Parsing JSON in Java without knowing JSON format

Question

I am trying to parse JSON strings in Java and find the key-value pairs so that I can determine the approximate structure of the JSON object since object structure of JSON string is unknown   For example  one execution may have a JSON string like this       id    12345   days       Monday    Wednesday      person       firstName     David    lastName     Menoyo        And another like this       url     http   someurl com    method     POST    isauth    false     How would I cycle through the various JSON elements and determine the keys and their values  I looked at jackson-core s JsonParser  I see how I can grab the next  token  and determine what type of token it is  i e   field name  value  array start  etc   but  I don t know how to grab the actual token s value   For example   public void parse String json       try        JsonFactory f   new JsonFactory         JsonParser parser   f createParser json        JsonToken token   parser nextToken         while  token    null            if  token equals JsonToken START ARRAY                logger debug  Start Array       token toString               else if  token equals JsonToken END ARRAY                logger debug  End Array       token toString               else if  token equals JsonToken START OBJECT                logger debug  Start Object       token toString               else if  token equals JsonToken END OBJECT                logger debug  End Object       token toString               else if  token equals JsonToken FIELD NAME                logger debug  Field Name       token toString               else if  token equals JsonToken VALUE FALSE                logger debug  Value False       token toString               else if  token equals JsonToken VALUE NULL                logger debug  Value Null       token toString               else if  token equals JsonToken VALUE NUMBER FLOAT                logger debug  Value Number Float       token toString               else if  token equals JsonToken VALUE NUMBER INT               logger debug  Value Number Int       token toString               else if  token equals JsonToken VALUE STRING                logger debug  Value String       token toString               else if  token equals JsonToken VALUE TRUE                logger debug  Value True       token toString               else              logger debug  Something else       token toString                       token   parser nextToken               catch  Exception e         logger error     e           Is there a class in jackson or some other library  gson or simple-json  that produces a tree  or allows one to cycle through the json elements and obtain the actual key names in addition to the values

User · Answer

Would you be satisfied with a Map from Jackson   ObjectMapper objectMapper   new ObjectMapper    Map lt String  Object gt  map   objectMapper readValue jsonString  new TypeReference lt HashMap lt String Object gt  gt          Or maybe a JsonNode   JsonNode jsonNode   objectMapper readTree String jsonString

User · Answer

Here is a sample I wrote shows how I parse a json and mess every number inside it   public class JsonParser        public static Object parseAndMess Object object  throws IOException           String json   JsonUtil toJson object           JsonNode jsonNode   parseAndMess json           if null    jsonNode              return JsonUtil toObject jsonNode  object getClass              return null             public static JsonNode parseAndMess String json  throws IOException           JsonNode rootNode   parse json           return mess rootNode  new Random                private static JsonNode parse String json  throws IOException           JsonFactory factory   new JsonFactory            ObjectMapper mapper   new ObjectMapper factory           JsonNode rootNode   mapper readTree json           return rootNode              private static JsonNode mess JsonNode rootNode  Random rand  throws IOException           if  rootNode instanceof ObjectNode                Iterator lt Map Entry lt String  JsonNode gt  gt  fieldsIterator   rootNode fields                while  fieldsIterator hasNext                      Map Entry lt String  JsonNode gt  field   fieldsIterator next                    replaceObjectNode  ObjectNode  rootNode  field  rand                           else if  rootNode instanceof ArrayNode                ArrayNode arrayNode     ArrayNode  rootNode               replaceArrayNode arrayNode  rand                     return rootNode             private static void replaceObjectNode ObjectNode rootNode  Map Entry lt String  JsonNode gt  field  Random rand              throws IOException           JsonNode childNode   field getValue            if  childNode instanceof IntNode                 rootNode  put field getKey    rand nextInt 1000              else if  childNode instanceof LongNode                 rootNode  put field getKey    rand nextInt 1000000              else if  childNode instanceof FloatNode                 rootNode  put field getKey    format rand nextFloat                else if  childNode instanceof DoubleNode                 rootNode  put field getKey    format rand nextFloat                else               mess childNode  rand                        private static void replaceArrayNode ArrayNode arrayNode  Random rand  throws IOException           int arrayLength   arrayNode size            if arrayLength    0              return          if  arrayNode get 0  instanceof IntNode                for  int i   0  i  lt  arrayLength  i                      arrayNode set i  new IntNode rand nextInt 10000                             else if  arrayNode get 0  instanceof LongNode                arrayNode removeAll                for  int i   0  i  lt  arrayLength  i                      arrayNode add rand nextInt 1000000                            else if  arrayNode get 0  instanceof FloatNode                arrayNode removeAll                for  int i   0  i  lt  arrayLength  i                      arrayNode add format rand nextFloat                              else if  arrayNode get 0  instanceof DoubleNode                arrayNode removeAll                for  int i   0  i  lt  arrayLength  i                      arrayNode add format rand nextFloat                              else               for  int i   0  i  lt  arrayLength  i                      mess arrayNode get i   rand                                      public static void print JsonNode rootNode  throws IOException           System out println rootNode toString                private static double format float a            return Math round a   10000 0    100 0

User · Answer

To get JSON quickly into Java objects  Maps  that you can then  drill  and work with  you can use json-io  https   github com jdereg json-io    This library will let you read in a JSON String  and get back a  Map of Maps  representation     If you have the corresponding Java classes in your JVM  you can read the JSON in and it will parse it directly into instances of the Java classes   JsonReader jsonToMaps String json    where json is the String containing the JSON to be    read   The return value is a Map where the keys will contain the JSON fields  and the values will contain the associated values   JsonReader jsonToJava String json     will read the same JSON string in  and the return value will be the Java instance that was serialized into the JSON   Use this API if you have the classes in your JVM that were written by   JsonWriter objectToJson MyClass foo

User · Answer

JSON of unknown format to HashMap  writing JSON And reading Json  public static JsonParser parser   new JsonParser    public static void main String args           writeJson  JsonFile json         readgson  JsonFile json      public static void readgson String file        try           System out println   Reading JSON file from Java program              FileReader fileReader   new FileReader  file            com google gson JsonObject object    JsonObject  parser parse  fileReader             Set  lt java util Map Entry lt String  com google gson JsonElement gt  gt  keys   object entrySet            if   keys isEmpty                   System out println   Empty JSON Object              else               Map lt String  Object gt  map   json UnKnown Format  keys                System out println  Json 2 Map     map                    catch  IOException ex            System out println  Input File Does not Exists             public static Map lt String  Object gt  json UnKnown Format  Set  lt java util Map Entry lt String  com google gson JsonElement gt  gt  keys        Map lt String  Object gt  jsonMap   new HashMap lt String  Object gt         for  Entry lt String  JsonElement gt  entry   keys            String keyEntry   entry getKey            System out println keyEntry                   JsonElement valuesEntry    entry getValue            if  valuesEntry isJsonNull                  System out println valuesEntry               jsonMap put keyEntry  valuesEntry            else if  valuesEntry isJsonPrimitive                  System out println  P -   valuesEntry               jsonMap put keyEntry  valuesEntry            else if  valuesEntry isJsonArray                  JsonArray array   valuesEntry getAsJsonArray                List lt Object gt  array2List   new ArrayList lt Object gt                 for  JsonElement jsonElements   array                    System out println  A -   jsonElements                   array2List add jsonElements                             jsonMap put keyEntry  array2List            else if  valuesEntry isJsonObject                                com google gson JsonObject obj    JsonObject  parser parse valuesEntry toString                                      Set  lt java util Map Entry lt String  com google gson JsonElement gt  gt  obj key   obj entrySet                 jsonMap put keyEntry  json UnKnown Format obj key                        return jsonMap     SuppressWarnings  unchecked   public static void writeJson  String file          JSONObject json   new JSONObject         json put  Key1    Value        json put  Key2   777      Converts to  777      json put  Key3   null       json put  Key4   false            JSONArray jsonArray   new JSONArray            jsonArray put  Array-Value1            jsonArray put 10            jsonArray put  Array-Value2         json put  Array      jsonArray       Array    Array-Value1   10  Array-Value2            JSONObject jsonObj   new JSONObject            jsonObj put  Obj-Key1   20           jsonObj put  Obj-Key2    Value2            jsonObj put 4   Value2       Converts to  4       json put  InnerObject   jsonObj            JSONObject jsonObjArray   new JSONObject                JSONArray objArray   new JSONArray                objArray put  Obj-Array1                objArray put 0   Obj-Array3            jsonObjArray put  ObjectArray   objArray        json put  InnerObjectArray   jsonObjArray            Map lt String  Integer gt  sortedTree   new TreeMap lt String  Integer gt             sortedTree put  Sorted1   10           sortedTree put  Sorted2   103           sortedTree put  Sorted3   14        json put  TreeMap   sortedTree                try           System out println  Writting JSON into file                System out println json           FileWriter jsonFileWriter   new FileWriter file           jsonFileWriter write json toJSONString             jsonFileWriter flush            jsonFileWriter close            System out println  Done           catch  IOException e             e printStackTrace

User · Answer

Find the following code for Unknown Json Object parsing using Gson library   public class JsonParsing   static JsonParser parser   new JsonParser     public static HashMap lt String  Object gt  createHashMapFromJsonString String json         JsonObject object    JsonObject  parser parse json       Set lt Map Entry lt String  JsonElement gt  gt  set   object entrySet        Iterator lt Map Entry lt String  JsonElement gt  gt  iterator   set iterator        HashMap lt String  Object gt  map   new HashMap lt String  Object gt          while  iterator hasNext               Map Entry lt String  JsonElement gt  entry   iterator next            String key   entry getKey            JsonElement value   entry getValue             if  null    value                if   value isJsonPrimitive                      if  value isJsonObject                           map put key  createHashMapFromJsonString value toString                        else if  value isJsonArray    amp  amp  value toString   contains                              List lt HashMap lt String  Object gt  gt  list   new ArrayList lt  gt                         JsonArray array   value getAsJsonArray                        if  null    array                            for  JsonElement element   array                                list add createHashMapFromJsonString element toString                                                        map put key  list                                           else if  value isJsonArray    amp  amp   value toString   contains                             map put key  value getAsJsonArray                                     else                   map put key  value getAsString                                       return map

User · Answer

Take a look at  Jacksons built-in tree model feature   And your code will be   public void parse String json            JsonFactory factory   new JsonFactory            ObjectMapper mapper   new ObjectMapper factory          JsonNode rootNode   mapper readTree json             Iterator lt Map Entry lt String JsonNode gt  gt  fieldsIterator   rootNode fields           while  fieldsIterator hasNext                  Map Entry lt String JsonNode gt  field   fieldsIterator next               System out println  Key      field getKey       tValue     field getValue

User · Answer

If a different library is fine for you  you could try org json   JSONObject object   new JSONObject myJSONString   String   keys   JSONObject getNames object    for  String key   keys        Object value   object get key          Determine type of value and do something with it

[java] Parsing JSON in Java without knowing JSON format

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