Question

State whether each of the following is true or false. If false, explain why. a) An object with page scope exists in every JSP of a particular Web application. b) Directives specify global information that is not associated with a particular JSP request. c) The JSP container invokes methods doInitBody and doAftexBody when it encounters the starting custom tag and the ending custom tag, respectively. d) Tag libraries are part of the tag extension mechanism that enables programmers to create new tags that encapsulate complex Java functionality. e) Action \(\langle j \text { sp } t \text { include }>\) is evaluated once at page translation time. f) Like XHTML comments, JSP comments and script language comments appear in the response to the client. g) Objects with application scope are part of a particular Web application. h) Each page has its own instances of the page-scope implicit objects. i) Action \(\langle\text { jsp } \text { t set Property }>\) has the ability to match request parameters to properties of the same name in a bean by specifying \(" *\) " for attribute property. j) Objects with session scope exist for the client's entire browsing session.

Short answer

a) False, b) True, c) False, d) True, e) False, f) False, g) True, h) True, i) True, j) True.

Step-by-step solution

Determine Page Scope Object Existence

Statement a) claims that an object with page scope exists in every JSP of a particular Web application. This is false. In the context of JSP, page scope means the object exists only for a particular single request/page processing. Therefore, objects with page scope are not shared across different JSPs.

Evaluate Directive Global Information

Statement b) indicates that directives specify global information not associated with a particular JSP request. This is true. Directives like <%@ page %>, <%@ include %>, and <%@ taglib %> provide global information relevant during the JSP translation phase, impacting the entire JSP page.

Examine Custom Tag Methods

Statement c) asserts that the JSP container invokes doInitBody and doAfterBody methods on custom tags' start and end. This is false. The correct methods are doStartTag and doEndTag. The doInitBody and doAfterBody methods are specific to body tags extending BodyTagSupport.

Analyze Tag Libraries Role

Statement d) states that tag libraries are part of the tag extension mechanism for creating new Java-enabling tags. This is true. Tag libraries allow developers to extend JSP's functionality by defining new custom tags that encapsulate complex behaviors.

Evaluate Action Timing

Statement e) claims the action is evaluated once at page translation time. This is false. The action is evaluated each time the page is requested, not during the translation phase, allowing dynamic content inclusion.

Assess Comments in Client Response

Statement f) suggests JSP and script language comments appear in client responses like XHTML comments. This is false. JSP comments do not appear in the final HTML output sent to the client, unlike XHTML comments.

Inspect Application Scope Objects

Statement g) claims objects with application scope are part of a particular Web application. This is true. Application scope objects live as long as the application context is active and are accessible across all servlets and JSPs within the same application.

Review Page-Scope Implicit Objects

Statement h) asserts each page has its own instances of page-scope implicit objects. This is true. Each JSP page maintains its own versions of page-scope objects like request and pageContext, which are not shared with other pages.

Understand Functionality

Statement i) suggests can match request parameters to bean properties using "*". This is true. The wildcard "*" attribute allows automatic mapping of request parameters to bean properties with the same name.

Clarify Session Scope Objects Duration

Statement j) indicates objects with session scope last for the entire browsing session. This is true. Session scope ensures objects exist as long as the user's session is active, across multiple requests in a single session.

Key concepts

page scope in JSP

In JavaServer Pages (JSP), the concept of page scope is quite specific. When an object is created with a page scope, it is bound to the request processing for only a single page. This means that such an object exists only during the lifecycle of that particular page's execution and is discarded thereafter.
This makes page scope useful for temporary objects that do not need to be shared across multiple pages or after the response is sent to the client.

• Objects with page scope are limited to the page where they were created.
• They are suitable for page-specific tasks where persistence beyond a page isn't necessary.
• Different JSPs will not share page scope objects.

Understanding this can help in optimizing resource usage and ensuring that unnecessary data is not retained longer than needed.

tag libraries in JSP

Tag libraries in JSP extend the capabilities of JSP by providing custom tags that can encapsulate complex Java functionalities. This powerful feature allows developers to define their own tags or reuse existing ones to simplify JSP code and improve readability.
Tag libraries are part of the JSP tag extension mechanism and are often packaged as Tag Library Definition (TLD) files. These files define the tags and their behaviors.

• Tag libraries promote code reusability and encapsulation.
• They can handle repetitive tasks and complex operations with ease.
• By integrating tag libraries, developers can enhance the modularity of JSP applications.

Using standard tags from libraries like JSTL (JavaServer Pages Standard Tag Library) can also help in standardized and consistent coding practices.

session scope in JSP

Session scope in JSP refers to objects bound to a user's browsing session. This scope is helpful when data needs persistence across multiple requests from the same user within their session.
Objects with session scope exist throughout the user's session, allowing them to navigate between pages without losing stored information. A user's session typically lasts until they close their browser or log out.

• Session scope allows objects to survive across multiple requests.
• It is useful for managing user-specific data, like login details or shopping cart content.
• The lifecycle of session scope objects aligns with the session's duration.

Understanding session scope is crucial for building web applications that require state management across different user interactions.

JSP directives

JSP directives provide global configuration information that affects an entire JSP file. They are essential during the JSP translation phase and do not correspond to any particular request.
Directives like <%@ page %>, <%@ include %>, and <%@ taglib %> help in defining page-level settings such as content type, error pages, and importing tag libraries.

• Directives do not produce any output to the client.
• They set up important parameters for JSP processing and execution.
• Proper use of directives can enhance application performance and modularity.

For example, the <%@ page %> directive can dictate the language used in the scriptlets or the buffer size, offering fine control over JSP behavior.