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Error Pages

ErrorPages configurations( Exception Handling configurations in JSP)
-->The page that executes only when exception is raised in jsp is called errorPage. It is useful to display non technical guiding messages to end user when exception is raised
-->There are 2 types of error pages configurations in jsp
a.)Local Error Page configuration
-->Using errorPage, isErrorPage attributes( <%@page%>)
-->Specific to one jsp page
b.)Global Error Page configuration
-->Using <error-page> tags of web.xml file)
-->Common for all jsp page of web applications

a.)Local Error page configuration

-->The error page (err.jsp) executes only when the exception is raised in main.jsp to display non-technical guiding messages to end user when exception is raised
  1. JspApp4-LocalErrorPage
  2. |-->webContent
  3.       |-->main.jsp
  4.       |-->err.jsp
main.jsp
  1. <%@page errorPage="err.jsp"%>
  2. <b>from main.jsp</b>
  3. <% int a=integer.parseInt("a10");%>
  4. Value is:- <%=a%>
err.jsp
  1. <%@page isErrorPage="true"%>
  2. <p>internal problem </p>
  3. <hr>
  4. <%=exception%>
-->Gives request to main.jsp
-->The implicit object exception is visible only in error jsp page and it can be used to display exception related messages as non technical guiding messages
b.)Global Error page configuration
-->Common for all the jsp pages of web application, must configurations in web.xml file
  1. JspApp5-GlobalErrorPage
  2. |-->webContent
  3.      |-->main.jsp
  4.      |-->err.jsp
  5.      |-->WEB-INF
  6.             |-->web.xml
-->We can take html file as error page but not recommend to take because we can't use the implicit object exception
-->While working with global error pages configurations we can configure different error pages for different exceptions
In web.xml
  1. <web-app>
  2.   <error-page>
  3.      <exception-type>java.lang.NumberFormatException</exception-type>
  4.      <location>/err.jsp</locations>
  5.   </error-page>
  6.   <error-page>
  7.      <exception-type>java.lang.NullPointerException</exception-type>
  8.      <location>/myErr.html</locations>
  9.   </error-page>
  10. </web-app>
Note: Jsp error pages configurations is no way related to servlet error pages
-->If we configure both local and global error pages on certain main jsp file , then the configurations done in local error page executes
(Q) What is the difference between  the implicit object page & pageContext ?
In JES class
  1. final java.lang.Object page=this;
  2. pageContext=_jspxFactory.getPageContext(this,request,response,"err.jsp"(error.jsp),true(session mode),8192(buffer size),true(autoFlush mode));
page
-->Holds JES class object reference
-->Useful to differentiate scriptlet tags variables from declaration tag variable when both have got same name
pageContext
-->Holds details about current jsp page like request, response, error page, buffer size and etc...
-->Useful to create different scopea of attributes like request /session/ application and etc...

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