Converting JSON data to Java object

Question

I want to be able to access properties from a JSON string within my Java action method  The string is available by simply saying myJsonString   object getJson    Below is an example of what the string can look like          title    ComputingandInformationsystems        id   1       children    true        groups               title    LeveloneCIS            id   2           children    true            groups                   title    IntroToComputingandInternet                id   3               children    false                groups                            In this string every JSON object contains an array of other JSON objects  The intention is to extract a list of IDs where any given object possessing a group property that contains other JSON objects  I looked at Google s Gson as a potential JSON plugin  Can anyone offer some form of guidance as to how I can generate Java from this JSON string

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Oddly  the only decent JSON processor mentioned so far has been GSON   Here are more good choices    Jackson  Github  -- powerful data binding  JSON to from POJOs   streaming  ultra fast   tree model  convenient for untyped access   Flex-JSON -- highly configurable serialization   EDIT  Aug 2013    One more to consider    Genson -- functionality similar to Jackson  aimed to be easier to configure by developer

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I looked at Google s Gson as a potential JSON plugin  Can anyone offer some form of guidance as to how I can generate Java from this JSON string   Google Gson supports generics and nested beans  The    in JSON represents an array and should map to a Java collection such as List or just a plain Java array  The    in JSON represents an object and should map to a Java Map or just some JavaBean class  You have a JSON object with several properties of which the groups property represents an array of nested objects of the very same type  This can be parsed with Gson the following way  package com stackoverflow q1688099   import java util List  import com google gson Gson   public class Test        public static void main String    args  throws Exception           String json                 quot   quot                     quot  title    Computing and Information systems   quot                     quot  id    1  quot                     quot  children     true   quot                     quot  groups       quot                         quot  title     Level one CIS   quot                         quot  id    2  quot                         quot  children     true   quot                         quot  groups       quot                             quot  title     Intro To Computing and Internet   quot                             quot  id    3  quot                             quot  children    false   quot                             quot  groups     quot                         quot    quot                      quot    quot                 quot   quot               Now do the magic          Data data   new Gson   fromJson json  Data class               Show it          System out println data             class Data       private String title      private Long id      private Boolean children      private List lt Data gt  groups       public String getTitle     return title        public Long getId     return id        public Boolean getChildren     return children        public List lt Data gt  getGroups     return groups         public void setTitle String title    this title   title        public void setId Long id    this id   id        public void setChildren Boolean children    this children   children        public void setGroups List lt Data gt  groups    this groups   groups             public String toString             return String format  quot title  s id  d children  s groups  s quot   title  id  children  groups            Fairly simple  isn t it  Just have a suitable JavaBean and call Gson fromJson    See also   Json org - Introduction to JSON Gson User Guide - Introduction to Gson

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What s wrong with the standard stuff     JSONObject jsonObject   new JSONObject someJsonString   JSONArray jsonArray   jsonObject getJSONArray  someJsonArray    String value   jsonArray optJSONObject i  getString  someJsonValue

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HashMap keyArrayList   new HashMap    Iterator itr   yourJson keys    while  itr hasNext          String key    String  itr next        keyArrayList put key  yourJson get key  toString

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The easiest way is that you can use this softconvertvalue method which is a custom method in which you can convert jsonData into your specific Dto class       Dto response   softConvertValue jsonData  Dto class     public static  lt T gt  T softConvertValue Object fromValue  Class lt T gt  toValueType         ObjectMapper objMapper   new ObjectMapper        return objMapper          configure DeserializationFeature FAIL ON UNKNOWN PROPERTIES  false           convertValue fromValue  toValueType

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Give boon a try   https   github com RichardHightower boon  It is wicked fast   https   github com RichardHightower json-parsers-benchmark  Don t take my word for it    check out the gatling benchmark   https   github com gatling json-parsers-benchmark   Up to 4x is some cases  and out of the 100s of test  It also has a index overlay mode that is even faster  It is young but already has some users    It can parse JSON to Maps and Lists faster than any other lib can parse to a JSON DOM and that is without Index Overlay mode  With Boon Index Overlay mode  it is even faster    It also has a very fast JSON lax mode and a PLIST parser mode      and has a super low memory  direct from bytes mode with UTF-8 encoding on the fly    It also has the fastest JSON to JavaBean mode too    It is new  but if speed and simple API is what you are looking for  I don t think there is a faster or more minimalist API

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If you use any kind of special maps with keys or values also of special maps  you will find it s not contemplated by the implementation of google

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Bewaaaaare of Gson  It s very cool  very great  but the second you want to do anything other than simple objects  you could easily need to start building your own serializers  which isn t that hard    Also  if you have an array of Objects  and you deserialize some json into that array of Objects  the true types are LOST  The full objects won t even be copied  Use XStream   Which  if using the jsondriver and setting the proper settings  will encode ugly types into the actual json  so that you don t loose anything  A small price to pay  ugly json  for true serialization    Note that Jackson fixes these issues  and is faster than GSON

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If  by any change  you are in an application which already uses http   restfb com  then you can do   import com restfb json JsonObject        JsonObject json   new JsonObject jsonString   json get  title      etc

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Or with Jackson   String json        ObjectMapper m   new ObjectMapper    Set lt Product gt  products   m readValue json  new TypeReference lt Set lt Product gt  gt

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Easy and working java code to convert JSONObject to Java Object  Employee java  import java util HashMap  import java util Map   import javax annotation Generated   import com fasterxml jackson annotation JsonAnyGetter  import com fasterxml jackson annotation JsonAnySetter  import com fasterxml jackson annotation JsonIgnore  import com fasterxml jackson annotation JsonInclude  import com fasterxml jackson annotation JsonProperty  import com fasterxml jackson annotation JsonPropertyOrder    JsonInclude JsonInclude Include NON NULL   Generated  org jsonschema2pojo    JsonPropertyOrder    id    firstName    lastName     public class Employee     JsonProperty  id   private Integer id   JsonProperty  firstName   private String firstName   JsonProperty  lastName   private String lastName   JsonIgnore private Map lt String  Object gt  additionalProperties   new HashMap lt String  Object gt               return   The id     JsonProperty  id   public Integer getId     return id              param id   The id     JsonProperty  id   public void setId Integer id    this id   id              return   The firstName     JsonProperty  firstName   public String getFirstName     return firstName              param firstName   The firstName     JsonProperty  firstName   public void setFirstName String firstName    this firstName   firstName              return   The lastName     JsonProperty  lastName   public String getLastName     return lastName              param lastName   The lastName     JsonProperty  lastName   public void setLastName String lastName    this lastName   lastName      JsonAnyGetter public Map lt String  Object gt  getAdditionalProperties     return this additionalProperties      JsonAnySetter public void setAdditionalProperty String name  Object value    this additionalProperties put name  value          LoadFromJSON java  import org codehaus jettison json JSONObject   import com fasterxml jackson databind ObjectMapper   public class LoadFromJSON        public static void main String args    throws Exception           JSONObject json   new JSONObject            json put  id   2           json put  firstName    hello            json put  lastName    world             byte   jsonData   json toString   getBytes             ObjectMapper mapper   new ObjectMapper            Employee employee   mapper readValue jsonData  Employee class            System out print employee getLastName

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Depending on the input JSON format string file  create a jSONString  Sample Message class object corresponding to JSON can be obtained as below  Message msgFromJSON   new ObjectMapper   readValue jSONString  Message class

[java] Converting JSON data to Java object

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