Discussion on sendRedirect() method of HttpServletResponse in JEE

The sendRedirect is a method defined in the HttpServletResponse interface. The signature of the method is like void sendRedirect(java.lang.String location) .

With this method, a servlet that implements HttpServletResponse , can send a redirect response back to the client so that the client can make a fresh request to the location URL sent as a parameter.

In this current tutorial, we will assist you in understanding when and how it could be applied, moreover, we will also point out the difference between servlet interactions through RequestDispatcher and sendRedirect

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How and when sendRedirect() is called

The below code snippet explains how you can call a sendRedirect method

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { int firstNo = Integer.parseInt(request.getParameter("first")); int secNo = Integer.parseInt(request.getParameter("second")); String msg = "First Number is Greater"; if(firstNo < secNo) msg = "Second Number is Greater"; response.sendRedirect("ResultServ?msg=" + msg); }

The above code shows the doGet method of a sample Servlet called DemoServ. It takes up two numbers from an HTML form having names first & second and stores it in two variables firstNo & secNo .

Depending on the condition whether firstNo or secNo is greater, an appropriate String object msg is computed.

Finally, the sendRedirect method of the response object is called with a specific URL call to another servlet ResultServ which is within the same package as that of DemoServ, along with the precomputed msg as the value of a parameter msg

Below is the code snippet of doGet() method of ResultServ

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String resultMsg = request.getParameter("msg") ; response.setContentType("text/html"); PrintWriter out = response.getWriter(); out.println("" + resultMsg + ""); }

When requested, doGet() method gets the value of the msg parameter and ultimately shows that in html

So this was how you can apply sendRedirect() method, but more importantly, you need to understand the course of actions that take place within this.

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When sendRedirect() is called with a URL of ResultServ from DemoServ, the response gets back to the client and a fresh request is generated from that client to the ResultServ as per the URL and consequently it is served by the ResultServ. This means with every sendRedirect() call, the existing server cycle gets completed, and another new one is created.

It is evident that whenever the ResultServ is called through the sendRedirect() call, the parameter values are always visible in the browser.

With all the previous discussions in mind, we can conclude that we can use sendRedirect() if server cycles are not that costly, and the application information are trivial enough to be exposed in the browser.

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The result of applying sendRedirect() method looks pretty much similar to the application of RequestDispatcher as with both of them, inter resource communications take place. But a closer look to both of them will reveal the differences between these two.

The difference between using RequestDispatcher object and sendRedirect method

The prime difference between dispatching a request through RequestDispatcher and redirecting an URL through sendRedirect() is like following

• Dispatching requests is request object-centric whereas redirecting an URL is response object-centric
• When a request is dispatched, it can only communicate another resource present in the same web container, but with URL redirecting, any resource even outside the web container can also be communicated.
• Every new call to sendRedirect() creates a new server cycle from the client, whereas using include() or forward() ensures that the same server cycle is being continued.

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In case, you want a clear concept of how RequestDispatcher works, you can follow this tutorial

Hope you have enjoyed this tutorial.

Happy Exploring!