CODEWITHSUNDEEP
javahttpservlets
Dilip B S
Dilip B S

Reputation: 203

reading custom headers in servlets

I have a requirement to set custom headers in http response and read them whenever required. I use the following code to read the header.

servlet1:

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  response.addHeader("cust-header", "cust-value");
  RequestDispatcher rd = request.getRequestDispatcher("servlet2");
  rd.include(request, response);
}

servlet2:

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  System.out.println(request.getHeader("cust-header"));
}

When I tried to read the custom header value, I got "null" in the console. Why this is happening? How can I read custom headers set in response whenever required?

Upvotes: 1

Views: 2381

Answers (1)

Tomas Narros
Tomas Narros

Reputation: 13468

From the RequestDipatcher include method API doc:

[...] The ServletResponse object has its path elements and parameters remain unchanged from the caller's. The included servlet cannot change the response status code or set headers; any attempt to make a change is ignored. [...]

So, if you look at your code, you are setting the header at the response object, but trying to get it from the request. As they remain unchanged, it won't work.

The most common way to pass values from a servlet to another in a forward or include redirection, is passing it as a request attribute:

servlet1:

//set a request attribute
request.setAttribute("cust-header", "cust-value");
RequestDispatcher rd = request.getRequestDispatcher("servlet2");
rd.include(request, response);

servlet2:

System.out.println(request.getAttribute("cust-header"));

Upvotes: 2

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