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Hidden field in servlet


Hidden field:

Hidden field is an input text with hidden type. This field will not be visible to the user.

Syntax:<input name=”fieldName” value=”fieldValue” type=”hidden”/> 

How to get hidden field value in servlet?

HttpServletRequest interface’s getParameter() method is used to get hidden field value in servlet.

Syntax: String value = request.getParameter(“fieldName”);  

Note: Hidden field only works in case of form submission so they will not work in case of anchor tag as no form submission is there.

Advantages of hidden field:

1.  All browsers support hidden fields.
2. Simple to use.

Disadvantages of hidden fields:

1.  Not secure.
2.  Only work in case of form submission.

Session management example using hidden field:

SetHiddenFieldServlet.java

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
/**
* This class is used to set values in hidden fields.
* @author codesjava
*/
public class SetHiddenFieldServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
 
    //no-argument constructor.
    public SetHiddenFieldServlet() {
 
    }
 
    protected void doPost(HttpServletRequest request, 
	HttpServletResponse response)
	             throws ServletException, IOException {
	response.setContentType("text/html"); 
    	PrintWriter out = response.getWriter();
 
    	//get parameters from request object.
    	String userName = request.getParameter("userName").trim();
    	String password = request.getParameter("password").trim();
 
    	//check for null and empty values.
    	if(userName == null || userName.equals("") || 
    			password == null || password.equals("")){
    		out.print("Please enter both username " +
    				"and password. <br/><br/>");
    		RequestDispatcher requestDispatcher = 
    			request.getRequestDispatcher("/login.html");
    		requestDispatcher.include(request, response);
    	}//Check for valid username and password.
    	else if(userName.equals("jai") && password.equals("1234")){
    	    out.println("Logged in successfully.<br/>"); 
    	    out.println("Click on the below button to see " +
    			"the values of Username and Password.<br/>");
    	    out.print("<form action='GetHiddenFieldServlet'" +
    	    		" method='POST'>");
    	    out.print("<input type='hidden' name='userName'" +
    	    		" value='" + userName + "'>");
    	    out.print("<input type='hidden' name='password'" +
    	    		" value='" + password + "'>");
    	    out.print("<input type='submit' value='See Values'>");  
    	    out.print("</form>");
    	    out.close();
    	}else{
    		out.print("Wrong username or password. <br/><br/>");
    		RequestDispatcher requestDispatcher = 
    			request.getRequestDispatcher("/login.html");
    		requestDispatcher.include(request, response);
    	}
    }
}

GetHiddenFieldServlet.java

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
/**
* This class is used to get hidden fields values.
* @author codesjava
*/
public class GetHiddenFieldServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
 
    //no-argument constructor.
    public GetHiddenFieldServlet() {
 
    }
 
    protected void doPost(HttpServletRequest request, 
	HttpServletResponse response)
	             throws ServletException, IOException {
	response.setContentType("text/html"); 
    	PrintWriter out = response.getWriter();
 
    	//get parameters from request object.
    	String userName = request.getParameter("userName").trim();
    	String password = request.getParameter("password").trim();
 
    	out.println("Username: " + userName + "<br/><br/>");
    	out.println("Password: " + password);
 
    	out.close();
   }
}

login.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 
Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Login</title>
</head>
<body>
	<form action="SetHiddenFieldServlet" method="post">
		Username:<input type="text" name="userName"/>
		<br/><br/>
		Password:<input type="password" name="password"/>
		<br/><br/> 
		<input type="submit" value="login"/> 
	</form>  
</body>
</html>

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app id="WebApp_ID" version="2.4" 
xmlns="http://java.sun.com/xml/ns/j2ee" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee 
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
 
  <servlet>
    <servlet-name>SetHiddenFieldServlet</servlet-name>
    <servlet-class>
    	com.codesjava.business.SetHiddenFieldServlet
    </servlet-class>
  </servlet>
 
  <servlet-mapping>
    <servlet-name>SetHiddenFieldServlet</servlet-name>
    <url-pattern>/SetHiddenFieldServlet</url-pattern>
  </servlet-mapping>
 
  <servlet>
    <servlet-name>GetHiddenFieldServlet</servlet-name>
    <servlet-class>
    	com.codesjava.business.GetHiddenFieldServlet
    </servlet-class>
  </servlet>
 
  <servlet-mapping>
    <servlet-name>GetHiddenFieldServlet</servlet-name>
    <url-pattern>/GetHiddenFieldServlet</url-pattern>
  </servlet-mapping>
 
  <welcome-file-list>
    <welcome-file>login.html</welcome-file>
  </welcome-file-list>
 
</web-app>

Output:

servlet example 11 login
 
Enter username: jai and password: 1234
Click on login button.

servlet example 11 value
 
Click on See Values.
 
Download this example.
 
Next Topic: URL rewriting in servlet with example.
Previous Topic: Cookie in servlet with example.

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