Extracting a byte array from a JSON

Question

I have a JSON of the following format:

[{"fingerprint":"[79,0,0,0,18,0,0,0,18,0,0,0,19,0,0,0,23,0,0,0,40,0,0,0,42,0,0,0,63,0,0,0,68,0,0,0,71,0,....]"}]

I have been trying to extract the byte array from it using the following:

JSONFingerprint fingerprintData = gson.fromJson(obj, JSONFingerprint.class);

Where JSONFingerprint is:

public class JSONFingerprint {

    byte[] fingerprint;

    public byte[] getfingerprintData() {
        return fingerprint;
    }

}

I have been getting this error:

Exception in thread "Thread-0" com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was STRING
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:176)
    at com.google.gson.Gson.fromJson(Gson.java:795)
    at com.google.gson.Gson.fromJson(Gson.java:859)
    at com.google.gson.Gson.fromJson(Gson.java:832)

Does anybody have any ideas??

Answer 1

It seems your JSON and POJO don't match. There can be 2 possible solutions for this.

Solution 1:-

If you cannot change the JSON format(ie)your JSON is gonna be this,

[{"fingerprint":"[79,0,0,0,18,0,0,0,18,0,0,0,19,0,0,0,23,0,0,0,40,0,0,0,42,0,0,0,63,0,0,0,68,0,0,0,71,0,....]"}]

Then you need to change your JSONFingerprint class to this:-

public class JSONFingerprint {

    String fingerprint;

    public String getfingerprintData() {
        return fingerprint;
    }
}

and you need to parse your JSON like this:-

JSONFingerprint[] dummy = new JSONFingerprint[0]; 
JSONFingerprint[] fingerPrint = gson.fromJson(json, dummy.getClass());
System.out.println(fingerPrint[0].getfingerprintData());

Solution 2:-

If your POJO cannot change(ie)your POJO is gonna be this,

public class JSONFingerprint {

    byte[] fingerprint;

    public byte[] getfingerprintData() {
        return fingerprint;
    }
}

Then you'll have to change your JSON format to something like this:-

{"fingerprint":[1,2,3,4,5,6,7,8,9,10]}

which you can parse it usually, as you've already done:-

JSONFingerprint fingerprintData = gson.fromJson(obj, JSONFingerprint.class);

Hope this helps you!