Get a NullPointerException when converting a JAVA String to a JSON object

Question

I am writing a java web application to extract tweets using the Twitter API. I got the search method and tried to call the method on the jsp page.

public class SearchTwitter {

private static final String CONSUMER_KEY = "*************";
private static final String CONSUMER_SECRET = "****************";
private static final String OAUTH_TOKEN = "*********************";
private static final String OAUTH_TOKEN_SECRET = "*****************";

public String Search(String query) throws Exception {
    OAuthConsumer consumer = new DefaultOAuthConsumer(CONSUMER_KEY,
            CONSUMER_SECRET);
    consumer.setTokenWithSecret(OAUTH_TOKEN, OAUTH_TOKEN_SECRET);
    query = query.replaceAll(" ", "%20");
    String twitterURL = "https://api.twitter.com/1.1/search/tweets.json?q=" + query + "&src=typd";
    URL url = new URL(twitterURL);
    HttpURLConnection request = (HttpURLConnection) url.openConnection();
    request.setDoOutput(true);
    request.setRequestProperty("Content-Type", "application/json");
    request.setRequestProperty("Accept", "application/json");
    request.setRequestMethod("GET");
    consumer.sign(request);
    request.connect();
    StringBuilder text = new StringBuilder();
    InputStreamReader in = new InputStreamReader((InputStream) request.getContent());
    BufferedReader buff = new BufferedReader(in);
    System.out.println("Getting data ...");
    String line;
    do {
        line = buff.readLine();
        text.append(line);
    } while (line != null);
    String strResponse = text.toString();
    return strResponse;
}

}

The search method returns a string.

            <%
            SearchTwitter stw = new SearchTwitter();
            String tweet = request.getParameter("query");

            JSONObject result = new JSONObject(stw.Search(tweet));
            JSONArray statuses = result.getJSONArray("statuses");
            for (int i = 0; i < statuses.length(); i++) {
                String time = statuses.getJSONObject(i).getString("created_at");
                String user = statuses.getJSONObject(i).getJSONObject("user").getString("screen_name");
                String text = statuses.getJSONObject(i).getString("text");
                System.out.println(time.toString());
                System.out.println(user.toString());
                System.out.println(text.toString());
            }
        %>

And I'm trying to convert a String object to JSON, but it shows an HTTP 500 error NullPointerException I don’t know where I am mistaken because I am new to JAVA. Can anyone help? I really appreciate it!

Answer 1

Your mistake is likely to happen because

String tweet = request.getParameter("query");

returns null, that is, it cannot find the parameter and returns null.

After that, you try to perform actions with a null value:

query = query.replaceAll(" ", "%20");

null .replaceAll, NullPointerException

:

, null :

    <%
        SearchTwitter stw = new SearchTwitter();
        String tweet = request.getParameter("query");

        if(tweet!=null){
            JSONObject result = new JSONObject(stw.Search(tweet));
            JSONArray statuses = result.getJSONArray("statuses");
            for (int i = 0; i < statuses.length(); i++) {
                String time = statuses.getJSONObject(i).getString("created_at");
                String user = statuses.getJSONObject(i).getJSONObject("user").getString("screen_name");
                String text = statuses.getJSONObject(i).getString("text");
                System.out.println(time.toString());
                System.out.println(user.toString());
                System.out.println(text.toString());
            }
        } else {
            System.out.println("Unable to retrieve query!");
        }
    %>

, tweet null, " !". .