31.How can I declare methods within my JSP page?
You can declare methods for use within your JSP page as declarations. The methods can then be invoked within any other methods you declare, or within JSP scriptlets and expressions.
Do note that you do not have direct access to any of the JSP implicit objects like request, response, session and so forth from within JSP methods. However, you should be able to pass any of the implicit JSP variables as parameters to the methods you declare.
For example:
Another Example:
file1.jsp:
file2.jsp
<%test(out);% >
32.Can I stop JSP execution while in the midst of processing a request?
Yes. Preemptive termination of request processing on an error condition is a good way to maximize the throughput of a high-volume JSP engine. The trick (assuming Java is your scripting language) is to use the return statement when you want to terminate further processing.
33.Can a JSP page process HTML FORM data?
Yes. However, unlike Servlet, you are not required to implement HTTP-protocol specific methods like doGet() or doPost() within your JSP page. You can obtain the data for the FORM input elements via the request implicit object within a scriptlet or expression as.
34.Is there a way to reference the "this" variable within a JSP page?
Yes, there is. Under JSP 1.0, the page implicit object is equivalent to "this", and returns a reference to the Servlet generated by the JSP page.
35.How do you pass control from one JSP page to another?
Use the following ways to pass control of a request from one servlet to another or one jsp to another.
The RequestDispatcher object ‘s forward method to pass the control.
The response.sendRedirect method
36.Is there a way I can set the inactivity lease period on a per-session basis?
Typically, a default inactivity lease period for all sessions is set within your JSPengine admin screen or associated properties file. However, if your JSP engine supports the Servlet 2.1 API, you can manage the inactivity lease period on a per-session basis.
This is done by invoking the HttpSession.setMaxInactiveInterval() method, right after the session has been created.
37.How does a servlet communicate with a JSP page?
The following code snippet shows how a servlet instantiates a bean and initializes it with FORM data posted by a browser. The bean is then placed into the request, and the call is then forwarded to the JSP page, Bean1.jsp, by means of a request dispatcher for downstream processing.
public void doPost (HttpServletRequest request, HttpServletResponse response)
{
try {
govi.FormBean f = new govi.FormBean();
String id = request.getParameter("id");
f.setName(request.getParameter("name"));
f.setAddr(request.getParameter("addr"));
f.setAge(request.getParameter("age"));
//use the id to compute
//additional bean properties like info
//maybe perform a db query, etc.
// . . .
f.setPersonalizationInfo(info);
request.setAttribute("fBean",f);
getServletConfig().getServletContext().getRequestDispatcher
("/jsp/Bean1.jsp").forward(request, response);
} catch (Exception ex) {
. . .
}
}
The JSP page Bean1.jsp can then process fBean, after first extracting it from the default request
scope via the useBean action.
jsp:useBean id="fBean" class="govi.FormBean" scope="request"/ jsp:getProperty
name="fBean" property="name" / jsp:getProperty name="fBean" property="addr"
/ jsp:getProperty name="fBean" property="age" / jsp:getProperty name="fBean"
property="personalizationInfo" /
38.Can you make use of a ServletOutputStream object from within a JSP page?
No. You are supposed to make use of only a JSPWriter object (given to you in the form of the implicit object out) for replying to clients.
A JSPWriter can be viewed as a buffered version of the stream object returned by response.getWriter(), although from an implementational perspective, it is not.
39.How do I include static files within a JSP page?
Static resources should always be included using the JSP include directive. This way, the inclusion is performed just once during the translation phase.
The following example shows the syntax:
< % @ include file="copyright.html" % >
Do note that you should always supply a relative URL for the file attribute. Although you can also include static resources using the action, this is not advisable as the inclusion is then performed for each and every request.
How do I have the JSP-generated servlet subclass my own custom servlet class, instead of the default? One should be very careful when having JSP pages extend custom servlet classes as opposed to the default one generated by the JSP engine. In doing so, you may lose out on any advanced optimization that may be provided by the JSPengine.
In any case, your new super class has to fulfill the contract with the JSP engine by: Implementing the HttpJspPage interface, if the protocol used is HTTP, or implementing JspPage otherwise Ensuring that all the methods in the Servlet interface are declared final.
Additionally, your servlet super class also needs to do the following:
The service() method has to invoke the _jspService() method
The init() method has to invoke the jspInit() method
The destroy() method has to invoke jspDestroy()
If any of the above conditions are not satisfied, the JSP engine may throw a translation error. Once the super class has been developed, you can have your JSP extend it as follows:
40.Can a JSP page instantiate a serialized bean?
No problem! The use Bean action specifies the beanName attribute, which can be used for indicating a serialized bean.
For example:
A couple of important points to note. Although you would have to name your serialized file "filename.ser", you only indicate "filename" as the value for the beanName attribute. Also, you will have to place your serialized file within the WEB-INFjspbeans directory for it to be located by the JSP engine.
You can declare methods for use within your JSP page as declarations. The methods can then be invoked within any other methods you declare, or within JSP scriptlets and expressions.
Do note that you do not have direct access to any of the JSP implicit objects like request, response, session and so forth from within JSP methods. However, you should be able to pass any of the implicit JSP variables as parameters to the methods you declare.
For example:
Another Example:
file1.jsp:
file2.jsp
<%test(out);% >
32.Can I stop JSP execution while in the midst of processing a request?
Yes. Preemptive termination of request processing on an error condition is a good way to maximize the throughput of a high-volume JSP engine. The trick (assuming Java is your scripting language) is to use the return statement when you want to terminate further processing.
33.Can a JSP page process HTML FORM data?
Yes. However, unlike Servlet, you are not required to implement HTTP-protocol specific methods like doGet() or doPost() within your JSP page. You can obtain the data for the FORM input elements via the request implicit object within a scriptlet or expression as.
34.Is there a way to reference the "this" variable within a JSP page?
Yes, there is. Under JSP 1.0, the page implicit object is equivalent to "this", and returns a reference to the Servlet generated by the JSP page.
35.How do you pass control from one JSP page to another?
Use the following ways to pass control of a request from one servlet to another or one jsp to another.
The RequestDispatcher object ‘s forward method to pass the control.
The response.sendRedirect method
36.Is there a way I can set the inactivity lease period on a per-session basis?
Typically, a default inactivity lease period for all sessions is set within your JSPengine admin screen or associated properties file. However, if your JSP engine supports the Servlet 2.1 API, you can manage the inactivity lease period on a per-session basis.
This is done by invoking the HttpSession.setMaxInactiveInterval() method, right after the session has been created.
37.How does a servlet communicate with a JSP page?
The following code snippet shows how a servlet instantiates a bean and initializes it with FORM data posted by a browser. The bean is then placed into the request, and the call is then forwarded to the JSP page, Bean1.jsp, by means of a request dispatcher for downstream processing.
public void doPost (HttpServletRequest request, HttpServletResponse response)
{
try {
govi.FormBean f = new govi.FormBean();
String id = request.getParameter("id");
f.setName(request.getParameter("name"));
f.setAddr(request.getParameter("addr"));
f.setAge(request.getParameter("age"));
//use the id to compute
//additional bean properties like info
//maybe perform a db query, etc.
// . . .
f.setPersonalizationInfo(info);
request.setAttribute("fBean",f);
getServletConfig().getServletContext().getRequestDispatcher
("/jsp/Bean1.jsp").forward(request, response);
} catch (Exception ex) {
. . .
}
}
The JSP page Bean1.jsp can then process fBean, after first extracting it from the default request
scope via the useBean action.
jsp:useBean id="fBean" class="govi.FormBean" scope="request"/ jsp:getProperty
name="fBean" property="name" / jsp:getProperty name="fBean" property="addr"
/ jsp:getProperty name="fBean" property="age" / jsp:getProperty name="fBean"
property="personalizationInfo" /
38.Can you make use of a ServletOutputStream object from within a JSP page?
No. You are supposed to make use of only a JSPWriter object (given to you in the form of the implicit object out) for replying to clients.
A JSPWriter can be viewed as a buffered version of the stream object returned by response.getWriter(), although from an implementational perspective, it is not.
39.How do I include static files within a JSP page?
Static resources should always be included using the JSP include directive. This way, the inclusion is performed just once during the translation phase.
The following example shows the syntax:
< % @ include file="copyright.html" % >
Do note that you should always supply a relative URL for the file attribute. Although you can also include static resources using the action, this is not advisable as the inclusion is then performed for each and every request.
How do I have the JSP-generated servlet subclass my own custom servlet class, instead of the default? One should be very careful when having JSP pages extend custom servlet classes as opposed to the default one generated by the JSP engine. In doing so, you may lose out on any advanced optimization that may be provided by the JSPengine.
In any case, your new super class has to fulfill the contract with the JSP engine by: Implementing the HttpJspPage interface, if the protocol used is HTTP, or implementing JspPage otherwise Ensuring that all the methods in the Servlet interface are declared final.
Additionally, your servlet super class also needs to do the following:
The service() method has to invoke the _jspService() method
The init() method has to invoke the jspInit() method
The destroy() method has to invoke jspDestroy()
If any of the above conditions are not satisfied, the JSP engine may throw a translation error. Once the super class has been developed, you can have your JSP extend it as follows:
40.Can a JSP page instantiate a serialized bean?
No problem! The use Bean action specifies the beanName attribute, which can be used for indicating a serialized bean.
For example:
A couple of important points to note. Although you would have to name your serialized file "filename.ser", you only indicate "filename" as the value for the beanName attribute. Also, you will have to place your serialized file within the WEB-INFjspbeans directory for it to be located by the JSP engine.
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