Parse JSON Array in Java

Question

I am having trouble to parse a json array in java.

I have a JSON array like below returning from server

   [
{
    "User": "538000001",
    "Transaction-Id": "oHbgP2y2OXfdDcxAOI/q9HxY68PNs+xS+8CvfGpoN2ZUU/8mavBaI0564VeZXYBDMnk84kkfZeCJM51I92rFdf4Zi4uKEoqJd7jr78bXo4MOyoSs5mntIir7aVJ9/b+4nz6x2+g0LPY7+Sq8RHvbr+c4Evhg+VXeKDzE3f6+bJo=,YWFhd3MxLnJlYWxtMTsxNDE4MDczNTk0MjkxOzUyQDUzODAwMDAwMQ==",
    "Challenge-Response": "7ZGlkpVfYvQDjvTa2EShZwZ3dGc=",
    "Challenge": "MzcrMzM3NzA4MTM3KzE0MTgwNzM1OTQ="
},
{
    "User": "538000000",
    "Transaction-Id": "+5Oi4NnG9HOVMPx4nM/TP4ZBONG4HtOBbA5+uf/d+hik7o1Aes9H0PLCqAgG/Td2xLDPOdZJJW7ppj3MLkZBvJr+t9JWKdSGpGHAYTp0oonRTVsesPVCtNI6dXvMY9P+bHDiBWkZiqjSjOZuuzImLaJ17G1/D/GNqIonaNCjqjo=,YWFhd3MxLnJlYWxtMTsxNDE4MDczNTk0Mjk1OzUzQDUzODAwMDAwMA==",
    "Challenge-Response": "eEzLzYLmzo5R2tNwokG0mfbuLZY=",
    "Challenge": "MzgrNDY2NjY4NjgyKzE0MTgwNzM1OTQ="
}
]

I am using GSON to parse this array but so far not successful.I wrote the following code

     class round1Body
     {
         String User;
         String Transaction_Id;
         String Challenge_Response;
         String Challenge;

         round1Body(String User,String Transaction_Id,String Challenge_Response,String Challenge)
         {
            this.User = User;
            this.Transaction_Id=Transaction_Id;
            this.Challenge_Response = Challenge_Response;
            this.Challenge=Challenge;
         }
         @Override
         public String toString()
        {
            return "User = " + User + " Transaction-Id = " + Transaction_Id + " Challenge-Response = " + Challenge_Response + "Challenge = "
                    + Challenge;
        }
     }
  Type listType = new TypeToken<ArrayList<round1Body>>(){}.getType();
  Object jsonE = new Gson().fromJson(firstResponse.readEntity(String.class),listType);
  System.out.println(jsonE);

The output when I try to print is [null, null].

Can anybody help me out ?

Thanks in advance !

Before you try to use a fancy "POJO" parser, learn how to deal with JSON as simple Maps and Lists. The concepts are very simple. — Hot Licks
– Hot Licks, Commented Dec 8, 2014 at 22:09

Alexis C. · Accepted Answer · 2014-12-08 21:51:52Z

1

It seems like you have a problem with the firstResponse.readEntity(String.class) call. Otherwise you wouldn't have [null, null] as output. So the problem came from here first. Try to have that working.

Then if you don't specify a SerializedName rule on your class' fields, GSON requires that the name must match exactly the key's name in your JSON file.

You have "Transaction-Id" on the JSON side but you defined it as Transaction_Id in your Java file, same for Challenge_Response.

Since in Java an identifier can't have a -, you need to specify a rule for those two attributes.

class round1Body {
    String User;
    @SerializedName("Transaction-Id")
    String Transaction_Id;
    @SerializedName("Challenge-Response")
    String Challenge_Response;
    String Challenge;
    //...
}

With these changes, it successfully print (I'm reading your JSON string from a file):

[User = 538000001 Transaction-Id = oHbgP2y2OXfdDcxAOI/q9HxY68PNs+xS+8CvfGpoN2ZUU/8mavBaI0564VeZXYBDMnk84kkfZeCJM51I92rFdf4Zi4uKEoqJd7jr78bXo4MOyoSs5mntIir7aVJ9/b+4nz6x2+g0LPY7+Sq8RHvbr+c4Evhg+VXeKDzE3f6+bJo=,YWFhd3MxLnJlYWxtMTsxNDE4MDczNTk0MjkxOzUyQDUzODAwMDAwMQ== Challenge-Response = 7ZGlkpVfYvQDjvTa2EShZwZ3dGc=Challenge = MzcrMzM3NzA4MTM3KzE0MTgwNzM1OTQ=, User = 538000000 Transaction-Id = +5Oi4NnG9HOVMPx4nM/TP4ZBONG4HtOBbA5+uf/d+hik7o1Aes9H0PLCqAgG/Td2xLDPOdZJJW7ppj3MLkZBvJr+t9JWKdSGpGHAYTp0oonRTVsesPVCtNI6dXvMY9P+bHDiBWkZiqjSjOZuuzImLaJ17G1/D/GNqIonaNCjqjo=,YWFhd3MxLnJlYWxtMTsxNDE4MDczNTk0Mjk1OzUzQDUzODAwMDAwMA== Challenge-Response = eEzLzYLmzo5R2tNwokG0mfbuLZY=Challenge = MzgrNDY2NjY4NjgyKzE0MTgwNzM1OTQ=]

Note that you could use this annotation to respect naming conventions.

edited Dec 8, 2014 at 21:51

answered Dec 8, 2014 at 21:37

Alexis C.

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9 Comments

shbolise Over a year ago

Thank you very much for the response. I just used System.out.println(firstResponse.readEntity(String.class)); and it printed correctly but I am still getting same [null,null] :( Maybe problem with the listType ?? Type listType = new TypeToken<ArrayList<round1Body>>(){}.getType(); ??

shbolise Over a year ago

Did you use same listType I used ?? in new Gson().fromJson(firstResponse.readEntity(String.class),listType);

Alexis C. Over a year ago

@shbolise Yes, I copy pasted your code. The only difference is that I'm reading the json data from a file, that's why I suspect firstResponse.readEntity(String.class) is the problem.

shbolise Over a year ago

String json = firstResponse.readEntity(String.class); System.out.println(json); // Works Fine Object jsonE = new Gson().fromJson(json,listType); System.out.println(jsonE); // [null,null] .... I must be doing some thing stupidly wrong :(

Alexis C. Over a year ago

@shbolise What do you mean by work fine? What is the content of json? What happens if you put the json in a file and try to read it from there?

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