How to use GSON to encode String array data into JSON properly?

Question

I am using GSON in my Java project to encode data ( that are fetched from database and stored into a String array ) in JSON format. Everything looks OK but the problem is with the size of String. For example I have the following String array:

String [] data = new String[12];

Suppose my String array contains the following data: {"ABC", "DEF", "GH", "IJ"}

Then the encoded JSON data are: ["ABC", "DEF", "GH", "IJ", "\u0000", null, null, null, null, null, null]

The number of null value in the JSON data is depends on the number of data available in my String array.

As the data is retrieved from database so I can't declare a specific size for my String array.

I am using the following code to encode String data into JSON format.

Gson gs = new Gson();
gs.toJson(data); //data String array contains data from database

Can anyone tell me how can I skip/remove those null value from my JSON data?

The data array is always defined as 12 in size? When you load the data form the database the excess capacity is padded with null? What about the \u0000 String? — sargue
– sargue, Commented Apr 18, 2016 at 16:08
No, it is just an example. It may be less than 12 for one type of data and more than 12 for other data [depends on the requirements of the project]. Yes the excess capacity is padded with null. I don't know why '\u000' is added. As I load data in the format data[index++], to remove unwanted garbage, I use data[index] = "\0". maybe \u000 is added for this. — Shimul
– Shimul, Commented Apr 18, 2016 at 16:45

Zircon · Accepted Answer · 2016-04-18 14:03:28Z

1

If you're uncomfortable working with array sizes, use an ArrayList and add each result from your database to it. Then when you're done with the database side of things:

data = arrayList.toArray(new String[arrayList.size()]);

This guarantees that the data object is just the right size to hold your data.

answered Apr 18, 2016 at 14:03

Zircon

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Comments

sargue · Accepted Answer · 2016-04-19 08:03:31Z

First of all an advice not directly related to the question. In a comment you say:

As I load data in the format data[index++], to remove unwanted garbage, I use data[index] = "\0". maybe \u000 is added for this.

I strongly suggest you load data into a List as you don't seem very comfortable working with arrays.

Instead of String [] data = new String[12] use List<String> data = new ArrayList<>(). Then, when loading data, instead of data[index++] use data.add(s).

Then the call new Gson().toJson(data) will work as you expect.

Anyway, to answer exactly your question you can just clean the array.

String [] data = {"ABC", "DEF", "GH", "IJ", "\u0000", null, null, null, null, null, null};
System.out.println("data = " + new Gson().toJson(data));
int i = 0;
for (; i < data.length && data[i] != null && !Objects.equals(data[i],"\u0000"); i++) ;
String[] cleanData = Arrays.copyOf(data, i);
System.out.println("cleanData = " + new Gson().toJson(cleanData));

The output of that code is this:

data = ["ABC","DEF","GH","IJ","\u0000",null,null,null,null,null,null]
data = ["ABC","DEF","GH","IJ"]

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