How to parse JSON in Java

Question

I have the following JSON text  How can I parse it to get the values of pageName  pagePic  post id  etc                 quot pageInfo quot                   quot pageName quot    quot abc quot                 quot pagePic quot    quot http   example com content jpg quot                      quot posts quot                                       quot post id quot    quot 123456789012 123456789012 quot                      quot actor id quot    quot 1234567890 quot                      quot picOfPersonWhoPosted quot    quot http   example com photo jpg quot                      quot nameOfPersonWhoPosted quot    quot Jane Doe quot                      quot message quot    quot Sounds cool  Can t wait to see it  quot                      quot likesCount quot    quot 2 quot                      quot comments quot                          quot timeOfPost quot    quot 1234567890 quot

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You can use Jayway JsonPath  Below is a GitHub link with source code  pom details and good documentation   https   github com jayway JsonPath  Please follow the below steps   Step 1  Add the jayway JSON path dependency in your class path using Maven or download the JAR file and manually add it    lt dependency gt               lt groupId gt com jayway jsonpath lt  groupId gt               lt artifactId gt json-path lt  artifactId gt               lt version gt 2 2 0 lt  version gt   lt  dependency gt    Step 2  Please save your input JSON as a file for this example  In my case I saved your JSON as sampleJson txt  Note you missed a comma between pageInfo and posts   Step 3  Read the JSON contents from the above file using bufferedReader and save it as String   BufferedReader br   new BufferedReader new FileReader  D   sampleJson txt              StringBuilder sb   new StringBuilder            String line   br readLine             while  line    null                sb append line               sb append System lineSeparator                 line   br readLine                      br close            String jsonInput   sb toString      Step 4  Parse your JSON string using jayway JSON parser   Object document   Configuration defaultConfiguration   jsonProvider   parse jsonInput     Step 5  Read the details like below   String pageName   JsonPath read document     pageInfo pageName    String pagePic   JsonPath read document     pageInfo pagePic    String post id   JsonPath read document     posts 0  post id     System out println    pageInfo pageName     pageName   System out println    pageInfo pagePic     pagePic   System out println    posts 0  post id     post id     The output will be     pageInfo pageName   abc   pageInfo pagePic   http   example com content jpg   posts 0  post id    123456789012 123456789012

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If you have some Java class say Message  representing the JSON string jsonString   you can use Jackson  JSON library with   Message message  new ObjectMapper   readValue jsonString  Message class     and from message object you can fetch any of its attribute

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Use minimal-json which is very fast and easy to use  You can parse from String obj and Stream   Sample data        order   4711     items                  name    NE555 Timer IC          cat-id    645723          quantity   10                      name    LM358N OpAmp IC          cat-id    764525          quantity   2               Parsing   JsonObject object   Json parse input  asObject    int orders   object get  order   asInt    JsonArray items   object get  items   asArray      Creating JSON   JsonObject user   Json object   add  name    Sakib   add  age   23     Maven    lt dependency gt     lt groupId gt com eclipsesource minimal-json lt  groupId gt     lt artifactId gt minimal-json lt  artifactId gt     lt version gt 0 9 4 lt  version gt   lt  dependency gt

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Gson is easy to learn and implement  what we need to know are following two methods   toJson       Convert Java object to JSON format fromJson       Convert JSON into Java object      import java io BufferedReader  import java io FileReader  import java io IOException  import com google gson Gson   public class GsonExample       public static void main String   args         Gson gson   new Gson         try            BufferedReader br   new BufferedReader              new FileReader  c   file json                convert the json string back to object         DataObject obj   gson fromJson br  DataObject class            System out println obj          catch  IOException e            e printStackTrace

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jsoniter  jsoniterator  is a relatively new and simple json library  designed to be simple and fast  All you need to do to deserialize json data is  JsonIterator deserialize jsonData  int   class     where jsonData is a string of json data   Check out the official website for more information

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You need to use JsonNode and ObjectMapper class from the  jackson library to fetch the nodes of your Json tree Add the below dependency in your pom xml to get an access to the Jackson classes    lt  -- https   mvnrepository com artifact com fasterxml jackson core jackson-databind -- gt   lt dependency gt       lt groupId gt com fasterxml jackson core lt  groupId gt       lt artifactId gt jackson-databind lt  artifactId gt       lt version gt 2 9 5 lt  version gt   lt  dependency gt    You shall give a try on the below code  this would work    import com fasterxml jackson core JsonGenerationException  import com fasterxml jackson databind JsonMappingException  import com fasterxml jackson databind JsonNode  import com fasterxml jackson databind ObjectMapper   Class JsonNodeExtractor   public void convertToJson      String filepath    c   data json   ObjectMapper mapper   new ObjectMapper    JsonNode node    mapper readTree filepath       create a JsonNode for every root or subroot element in the Json String JsonNode pageInfoRoot   node path  pageInfo        Fetching elements under  pageInfo  String pageName    pageInfoRoot path  pageName   asText    String pagePic   pageInfoRoot path  pagePic   asText        Now fetching elements under posts JsonNode  postsNode   node path  posts    String post id   postsNode  path  post id   asText    String nameOfPersonWhoPosted   postsNode   path  nameOfPersonWhoPosted   asText

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Jakarta  Java  Enterprise Edition 8 includes the JSON-B  Java API for JSON Binding   So  if you are using a Jakarta EE 8 server  like Payara 5  JSON-B will be available out of the box   A simple example  without custom configuration   public static class Dog       public String name      public int age      public boolean bites        Create a dog instance Dog dog   new Dog    dog name    Falco   dog age   4  dog bites   false      Create Jsonb and serialize Jsonb jsonb   JsonbBuilder create    String result   jsonb toJson dog       Deserialize back dog   jsonb fromJson     name     Falco     age   4   bites   false    Dog class     You can customize the mapping by using configuration  annotations  adapters and  de serializers   If you are not using a Jakarta EE 8 use can always install JSON-B

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You can use JsonNode for a structured tree representation of your JSON string  It s part of the rock solid jackson library which is omnipresent   ObjectMapper mapper   new ObjectMapper    JsonNode yourObj   mapper readTree     k     v

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This blew my mind with how easy it was  You can just pass a String holding your JSON to the constructor of a JSONObject in the default org json package    JSONArray rootOfPage    new JSONArray JSONString     Done  Drops microphone  This works with JSONObjects as well  After that  you can just look through your hierarchy of Objects using the get   methods on your objects

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For the sake of the example lets assume you have a class Person with just a name   private class Person       public String name       public Person String name            this name   name            Google GSON  Maven   My personal favourite as to the great JSON serialisation   de-serialisation of objects   Gson g   new Gson     Person person   g fromJson     name      John      Person class   System out println person name     John  System out println g toJson person         name   John     Update  If you want to get a single attribute out you can do it easily with the Google library as well   JsonObject jsonObject   new JsonParser   parse     name      John      getAsJsonObject     System out println jsonObject get  name   getAsString       John   Org JSON  Maven   If you don t need object de-serialisation but to simply get an attribute  you can try org json  or look GSON example above    JSONObject obj   new JSONObject     name      John        System out println obj getString  name       John   Jackson  Maven   ObjectMapper mapper   new ObjectMapper    Person user   mapper readValue     name      John      Person class    System out println user name     John

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There are 2 main options      Object mapping  When you deserialize JSON data to a number of instances of   1 1  Some predefined classes  like Maps  In this case  you don t have to design your own POJO classes  Some libraries  org json simple https   www mkyong com java json-simple-example-read-and-write-json   1 2  Your own POJO classes  You have to design your own POJO classes to present JSON data  but this may be helpful if you are going to use them into your business logic as well  Some libraries  Gson  Jackson  see http   tutorials jenkov com java-json index html    The main backwards of the mapping is that it leads to intensive memory allocation  and GC pressure  and CPU utilization    Stream oriented parsing  For example  both Gson and Jackson support such lightweight parsing  Also  you can take a look at an example of custom  fast and GC-free parser https   github com anatolygudkov green-jelly  Prefer this way in case you need to parse a lot of data and in latency sensitivity applications

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If you have maven project then add below dependency  or normal project add json-simple jar   lt dependency gt       lt groupId gt org json lt  groupId gt       lt artifactId gt json lt  artifactId gt       lt version gt 20180813 lt  version gt   lt  dependency gt   Write below java code for convert JSON string to JSON array  JSONArray ja   new JSONArray String jsonString

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Please do something like this   JSONParser jsonParser   new JSONParser    JSONObject obj    JSONObject  jsonParser parse contentString   String product    String  jsonObject get  productId

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You can use the Gson Library to parse the JSON string   Gson gson   new Gson    JsonObject jsonObject   gson fromJson jsonAsString  JsonObject class    String pageName   jsonObject getAsJsonObject  pageInfo   get  pageName   getAsString    String pagePic   jsonObject getAsJsonObject  pageInfo   get  pagePic   getAsString    String postId   jsonObject getAsJsonArray  posts   get 0  getAsJsonObject   get  post id   getAsString      You can also loop through the  posts  array as so   JsonArray posts   jsonObject getAsJsonArray  posts    for  JsonElement post   posts      String postId   post getAsJsonObject   get  post id   getAsString        do something

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First you need to select an implementation library to do that   The Java API for JSON Processing  JSR 353  provides portable APIs to parse  generate  transform  and query JSON using object model and streaming APIs    The reference implementation is here  https   jsonp java net    Here you can find a list of implementations of JSR 353   What are the API that does implement JSR-353  JSON   And to help you decide    I found this article as well   http   blog takipi com the-ultimate-json-library-json-simple-vs-gson-vs-jackson-vs-json   If you go for Jackson  here is a good article about conversion between JSON to from Java using Jackson  https   www mkyong com java how-to-convert-java-object-to-from-json-jackson   Hope it helps

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We can use the JSONObject class to convert a JSON string to a JSON object  and to iterate over the JSON object  Use the following code   JSONObject jObj   new JSONObject contents trim     Iterator lt   gt  keys   jObj keys     while  keys hasNext         String key    String keys next      if   jObj get key  instanceof JSONObject                    System out println jObj getString String key

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I have JSON like this         pageInfo               pageName    abc             pagePic    http   example com content jpg            Java class  class PageInfo        private String pageName      private String pagePic          Getters and setters     Code for converting this JSON to a Java class       PageInfo pageInfo   JsonPath parse jsonString  read    pageInfo   PageInfo class     Maven   lt dependency gt       lt groupId gt com jayway jsonpath lt  groupId gt       lt artifactId gt json-path lt  artifactId gt       lt version gt 2 2 0 lt  version gt   lt  dependency gt

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Since nobody mentioned it yet  here is a beginning of a solution using Nashorn  JavaScript runtime part of Java 8  but deprecated in Java 11    Solution  private static final String EXTRACTOR SCRIPT        var fun   function raw             var json   JSON parse raw            return  json pageInfo pageName  json pageInfo pagePic  json posts 0  post id        public void run   throws ScriptException  NoSuchMethodException       ScriptEngine engine   new ScriptEngineManager   getEngineByName  nashorn        engine eval EXTRACTOR SCRIPT       Invocable invocable    Invocable  engine      JSObject result    JSObject  invocable invokeFunction  fun   JSON       result values   forEach e - gt  System out println e        Performance comparison  I wrote JSON content containing three arrays of respectively 20  20 and 100 elements  I only want to get the 100 elements from the third array  I use the following JavaScript function to parse and get my entries   var fun   function raw   JSON parse raw  entries     Running the call a million times using Nashorn takes 7 5 7 8 seconds   JSObject  invocable invokeFunction  fun   json     org json takes 20 21 seconds  new JSONObject JSON  getJSONArray  entries      Jackson takes 6 5 7 seconds  mapper readValue JSON  Entries class  getEntries      In this case Jackson performs better than Nashorn  which performs much better than org json  Nashorn API is harder to use than org json s or Jackson s  Depending on your requirements Jackson and Nashorn both can be viable solutions

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A - Explanation  You can use Jackson libraries  for binding JSON String into POJO  Plain Old Java Object  instances  POJO is simply a class with only private fields and public getter setter methods  Jackson is going to traverse the methods  using reflection   and maps the JSON object into the POJO instance as the field names of the class fits to the field names of the JSON object   In your JSON object  which is actually a composite object  the main object consists o two sub-objects  So  our POJO classes should have the same hierarchy  I ll call the whole JSON Object as Page object  Page object consist of a PageInfo object  and a Post object array   So we have to create three different POJO classes    Page Class  a composite of PageInfo Class and array of Post Instances PageInfo Class Posts Class   The only package I ve used is Jackson ObjectMapper  what we do is binding data   com fasterxml jackson databind ObjectMapper   The required dependencies  the jar files is listed below    jackson-core-2 5 1 jar jackson-databind-2 5 1 jar jackson-annotations-2 5 0 jar   Here is the required code   B - Main POJO Class   Page  package com levo jsonex model   public class Page        private PageInfo pageInfo      private Post   posts       public PageInfo getPageInfo             return pageInfo             public void setPageInfo PageInfo pageInfo            this pageInfo   pageInfo             public Post   getPosts             return posts             public void setPosts Post   posts            this posts   posts             C - Child POJO Class   PageInfo  package com levo jsonex model   public class PageInfo        private String pageName      private String pagePic       public String getPageName             return pageName             public void setPageName String pageName            this pageName   pageName             public String getPagePic             return pagePic             public void setPagePic String pagePic            this pagePic   pagePic             D - Child POJO Class   Post  package com levo jsonex model   public class Post        private String post id      private String actor id      private String picOfPersonWhoPosted      private String nameOfPersonWhoPosted      private String message      private int likesCount      private String   comments      private int timeOfPost       public String getPost id             return post id             public void setPost id String post id            this post id   post id             public String getActor id             return actor id             public void setActor id String actor id            this actor id   actor id             public String getPicOfPersonWhoPosted             return picOfPersonWhoPosted             public void setPicOfPersonWhoPosted String picOfPersonWhoPosted            this picOfPersonWhoPosted   picOfPersonWhoPosted             public String getNameOfPersonWhoPosted             return nameOfPersonWhoPosted             public void setNameOfPersonWhoPosted String nameOfPersonWhoPosted            this nameOfPersonWhoPosted   nameOfPersonWhoPosted             public String getMessage             return message             public void setMessage String message            this message   message             public int getLikesCount             return likesCount             public void setLikesCount int likesCount            this likesCount   likesCount             public String   getComments             return comments             public void setComments String   comments            this comments   comments             public int getTimeOfPost             return timeOfPost             public void setTimeOfPost int timeOfPost            this timeOfPost   timeOfPost             E - Sample JSON File   sampleJSONFile json  I ve just copied your JSON sample into this file and put it under the project folder         pageInfo               pageName    abc             pagePic    http   example com content jpg              posts                               post id    123456789012 123456789012                  actor id    1234567890                  picOfPersonWhoPosted    http   example com photo jpg                  nameOfPersonWhoPosted    Jane Doe                  message    Sounds cool  Can t wait to see it                   likesCount    2                  comments                      timeOfPost    1234567890                       F - Demo Code  package com levo jsonex   import java io File  import java io IOException  import java util Arrays   import com fasterxml jackson databind ObjectMapper  import com levo jsonex model Page  import com levo jsonex model PageInfo  import com levo jsonex model Post   public class JSONDemo        public static void main String   args            ObjectMapper objectMapper   new ObjectMapper             try               Page page   objectMapper readValue new File  sampleJSONFile json    Page class                printParsedObject page             catch  IOException e                e printStackTrace                          private static void printParsedObject Page page            printPageInfo page getPageInfo             System out println            printPosts page getPosts                private static void printPageInfo PageInfo pageInfo            System out println  Page Info             System out println                        System out println   tPage Name       pageInfo getPageName             System out println   tPage Pic        pageInfo getPagePic                private static void printPosts Post   posts            System out println  Page Posts             System out println                        for Post post   posts                printPost post                        private static void printPost Post post            System out println   tPost Id                         post getPost id             System out println   tActor Id                        post getActor id             System out println   tPic Of Person Who Posted        post getPicOfPersonWhoPosted             System out println   tName Of Person Who Posted       post getNameOfPersonWhoPosted             System out println   tMessage                         post getMessage             System out println   tLikes Count                     post getLikesCount             System out println   tComments                        Arrays toString post getComments              System out println   tTime Of Post                    post getTimeOfPost                G - Demo Output  Page Info                 Page Name   abc     Page Pic    http   example com content jpg Page Posts                 Post Id                     123456789012 123456789012     Actor Id                    1234567890     Pic Of Person Who Posted    http   example com photo jpg     Name Of Person Who Posted   Jane Doe     Message                     Sounds cool  Can t wait to see it      Likes Count                 2     Comments                           Time Of Post                1234567890

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You can use DSM stream parsing library for parsing complex json and XML document  DSM parse data only once and not load all data into memory    Let s say we have Page class to deserialize given json data   Page class  public class Page       private String pageName      private String pageImage      private List lt Sting gt  postIds          getter setter      Create a yaml Mapping file   result    type  object       result is array   path   posts   fields      pageName          path   pageInfo pageName     pageImage          path   pageInfo pagePic     postIds        path  post id       type  array   Use DSM to extract fields   DSM dsm new DSMBuilder new File  path-to-yaml-config yaml    create Page class   Page page   Page dsm toObject new path-to-json-data json      page variable serialized to json        pageName     abc      pageImage     http   example com content jpg      postIds       123456789012 123456789012        DSM is very good for complex json and xml

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The org json library is easy to use  Just remember  while casting or using methods like getJSONObject and getJSONArray  that in JSON notation          represents an array  so library will parse it to JSONArray         represents an object  so library will parse it to JSONObject  Example code below  import org json     String jsonString           assign your JSON String here JSONObject obj   new JSONObject jsonString   String pageName   obj getJSONObject  quot pageInfo quot   getString  quot pageName quot     JSONArray arr   obj getJSONArray  quot posts quot       notice that   quot posts quot          for  int i   0  i  lt  arr length    i          String post id   arr getJSONObject i  getString  quot post id quot                  You may find more examples from  Parse JSON in Java Downloadable jar   http   mvnrepository com artifact org json json

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There are many open source libraries present to parse JSON content to an object or just to read JSON values  Your requirement is just to read values and parsing it to custom object  So org json library is enough in your case   Use org json library to parse it and create JsonObject   JSONObject jsonObj   new JSONObject  lt jsonStr gt      Now  use this object to get your values   String id   jsonObj getString  pageInfo      You can see a complete example here   How to parse JSON in Java

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Read the following blog post  JSON in Java  This post is a little bit old  but still I want to answer you question  Step 1  Create a POJO class of your data  Step 2  Now create a object using JSON  Employee employee   null  ObjectMapper mapper   new ObjectMapper    try       employee    mapper readValue newFile  quot  home sumit employee json quot    Employee class      catch JsonGenerationException e        e printStackTrace       For further reference you can refer to the following link

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You could use Google Gson   Using this library you only need to create a model with the same JSON structure  Then the model is automatically filled in  You have to call your variables as your JSON keys  or use  SerializedName if you want to use different names   JSON  From your example          pageInfo              pageName    abc            pagePic    http   example com content jpg             posts                            post id    123456789012 123456789012                actor id    1234567890                picOfPersonWhoPosted    http   example com photo jpg                nameOfPersonWhoPosted    Jane Doe                message    Sounds cool  Can t wait to see it                 likesCount    2                comments                    timeOfPost    1234567890                      Model  class MyModel        private PageInfo pageInfo      private ArrayList lt Post gt  posts   new ArrayList lt  gt        class PageInfo        private String pageName      private String pagePic     class Post        private String post id        SerializedName  actor id       lt - example SerializedName     private String actorId       private String picOfPersonWhoPosted      private String nameOfPersonWhoPosted      private String message      private String likesCount      private ArrayList lt String gt  comments      private String timeOfPost      Parsing  Now you can parse using Gson library   MyModel model   gson fromJson jsonString  MyModel class     Gradle import  Remember to import the library in the app Gradle file  implementation  com google code gson gson 2 8 6     or earlier versions   Automatic model generation  You can generate model from JSON automatically using online tools like this

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pageInfo               pageName    abc             pagePic    http   example com content jpg              posts                               post id    123456789012 123456789012                  actor id    1234567890                  picOfPersonWhoPosted    http   example com photo jpg                  nameOfPersonWhoPosted    Jane Doe                  message    Sounds cool  Can t wait to see it                   likesCount    2                  comments                      timeOfPost    1234567890                      Java code    JSONObject obj   new JSONObject responsejsonobj   String pageName   obj getJSONObject  pageInfo   getString  pageName     JSONArray arr   obj getJSONArray  posts    for  int i   0  i  lt  arr length    i          String post id   arr getJSONObject i  getString  post id              etc

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Top answers on this page use too simple examples like object with one property  e g   name  value    I think that still simple but real life example can help someone    So this is the JSON returned by Google Translate API         data                    translations                                             translatedText    Arbeit                                        I want to retrieve the value of  translatedText  attribute e g   Arbeit  using Google s Gson   Two possible approaches     Retrieve just one needed attribute  String json    callToTranslateApi  work    de    JsonObject jsonObject   new JsonParser   parse json  getAsJsonObject    return jsonObject get  data   getAsJsonObject            get  translations   getAsJsonArray            get 0  getAsJsonObject            get  translatedText   getAsString     Create Java object from JSON  class ApiResponse       Data data            class Data           Translation   translations                   class Translation               String translatedText                              Gson g   new Gson     String json  callToTranslateApi  work    de     ApiResponse response   g fromJson json  ApiResponse class    return response data translations 0  translatedText

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I believe the best practice should be to go through the official Java JSON API which are still work in progress

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If one wants to create Java object from JSON and vice versa  use GSON or JACKSON third party jars etc     from object to JSON  Gson gson   new Gson    gson toJson yourObject       from JSON to object  yourObject o   gson fromJson JSONString yourObject class    But if one just want to parse a JSON string and get some values   OR create a JSON string from scratch to send over wire  just use JaveEE jar which contains JsonReader  JsonArray  JsonObject etc  You may want to download the implementation of that spec like javax json  With these two jars I am able to parse the json and use the values     These APIs actually follow the DOM SAX parsing model of XML          Response response   request get       REST call      JsonReader jsonReader   Json createReader new StringReader response readEntity String class         JsonArray jsonArray   jsonReader readArray        ListIterator l   jsonArray listIterator        while   l hasNext                 JsonObject j    JsonObject l next              JsonObject ciAttr   j getJsonObject  ciAttributes

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quick-json parser is very straightforward  flexible  very fast and customizable  Try it  Features    Compliant with JSON specification  RFC4627   High-Performance JSON parser  Supports Flexible Configurable parsing approach  Configurable validation of key value pairs of any JSON Hierarchy  Easy to use   Very small footprint Raises developer friendly and easy to trace exceptions  Pluggable Custom Validation support - Keys Values can be validated by configuring custom validators as and when encountered  Validating and Non-Validating parser support  Support for two types of configuration  JSON XML  for using quick-JSON validating parser  Requires JDK 1 5 No dependency on external libraries  Support for JSON Generation through object serialisation  Support for collection type selection during parsing process    It can be used like this   JsonParserFactory factory JsonParserFactory getInstance    JSONParser parser factory newJsonParser    Map jsonMap parser parseJson jsonString

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Almost all the answers given requires a full deserialization of the JSON into a Java object before accessing the value in the property of interest  Another alternative  which does not go this route is to use JsonPATH which is like XPath for JSON and allows traversing of JSON objects   It is a specification and the good folks at JayWay have created a Java implementation for the specification which you can find here  https   github com jayway JsonPath  So basically to use it  add it to your project  eg    lt dependency gt       lt groupId gt com jayway jsonpath lt  groupId gt       lt artifactId gt json-path lt  artifactId gt       lt version gt   version  lt  version gt   lt  dependency gt    and to use   String pageName   JsonPath read yourJsonString     pageInfo pageName    String pagePic   JsonPath read yourJsonString     pageInfo pagePic    String post id   JsonPath read yourJsonString     pagePosts 0  post id      etc     Check the JsonPath specification page for more information on the other ways to transverse JSON

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In addition to other answers  I recomend this online opensource service jsonschema2pojo org for quick generating Java classes from json or json schema for GSON  Jackson 1 x or Jackson 2 x  For example  if you have         pageInfo               pageName    abc             pagePic    http   example com content jpg             posts                               post id    123456789012 123456789012                  actor id   1234567890                 picOfPersonWhoPosted    http   example com photo jpg                  nameOfPersonWhoPosted    Jane Doe                  message    Sounds cool  Can t wait to see it                   likesCount   2                 comments                      timeOfPost   1234567890                      The jsonschema2pojo org for GSON generated    Generated  org jsonschema2pojo   public class Container        SerializedName  pageInfo        Expose     public PageInfo pageInfo       SerializedName  posts        Expose     public List lt Post gt  posts   new ArrayList lt Post gt         Generated  org jsonschema2pojo   public class PageInfo        SerializedName  pageName        Expose     public String pageName       SerializedName  pagePic        Expose     public String pagePic      Generated  org jsonschema2pojo   public class Post        SerializedName  post id        Expose     public String postId       SerializedName  actor id        Expose     public long actorId       SerializedName  picOfPersonWhoPosted        Expose     public String picOfPersonWhoPosted       SerializedName  nameOfPersonWhoPosted        Expose     public String nameOfPersonWhoPosted       SerializedName  message        Expose     public String message       SerializedName  likesCount        Expose     public long likesCount       SerializedName  comments        Expose     public List lt Object gt  comments   new ArrayList lt Object gt          SerializedName  timeOfPost        Expose     public long timeOfPost

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One can use Apache  Model annotation to create Java model classes representing structure of JSON files and use them to access various elements in the JSON tree  Unlike other solutions this one works completely without reflection and is thus suitable for environments where reflection is impossible or comes with significant overhead   There is a sample Maven project showing the usage  First of all it defines the structure    Model className  RepositoryInfo   properties          Property name    id   type   int class        Property name    name   type   String class        Property name    owner   type   Owner class        Property name    private   type   boolean class      final class RepositoryCntrl        Model className    Owner   properties              Property name    login   type   String class             static final class OwnerCntrl             and then it uses the generated RepositoryInfo and Owner classes to parse the provided input stream and pick certain information up while doing that   List lt RepositoryInfo gt  repositories   new ArrayList lt  gt     try  InputStream is   initializeStream args         Models parse CONTEXT  RepositoryInfo class  is  repositories      System err println  there is     repositories size       repositories    repositories stream   filter  repo  - gt  repo    null  forEach  repo  - gt        System err println  repository     repo getName                is owned by     repo getOwner   getLogin               That is it  In addition to that here is a live gist showing similar example together with asynchronous network communication

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The below example shows how to read the text in the question  represented as the  jsonText  variable   This solution uses the Java EE7 javax json API  which is mentioned in some of the other answers    The reason I ve added it as a separate answer is that the following code shows how to actually access some of the values shown in the question   An implementation of the javax json API would be required to make this code run   The full package for each of the classes required was included as I didn t want to declare  import  statements   javax json JsonReader jr        javax json Json createReader new StringReader jsonText    javax json JsonObject jo   jr readObject       Read the page info  javax json JsonObject pageInfo   jo getJsonObject  pageInfo    System out println pageInfo getString  pageName        Read the posts  javax json JsonArray posts   jo getJsonArray  posts      Read the first post  javax json JsonObject post   posts getJsonObject 0     Read the post id field  String postId   post getString  post id      Now  before anyone goes and downvotes this answer because it doesn t use GSON  org json  Jackson  or any of the other 3rd party frameworks available  it s an example of  required code  per the question to parse the provided text   I am well aware that adherence to the current standard JSR 353 was not being considered for JDK 9 and as such the JSR 353 spec should be treated the same as any other 3rd party JSON handling implementation

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There are many JSON libraries available in Java   The most notorious ones are  Jackson  GSON  Genson  FastJson and org json   There are typically three things one should look at for choosing any library    Performance Ease of use  code is simple to write and legible  - that goes with features  For mobile apps  dependency jar size   Specifically for JSON libraries  and any serialization deserialization libs   databinding is also usually of interest as it removes the need of writing boiler-plate code to pack unpack the data   For 1  see this benchmark  https   github com fabienrenaud java-json-benchmark I did using JMH which compares  jackson  gson  genson  fastjson  org json  jsonp  performance of serializers and deserializers using stream and databind APIs  For 2  you can find numerous examples on the Internet  The benchmark above can also be used as a source of examples     Quick takeaway of the benchmark  Jackson performs 5 to 6 times better than org json and more than twice better than GSON   For your particular example  the following code decodes your json with jackson   public class MyObj        private PageInfo pageInfo      private List lt Post gt  posts       static final class PageInfo           private String pageName          private String pagePic             static final class Post           private String post id           JsonProperty  actor id            private String actorId           JsonProperty  picOfPersonWhoPosted           private String pictureOfPoster           JsonProperty  nameOfPersonWhoPosted           private String nameOfPoster          private String likesCount          private List lt String gt  comments          private String timeOfPost             private static final ObjectMapper JACKSON   new ObjectMapper        public static void main String   args  throws IOException           MyObj o   JACKSON readValue args 0   MyObj class      assumes args 0  contains your json payload provided in your question            Let me know if you have any questions

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