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HttpServletRequest

HTTP Header Records

  • Remember these?
GET / HTTP/1.1
Host: localhost:4444
User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:58.0) Gecko/20100101 Firefox/58.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
Upgrade-Insecure-Requests: 1
Cache-Control: max-age=0
  • When a browser submits a request to a Java Application Server, like tomcat, the header records are parsed set into an object that is an HttpServletRequest type.
  • All the information that is part of the browser request is available via this object.

  • The object is delivered to a servlet or JSP page in a method.

    public void doGet(HttpServletRequest request, HttpServletResponse response) 
throws ServletException, IOException {

  • In addition to the header records, there is a lot more information available through this object.

Getting Information from the HttpServletRequest Object in a Servlet

  • In a servlet we get information from the request object like this.

    public void doGet(HttpServletRequest request, HttpServletResponse response) 
    throws ServletException, IOException {

    PrintWriter out = response.getWriter();
    out.print("<HTML>");
    out.print("<HEAD><TITLE>Sample Output</TITLE></HEAD>");
    out.print("<BODY>");
    out.print("<h1>Server Name</h1>");
    out.print("<p>" + request.getServerName() + "</p>");
    out.print("</BODY>");
    out.print("</HTML>");
    out.close();
}

  • The statement request.getServerName() returns a string with the server’s names.

HttpServletRequest is also an Attribute Map

  • An Attribute Map is a map with keys that are strings and values that can be any object.

  • We know three types of Maps now.

    • A normal Map

      • Key: any object
      • Value: any object

    • A Property Map

      • Key: String
      • Value: String

    • An Attribute Map

      • Key: String
      • Value: any object

  • Here are some of the methods we can use with an HttpServletRequest object.

    • setAttribute("key", <value>)
    • getAttribute("key")
    • removeAttribute("key")

  • Example:

    public void doGet(HttpServletRequest request, HttpServletResponse response) 
        throws ServletException, IOException {

    request.setAttribute("test", "This is just a test!");

    ...
}