Converting Java objects to JSON with Jackson

Question

I want my JSON to look like this          information               timestamp    xxxx            feature    xxxx            ean   1234           data    xxxx                    timestamp    yyy            feature    yyy            ean   12345           data    yyy             Code so far   import java util List   public class ValueData        private List lt ValueItems gt  information       public ValueData                public List lt ValueItems gt  getInformation             return information             public void setInformation List lt ValueItems gt  information            this information   information              Override     public String toString             return String format   information  s    information              and  public class ValueItems        private String timestamp      private String feature      private int ean      private String data        public ValueItems                public ValueItems String timestamp  String feature  int ean  String data           this timestamp   timestamp          this feature   feature          this ean   ean          this data   data             public String getTimestamp             return timestamp             public void setTimestamp String timestamp            this timestamp   timestamp             public String getFeature             return feature             public void setFeature String feature            this feature   feature             public int getEan             return ean             public void setEan int ean            this ean   ean             public String getData             return data             public void setData String data            this data   data              Override     public String toString             return String format   timestamp  s feature  s ean  s data  s    timestamp  feature  ean  data             I just missing the part how I can convert the Java object to JSON with Jackson   public static void main String   args          CONVERT THE JAVA OBJECT TO JSON HERE     System out println json       My Question is  Are my classes correct  Which instance do I have to call and how that I can achieve this JSON output

User · Answer

public class JSONConvector        public static String toJSON Object object  throws JSONException  IllegalAccessException           String str               Class c   object getClass            JSONObject jsonObject   new JSONObject            for  Field field   c getDeclaredFields                  field setAccessible true               String name   field getName                String value   String valueOf field get object                jsonObject put name  value                     System out println jsonObject toString             return jsonObject toString                public static String toJSON List list   throws JSONException  IllegalAccessException           JSONArray jsonArray   new JSONArray            for  Object i   list                String jstr   toJSON i               JSONObject jsonObject   new JSONObject jstr               jsonArray put jsonArray                     return jsonArray toString

User · Answer

This might be useful   objectMapper writeValue new File  c   employee json    employee       display to console Object json   objectMapper readValue       objectMapper writeValueAsString employee   Object class    System out println objectMapper writerWithDefaultPrettyPrinter         writeValueAsString json

User · Answer

To convert your object in JSON with Jackson   ObjectWriter ow   new ObjectMapper   writer   withDefaultPrettyPrinter    String json   ow writeValueAsString object

User · Answer

Note  To make the most voted solution work  attributes in the POJO have to be public or have a public getter setter      By default  Jackson 2 will only work with fields that are either   public  or have a public getter method     serializing an entity that   has all fields private or package private will fail    Not tested yet  but I believe that this rule also applies for other JSON libs like google Gson

User · Answer

Well  even the accepted answer does not exactly output what op has asked for  It outputs the JSON string but with   characters escaped  So  although might be a little late  I am answering hopeing it will help people  Here is how I do it   StringWriter writer   new StringWriter    JsonGenerator jgen   new JsonFactory   createGenerator writer   jgen setCodec new ObjectMapper     jgen writeObject object   jgen close    System out println writer toString

User · Answer

You can use Google Gson like this     UserEntity user   new UserEntity    user setUserName  UserName    user setUserAge 18    Gson gson   new Gson    String jsonStr   gson toJson user

User · Answer

Just follow any of these   For jackson it should work        ObjectMapper mapper   new ObjectMapper            return mapper writeValueAsString object           will return json in string   For gson it should work      Gson gson   new Gson        return Response ok gson toJson yourClass   build

User · Answer

I know this is old  and I am new to java   but I ran into the same problem  And the answers were not as clear to me as a newbie    so I thought I would add what I learned   I used a third-party library to aid in the endeavor  org codehaus jackson All of the downloads for this can be found here   For base JSON functionality  you need to add the following jars to your project s libraries     jackson-mapper-asl and     jackson-core-asl  Choose the version your project needs   Typically you can go with the latest stable build      Once they are imported in to your project s libraries  add the following import lines to your code    import org codehaus jackson JsonGenerationException   import org codehaus jackson map JsonMappingException   import org codehaus jackson map ObjectMapper    With the java object defined and assigned values that you wish to convert to JSON and return as part of a RESTful web service  User u   new User    u firstName    Sample   u lastName    User   u email    sampleU example com    ObjectMapper mapper   new ObjectMapper     try          convert user object to json string and return it      return mapper writeValueAsString u     catch  JsonGenerationException   JsonMappingException  e           catch various errors     e printStackTrace        The result should looks like this    firstName   Sample   lastName   User   email   sampleU example com

User · Answer

You could do this   String json   new ObjectMapper   writeValueAsString yourObjectHere

[java] Converting Java objects to JSON with Jackson

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