Parse json array of different object types

Question

I am trying to send an array of different types from Javascript to a Java servlet.

The Javascript code used to generate and send the data is:

function sendDataOnButtonPress()
{
  var obj1 = {'key_11': "val_11", 'key_12': "val_12"};
  var obj2 = {'key_21': "val_21", 'key_22': "val_22"};
  var myArray = [obj1, obj2];

  var params = {
      data: JSON.stringify(myArray)
  };

  $.post("serv1", $.param(params), function(response) {
    console.log("response = " + response);
  });
}

The Java code used to process this data is:

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.fasterxml.jackson.databind.ObjectMapper;

@WebServlet("/serv1")
public class serv1 extends HttpServlet {
  private static final long serialVersionUID = 1L;

    public serv1() {
        super();
        // TODO Auto-generated constructor stub
    }

  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    String data = request.getParameter("data");
    //System.out.println(data);

    ObjectMapper mapper = new ObjectMapper();
    Object[] objs = mapper.readValue(data, Object[].class);
    System.out.println(objs[0]);

    PrintWriter writer1 = response.getWriter();
    String htmlRespone = "Dummy response";
    writer1.println(htmlRespone);

  }

  /**
   * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
   */
  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    doGet(request, response);
  }

}

Although the line System.out.println(objs[0]); is correctly outputting the first object of the array, I am not able to figure out how to access the properties of the object:

System.out.println(objs[0]["key_11"]);

is not able to compile.

So, my question is how to correctly parse the data sent from javascript inside Java?

I am open to using any json parsing library other than Jackson too.

Ramachandran.A.G · Accepted Answer · 2016-09-06 10:21:53Z

1

You can get it as follows. The super class Object does not have a way to get the value as you indicated , hence the compiler error.

To understand which is the specific type , i printed the object's class. In this case it is a LinkedHashMap. I hence safely casted obj[0] into that. Once i have a map , i can always get a value looking up a key. Hope this helps

String data = "[{\"key_11\": \"val_11\", \"key_12\": \"val_12\"}, {\"key_21\": \"val_21\", \"key_22\": \"val_22\"}]";
ObjectMapper mapper = new ObjectMapper();
Object[] objs = mapper.readValue(data, Object[].class);
System.out.println(objs[0].getClass().getName());

LinkedHashMap<String, Object> keyValues = (LinkedHashMap) objs[0];

System.out.println(keyValues.get("key_11"));

answered Sep 6, 2016 at 10:21

Ramachandran.A.G

4,9481 gold badge14 silver badges28 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Jekin Kalariya · Accepted Answer · 2016-09-06 10:15:53Z

0

You can do something like this with jsonNode

String json = "{ \"query\": { \"pageids\": [ \"736\" ], \"pages\": { \"736\": { \"pageid\": 736, \"ns\": 0, \"title\": \"Albert Einstein\", \"contentmodel\": \"wikitext\", \"pagelanguage\": \"en\", \"touched\": \"2014-01-05T03:14:23Z\", \"lastrevid\": 588780054, \"counter\": \"\", \"length\": 106159 } } } }";
    ObjectMapper mapper = new ObjectMapper();
    JsonNode node =mapper.readTree(json);

    node = node.get("query").get("pages");

    Map<String, Page> pages = mapper.readValue(node.traverse(), new TypeReference<Map<String, Page>>() {
    });

    System.out.println(pages.get("yourkey");

answered Sep 6, 2016 at 10:15

Jekin Kalariya

3,5072 gold badges22 silver badges32 bronze badges

Comments

S Kumar · Accepted Answer · 2016-09-06 10:45:17Z

0

GSON library can also be used to parse the data (https://github.com/google/gson)

String data = request.getParameter("data");        
JsonElement jelement = new JsonParser().parse(data);       
JsonArray output =  jelement.getAsJsonArray();             
JsonElement outputElement=output.get(0);           
JsonObject iObjectOutput=outputElement.getAsJsonObject();       
String value1 = iObjectOutput.get("key_11");

answered Sep 6, 2016 at 10:45

S Kumar

5957 silver badges23 bronze badges

Comments

Community · Accepted Answer · 2017-05-23 12:01:03Z

0

The accepted answer's solution can be shortened to:

System.out.println(((LinkedHashMap)objs[0]).get("key_11"));

edited May 23, 2017 at 12:01

CommunityBot

11 silver badge

answered Sep 6, 2016 at 10:54

Anmol Singh Jaggi

8,6964 gold badges40 silver badges82 bronze badges

Collectives™ on Stack Overflow

Parse json array of different object types

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related