How to ignore the EL expression evaluation in a JSP?

We can ignore EL evaluation in JSP page by two ways.

1. Using page directive as <%@ page isELIgnored="true" %>
2. Configuring in web.xml – better approach when you want to disable EL evaluation for many JSP pages.

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   <jsp-config>     <jsp-property-group>         <url-pattern>*.jsp</url-pattern>         <el-ignored>true</el-ignored>     </jsp-property-group> </jsp-config>

Why don’t we need to configure JSP standard tags in web.xml?

We don’t need to configure JSP standard tags in web.xml because the TLD files are inside the META-INF directory of the JSTL jar files. When container loads the web application and find TLD files inside the META-INF directory of JAR file, it automatically configures them to be used directly in the application JSP pages. All we need to do it to include it in the JSP page using taglib directive.

How do we catch exception and process it using JSTL?

We can use JSTL Core tags c:catch and c:if to catch exception inside the JSP service method and process it. c:catch tag catches the exception and wraps it into the exception variable and we can use c:if condition tag to process it. Below code snippet provide sample usage.

<c:catch var ="exception">

   <% int x = 5/0;%>

</c:catch>

   

<c:if test = "${exception ne null}">

   <p>Exception is : ${exception} <br />

   Exception Message: ${exception.message}</p>

</c:if>

How can we handle exceptions thrown by JSP service method?

To handle exceptions thrown by the JSP page, all we need is an error page and define the error page in JSP using page directive.

To create a JSP error page, we need to set page directive attribute isErrorPage value to true, then we can access exception implicit object in the JSP and use it to send customized error message to the client.

We need to define exception and error handler JSP pages in the deployment descriptor like below.

<error-page>

     <error-code>404</error-code>

     <location>/error.jsp</location>

</error-page>

   

<error-page>

     <exception-type>java.lang.Throwable</exception-type>

     <location>/error.jsp</location>

</error-page>

What is JSP Standard Tag Library, provide some example usage?

JSP Standard Tag Library or JSTL is more versatile than JSP EL or Action elements because we can loop through a collection or escape HTML tags to show them like text in response.

JSTL is part of the Java EE API and included in most servlet containers. But to use JSTL in our JSP pages, we need to download the JSTL jars for your servlet container. Most of the times, you can find them in the example projects and you can use them. You need to include these libraries in the project WEB-INF/lib directory. These jars are container specific, for example in Tomcat, we need to include jstl.jar and standard.jar jar files in project build path.

How to use JSP EL to get HTTP method name?

We can use pageContext JSP EL implicit object to get the request object reference and use dot operator to get the HTTP method name in JSP page. The JSP EL code for this will be${pageContext.request.method}.

Give an example where you need JSP Custom Tag?

Let’s say we want to show a number with formatting with commas and spaces. This can be very useful for user when the number is really long. So we want some custom tags like below:

<mytags:formatNumber number="123456.789" format="#,###.00"/>

Based on the number and format passed, it should write the formatted number in JSP page, for above example it should print 123,456.79

We know that JSTL doesn’t provide any inbuilt tags to achieve this, so we will create our own custom tag implementation and use it in the JSP page.