JSON parsing using Gson for Java

Question

I would like to parse data from JSON which is of type String. I am using Google Gson.

I have:

jsonLine = \"
{
 \"data\": {
  \"translati         


        

Answer 1

    JsonParser parser = new JsonParser();
    JsonObject jo = (JsonObject) parser.parse(data);
    JsonElement je = jo.get("some_array");

    //Parsing back the string as Array
    JsonArray ja = (JsonArray) parser.parse(o.get("some_array").getAsString());
    for (JsonElement jo : ja) {
    JsonObject j = (JsonObject) jo;
        // Your Code, Access json elements as j.get("some_element")
    }

A simple example to parse a JSON like this

{ "some_array" : "[\"some_element\":1,\"some_more_element\":2]" , "some_other_element" : 3 }

Answer 2

You can create corresponding java classes for the json objects. The integer, string values can be mapped as is. Json can be parsed like this-

Gson gson = new GsonBuilder().create(); 
Response r = gson.fromJson(jsonString, Response.class);

Here is an example- http://rowsandcolumns.blogspot.com/2013/02/url-encode-http-get-solr-request-and.html

Answer 3

Simplest thing usually is to create matching Object hierarchy, like so:

public class Wrapper {
   public Data data;
}
static class Data {
   public Translation[] translations;
}
static class Translation {
   public String translatedText;
}

and then bind using GSON, traverse object hierarchy via fields. Adding getters and setters is pointless for basic data containers.

So something like:

Wrapper value = GSON.fromJSON(jsonString, Wrapper.class);
String text = value.data.translations[0].translatedText;

Answer 4

You can use a JsonPath query to extract the value. And with JsonSurfer which is backed by Gson, your problem can be solved by simply two line of code!

    JsonSurfer jsonSurfer = JsonSurfer.gson();
    String result = jsonSurfer.collectOne(jsonLine, String.class, "$.data.translations[0].translatedText");

Answer 5

In my first gson application I avoided using additional classes to catch values mainly because I use json for config matters

despite the lack of information (even gson page), that's what I found and used:

starting from

Map jsonJavaRootObject = new Gson().fromJson("{/*whatever your mega complex object*/}", Map.class)

Each time gson sees a {}, it creates a Map (actually a gson StringMap )

Each time gson sees a '', it creates a String

Each time gson sees a number, it creates a Double

Each time gson sees a [], it creates an ArrayList

You can use this facts (combined) to your advantage

Finally this is the code that makes the thing

        Map<String, Object> javaRootMapObject = new Gson().fromJson(jsonLine, Map.class);

    System.out.println(
        (
            (Map)
            (
                (List)
                (
                    (Map)
                    (
                        javaRootMapObject.get("data")
                    )
                 ).get("translations")
            ).get(0)
        ).get("translatedText")
    );

Answer 6

One way would be created a JsonObject and iterating through the parameters. For example

JsonObject jobj = new Gson().fromJson(jsonString, JsonObject.class);

Then you can extract bean values like:

String fieldValue = jobj.get(fieldName).getAsString();
boolean fieldValue = jobj.get(fieldName).getAsBoolean();
int fieldValue = jobj.get(fieldName).getAsInt();

Hope this helps.