JSON parsing using Gson for Java

Question

I would like to parse data from JSON which is of type String  I am using Google Gson   I have   jsonLine         data        translations               translatedText    Hello world                     and my class is   public class JsonParsing      public void parse String jsonLine              there I would like to get String  Hello world

User · Answer

Using Gson to Solve I would create a class for individual parameter in the json String  Alternatively you can create one main class called  Data  and then create inner classes similarly  I created separate classes for clarity   The classes are as follows    Data  Translations  TranslatedText   In the class JsonParsing the method  parse  we call gson fromJson jsonLine  Data class  which will convert the String in java objects using Reflection   Once we have access to the  Data  object we can access each parameter individually   Didn t get a chance to test this code as I am away from my dev machine  But this should help   Some good examples and articles  http   albertattard blogspot com 2009 06 practical-example-of-gson html  http   sites google com site gson gson-user-guide  Code  public class JsonParsing          public void parse String jsonLine                Gson gson   new GsonBuilder   create               Data data   gson fromJson jsonLine  Data class               Translations translations   data getTranslation               TranslatedText   arrayTranslatedText   translations getArrayTranslatedText      this returns an array  based on json string             for TranslatedText translatedText arrayTranslatedText                                  System out println translatedText getArrayTranslatedText                                        public class Data             private  Translations translations            public Translations getTranslation                            return translations                         public void setTranslation Translations translations                                 this translations   translations                          public class Translations               private  TranslatedText   translatedText           public TranslatedText   getArrayTranslatedText                           return translatedText                         public void setTranslatedText TranslatedText   translatedText                                 this translatedText  translatedText                          public class TranslatedText               private String translatedText          public String getTranslatedText                        return translatedText                     public void setTranslatedText String translatedText                       this translatedText   translatedText

User · Answer

You can create corresponding java classes for the json objects  The integer  string values can be mapped as is  Json can be parsed like this-   Gson gson   new GsonBuilder   create     Response r   gson fromJson jsonString  Response class     Here is an example- http   rowsandcolumns blogspot com 2013 02 url-encode-http-get-solr-request-and html

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Firstly generate getter and setter using below parsing site http   www jsonschema2pojo org  Now use Gson GettetSetterClass object new Gson   fromjson jsonLine  GettetSetterClass class    Now use object to get values such as data translationText

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In my first gson application I avoided using additional classes to catch values mainly because I use json for config matters  despite the lack of information  even gson page   that s what I found and used   starting from  Map jsonJavaRootObject   new Gson   fromJson     whatever your mega complex object      Map class    Each time gson sees a     it creates a Map  actually a gson StringMap    Each time gson sees a     it creates a String  Each time gson sees a number  it creates a Double  Each time gson sees a     it creates an ArrayList  You can use this facts  combined  to your advantage  Finally this is the code that makes the thing          Map lt String  Object gt  javaRootMapObject   new Gson   fromJson jsonLine  Map class        System out println                         Map                                 List                                         Map                                                javaRootMapObject get  data                                            get  translations                 get 0            get  translatedText

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Simplest thing usually is to create matching Object hierarchy  like so   public class Wrapper      public Data data    static class Data      public Translation   translations    static class Translation      public String translatedText      and then bind using GSON  traverse object hierarchy via fields  Adding getters and setters is pointless for basic data containers   So something like   Wrapper value   GSON fromJSON jsonString  Wrapper class   String text   value data translations 0  translatedText

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One way would be created a JsonObject and iterating through the parameters  For example  JsonObject jobj   new Gson   fromJson jsonString  JsonObject class     Then you can extract bean values like    String fieldValue   jobj get fieldName  getAsString    boolean fieldValue   jobj get fieldName  getAsBoolean    int fieldValue   jobj get fieldName  getAsInt      Hope this helps

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This is simple code to do it  I avoided all checks but this is the main idea    public String parse String jsonLine        JsonElement jelement   new JsonParser   parse jsonLine       JsonObject  jobject   jelement getAsJsonObject        jobject   jobject getAsJsonObject  data        JsonArray jarray   jobject getAsJsonArray  translations        jobject   jarray get 0  getAsJsonObject        String result   jobject get  translatedText   getAsString        return result      To make the use more generic - you will find that Gson s javadocs are pretty clear and helpful

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JsonParser parser   new JsonParser        JsonObject jo    JsonObject  parser parse data       JsonElement je   jo get  some array           Parsing back the string as Array     JsonArray ja    JsonArray  parser parse o get  some array   getAsString         for  JsonElement jo   ja        JsonObject j    JsonObject  jo             Your Code  Access json elements as j get  some element           A simple example to parse a JSON like this          some array        some element   1   some more element   2        some other element    3

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One line code   System out println new Gson   fromJson jsonLine JsonObject class  getAsJsonObject   get  data   getAsJsonObject   get  translations   getAsJsonArray   get 0  getAsJsonObject   get  translatedText   getAsString

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You can use a JsonPath query to extract the value  And with JsonSurfer which is backed by Gson  your problem can be solved by simply two line of code       JsonSurfer jsonSurfer   JsonSurfer gson        String result   jsonSurfer collectOne jsonLine  String class     data translations 0  translatedText

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You can use a separate class to represent the JSON object and use  SerializedName annotations to specify the field name to grab for each data member   public class Response        SerializedName  data      private Data data      private static class Data          SerializedName  translations         public Translation   translations           private static class Translation          SerializedName  translatedText         public String translatedText           public String getTranslatedText           return data translations 0  translatedText           Then you can do the parsing in your parse   method using a Gson object   Gson gson   new Gson    Response response   gson fromJson jsonLine  Response class    System out println  Translated text      response getTranslatedText       With this approach  you can reuse the Response class to add any other additional fields to pick up other data members you might want to extract from JSON -- in case you want to make changes to get results for  say  multiple translations in one call  or to get an additional string for the detected source language

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