JSP Syntax Elements

There are three types of JSP elements you can use: directive, action, and scripting.

Directive elements

The directive elements specify information about the page itself that remains the same between requests--for example, if session tracking is required or not, buffering requirements, and the name of a page that should be used to report errors, if any. Details About Directive .

Action elements -

Action elements typically perform some action based on information that is required at the exact time the JSP page is requested by a browser. An action can, for instance, access parameters sent with the request to do a database lookup. It can also dynamically generate HTML, such as a table filled with information retrieved from an external system.
The JSP specification defines a few standard action elements, listed in Table 3-2.
Table 3-2: Standard action elements
Action element
Description
1)<jsp:useBean>     
Makes a JavaBeans component available in a page. <jsp:useBean id="name" class="package.class" />   This usually means "instantiate an object of the class specified by class, and bind it to a variable with the name specified by id." However, as we'll see shortly, you can specify a scope attribute that makes the bean associated with more than just the current page.
id="name"
scope="page|request|session|application"
class="package.class"
type="package.class"
beanName="package.class"
2)<jsp:getProperty>              
Gets a property value from a JavaBeans component and adds it to the response. Retrieve and output bean properties. <jsp:getProperty name="itemBean" property="numItems" />
Legal attributes are
name="beanName"
property="propertyName|*"
param="parameterName"
value="val"
3)<jsp:setProperty>              
Sets a JavaBeans component property value. Set bean properties, either explicitly or by designating that value comes from a request parameter. <jsp:setProperty name="primeTable" property="numDigits" />
3)<jsp:include>       
Includes the response from a servlet or JSP page during the request processing phase. A file on the local system to be included when the JSP page is translated into a servlet.
<jsp:forward>  
Forwards the processing of a request to servlet or JSP page
<jsp:forward page="/utils/errorReporter.jsp" />
<jsp:param>     
Adds a parameter value to a request handed off to another servlet or JSP page using <jsp:include> or <jsp:forward>
<jsp:plugin>     
Generates HTML that contains the appropriate browser-dependent elements (OBJECT or EMBED) needed to execute an applet with the Java Plug-in software

Scripting elements -

Scripting elements, shown in Table 3-3, allow you to add small pieces of code (typically Java code) in a JSP page, such as an if statement to generate different HTML depending on a certain condition. Like actions, they are also executed when the page is requested. You should use scripting elements with extreme care: if you embed too much code in your JSP pages, you will end up with the same kind of maintenance problems as with servlets embedding HTML.
Table 3-3: Scripting elements
Element              
Description
<% ... %>            
Scriptlet, used to embed scripting code. Code is inserted in service method.
<%= ... %>          
Expression, used to embed scripting code expressions when the result shall be added to the response. Also used as request-time action attribute values. Expression is evaluated and placed in output. The Java expression is evaluated, converted to a string, and inserted in the page. This evaluation is performed at run-time (when the page is requested)
<%! ... %>           
Declaration, used to declare instance variables and methods in the JSP page implementation class. Code is inserted in body of servlet class, outside of service method.
<%-- comment --%>
Comment; ignored when JSP page is translated into servlet.
JavaBeans components

JSP elements, such as action and scripting elements, are often used to work with JavaBeans. Put succinctly, a JavaBeans component is a Java class that complies with certain coding conventions. JavaBeans components are typically used as containers for information that describes application entities, such as a customer or an order.

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