Question

我是Java的初学者，我正在编写一个代码来将json twitter数据集输入到MYSQL数据库中。我使用文件名“file”作为输入，解析它，并将其写入SQL数据库。但是，我一直收到错误：

线程“main”java.lang.NullPointerException中的异常在edu.mbhs.twitter.test.main（test.java:42）

第42行包含：

  if (tweet.getLang().equals("en")){

这是我的主要类代码：

public class test {

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

public static void main(String[] args) throws FileNotFoundException, InterruptedException, SQLException {

    JSONParser j = new JSONParser(new File("file"));
    ArrayList<Tweet> tweets = j.getTweets();


   String sql = "insert into twitterdatasets (tweet_created_at, tweet_id, tweet_text, user_id, user_screen_name, user_location, user_followers_count, user_friends_count, user_created_at, user_verified, user_lang, tweet_retweeted_count, tweet_favorite_count, tweet_lang) values (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)";
   Connection conn = getConnection();
   PreparedStatement ps = conn.prepareStatement(sql);

   final int batchSize = 1000;
   int count = 0;

   for (Tweet tweet: tweets){

       if (tweet.getLang().equals("en")){
           User user = tweet.getUser();
           ps.setString(1, tweet.getCreatedAt());
           ps.setString(2, tweet.getIdStr());
           ps.setString(3, tweet.getText());
           ps.setString(4, user.getIdStr());
           ps.setString(5, user.getScreenName());
           ps.setString(6, user.getLocation());
           ps.setInt(7, user.getFollowersCount());
           ps.setInt(8, user.getFriendsCount());
           ps.setString(9, user.getCreatedAt());
           ps.setBoolean(10, user.getVerified());
           ps.setString(11, user.getLang());
           ps.setInt(12, tweet.getRetweetCount());
           ps.setInt(13, tweet.getFavoriteCount());
           ps.setString(14, tweet.getLang());
           ps.addBatch();
       if (++count % batchSize == 0){
           ps.executeBatch();
       }

       }
   }

   ps.executeBatch();
   ps.close();
   conn.close();
   System.out.println("File has been successfully written to database");
}

private static Connection getConnection() {
      Connection con = null;
      String url = "jdbc:mysql://localhost:3306/";
      String db =  "dbo";
      String driver = "com.mysql.jdbc.Driver";
      String user = "root";
      String pass = "elvira03";
      try {
       Class.forName(driver);
       con = DriverManager.getConnection(url + db, user, pass);
      } catch (ClassNotFoundException e) {
       e.printStackTrace();
      } catch (SQLException e) {
       e.printStackTrace();
      }
      return con;
     }
}

Answer 1

尝试

if(tweet.getLang()!= null && tweet.getLang().equals("en") { ... }

我认为在某些推文中，如果用户没有设置它，语言可以是null。

Answer 2

我在使用Streaming API时遇到了同样的问题...如果你的应用程序处理的邮件太慢，你就会断开连接。解决方案是在消息处理过程中放弃检查lang。

相反，您可以在OAuth参数中启用语言过滤器...我正在使用scribe，这就是我的解决方案：

    OAuthService service = new ServiceBuilder().provider(TwitterApi.class).apiKey("your_twitter_api_key")
                .apiSecret("your_twitter_api_secret").build();
    // Set your access token
    Token accessToken = new Token("your_twitter_token", "your_twitter_secret");
    // Let's generate the request
    System.out.println("Connecting to Twitter Public Stream");
    OAuthRequest request = new OAuthRequest(Verb.POST, STREAM_URI);
    request.addHeader("version", "HTTP/1.1");
    request.addHeader("host", "stream.twitter.com");
    request.setConnectionKeepAlive(true);
    request.addHeader("user-agent", "Twitter Stream Reader");

        // ADD YOUR LANGUAGE PREFS HERE...
        request.addBodyParameter("language", "en");

    service.signRequest(accessToken, request);
    Response response = request.send();

    // Create a reader to read Twitter's stream
    BufferedReader reader = new BufferedReader(new InputStreamReader(response.getStream()));

转换为MYSQL时java中线程“main”java.lang.NullPointerException中的异常

2 个答案: