功能概述

• PojoUtils是一個(gè)工具類，能夠進(jìn)行深度遍歷，將簡單類型與復(fù)雜類型的對象進(jìn)行轉(zhuǎn)換，在泛化調(diào)用時(shí)用到（在泛化調(diào)用中，主要將Pojo對象與Map對象進(jìn)行相互轉(zhuǎn)換）

功能分析

核心類PojoUtils分析

主要成員變量分析

private static final ConcurrentMap<String, Method> NAME_METHODS_CACHE = new ConcurrentHashMap<String, Method>(); //方法名與Method的緩存（為了減少反射獲取Method調(diào)用），key的值用類名和參數(shù)類型拼接，如："org.apache.dubbo.common.model.Person.setName(java.lang.String)"
private static final ConcurrentMap<Class<?>, ConcurrentMap<String, Field>> CLASS_FIELD_CACHE = new ConcurrentHashMap<Class<?>, ConcurrentMap<String, Field>>(); //字段所在類Class、字段名、字段信息Filed的緩存

主要成員方法分析

generalize將復(fù)雜對象轉(zhuǎn)換為簡單對象

private static Object generalize(Object pojo, Map<Object, Object> history) { //pojo對象的成員屬性（會遞歸轉(zhuǎn)換，pojo=》Map，直到所有屬性為dubbo定義的基本類型）if (pojo == null) {return null;}if (pojo instanceof Enum<?>) {return ((Enum<?>) pojo).name(); //枚舉類型，輸出枚舉的名稱}if (pojo.getClass().isArray() && Enum.class.isAssignableFrom(pojo.getClass().getComponentType())) { //處理Enum數(shù)組int len = Array.getLength(pojo);String[] values = new String[len];for (int i = 0; i < len; i++) { //枚舉數(shù)組會轉(zhuǎn)換為String數(shù)組，數(shù)組元素的值為枚舉名values[i] = ((Enum<?>) Array.get(pojo, i)).name();}return values;}if (ReflectUtils.isPrimitives(pojo.getClass())) { //基本類型直接返回，不做處理return pojo;}if (pojo instanceof Class) { //Class類的實(shí)例，返回類名稱return ((Class) pojo).getName();}Object o = history.get(pojo);if (o != null) {return o;}history.put(pojo, pojo);if (pojo.getClass().isArray()) { //pojo對象為數(shù)組類型int len = Array.getLength(pojo);Object[] dest = new Object[len];history.put(pojo, dest);for (int i = 0; i < len; i++) {Object obj = Array.get(pojo, i);dest[i] = generalize(obj, history);}return dest;}if (pojo instanceof Collection<?>) { //pojo對象為集合類型Collection<Object> src = (Collection<Object>) pojo;int len = src.size();Collection<Object> dest = (pojo instanceof List<?>) ? new ArrayList<Object>(len) : new HashSet<Object>(len); //區(qū)分出List或Set類型，并創(chuàng)建對應(yīng)的集合實(shí)例history.put(pojo, dest);for (Object obj : src) { //遍歷集合元素，依次將元素進(jìn)行轉(zhuǎn)換dest.add(generalize(obj, history));}return dest;}if (pojo instanceof Map<?, ?>) { //pojo對象為Map類型Map<Object, Object> src = (Map<Object, Object>) pojo;Map<Object, Object> dest = createMap(src); //根據(jù)原Map類型，創(chuàng)建對應(yīng)的Map對象history.put(pojo, dest);for (Map.Entry<Object, Object> obj : src.entrySet()) {dest.put(generalize(obj.getKey(), history), generalize(obj.getValue(), history)); //key、value都可能是pojo對象，所以都需要進(jìn)行轉(zhuǎn)換}return dest;}Map<String, Object> map = new HashMap<String, Object>();history.put(pojo, map);if (GENERIC_WITH_CLZ) {map.put("class", pojo.getClass().getName()); //設(shè)置pojo對象的Class類}for (Method method : pojo.getClass().getMethods()) {if (ReflectUtils.isBeanPropertyReadMethod(method)) { //判斷是否讀取bean的方法（即get/is方法）try {/*** 處理步驟：* 1）從方法名中獲取到屬性名* 2）調(diào)用pojo對應(yīng)的方法獲取值，并通過generalize轉(zhuǎn)換（傳入history是做臨時(shí)緩存，若能從history取到則用之）* 3）將屬性名和值設(shè)置到map中*/map.put(ReflectUtils.getPropertyNameFromBeanReadMethod(method), generalize(method.invoke(pojo), history));} catch (Exception e) {throw new RuntimeException(e.getMessage(), e);}}}// public fieldfor (Field field : pojo.getClass().getFields()) {if (ReflectUtils.isPublicInstanceField(field)) { //判斷是否是公共的實(shí)例字段try {Object fieldValue = field.get(pojo);if (history.containsKey(pojo)) {Object pojoGeneralizedValue = history.get(pojo); //已經(jīng)轉(zhuǎn)換過的字段，就不再轉(zhuǎn)換if (pojoGeneralizedValue instanceof Map&& ((Map) pojoGeneralizedValue).containsKey(field.getName())) {continue;}}if (fieldValue != null) {map.put(field.getName(), generalize(fieldValue, history));}} catch (Exception e) {throw new RuntimeException(e.getMessage(), e);}}}return map;
}

• 代碼分析：generalize方法的作用是把復(fù)雜類型對象轉(zhuǎn)換為簡單類型的對象，如將Pojo對象轉(zhuǎn)換為Map對象，Pojo對象的成員對象若還是復(fù)雜類型，會遞歸調(diào)用進(jìn)行轉(zhuǎn)換。

realize將簡單對象轉(zhuǎn)換為復(fù)雜對象

private static Object realize0(Object pojo, Class<?> type, Type genericType, final Map<Object, Object> history) { //將簡單類型轉(zhuǎn)換為復(fù)雜類型（如：將Map對象轉(zhuǎn)換為指定類型的pojo對象，將Map的屬性值，通過set方法設(shè)置到pojo對象中，type為目標(biāo)類型）if (pojo == null) {return null;}if (type != null && type.isEnum() && pojo.getClass() == String.class) { //將String轉(zhuǎn)換為枚舉類型return Enum.valueOf((Class<Enum>) type, (String) pojo);}if (ReflectUtils.isPrimitives(pojo.getClass())&& !(type != null && type.isArray()&& type.getComponentType().isEnum()&& pojo.getClass() == String[].class)) { //將String數(shù)組轉(zhuǎn)換為枚舉數(shù)組return CompatibleTypeUtils.compatibleTypeConvert(pojo, type);}Object o = history.get(pojo); //history：當(dāng)方法在遞歸調(diào)用時(shí)，會用到（用緩存使用）if (o != null) {return o;}history.put(pojo, pojo);if (pojo.getClass().isArray()) { //處理數(shù)組類型的pojoif (Collection.class.isAssignableFrom(type)) { //目標(biāo)類型是集合類型Class<?> ctype = pojo.getClass().getComponentType(); //獲取數(shù)組元素的類型int len = Array.getLength(pojo); //獲取數(shù)組對應(yīng)長度Collection dest = createCollection(type, len);history.put(pojo, dest);for (int i = 0; i < len; i++) {Object obj = Array.get(pojo, i); //返回?cái)?shù)組中指定下標(biāo)的值Object value = realize0(obj, ctype, null, history); //依次將對象轉(zhuǎn)換為目標(biāo)類型，如Map轉(zhuǎn)換為pojo類型dest.add(value);}return dest;} else {Class<?> ctype = (type != null && type.isArray() ? type.getComponentType() : pojo.getClass().getComponentType());int len = Array.getLength(pojo);Object dest = Array.newInstance(ctype, len);history.put(pojo, dest);for (int i = 0; i < len; i++) {Object obj = Array.get(pojo, i);Object value = realize0(obj, ctype, null, history);Array.set(dest, i, value);}return dest;}}if (pojo instanceof Collection<?>) { //處理集合類型的pojoif (type.isArray()) { //集合轉(zhuǎn)換為數(shù)組Class<?> ctype = type.getComponentType();Collection<Object> src = (Collection<Object>) pojo;int len = src.size();Object dest = Array.newInstance(ctype, len); //創(chuàng)建指定類型和長度的數(shù)組history.put(pojo, dest);int i = 0;for (Object obj : src) {Object value = realize0(obj, ctype, null, history); //將數(shù)組中的元素依次轉(zhuǎn)換為指定類型pojo對象Array.set(dest, i, value);i++;}return dest;} else {Collection<Object> src = (Collection<Object>) pojo;int len = src.size();Collection<Object> dest = createCollection(type, len);history.put(pojo, dest);for (Object obj : src) { //遍歷集合元素，依次轉(zhuǎn)化到目標(biāo)類型的pojo對象Type keyType = getGenericClassByIndex(genericType, 0);Class<?> keyClazz = obj == null ? null : obj.getClass();if (keyType instanceof Class) {keyClazz = (Class<?>) keyType;}Object value = realize0(obj, keyClazz, keyType, history);dest.add(value);}return dest;}}if (pojo instanceof Map<?, ?> && type != null) { //處理Map類型的pojo（JSONObject：JSON對象，實(shí)現(xiàn)了Map接口，也屬于Map的實(shí)例對象，所以會進(jìn)入此處）Object className = ((Map<Object, Object>) pojo).get("class"); //獲取Map中的"class"鍵對應(yīng)的值，是在generalize方法中設(shè)置的（單個(gè)的pojo中設(shè)置的）if (className instanceof String) {try {type = ClassUtils.forName((String) className); //解析的目標(biāo)類的Class類} catch (ClassNotFoundException e) {// ignore}}// special logic for enumif (type.isEnum()) { //目標(biāo)類型為枚舉Object name = ((Map<Object, Object>) pojo).get("name"); //取出枚舉名稱if (name != null) {return Enum.valueOf((Class<Enum>) type, name.toString()); //使用枚舉名，構(gòu)建枚舉對象}}Map<Object, Object> map;// when return type is not the subclass of return type from the signature and not an interfaceif (!type.isInterface() && !type.isAssignableFrom(pojo.getClass())) { //type非接口且pojo不是type的子類型try {map = (Map<Object, Object>) type.newInstance();Map<Object, Object> mapPojo = (Map<Object, Object>) pojo;map.putAll(mapPojo);if (GENERIC_WITH_CLZ) {map.remove("class");}} catch (Exception e) {//ignore errormap = (Map<Object, Object>) pojo; //type類型不為Map時(shí)，使用原始的pojo轉(zhuǎn)換}} else {map = (Map<Object, Object>) pojo; //直接強(qiáng)轉(zhuǎn)為Map類型}if (Map.class.isAssignableFrom(type) || type == Object.class) { //解析的目標(biāo)類為Map時(shí)final Map<Object, Object> result;// fix issue#5939Type mapKeyType = getKeyTypeForMap(map.getClass()); //獲取key的泛型參數(shù)對應(yīng)的實(shí)際類型Type typeKeyType = getGenericClassByIndex(genericType, 0); //獲取目標(biāo)類型的泛型參數(shù)的第一個(gè)實(shí)際參數(shù)boolean typeMismatch = mapKeyType instanceof Class //Type為Class實(shí)例時(shí)，表明是基本類型或原始類型，如String、int等&& typeKeyType instanceof Class&& !typeKeyType.getTypeName().equals(mapKeyType.getTypeName()); //判斷key、value類型為基本類型或原始類型，且類型相同if (typeMismatch) { //輸入對象的key與目標(biāo)Map的key類型不匹配是，創(chuàng)建新的Mapresult = createMap(new HashMap(0));} else {result = createMap(map); //類型匹配時(shí)，直接使用目標(biāo)Map（會轉(zhuǎn)換為具體的Map類型，如：轉(zhuǎn)換為LinkedHashMap類型）}history.put(pojo, result);for (Map.Entry<Object, Object> entry : map.entrySet()) {Type keyType = getGenericClassByIndex(genericType, 0); //獲取泛型參數(shù)列表指定位置的實(shí)際類型Type valueType = getGenericClassByIndex(genericType, 1);Class<?> keyClazz; //獲取key參數(shù)類型對應(yīng)的Classif (keyType instanceof Class) { //基本類型或原始類型（如：int、Boolean、String等）keyClazz = (Class<?>) keyType;} else if (keyType instanceof ParameterizedType) { //參數(shù)化類型（如：List<ArrayList<String>> 是泛型參數(shù)，取實(shí)際類型后為ArrayList<String>，實(shí)際參數(shù)屬于參數(shù)類型）keyClazz = (Class<?>) ((ParameterizedType) keyType).getRawType();} else { //keyType為Null時(shí)，取條目中key的類型（其它類型，如類型變量類型T、通配符類型?等）keyClazz = entry.getKey() == null ? null : entry.getKey().getClass();}Class<?> valueClazz; //獲取value參數(shù)類型對應(yīng)的Classif (valueType instanceof Class) {valueClazz = (Class<?>) valueType;} else if (valueType instanceof ParameterizedType) {valueClazz = (Class<?>) ((ParameterizedType) valueType).getRawType();} else {valueClazz = entry.getValue() == null ? null : entry.getValue().getClass();}Object key = keyClazz == null ? entry.getKey() : realize0(entry.getKey(), keyClazz, keyType, history); //遞歸調(diào)用，將key轉(zhuǎn)換為目標(biāo)類型的對象Object value = valueClazz == null ? entry.getValue() : realize0(entry.getValue(), valueClazz, valueType, history); //遞歸調(diào)用，將value轉(zhuǎn)換為目標(biāo)類型的對象result.put(key, value);}return result;} else if (type.isInterface()) { //解析的目標(biāo)類為接口時(shí)，產(chǎn)生接口對應(yīng)的代理類Object dest = Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(), new Class<?>[] {type}, new PojoInvocationHandler(map)); //使用jdk代理機(jī)制為接口創(chuàng)代理對象，并指定處理器PojoInvocationHandler，在接口方法被調(diào)用時(shí)，就會觸發(fā)處理器中方法執(zhí)行指定邏輯history.put(pojo, dest);return dest;} else {Object dest = newInstance(type); //構(gòu)造解析的目標(biāo)類的實(shí)例history.put(pojo, dest); //設(shè)置到緩存Map中for (Map.Entry<Object, Object> entry : map.entrySet()) { //遍歷Map中的條目，找到對應(yīng)目標(biāo)對象的屬性，使用反射機(jī)制調(diào)用Method，依次設(shè)置值Object key = entry.getKey();if (key instanceof String) { //只處理key為String的條目String name = (String) key;Object value = entry.getValue();if (value != null) {Method method = getSetterMethod(dest.getClass(), name, value.getClass()); //通過屬性獲取set方法（從緩存中獲取，若沒有則通過反射獲取Method，再設(shè)置到緩存中）Field field = getField(dest.getClass(), name); //獲取屬性對應(yīng)的字段Filed信息if (method != null) {if (!method.isAccessible()) {method.setAccessible(true);}Type ptype = method.getGenericParameterTypes()[0]; //獲取set方法的第一個(gè)參數(shù)類型value = realize0(value, method.getParameterTypes()[0], ptype, history); //將值轉(zhuǎn)換為指定類型的對象try {method.invoke(dest, value); //使用反射機(jī)制，設(shè)置目標(biāo)對象的屬性值} catch (Exception e) {String exceptionDescription = "Failed to set pojo " + dest.getClass().getSimpleName() + " property " + name+ " value " + value + "(" + value.getClass() + "), cause: " + e.getMessage();logger.error(exceptionDescription, e);throw new RuntimeException(exceptionDescription, e);}} else if (field != null) {value = realize0(value, field.getType(), field.getGenericType(), history);try {field.set(dest, value);} catch (IllegalAccessException e) {throw new RuntimeException("Failed to set field " + name + " of pojo " + dest.getClass().getName() + " : " + e.getMessage(), e);}}}}}if (dest instanceof Throwable) { //目標(biāo)對象為異常對象時(shí)，設(shè)置異常信息Object message = map.get("message");if (message instanceof String) {try {Field field = Throwable.class.getDeclaredField("detailMessage");if (!field.isAccessible()) {field.setAccessible(true);}field.set(dest, message);} catch (Exception e) {}}}return dest;}}return pojo;}

關(guān)聯(lián)類PojoInvocationHandler分析

類中核心代碼分析

private static class PojoInvocationHandler implements InvocationHandler { //Pojo代理處理器private Map<Object, Object> map; //在創(chuàng)建代理對象時(shí)指定的public PojoInvocationHandler(Map<Object, Object> map) {this.map = map;}@Override@SuppressWarnings("unchecked")public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { //為接口生成代理對象，在調(diào)用接口方法時(shí)，會回調(diào)該方法if (method.getDeclaringClass() == Object.class) {return method.invoke(map, args);}String methodName = method.getName();Object value = null;if (methodName.length() > 3 && methodName.startsWith("get")) {value = map.get(methodName.substring(3, 4).toLowerCase() + methodName.substring(4)); //截取方法名，獲取屬性名，從map中獲取相應(yīng)的值} else if (methodName.length() > 2 && methodName.startsWith("is")) {value = map.get(methodName.substring(2, 3).toLowerCase() + methodName.substring(3));} else {value = map.get(methodName.substring(0, 1).toLowerCase() + methodName.substring(1));}if (value instanceof Map<?, ?> && !Map.class.isAssignableFrom(method.getReturnType())) { //返回類型非Map時(shí)，調(diào)用realize0進(jìn)行轉(zhuǎn)換value = realize0((Map<String, Object>) value, method.getReturnType(), null, new IdentityHashMap<Object, Object>());}return value;}
}

• 代碼分析：在轉(zhuǎn)換的目標(biāo)類型為接口時(shí)type.isInterface()，使用jdk動態(tài)代理創(chuàng)建接口的代理對象，PojoInvocationHandler為代理對象的調(diào)用處理器，包含了提取屬性的邏輯

問題點(diǎn)答疑

• 在realize、generalize方法中都包含了參數(shù)Map<Object, Object> history，用途是什么？
  • 解答：在Pojo屬性為復(fù)雜類型時(shí)，即需要遞歸轉(zhuǎn)換或解析時(shí)，就可以把已經(jīng)處理過的結(jié)果放入Map中，傳遞給下一個(gè)轉(zhuǎn)換或解析。下次處理前，會判斷是否已經(jīng)處理過，處理過的就不再處理。這樣已經(jīng)處理過的類型就不用處理了，提升處理性能。

歸納總結(jié)

• PojoUtils轉(zhuǎn)換中，簡單類型包含：基本類型、Number、Date、元素為基本類型的數(shù)組、集合類型等。
• 在類型轉(zhuǎn)換時(shí)，會進(jìn)行遞歸調(diào)用，一直解析到位簡單類型為止。