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JSP Interview Questions


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21.Differentiate between pageContext.include and jsp:include?

The <jsp:include> standard action and the pageContext.include() method are both used to include resources at runtime. However, the pageContext.include() method always flushes the output of the current page before including the other components, whereas <jsp:include> flushes the output of the current page only if the value of flush is explicitly set to true as follows:

         <jsp:include page="/index.jsp" flush="true"/> 

22.What is the jsp:setProperty action?

You use jsp:setProperty to give values to properties of beans that have been referenced earlier. You can do this in two contexts. First, you can use jsp:setProperty after, but outside of, a jsp:useBean element, as below:

<jsp:useBean id="myName" ... />
...
<jsp:setProperty name="myName" property="myProperty" ... />
In this case, the jsp:setProperty is executed regardless of whether a new bean was instantiated or an existing bean was found.

A second context in which jsp:setProperty can appear is inside the body of a jsp:useBean element, as below:
<jsp:useBean id="myName" ... >
  ...
  <jsp:setProperty name="myName" 
                   property="someProperty" ... />
</jsp:useBean>
Here, the jsp:setProperty is executed only if a new object was instantiated, not if an existing one was found.



23.What is the jsp:getProperty action?

The <jsp:getProperty> action is used to access the properties of a bean that was set using the <jsp:getProperty> action. The container converts the property to a String as follows:

  • If it is an object, it uses the toString() method to convert it to a String.
  • If it is a primitive, it converts it directly to a String using the valueOf() method of the corresponding Wrapper class.
  • The syntax of the <jsp:getProperty> method is: <jsp:getProperty name="Name" property="Property" />
Here, name is the id of the bean from which the property was set. The property attribute is the property to get. A user must create or locate a bean using the <jsp:useBean> action before using the <jsp:getProperty> action.



24.What is the <jsp:param> standard action?

The <jsp:param> standard action is used with <jsp:include> or <jsp:forward> to pass parameter names and values to the target resource. The syntax of the <jsp:param> standard action is as follows:
<jsp:param name="paramName" value="paramValue"/>


25.What is the jsp:plugin action ?

This action lets you insert the browser-specific OBJECT or EMBED element needed to specify that the browser run an applet using the Java plugin.


26.What are scripting elements?

JSP scripting elements let you insert Java code into the servlet that will be generated from the current JSP page. There are three forms:

  1. Expressions of the form <%= expression %> that are evaluated and inserted into the output,
  2. Scriptlets of the form <% code %> that are inserted into the servlet's service method,
  3. Declarations of the form <%! code %> that are inserted into the body of the servlet class, outside of any existing methods.


27.What is a scriptlet?

A scriptlet contains Java code that is executed every time a JSP is invoked. When a JSP is translated to a servlet, the scriptlet code goes into the service() method. Hence, methods and variables written in scriptlets are local to the service() method. A scriptlet is written between the <% and %> tags and is executed by the container at request processing time.


28.What are JSP declarations?

As the name implies, JSP declarations are used to declare class variables and methods in a JSP page. They are initialized when the class is initialized. Anything defined in a declaration is available for the whole JSP page. A declaration block is enclosed between the <%! and %> tags. A declaration is not included in the service() method when a JSP is translated to a servlet.


29.What is a JSP expression?

A JSP expression is used to write an output without using the out.print statement. It can be said as a shorthand representation for scriptlets. An expression is written between the <%= and %> tags. It is not required to end the expression with a semicolon, as it implicitly adds a semicolon to all the expressions within the expression tags.


30.How is scripting disabled?

Scripting is disabled by setting the scripting-invalid element of the deployment descriptor to true. It is a subelement of jsp-property-group. Its valid values are true and false. The syntax for disabling scripting is as follows:

<jsp-property-group>
   <url-pattern>*.jsp</url-pattern>
   <scripting-invalid>true</scripting-invalid>
</jsp-property-group>


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