Blackberry HttpPost null pointer exception Java

问题:

With the following code, the server is getting hit, but I also want to send variables in POST method.

But it just gives me a null pointer exception. It has something to do with the OutputStream. I have checked postData ... it has some address, which means it is not null.

So why I am given null pointer exception?

ConnectionFactory connFact = new ConnectionFactory();
ConnectionDescriptor connDesc;
try {
    connDesc = connFact.getConnection("http://example.com/login.php", Connector.READ_WRITE, returnContent);
    httpConn.setRequestMethod(HttpConnection.POST);
    httpConn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");

    URLEncodedPostData encPostData = new URLEncodedPostData("UTF-8", false);
    encPostData.append("count", "Hell Yeah!");
    byte[] postData = encPostData.toString().getBytes("UTF-8");

    httpConn.setRequestProperty("Content-length", String.valueOf(postData.length));
    Dialog.alert("Post Data: " + postData);

    OutputStream os = httpConn.openOutputStream();
    os.write(postData);
    os.flush();
    httpConn = (HttpConnection) connDesc.getConnection();

    final int iResponseCode = httpConn.getResponseCode();
    UiApplication.getUiApplication().invokeLater(new Runnable() {
        public void run() {
            //Dialog.alert("Response code: " +  Integer.toString(iResponseCode));
        }
    });
} catch (IOException e) {
    System.err.println("Caught IOException: " + e.getMessage());
}

回答1:

You are misusing the ConnectionFactory.getConnection(String url, int transportType, String ConnectionUID) method. For instance, check what you pass as transportType...

Here is what API says about return value:

Returns: a ConnectionDescriptor if a connection can be established; null otherwise

So, it just fails and returns null. And that's why you get a NPE.

UPDATE:

I would recommend to just use a simpler API ConnectionFactory.getConnection(String url):

ConnectionDescriptor cd = connFact.getConnection("http://example.com/login.php");
if (cd == null) {
    // throw an error signalling there is no connectivity right now
}
HttpConnection httpConn = (HttpConnection) cd.getConnection();
// the rest of the code working with httpConn ..

回答2:

Have a look to the linked answer and verify if that implementation of 'login' procedure is ok for your needs: authentication username password url in blackberry