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Servlets – Form Data ”; Previous Next You must have come across many situations when you need to pass some information from your browser to web server and ultimately to your backend program. The browser uses two methods to pass this information to web server. These methods are GET Method and POST Method. GET Method The GET method sends the encoded user information appended to the page request. The page and the encoded information are separated by the ? (question mark) symbol as follows − http://www.test.com/hello?key1 = value1&key2 = value2 The GET method is the default method to pass information from browser to web server and it produces a long string that appears in your browser”s Location:box. Never use the GET method if you have password or other sensitive information to pass to the server. The GET method has size limitation: only 1024 characters can be used in a request string. This information is passed using QUERY_STRING header and will be accessible through QUERY_STRING environment variable and Servlet handles this type of requests using doGet() method. POST Method A generally more reliable method of passing information to a backend program is the POST method. This packages the information in exactly the same way as GET method, but instead of sending it as a text string after a ? (question mark) in the URL it sends it as a separate message. This message comes to the backend program in the form of the standard input which you can parse and use for your processing. Servlet handles this type of requests using doPost() method. Reading Form Data using Servlet Servlets handles form data parsing automatically using the following methods depending on the situation − getParameter() − You call request.getParameter() method to get the value of a form parameter. getParameterValues() − Call this method if the parameter appears more than once and returns multiple values, for example checkbox. getParameterNames() − Call this method if you want a complete list of all parameters in the current request. GET Method Example using URL Here is a simple URL which will pass two values to HelloForm program using GET method. http://localhost:8080/HelloForm?first_name = ZARA&last_name = ALI Given below is the HelloForm.java servlet program to handle input given by web browser. We are going to use getParameter() method which makes it very easy to access passed information − // Import required java libraries import java.io.*; import javax.servlet.*; import javax.servlet.http.*; // Extend HttpServlet class public class HelloForm extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // Set response content type response.setContentType(“text/html”); PrintWriter out = response.getWriter(); String title = “Using GET Method to Read Form Data”; String docType = “<!doctype html public “-//w3c//dtd html 4.0 ” + “transitional//en”>n”; out.println(docType + “<html>n” + “<head><title>” + title + “</title></head>n” + “<body bgcolor = “#f0f0f0″>n” + “<h1 align = “center”>” + title + “</h1>n” + “<ul>n” + ” <li><b>First Name</b>: ” + request.getParameter(“first_name”) + “n” + ” <li><b>Last Name</b>: ” + request.getParameter(“last_name”) + “n” + “</ul>n” + “</body>” + “</html>” ); } } Assuming your environment is set up properly, compile HelloForm.java as follows − $ javac HelloForm.java If everything goes fine, above compilation would produce HelloForm.class file. Next you would have to copy this class file in <Tomcat-installationdirectory>/webapps/ROOT/WEB-INF/classes and create following entries in web.xml file located in <Tomcat-installation-directory>/webapps/ROOT/WEB-INF/ <servlet> <servlet-name>HelloForm</servlet-name> <servlet-class>HelloForm</servlet-class> </servlet> <servlet-mapping> <servlet-name>HelloForm</servlet-name> <url-pattern>/HelloForm</url-pattern> </servlet-mapping> Now type http://localhost:8080/HelloForm?first_name=ZARA&last_name=ALI in your browser”s Location:box and make sure you already started tomcat server, before firing above command in the browser. This would generate following result − Using GET Method to Read Form Data First Name: ZARA Last Name: ALI GET Method Example Using Form Here is a simple example which passes two values using HTML FORM and submit button. We are going to use same Servlet HelloForm to handle this input. <html> <body> <form action = “HelloForm” method = “GET”> First Name: <input type = “text” name = “first_name”> <br /> Last Name: <input type = “text” name = “last_name” /> <input type = “submit” value = “Submit” /> </form> </body> </html> Keep this HTML in a file Hello.htm and put it in <Tomcat-installationdirectory>/webapps/ROOT directory. When you would access http://localhost:8080/Hello.htm, here is the actual output of the above form. First Name: Last Name: Try to enter First Name and Last Name and then click submit button to see the result on your local machine where tomcat is running. Based on the input provided, it will generate similar result as mentioned in the above example. POST Method Example Using Form Let us do little modification in the above servlet, so that it can handle GET as well as POST methods. Below is HelloForm.java servlet program to handle input given by web browser using GET or POST methods. // Import required java libraries import java.io.*; import javax.servlet.*; import javax.servlet.http.*; // Extend HttpServlet class public class HelloForm extends HttpServlet { // Method to handle GET method request. public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // Set response content type response.setContentType(“text/html”); PrintWriter out = response.getWriter(); String title = “Using GET Method to Read Form Data”; String docType = “<!doctype html public “-//w3c//dtd html 4.0 ” + “transitional//en”>n”; out.println(docType + “<html>n” + “<head><title>” + title + “</title></head>n” + “<body bgcolor = “#f0f0f0″>n” + “<h1 align = “center”>” + title + “</h1>n” + “<ul>n” + ” <li><b>First Name</b>: ” + request.getParameter(“first_name”) + “n” + ” <li><b>Last Name</b>: ” + request.getParameter(“last_name”) + “n” + “</ul>n” + “</body>” “</html>” ); } // Method to handle POST method request. public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } } Now compile and deploy the above Servlet and test it using Hello.htm with the POST method as follows − <html> <body> <form action = “HelloForm” method = “POST”> First Name: <input type = “text” name = “first_name”> <br /> Last Name: <input type = “text” name = “last_name” /> <input type = “submit” value = “Submit” /> </form> </body> </html> Here is the actual output of the above