Question

I have just a curiosity question. I have an HttpPost request in Android that looks something like this:

HttpClient client = new DefaultHttpClient();
HttpPost post = new HttpPost(getString(R.string.url));

//This code does not work
HttpParams params = new BasicHttpParams();
params.setParameter("type", "20");
post.setParams(params);

try {
    HttpResponse response = client.execute(post);
} catch (ClientProtocolException e) {
    e.printStackTrace();
} catch (IOException e) {
    e.printStackTrace();
}

On my server side, I have a servlet that listens for requests and parses the parameters:

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    Enumeration en = request.getParameterNames();
    while (en.hasMoreElements()){
        System.out.println(en.nextElement());
    }
} 

When I execute this code, the servlet does not see any parameters at all. But if I replace the whole “parameter” chunk with this code:

//This code works
List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(5);
nameValuePairs.add(new BasicNameValuePair("type", "20"));

try {
    post.setEntity(new UrlEncodedFormEntity(nameValuePairs));
} catch (UnsupportedEncodingException e1) {
// TODO Auto-generated catch block
    e1.printStackTrace();
}

My servlet can parse parameters. It’s not a problem, I’m just going to use the entity but my question is, why can’t my servlet getthe parameters from the first code chunk? What’s wrong with setParams? Why can the servlet see parameters if I make them an entity?

Answer 1

In HTML when we have something like “http://host/path?user=uname&passwd=pass”, we call the part (user=uname&passwd=pass) after the question mark “form data”.The “form data” can be attached to the end of the URL after a question mark (as above), for GET requests, or sent to the server on a separate line, for POST requests.The “form data” are split to parameters. The parameters are separated by & when we use GET.

In our case the HttpPost and HttpGet classes extend the AbstractHttpMessage which implements the setParams method. This method is same for GET and POST but does the job only for GET! In the case of GET the parameters are put in the URL. In the case of POST you need to set the entity for the parameters to be on a “separate line”.

On the server side when using servlets the getParameters is clever enough to find the parameters for GET and POST.

Thats why on the server side we do not need to change the code for getting the parameters!

Hope I helped!