(); if (methodType.equals(getterType)) { throw new ReflectionException("Illegal overloaded getter method with ambiguous type for property " + propName + " in class " + firstMethod.getDeclaringClass() + ". This breaks the JavaBeans " + "specification and can cause unpredictable results."); } else if (methodType.isAssignableFrom(getterType)) { // OK getter type is descendant } else if (getterType.isAssignableFrom(methodType)) { getter = method; getterType = methodType; } else { throw new ReflectionException("Illegal overloaded getter method with ambiguous type for property " + propName + " in class " + firstMethod.getDeclaringClass() + ". This breaks the JavaBeans " + "specification and can cause unpredictable results."); } } addGetMethod(propName, getter); } } } private void addGetMethod(String name, Method method) { if (isValidPropertyName(name)) { getMethods.put(name, new MethodInvoker(method)); Type returnType = TypeParameterResolver.resolveReturnType(method, type); getTypes.put(name, typeToClass(returnType)); } } private void addSetMethods(Class<?> cls) { Map<String, List<Method>> conflictingSetters = new HashMap<String, List<Method>>(); Method[] methods = getClassMethods(cls); for (Method method : methods) { String name = method.getName(); if (name.startsWith("set") && name.length() > 3) { if (method.getParameterTypes().length == 1) { name = PropertyNamer.methodToProperty(name); addMethodConflict(conflictingSetters, name, method); } } } resolveSetterConflicts(conflictingSetters); } private void addMethodConflict(Map<String, List<Method>> conflictingMethods, String name, Method method) { List<Method> list = conflictingMethods.get(name); if (list == null) { list = new ArrayList<Method>(); conflictingMethods.put(name, list); } list.add(method); } private void resolveSetterConflicts(Map<String, List<Method>> conflictingSetters) { for (String propName : conflictingSetters.keySet()) { List<Method> setters = conflictingSetters.get(propName); Class<?> getterType = getTypes.get(propName); Method match = null; ReflectionException exception = null; for (Method setter : setters) { Class<?> paramType = setter.getParameterTypes()[0]; if (paramType.equals(getterType)) { // should be the best match match = setter; break; } if (exception == null) { try { match = pickBetterSetter(match, setter, propName); } catch (ReflectionException e) { // there could still be the 'best match' match = null; exception = e; } } } if (match == null) { throw exception; } else { 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; } throw new ReflectionException("Ambiguous setters defined for property '" + property + "' in class '" + setter2.getDeclaringClass() + "' with types '" + paramType1.getName() + "' and '" + paramType2.getName() + "'."); } private void addSetMethod(String name, Method method) { if (isValidPropertyName(name)) { setMethods.put(name, new MethodInvoker(method));
// TypeParameterResolver解析类型，下一篇博文介绍 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((Class<?>) 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 (canAccessPrivateMethods()) { try { field.setAccessible(true); } catch (Exception e) { // Ignored. This is only a final precaution, nothing we can do. } } if (field.isAccessible()) { 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 classloader int modifiers = field.getModifiers(); if (!(Modifier.isFinal(modifiers) && Modifier.isStatic(modifiers))) { addSetField(field); } } if (!getMethods.containsKey(field.getName())) { addGetField(field); } } } //递归 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 Class.getMethods(), * because we want to look for private methods as well. * * @param cls The class * @return An array containing all methods in this class */ private Method[] getClassMethods(Class<?> cls) { //key是方法签名（唯一标识，下文生成），value是Method对象 Map<String, Method> uniqueMethods = new HashMap<String, Method>(); Class<?> currentClass = cls; while (currentClass != null) { /** * currentClass.getDeclaredMethods()返回当前类或接口中所有被声明的方法，包括 * public、protected、default、private，但是排除集成的方法 * * 此方法是将当前类中非桥接（下文有介绍）方法填入uniqueMethods集合 */ addUniqueMethods(uniqueMethods, currentClass.getDeclaredMethods()); // we also need to look for interface methods - // because the class may be abstract Class<?>[] interfaces = currentClass.getInterfaces(); for (Class<?> anInterface : interfaces) { addUniqueMethods(uniqueMethods, anInterface.getMethods()); } /** * Returns the {@code Class} representing the superclass of the entity * (class, interface, primitive type or void) represented by this * {@code Class}. If this {@code Class} represents either the * {@code Object} class, an interface, a primitive type, or void, then * null is returned. If this object represents an array class then the * {@code Class} object representing the {@code Object} class is * returned */ currentClass = currentClass.getSuperclass(); } Collection<Method> methods = uniqueMethods.values(); return methods.toArray(new Method[methods.size()]); } private void addUniqueMethods(Map<String, Method> uniqueMethods, Method[] methods) { for (Method currentMethod : methods) { /** * 桥接方法是 JDK 1.5 引入泛型后，为了使Java的泛型方法生成的字节码和 1.5 版本前的字节码相兼容， * 由编译器自动生成的方法。我们可以通过Method.isBridge()方法来判断一个方法是否是桥接方法。 */ if (!currentMethod.isBridge()) { //获取当前方法的签名 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 method if (!uniqueMethods.containsKey(signature)) { if (canAccessPrivateMethods()) { try { currentMethod.setAccessible(true); } catch (Exception e) { // Ignored. This is only a final precaution, nothing we can do. } } uniqueMethods.put(signature, currentMethod); } } } } /** * 获取一个方法的签名，根据方法的返回值、方法、方法参数构建一个签名 */ 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++) { if (i == 0) { sb.append(':'); } else { sb.append(','); } sb.append(parameters[i].getName()); } return sb.toString(); } private static boolean canAccessPrivateMethods() { try { //java安全管理器具体细节，可看博客中另一篇介绍 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 propery 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 propery 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 writeable properties for an object * * @return The array */ public String[] getSetablePropertyNames() { return writeablePropertyNames; } /* * Check to see if a class has a writeable property by name * * @param propertyName - the name of the property to check * @return True if the object has a writeable property by the name */ public boolean hasSetter(String propertyName) { return setMethods.keySet().contains(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.keySet().contains(propertyName); } public String findPropertyName(String name) { return caseInsensitivePropertyMap.get(name.toUpperCase(Locale.ENGLISH)); } }
ReflectorFactory接口主要实现了对Reflector对象的创建和缓存，Mybatis为该接口提供了仅有的一个实现类DefaultReflectorFactory：
public interface ReflectorFactory { /** * 检测ReflectorFactory对象是否启用缓存Reflector功能 */ boolean isClassCacheEnabled(); /** * 设置ReflectorFactory对象是否启用缓存Reflector功能 */ void setClassCacheEnabled(boolean classCacheEnabled); /** * 创建指定Class对象对应的Reflector，如果缓存有，就从缓存取，否则新建一个 */ Reflector findForClass(Class<?> type); }
public class DefaultReflectorFactory implements ReflectorFactory { /** * 默认启用缓存Reflector的功能 */ private boolean classCacheEnabled = true; /** * 缓存Reflector的数据结构，key[Class对象]，value[Class对应的Reflector对象] */ private final ConcurrentMap<Class<?>, Reflector> reflectorMap = new ConcurrentHashMap<Class<?>, Reflector>(); public DefaultReflectorFactory() { } @Override public boolean isClassCacheEnabled() { return classCacheEnabled; } @Override public void setClassCacheEnabled(boolean classCacheEnabled) { this.classCacheEnabled = classCacheEnabled; } @Override public Reflector findForClass(Class<?> type) { if (classCacheEnabled) { // synchronized (type) removed see issue #461 Reflector cached = reflectorMap.get(type); if (cached == null) { cached = new Reflector(type); reflectorMap.put(type, cached); } return cached; } else { return new Reflector(type); } } }
