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Trail: Servlets
Lesson: Interacting with Clients

Handling GET and POST Requests

To handle HTTP requests in a servlet, extend the HttpServlet class and override the servlet methods that handle the HTTP requests that your servlet supports. This lesson illustrates the handling of GET and POST requests. The methods that handle these requests are doGet and doPost.

 

Handling GET requests

Handling GET requests involves overriding the doGet method. The following example shows the BookDetailServlet doing this. The methods discussed in the Requests and Responses section are shown in bold.
  

public class BookDetailServlet extends HttpServlet {

    public void doGet (HttpServletRequest request,
                       HttpServletResponse response)
        throws ServletException, IOException
    {
        ...
	// set content-type header before accessing the Writer
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();

	// then write the response
        out.println("<html>" +
                    "<head><title>Book Description</title></head>" +
                    ...);

        //Get the identifier of the book to display
        String bookId = request.getParameter("bookId");
        if (bookId != null) {
            // and the information about the book and print it
            ...
        }
        out.println("</body></html>");
        out.close();
    }
    ...
}

The servlet extends the HttpServlet class and overrides the doGet method.

Within the doGet method, the getParameter method gets the servlet's expected argument.

To respond to the client, the example doGet method uses a Writer from the HttpServletResponse object to return text data to the client. Before accessing the writer, the example sets the content-type header. At the end of the doGet method, after the response has been sent, the Writer is closed.

 

Handling POST Requests

Handling POST requests involves overriding the doPost method. The following example shows the ReceiptServlet doing this. Again, the methods discussed in the Requests and Responses section are shown in bold.
  

public class ReceiptServlet extends HttpServlet { 

    public void doPost(HttpServletRequest request,
                       HttpServletResponse response)
	throws ServletException, IOException
    {
        ...
        // set content type header before accessing the Writer
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        
        // then write the response
        out.println("<html>" +
                    "<head><title> Receipt </title>" +
                    ...);
        
        out.println("<h3>Thank you for purchasing your books from us " +
                    request.getParameter("cardname") +
                    ...);
        out.close();
    }
    ...
}

The servlet extends the HttpServlet class and overrides the doPost method.

Within the doPost method, the getParameter method gets the servlet's expected argument.

To respond to the client, the example doPost method uses a Writer from the HttpServletResponse object to return text data to the client. Before accessing the writer the example sets the content-type header. At the end of the doPost method, after the response has been set, the Writer is closed.
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