String string = request.getParameter("data") is null

Question

I am writing a servlet that will accept POST data coming from an AJAX request.

Here is the code I send from the client:

$.ajax({
            type: "POST",
            url: "urlservlet",
            data: "{type:'" + "country" + 
            "', country:'" + $('#country').val() +
            "'}",
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            success: function(response) {

            }

And this is the servlet code:

protected void doPost(HttpServletRequest request, HttpServletResponse response)
                      throws ServletException, IOException {
    string test = request.getParameter("type");
}

But the thing is I always get the type equal to null. I don't know why.

Kindly help me.

Your title says getP(data), whereas your code says getP(type). What is the actual problem? — Rahul
– Rahul, Commented Oct 17, 2013 at 16:10

informatik01 · Accepted Answer · 2013-10-17 23:14:02Z

5

You are writing JSON to your request body and expecting request parameters. From the javadoc:

Returns the value of a request parameter as a String, or null if the parameter does not exist. Request parameters are extra information sent with the request. For HTTP servlets, parameters are contained in the query string or posted form data.

You haven't posted form data and don't have a query string.

What you want is to read the HTTP request body with HtppServletRequest#getInputStream() and parse the JSON to extract your element.

edited Oct 17, 2013 at 23:14

informatik01

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answered Oct 17, 2013 at 16:08

Sotirios Delimanolis

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4 Comments

Lego_blocks Over a year ago

oh okay. please elaborate more. please. :)

Sotirios Delimanolis Over a year ago

@pepsi Elaborate on what subject? There are keywords in my answer that will help you find what you want.

Lego_blocks Over a year ago

Thanks man, appreciated your time. just asking about a sample code. since I am very new to java.:)

Lego_blocks Over a year ago

I fixed this using the contentType: "application/x-www-form-urlencoded", then just get it on the server side using the getParameterMap() method and just manipulate the string to make it a valid json data. :)

Vidya · Accepted Answer · 2013-10-17 16:19:06Z

2

The problem is as @Sotirios describes. However, I would solve it by using a Java REST framework on the server side like RESTEasy, Spring MVC, or Restlet. It is preferable to use an abstraction so you can focus on your business logic rather than low-level details of the Servlet API.

And a JSON serializer/deserializer like Jackson to avoid dealing with the low-level details of parsing JSON. Jackson as well as its alternatives integrate seamlessly with the REST frameworks I mentioned.

I like good abstractions.

answered Oct 17, 2013 at 16:19

Vidya

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1 Comment

user16422658 Over a year ago

Jackson has made me bang my head against the wall for 8 hours, because the error handling is terrible at best

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