Manage HTTP headers with Java Servlets: Quick Notes

In Java Servlets API, both HttpServletRequest and HttpServletResponse interfaces (in javax.servlet.http package) provide methods to programatically manipulate HTTP headers. There are a number of standard HTTP headers exchanged between a web server and a client (eg: a browser). "Content-Type" is a commonly used header (which is used to specify MIME type) in Servlets. In this article we are discussing how headers are read/written with Servlet classes.

Reading Headers

A servlet can read HTTP headers sent by a client request using HttpServletRequest interface. This interface has two methods for this.

String getHeader(String headerName);
int getintHeader(String headerName);

Both these methods are similar except getIntHeader() method is used to return value of headers with int type values. Below code shows how value of "Content-type" header is read from the user request. (HttpServlet.doGet() method is used in the example).

import javax.servlet.http.*;
import java.io.*;

public class MyServlet extends HttpServlet {
    public void doGet(re, res) throws IOException{
        String contentType = request.getHeader("Content-type");
        //....
    }
}

Creating/Writing Headers

A servlet can create a header and send back to the client using HttpServletResponse interface; using the following setter methods.

void setHeader(String headerName, String headerValue);
int setintHeader(String headerName, int headerValue);

Below code shows how a new header named "My_Header" is created and set on response.

import javax.servlet.http.*;
import java.io.*;

public class MyServlet extends HttpServlet {
    public void doGet(re, res) throws IOException{
        response.setHeader("My_Header", "new Header value");
        //....
    }
}

Now the client (generally the browser) will receive this new header.

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