JSON解析器-写入文本文件-线程“ main”中的异常java.lang.NullPointerException

Question

I am trying to write a list JSON that has been parsed into ArrayList String to a txt file. However I keep getting this error:

Exception in thread "main" java.lang.NullPointerException
    at kr.ac.uos.datamining.JSONParser.parseForTweets(JSONParser.java:47)
    at kr.ac.uos.datamining.JSONParser.<init>(JSONParser.java:25)
    at kr.ac.uos.datamining.test.main(test.java:21)

This is the main class code test.java:

    package kr.ac.uos.datamining;

    import java.io.File; 
    import java.io.FileWriter;
    import java.io.FileNotFoundException; 
    import java.util.ArrayList;
    import java.util.List;
    import kr.ac.uos.datamining.JSONParser; 
    import kr.ac.uos.datamining.Tweet; 
    import kr.ac.uos.datamining.User;

    public class test {

    public static List <String> list = new ArrayList<String>();

    public static void main(String[] args) throws IOException, FileNotFoundException, InterruptedException, SQLException {
   **Line 21**
        JSONParser j = new JSONParser(new File("D:/usr/samsunggalaxy.txt"));
        ArrayList<Tweet> tweets = j.getTweets();

        for(Tweet tweet : tweets){
            User user = tweet.getUser();
            list.add(tweet.getText() + " | " + user.getScreenName());
        }

        FileWriter writer = new FileWriter("samsunggalaxy.txt");
        for(String str: list) {
            writer.write(str);
        }
        writer.close();
        }
    }

And this is the JSON Parser line of which the error trace shows:

    private void parseForTweets(){
            Scanner in = null;
            try {
                in = new Scanner(json);
            } catch (FileNotFoundException e) {

            }

**Line47**          while(in.hasNextLine()){
                String rawTweet = in.nextLine();

                if(!rawTweet.contains("\"retweeted\":true")){
                    Tweet tweet = TweetParser.parseTweet(rawTweet);
                    tweets.add(tweet);
                }
            }
        }

I think the error is in the line String rawTweet = in.nextLine(); However I cant seem to figure this out. Is the JSON data itself has any influence on this? I mean is it because I parsed the data wrongly? Or is it because of another reason?

Any help would be really appreciated

Answer 1

It seems that the problem is that you're not handling the exception, therefore, if the new Scanner(json) line failed, the in reference would be null. In such a case, you'd fail in the while(in.hasNextLine()) line.

However, without line numbers in the code it's hard to tell exactly if that's really the problem.

Answer 2

if you are sure the problem is in.nextLine() ( please debug your code to be sure where is the problem) then try this one :

 Iterator<JSONObject> iterator = yourJsonObject.iterator();
 while (iterator.hasNext()) {
 JSONObject factObj = (JSONObject) iterator.next();
 ...

 }