於一次JSON格式錯誤 之 手把手帶你走一波FastJSON將對象轉成JSON字符串流程
1、前言
最近老大說要新增一個試用廣告的功能，我巴拉巴拉的從以前推送廣告那裏將代碼cv過來，而後跟老大說搞定了！過一會老大說返回的json格式不對！因而乎我瞧了瞧：java
{
"adsArea1":{
"adsMaterials":[
{
"animType":"99",
"materialName":"b6d767d2f8ed5d21a44b0e5886680cb9.jpg",
"materialType":"0",
"materialUrl":"http://xxx/059492d7-66f1-4052-891a-c512f957342d22.jpg",
"playTime":5,
"sort":1
}],
"areaDirection":"",
"areaId":"3721",
"areaType":"0",
"createBy":"",// 空值
"createDate":"",// 空值
"deleteFlg":"",// 空值
"height":800,
"id":"418",
"materialList":"",// 空值
"playSettingList":"",// 空值
"updateBy":"",
"updateDate":"",// 空值
"width":1280,
"x":0,
"y":0},
···
}
咋看一下，感受沒什麼問題啊？而後他說以前返給個人格式不是這樣的，沒有這些中間的這些空值，那好吧，我看了下以往的推送歷史記錄裏，確實是沒有的，那返回的是同樣的對象怎麼就沒有了呢？
仔細看了下，在推送的時候，保存在推送歷史表裏的記錄是轉成json字符串存儲起來的 String json = JSON.toJSONString（pushAdvertisementDto）;
而存在表裏的數據則沒有null值。而我如今直接返回的是對象。
那麼問題就出在這裏了~json
2、直擊源碼
點進去JSON.class裏面進去看toJSONString（pushAdvertisementDto）方法 發現能夠帶上一些參數：app
讓咱們來看看SerializerFeature是一個什麼東西吧：this
在網上搜索了一下名詞解釋：spa
就是這個東西默認是false的，默認不輸出null值的字段，若是想攜帶該字段，那麼用這個方法就能夠了：
JSON.toJSONString(Object object, SerializerFeature.WriteMapNullValue).net
問題到這裏就已經知道是爲何了，返回的數據沒有通過FastJSON轉換，由於用的是@RestController，我默認返回的對象傳回去安卓那裏也是json格式，可是裏面的字段不對，由於業務緣由就只定義了一個 PushAdvertisementDto對象返回，因此在這裏用FastJSON轉一下再返回就能夠了。3d
咱們接着往下看：
JSON.toJSONString()本質仍是調的這個方法：code
public static String toJSONString(Object object, int defaultFeatures, SerializerFeature... features) {
SerializeWriter out = new SerializeWriter((Writer)null, defaultFeatures, features); // 1
String var5;
try {
JSONSerializer serializer = new JSONSerializer(out);
serializer.write(object);// 2
var5 = out.toString();
} finally {
out.close();
}
return var5;
}
1.若是咱們要輸出爲null值的字段，則SerializerFeature.WriteMapNullValue會被傳到SerializerWriter這裏作了一個初始化：orm
public SerializeWriter(Writer writer, int defaultFeatures, SerializerFeature... features) {
this.writer = writer;
this.buf = (char[])bufLocal.get();
if (this.buf != null) {
bufLocal.set((Object)null);
} else {
this.buf = new char[2048];
}
int featuresValue = defaultFeatures;
SerializerFeature[] var5 = features;
int var6 = features.length;
for(int var7 = 0; var7 < var6; ++var7) {
SerializerFeature feature = var5[var7];
featuresValue |= feature.getMask();
}
this.features = featuresValue;
this.computeFeatures();
}
2.讓咱們跟進來serializer.write(object); 裏面看一看：對象
public final void write(Object object) {
if (object == null) {
this.out.writeNull();
} else {
Class<?> clazz = object.getClass();
ObjectSerializer writer = this.getObjectWriter(clazz);
try {
writer.write(this, object, (Object)null, (Type)null, 0);// 在這裏作了寫的操做
} catch (IOException var5) {
throw new JSONException(var5.getMessage(), var5);
}
}
}
跟進去writer.write(this, object, (Object)null, (Type)null, 0);
public interface ObjectSerializer {
void write(JSONSerializer var1, Object var2, Object var3, Type var4, int var5) throws IOException;
}
發現是個可拓展的接口，讓咱們看看ObjectSerializer具體的實現類JavaBeanSerializer，這裏代碼比較長，雖然重點關注的代碼比較少，可是仍是完整的貼出來：
public void write(JSONSerializer serializer, Object object, Object fieldName, Type fieldType, int features) throws IOException {
SerializeWriter out = serializer.out;
if (object == null) {
out.writeNull();
} else if (!this.writeReference(serializer, object, features)) {
FieldSerializer[] getters;
if (out.sortField) {
getters = this.sortedGetters;
} else {
getters = this.getters;
}
SerialContext parent = serializer.context;
serializer.setContext(parent, object, fieldName, this.beanInfo.features, features);
boolean writeAsArray = this.isWriteAsArray(serializer, features);
try {
char startSeperator = writeAsArray ? 91 : 123;
char endSeperator = writeAsArray ? 93 : 125;
out.append((char)startSeperator);// 這裏開始拼接輸出
if (getters.length > 0 && out.isEnabled(SerializerFeature.PrettyFormat)) {
serializer.incrementIndent();
serializer.println();
}
boolean commaFlag = false;
if ((this.beanInfo.features & SerializerFeature.WriteClassName.mask) != 0 || serializer.isWriteClassName(fieldType, object)) {
Class<?> objClass = object.getClass();
if (objClass != fieldType) {
this.writeClassName(serializer, object);
commaFlag = true;
}
}
char seperator = commaFlag ? 44 : 0;
boolean directWritePrefix = out.quoteFieldNames && !out.useSingleQuotes;
char newSeperator = this.writeBefore(serializer, object, (char)seperator);
commaFlag = newSeperator == ',';
boolean skipTransient = out.isEnabled(SerializerFeature.SkipTransientField);
boolean ignoreNonFieldGetter = out.isEnabled(SerializerFeature.IgnoreNonFieldGetter);
for(int i = 0; i < getters.length; ++i) {
FieldSerializer fieldSerializer = getters[i];
Field field = fieldSerializer.fieldInfo.field;
FieldInfo fieldInfo = fieldSerializer.fieldInfo;
String fieldInfoName = fieldInfo.name;
Class<?> fieldClass = fieldInfo.fieldClass;
if ((!skipTransient || field == null || !fieldInfo.fieldTransient) && (!ignoreNonFieldGetter || field != null) && this.applyName(serializer, object, fieldInfo.name) && this.applyLabel(serializer, fieldInfo.label)) {
Object propertyValue;
try {
propertyValue = fieldSerializer.getPropertyValue(object);
} catch (InvocationTargetException var32) {
if (!out.isEnabled(SerializerFeature.IgnoreErrorGetter)) {
throw var32;
}
propertyValue = null;
}
if (this.apply(serializer, object, fieldInfoName, propertyValue)) {
String key = this.processKey(serializer, object, fieldInfoName, propertyValue);
Object originalValue = propertyValue;
propertyValue = this.processValue(serializer, fieldSerializer.fieldContext, object, fieldInfoName, propertyValue);
if (propertyValue != null || writeAsArray || fieldSerializer.writeNull || out.isEnabled(SerializerFeature.WriteMapNullValue)) {
if (propertyValue != null && out.notWriteDefaultValue) {
Class<?> fieldCLass = fieldInfo.fieldClass;
if (fieldCLass == Byte.TYPE && propertyValue instanceof Byte && (Byte)propertyValue == 0 || fieldCLass == Short.TYPE && propertyValue instanceof Short && (Short)propertyValue == 0 || fieldCLass == Integer.TYPE && propertyValue instanceof Integer && (Integer)propertyValue == 0 || fieldCLass == Long.TYPE && propertyValue instanceof Long && (Long)propertyValue == 0L || fieldCLass == Float.TYPE && propertyValue instanceof Float && (Float)propertyValue == 0.0F || fieldCLass == Double.TYPE && propertyValue instanceof Double && (Double)propertyValue == 0.0D || fieldCLass == Boolean.TYPE && propertyValue instanceof Boolean && !(Boolean)propertyValue) {
continue;
}
}
if (commaFlag) {
out.write(44);
if (out.isEnabled(SerializerFeature.PrettyFormat)) {
serializer.println();
}
}
if (key != fieldInfoName) {
if (!writeAsArray) {
out.writeFieldName(key, true);
}
serializer.write(propertyValue);
} else if (originalValue != propertyValue) {
if (!writeAsArray) {
fieldSerializer.writePrefix(serializer);
}
serializer.write(propertyValue);
} else {
if (!writeAsArray) {
if (directWritePrefix) {
out.write(fieldInfo.name_chars, 0, fieldInfo.name_chars.length);
} else {
fieldSerializer.writePrefix(serializer);
}
}
if (!writeAsArray) {
if (fieldClass == String.class) {
if (propertyValue == null) {
if ((out.features & SerializerFeature.WriteNullStringAsEmpty.mask) == 0 && (fieldSerializer.features & SerializerFeature.WriteNullStringAsEmpty.mask) == 0) {
out.writeNull();
} else {
out.writeString("");
}
} else {
String propertyValueString = (String)propertyValue;
if (out.useSingleQuotes) {
out.writeStringWithSingleQuote(propertyValueString);
} else {
out.writeStringWithDoubleQuote(propertyValueString, '\u0000');
}
}
} else {
fieldSerializer.writeValue(serializer, propertyValue);
}
} else {
fieldSerializer.writeValue(serializer, propertyValue);
}
}
commaFlag = true;
}
}
}
}
this.writeAfter(serializer, object, (char)(commaFlag ? ',' : '\u0000'));
if (getters.length > 0 && out.isEnabled(SerializerFeature.PrettyFormat)) {
serializer.decrementIdent();
serializer.println();
}
out.append((char)endSeperator); // 結束拼接
} catch (Exception var33) {
String errorMessage = "write javaBean error";
if (object != null) {
errorMessage = errorMessage + ", class " + object.getClass().getName();
}
if (fieldName != null) {
errorMessage = errorMessage + ", fieldName : " + fieldName;
}
if (var33.getMessage() != null) {
errorMessage = errorMessage + ", " + var33.getMessage();
}
throw new JSONException(errorMessage, var33);
} finally {
serializer.context = parent;
}
}
}
咱們挑重點的看，這裏咱們關注out.append( )代碼就能夠了，中間大體就是判斷一些前文說的SerializerFeature.WriteMapNullValue等條件。
跟進去out.append( )方法，在最後調用wirte方法將值付給this.buf 和this.count：
public void write(int c) {
int newcount = this.count + 1;
if (newcount > this.buf.length) {
if (this.writer == null) {
this.expandCapacity(newcount);
} else {
this.flush();
newcount = 1;
}
}
this.buf[this.count] = (char)c;
this.count = newcount;
}
再回到前面的var5 = out.toString( );SerializeWriter重寫toString方法最後返回轉換好的json字符串。到這裏整個json轉換流程就已經結束了。
3、結語
雖然只是一開始只是json格式的一個小問題，花了挺長的時間觀看源碼，可是感受收穫仍是很大的，也很值。由於我的水平緣由也不是全能看懂。。中間很長的那段源碼大體就是用反射獲取要轉成json的對象的屬性和值，而後中間通過一些條件判斷，經過輸出流拼接字符輸出字符串。
如文中有不對的地方，歡迎指出一塊兒討論 ~
關於SerializerFeature名詞解釋源自：https://blog.csdn.net/u010246...
相關文章
- 1. Json將對象轉換成字符串
- 2. 字符串，對象轉json格式
- 3. JSON字符串轉換成JSON對象
- 4. fastjson將json格式字符串轉成list集合
- 5. C#對象轉JSON字符串和JSON字符串轉對象
- 6. json對象轉字符串與json字符串轉對象
- 7. json 字符串轉換成對象,對象轉換成json字符串
- 8. 獲取JSON格式的字符串各個屬性對應的值 FastJson對於JSON格式字符串、JSON對象及JavaBean之間的相互轉換
- 9. json字符串，json對象
- 10. 將對象轉換爲JSON字符串
- 更多相關文章...
- • PHP JSON - PHP教程
- • Thymeleaf字符串轉義 - Thymeleaf 教程
- • RxJava操作符（一）Creating Observables
- • 再有人問你分佈式事務，把這篇扔給他
相關標籤/搜索
每日一句
-
每一个你不满意的现在，都有一个你没有努力的曾经。
歡迎關注本站公眾號,獲取更多信息
