How can I decode JWT token in android?

you should split string:
If you pass the first two sections through a base 64 decoder, you’ll get the following (formatting added for clarity):

header

{
  "alg": "HS256",
  "typ": "JWT"
}

body

    {
  "sub": "1234567890",
  "name": "John Doe",
  "admin": true
}

Code example:

public class JWTUtils {

    public static void decoded(String JWTEncoded) throws Exception {
        try {
            String[] split = JWTEncoded.split("\\.");
            Log.d("JWT_DECODED", "Header: " + getJson(split[0]));
            Log.d("JWT_DECODED", "Body: " + getJson(split[1]));
        } catch (UnsupportedEncodingException e) {
            //Error
        }
    }

    private static String getJson(String strEncoded) throws UnsupportedEncodingException{
        byte[] decodedBytes = Base64.decode(strEncoded, Base64.URL_SAFE);
        return new String(decodedBytes, "UTF-8");
    }
}

Call method for example

JWTUtils.decoded("eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iOnRydWV9.TJVA95OrM7E2cBab30RMHrHDcEfxjoYZgeFONFh7HgQ");

library reference:
https://github.com/jwtk/jjwt

jwt test:
https://jwt.io/