How do you return a JSON object from a Java Servlet

Question

How do you return a JSON object form a Java servlet   Previously when doing AJAX with a servlet I have returned a string  Is there a JSON object type that needs to be used  or do you just return a String that looks like a JSON object e g    String objectToReturn      key1   value1   key2   value2

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I used Jackson to convert Java Object to JSON string and send as follows   PrintWriter out   response getWriter    ObjectMapper objectMapper  new ObjectMapper    String jsonString   objectMapper writeValueAsString MyObject   response setContentType  application json    response setCharacterEncoding  UTF-8    out print jsonString   out flush

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Just write a string to the output stream  You might set the MIME-type to text javascript  edit  application json is apparently officialer  if you re feeling helpful   There s a small but nonzero chance that it ll keep something from messing it up someday  and it s a good practice

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By Using Gson you can send json response see below code  You can see this code   WebServlet urlPatterns      jsonResponse    public class JsonResponse extends HttpServlet     Override protected void doGet HttpServletRequest request  HttpServletResponse response          throws ServletException  IOException       response setContentType  application json        response setCharacterEncoding  utf-8        Student student   new Student 12   Ram Kumar    Male    1234565678        Subject subject1   new Subject 1   Computer Fundamentals        Subject subject2   new Subject 2   Computer Graphics        Subject subject3   new Subject 3   Data Structures        Set subjects   new HashSet        subjects add subject1       subjects add subject2       subjects add subject3       student setSubjects subjects       Address address   new Address 1   Street 23 NN West     Bhilai    Chhattisgarh    India        student setAddress address       Gson gson   new Gson        String jsonData   gson toJson student       PrintWriter out   response getWriter        try           out println jsonData         finally           out close                   helpful from json response from servlet in java

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You may use bellow like   If you want use json array    download  json-simple-1 1 1 jar  amp  add to your project class path Create A class named Model like bellow  public class Model     private String id        private String name           getter sertter here    In sevlet getMethod you can use like bellow   Override protected void doGet HttpServletRequest request  HttpServletResponse response      throws ServletException  IOException        begin get data from databse or other source   List lt Model gt  list   new ArrayList lt  gt       Model model   new Model      model setId  101      model setName  Enamul Haque      list add model      Model model1   new Model      model1 setId  102      model1 setName  Md Mohsin      list add model1       End get data from databse or other source try        JSONArray ja   new JSONArray        for  Model m   list            JSONObject jSONObject   new JSONObject            jSONObject put  id   m getId             jSONObject put  name   m getName             ja add jSONObject             System out println   json ja       ja       response addHeader  Access-Control-Allow-Origin             response setContentType  application json        response setCharacterEncoding  UTF-8        response getWriter   print ja toString         response getWriter   flush         catch  Exception e         e printStackTrace             Output          name   Enamul Haque   id   101     name   Md Mohsin   id   102       I you want json Object just use like    Override protected void doGet HttpServletRequest request  HttpServletResponse response          throws ServletException  IOException       try            JSONObject json   new JSONObject            json put  id    108            json put  name    Enamul Haque            System out println   json JSONObject      json           response addHeader  Access-Control-Allow-Origin                 response setContentType  application json            response setCharacterEncoding  UTF-8            response getWriter   print json toString             response getWriter   flush               System out println  Response Completed              catch  Exception e            e printStackTrace               Above function Output     name   Enamul Haque   id   108     Full source is given to GitHub  https   github com enamul95 ServeletJson git

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There might be a JSON object for Java coding convenience  But at last the data structure will be serialized to string  Setting a proper MIME type would be nice   I d suggest JSON Java from json org

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Close to BalusC answer in 4 simple lines using Google Gson lib  Add this lines to the servlet method   User objToSerialize   new User  Bill    Gates        ServletOutputStream outputStream   response getOutputStream     response setContentType  application json charset UTF-8    outputStream print new Gson   toJson objToSerialize      Good luck

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response setContentType  text json       create the JSON string  I suggest using some framework   String your string   out write your string getBytes  UTF-8

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Gson is very  usefull for this  easier even  here is my example   public class Bean   private String nombre  juan   private String apellido  machado   private List lt InnerBean gt  datosCriticos   class InnerBean       private int edad 12     public Bean         datosCriticos   new ArrayList lt  gt         datosCriticos add new InnerBean                Bean bean   new Bean        Gson gson   new Gson        String json  gson toJson bean        out print json          nombre   juan   apellido   machado   datosCriticos     edad  12      Have to say people if yours vars are empty when using gson it wont build the json for you Just the

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Write the JSON object to the response object s output stream   You should also set the content type  as follows  which will specify what you are returning             response setContentType  application json       Get the printwriter object from response to write the required json object to the output stream       PrintWriter out   response getWriter       Assuming your json object is   jsonObject    perform the following  it will return your json object   out print jsonObject   out flush

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Depending on the Java version  or JDK  SDK  JRE    i dunno  im new to the Java ecosystem   the JsonObject is abstract  So  this is a new implementation   import javax json Json  import javax json JsonObject        try  PrintWriter out   response getWriter          response setContentType  application json               response setCharacterEncoding  UTF-8         JsonObject json   Json createObjectBuilder   add  foo    bar   build         out print json toString

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First convert the JSON object to String  Then just write it out to the response writer along with content type of application json and character encoding of UTF-8  Here s an example assuming you re using Google Gson to convert a Java object to a JSON string  protected void doXxx HttpServletRequest request  HttpServletResponse response                    String json   new Gson   toJson someObject       response setContentType  quot application json quot        response setCharacterEncoding  quot UTF-8 quot        response getWriter   write json      That s all  See also   How to use Servlets and Ajax  What is the correct JSON content type

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How do you return a JSON object from a Java Servlet   response setContentType  application json    response setCharacterEncoding  utf-8    PrintWriter out   response getWriter         create Json Object   JsonObject json   new JsonObject            put some value pairs into the JSON object       json addProperty  Mobile   9999988888       json addProperty  Name    ManojSarnaik            finally output the json string            out print json toString

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I do exactly what you suggest  return a String    You might consider setting the MIME type to indicate you re returning JSON  though  according to this other stackoverflow post it s  application json

[java] How do you return a JSON object from a Java Servlet

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