Servlets- ServletRequest

• Servlets

ServletRequest

ServletRequest is send to Server to process particular request. It can send following details to servlet by submitting FORM or by URL. We can get these details at server side

Example to getRequest details

public class ServletReq extends HttpServlet {
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
 res.setContentType("text/html");
 PrintWriter pw = res.getWriter();
 pw.println("<br> getProtocol   \t:" + req.getProtocol());
 pw.println("<br> getServerName \t:" + req.getServerName());
 pw.println("<br> getServerPort \t:" + req.getServerPort());
 pw.println("<br> getRemotePort \t:" + req.getRemotePort());
 pw.println("<br> getLocalPort  \t:" + req.getLocalPort());

 pw.println("<br> getContentType   \t:" + req.getContentType());
 pw.println("<br> getContentLength \t:" + req.getContentLength());
	pw.println("<br> CharacterEncoding\t:" + req.getCharacterEncoding());
 pw.println("<br> req.getScheme    \t:" + req.getScheme());
	}
}
-----------------------------
getProtocol   :HTTP/1.1 
getServerName :localhost 
getServerPort :8080 
getRemotePort :63205 
getLocalPort  :8080 
getContentType :null 
getContentLength :-1 
CharacterEncoding :null 
req.getScheme  :http

We mainly use ServletRequest Object to retrieve data from FORM Submission or URL

We can get the parameters by using following methods

1. public String getParameter(-paramname”);

2. public Enumeration getParameterNames();

3. public String[] getParamterValues(-paramname”);

4. public Map getParameterMap();

Example: getParamater ()

Index.html

<form action="login" method="get">
 SNO:<input type="text" name="sno"><br> 
	      NAME:<input type="text" name="name"><br> 
	   <input type="submit" value="Submit">
</form>

LoginServlet.java

public class LoginServlet extends HttpServlet {
	protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
 PrintWriter pw = res.getWriter();
 res.setContentType("text/html");
 String sno = req.getParameter("sno");
 String name = req.getParameter("name");
 pw.println("<h1>Sno : " + sno);
 pw.println("<br>Name : " + name);
 pw.close();
	}
}

web.xml

<web-app 
  <servlet>
    <servlet-name>login</servlet-name>
    <servlet-class>demo.LoginServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>login</servlet-name>
    <url-pattern>/login</url-pattern>
  </servlet-mapping>   
</web-app>

Make sure if we use GET method in form we must use doGet (Req, Res) & for POST we have to use doPost(req,res). Otherwise it throws Get/Post not supported error.in this type of case write logic doGet() & call doGet() in doPost()

public Enumeration getParameterNames();

Sometimes we don’t know the request parameter names, in this case we use getParameterNames ();. See the same UI for this only Servlet code is changed

public class LoginServlet extends HttpServlet {
	protected void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
 PrintWriter pw = res.getWriter();
 res.setContentType("text/html");
 Enumeration e = req.getParameterNames();
 while (e.hasMoreElements()) {
 	String s = (String) e.nextElement();
pw.write("Param Name :" +s + ",Param Value : " + req.getParameter(s)+"<br>");
 }
 pw.close();
	}
}

getParamterValues(-paramname”), getParameterMap(); are used in the case of Single parameter can having multiple values, like checkboxes. See below example

getParamterValues(-paramname") Example

<form action="login" method="post">   
	   NAME:<input type="text" name="name"><br> 
	   Skills : <br>
           <input type="checkbox" name="skill" value="java">JAVA<br>
           <input type="checkbox" name="skill" value="cpp">CPP<br>
           <input type="checkbox" name="skill" value="hadoop">HADOOP<br>
           <input type="checkbox" name="skill" value="devops">DevOps<br>
	   <input type="submit" value="Submit">
	</form>
--------------------------------------------------------------------	
	
public class LoginServlet extends HttpServlet {
	protected void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
 PrintWriter pw = res.getWriter();
 res.setContentType("text/html");
 pw.write("<h1> Name : " + req.getParameter("name"));
 pw.write("<br> Skills : <br> ");
 String[] skills = req.getParameterValues("skill");
 for (int i = 0; i < skills.length; i++) {
 	pw.write(i + ". " + skills[i] + "<br>");
 }
 pw.close();
	}
}

getParameterMap(); Example

public class LoginServlet extends HttpServlet {
	protected void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
 PrintWriter pw = res.getWriter();
 res.setContentType("text/html");

 Map m = req.getParameterMap();
 Set s = m.entrySet();
 Iterator it = s.iterator();

 while (it.hasNext()) {
 Map.Entry  entry =  it.next();

 String key = entry.getKey();
 String[] value = entry.getValue();
 pw.println("Key is " + key + "<br>");

	if (value.length > 1) {
	  for (int i = 0; i < value.length; i++) {
 pw.println("<li>" + value[i].toString() + "</li><br>");
 }
	} else
	   pw.println("Value is " + value[0].toString() + "<br>");
	pw.println("-------------------<br>");
 }
 pw.close();
	}
}

PREVIOUSServlet Lifecycle

NEXTServletConfig