Server-side Scripting using JSP!

SERVER-SIDE SCRIPTING USING JSP!

JSP often present dynamically generated content as part of an HTML document sent to the client in response to a request. In some cases, the content is static, but is output only if certain conditions are met during a request. JSP programmers can insert Java code and logic in a JSP using script.

Scripting Components:

JSP scripting components include: scriptlets, comments, expressions, declarations and escape sequence characters. Scriptlets are blocks of code delimited by <% and %>. They contain Java statements that the container places in method –jspService at translation time.

JSPs supports three comment styles: JSP comments, HTML comments and comments from the scripting language like JavaScript. JSP comments are delimited by <%-- and --%>. HTML comments are delimited with . Scripting language comments are Java comments and are delimited by / and /. JSP comments and scripting-language comments are ignored and do not appear in the response to a client.

A JSP expression, delimited by <%= and %> contains Java code that is evaluated when a client requests the JSP containing the expression. The container converts the result of a JSP expression to a String object, and then outputs the string as part of the response to the client.

Declarations (delimited by <%! and %>) enable a JSP programmer to define variables and methods. The variables become instance variables of the Servlet class and the methods become members. Declarations of variables and methods in a JSP use Java syntax. Hence, declaring a variable without using a semicolon is a syntax error.

Escape sequences are sequence of characters used in JSP to make use of the special characters like <% and %> as part of the output. The escape sequences are as follows:

<\% %\> \’ \” \\

The following is an example for JSP code written using two of the JSP components - scriptlets and expression:

<? xml version = “1.0”>

<html>

<head>

<title> Processing “get” request with data </title>

</head>

<body>

<%

String name = request.getParameter(“fname”);

if (name != null)

{

%>

<h1>

Hello <%= name %> <br/>

Welcome to Java Servlet Pages!

</h1>

<%

}

else {

%>

<form action = “welcome.jsp” method = “get”>

<p>Type your first name and press Submit</p>

<p> <input type = “text” name = “fname” />

<input type = “submit” value = “Submit” />

</p>

</form>

<%

}

%>

</body>

</html>

Standard Actions:

Standard actions are special tags provided in JSP for performing some of the most common tasks in a JSP program, such as including content from other resources, forwarding requests to other resources and interacting with Java Beans. JSP containers process actions at request time.

Actions are delimited by <jsp:action> and </jsp:action> tags, where action is one of the standard actions defined in JSP as listed below:

Action	Description
<jsp:include>	Dynamically includes another resource in a JSP. As the JSP executes, the referenced resource is included and processed.
<jsp:forward>	Forwards request processing to another JSP, servlet or static page. This action terminates the current JSP’s execution.
<jsp:plugin>	Allows a plug-in component to be added to a page in the form of a browser-specific object or embed HTML element.
<jsp:param>	Used with the include, forward and plug-in actions to specify additional name/value pairs of information for use by these actions.
JavaBean Manipulation
<jsp:useBean>	Specifies that the JSP uses a JavaBean instance. This action specifies the scope of the bean and assigns it an ID that scripting components can use to manipulate the bean.
<jsp:setProperty>	Sets the property in the specified JavaBean instance.
<jsp:getProperty>	Gets a property in the specified JavaBean instance and converts the result to a String for output in the response.