CODEWITHSUNDEEP
javajsonlistgsondeserialization
Max Jones
Max Jones

Reputation: 140

GSON Deserialize object with member ArrayList<String>

I've seen a lot of similar questions. I haven't been able to find any that fit my exact issue. In all of the examples I've found the List is of an object type defined in the parent class, whereas I just have a list of Strings. I've tried using a simple array String[], and I've seen examples with overloading deserializers, and getting the TypeToken but I can't tie it together to make this work. My list is always empty (or null if I don't initialize it when I define the list). What am I missing here, it feels like I'm trying to do something very simple but everything I find on it looks overly complex.

This is my class:

public class MondoConfig {
private String merchantURL;
public ArrayList<String> targets = new ArrayList<String>();


public MondoConfig () {}

public String getMerchantURL() {
    return this.merchantURL;
}

public void setMerchantURL(String url) {
    this.merchantURL = url;
}

public ArrayList<String> getTargets() {
    return this.targets;
}

public void setTargets(ArrayList<String> t) {
    this.targets = t;


}
}

This is my json:

{
"merchantURL":"https://example.com/collections/posters",
"targets":[
"testing",
"another",
"one more"
]
}

And my code to deserialize:

BufferedReader br = new BufferedReader(new FileReader("C:\\mondo_config.json"));
MondoConfig config = gson.fromJson(br, MondoConfig.class);

Upvotes: 0

Views: 264

Answers (1)

Jim Nutt
Jim Nutt

Reputation: 1756

I'm seeing a few problems in your code, but I was able to get it to work without any issues. 

package org.nuttz.gsonTest;
import java.util.ArrayList;

public class MondoConfig {
   private String merchantURL;
   public ArrayList<String> targets = new ArrayList<String>();

   MondoConfig () {}

   public String getMerchantURL() {
      return this.merchantURL;
   }

   public void setMerchantURL(String url) {
      this.merchantURL = url;
   }

   public ArrayList<String> getTargets() {
      return this.targets;
   }

   public void setTargets(ArrayList<String> t) {
      this.targets = t;
   }
}

The setMerchantURL() function in your original code wasn't quite right, so I fixed it. Then I used this code to test it:

package org.nuttz.gsonTest;

import java.io.*;
import java.util.List;
import com.google.gson.*;

public class App 
{
    public static void main( String[] args )
    {
       Gson gson = new Gson();
       try {
          BufferedReader br = new BufferedReader(new FileReader("/home/jim/mondoconfig.json"));
          MondoConfig config = gson.fromJson(br, MondoConfig.class);
          System.out.println("Contents of config:");
          System.out.println(config.getMerchantURL());
          List<String> targets = config.targets;
          for (String t : targets) {
             System.out.println(t);
          }
       }
       catch (Exception x) {
          x.printStackTrace();
       }
    }
}

And got the following results:

Contents of config:
https://example.com/collections/posters
testing
another
one more

This is using the 2.8.2 version of GSON. In other words, you're on the right track, you've just need to fix the MondoConfig class.

Upvotes: 1

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