jsp:forward standard action examples

Details: Written by Nam Ha Minh; Last Updated on 22 July 2019 | Print Email

[Master REST API Development and Java and Spring Boot]

The <jsp:forward> action is used to forward the current request to another resource such as an HTML page, a JSP page or a servlet. Here’s a quick example:

<jsp:forward page="Another.jsp" />

1. Syntax of JSP forward action

The JSP forward action has two syntaxes. Here’s the simple one:

<jsp:forward page="relative URL" />

And here’s the syntax with sub elements <jsp:param> to pass additional parameters to the forwarded page:

<jsp:forward page="relative URL">

{ <jsp:param .... /> }*

</jsp:forward>

In the latter syntax, there can be one or more <jsp:param> elements in the form of:

<jsp:param name="name" value="value" />

2. Rules & Semantics of JSP forward action

The page’s URL must be either relative to the current JSP page or relative to the web application’s context path (URL starts with a slash: /).
The JSP forward action effectively terminates the execution of the current JSP page, so the forwarding should be used based on some dynamic conditions. For example: forward to an error page if an exception occurred or forward to a login page if the user has not logged in.
The forwarding happens on the server side which means that the browser is not notified, i.e. the URL in address bar does not get changed.
The page’s URL can be a runtime expression that evaluates to a String which is a relative URL.
The JSP/Servlet container will throw an HTTP 404 error if the forwarded page could not be found.

3. JSP forward action Examples

Following are some examples of how to use the <jsp:forward> action itself:

Forward the request to a page which is relative to the current page:

<jsp:forward page="login.jsp" />

<jsp:forward page="some/path/login.jsp" />

Forward the request to a page which is relative to the web application’s context path:
```
<jsp:forward page="/login.jsp" />

<jsp:forward page="/some/path/login.jsp" /> 
```

Passing additional parameters to the forwarded page:

<jsp:forward page="login.jsp" />
	<jsp:param name="username" value="Tom"/>
</jsp:forward>

In the forwarded page, access the parameters as follows:

Username: ${param.username}

Forward to a page which is a runtime expression:

<jsp:forward page="${pageName}" />

Let’s see a complete example which applies the <jsp:forward> action in real context. The divide.jsp page displays division of two numbers X and Y which are passed from URL’s query string as follows:

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>    
<!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=UTF-8">
<title>Divide X by Y</title>
</head>
<body>
	<c:if test="${param.Y == 0}">
		<jsp:forward page="error.jsp" />
	</c:if>
	
	<h2 align="center">
		Result of ${param.X} / ${param.Y} is ${param.X / param.Y}
	</h2> 
</body>
</html>

In case the number Y is zero, forward to the error.jsp as follows:

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Error</title>
</head>
<body>
	<h2 align="center">Error, cannot divide by zero!</h2>
</body>
</html>

Type the following URL to test the divide.jsp page:

http://localhost:8080/JSPActions/divide.jsp?X=1000&Y=50

Output:

Test JSP forward 1

If we pass Y = 0, as in the following URL:

http://localhost:8080/JSPActions/divide.jsp?X=1000&Y=0

Then the error.jsp will be forwarded:

Test JSP forward 2

Note that the URL does not change.

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