從Java訪問Servlet響應時發生NullPointerException

Question

我正在從Java文件中調用Java servlet。 Servlet文件具有SOP以返回JSON字符串。 現在，我希望在Java代碼中使用該字符串，然后將其解析為XML。

我的代碼如下：

URL urlS = new URL (servletURL);
URLConnection urlc;
urlc = urlS.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(urlc.getInputStream()));

String inputLine;
while ((inputLine = in.readLine()) != null)
    System.out.println("We got JSON Buddy: "+inputLine);
JSONObject js = new JSONObject(inputLine);
System.out.println("We got json object js: "+js.toString());
in.close();

問題是我的Java代碼的SOP是：

12-02 10:30:12.254: I/System.out(24169): We got JSON Buddy: {"movies": { "total": 19, "movie":[{"cover":"http://content9.flixster.com/movie/11/16/04/11160419_pro.jpg","tile":"A Very Harold & Kumar 3D Christmas","MovieDuration":"(R , 1 hr. 29 min.)","showtime":"                                                                                                                                                                                                                                                                                                                                                                                                                                                                           9:35 PM                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         12:00 AM                                                                                                                                                                                                                                                                                                                                                                                                                                                ","theatre":"Rave Motion Pictures 18 + IMAX","url":"http://www.flixster.com/movie/a-very-harold-and-kumar-christmas"},{"cover":"http://content6.flixster.com/movie/11/16/12/11161272_pro.jpg","tile":"Arthur Christmas 3D","MovieDuration":"(PG , 1 hr. 37 min.)","showtime":"                                                                                                                                                                                                                                                                                                                                                                                                                                                                           12:15 PM                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         3:00 PM                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         5:35 PM                                                                                                                                                                                                                                                                                                                                                                                                                                                ","theatre":"Rave Motion Pictures 18 + IMAX","url":"http://www.flixster.com/movie/arthur-christ
12-02 10:30:12.266: I/System.out(24169): Exception: java.lang.NullPointerException

問題是我沒有在inputLine中獲得完整的輸出，另一個問題是NullPointerException。 我不知道為什么會這樣。

Answer 1

您正在循環執行此操作：

  while ((inputLine = in.readLine()) != null)
                System.out.println("We got JSON Buddy: "+inputLine);

為了終止循環， inputLine必須為null，因此，當您到達此處時： JSONObject js = new JSONObject(inputLine); 您將得到一個空指針異常。

Answer 2

看看是否更好：

        URL urlS = new URL (servletURL);
        URLConnection urlc;
        urlc = urlS.openConnection();
        BufferedReader in = new BufferedReader(new         InputStreamReader(urlc.getInputStream()));
        String inputLine;
        while ((inputLine = in.readLine()) != null) {
            System.out.println("We got JSON Buddy: "+inputLine);
            JSONObject js = new JSONObject(inputLine);            
            System.out.println("We got json object js: "+js.toString());
        }
        in.close();

Answer 3

看看你在這里做什么：

while ((inputLine = in.readLine()) != null)
    System.out.println("We got JSON Buddy: "+inputLine);
JSONObject js = new JSONObject(inputLine);

您一直在閱讀， 直到 inputLine為null。 然后，您致電：

JSONObject js = new JSONObject(inputLine);

因此，您的代碼實際上是：

while ((inputLine = in.readLine()) != null)
    System.out.println("We got JSON Buddy: "+inputLine);
JSONObject js = new JSONObject(null);

大概就是問題所在。 因此，問題是：您想在哪里循環？