Package org.omnifaces.exceptionhandler

Class FullAjaxExceptionHandler

  • All Implemented Interfaces:
    FacesListener, SystemEventListener, FacesWrapper<ExceptionHandler>, EventListener
    public class FullAjaxExceptionHandler
extends ExceptionHandlerWrapper

    The FullAjaxExceptionHandler will transparently handle exceptions during ajax requests exactly the same way as exceptions during synchronous (non-ajax) requests.

    By default, when an exception occurs during a Faces ajax request, the enduser would not get any form of feedback if the action was successfully performed or not. In Mojarra, only when the project stage is set to Development, the enduser would see a bare JavaScript alert with only the exception type and message. It would make sense if exceptions during ajax requests are handled the same way as exceptions during synchronous requests, which is utilizing the standard Servlet API <error-page> mechanisms in web.xml.

    Installation

    This handler must be registered by a factory as follows in faces-config.xml in order to get it to run: 

     <factory>
     <exception-handler-factory>org.omnifaces.exceptionhandler.FullAjaxExceptionHandlerFactory</exception-handler-factory>
 </factory>

    Error pages

    This exception handler will parse the web.xml and web-fragment.xml files to find the error page locations of the HTTP error code 500 and all declared specific exception types. Those locations need to point to Facelets files (JSP is not supported) and the URL must match the FacesServlet mapping (just mapping it on *.xhtml should eliminate confusion about virtual URLs). E.g. 

     <error-page>
     <exception-type>jakarta.faces.application.ViewExpiredException</exception-type>
     <location>/WEB-INF/errorpages/expired.xhtml</location>
 </error-page>

    The location of the HTTP error code 500 or the exception type java.lang.Throwable is required in order to get the FullAjaxExceptionHandler to work, because there's then at least a fall back error page when there's no match with any of the declared specific exceptions types. You can have both, but the java.lang.Throwable one will always get precedence over all others. When you have error pages for specific exception types, then you'd better use the 500 one as fallback error page. 

     <error-page>
     <error-code>500</error-code>
     <location>/WEB-INF/errorpages/500.xhtml</location>
 </error-page>

    The exception detail is available in the request scope by the standard Servlet error request attributes like as in a normal synchronous error page response. You could for example show them in the error page as follows: 

     <ul>
     <li>Date/time: #{of:formatDate(now, 'yyyy-MM-dd HH:mm:ss')}</li>
     <li>User agent: #{header['user-agent']}</li>
     <li>User IP: #{request.remoteAddr}</li>
     <li>Request URI: #{requestScope['jakarta.servlet.error.request_uri']}</li>
     <li>Ajax request: #{facesContext.partialViewContext.ajaxRequest ? 'Yes' : 'No'}</li>
     <li>Status code: #{requestScope['jakarta.servlet.error.status_code']}</li>
     <li>Exception type: #{requestScope['jakarta.servlet.error.exception_type']}</li>
     <li>Exception message: #{requestScope['jakarta.servlet.error.message']}</li>
     <li>Exception UUID: #{requestScope['org.omnifaces.exception_uuid']}</li>
     <li>Stack trace:
         <pre>#{of:printStackTrace(requestScope['jakarta.servlet.error.exception'])}</pre>
     </li>
 </ul>

    Exceptions during render response can only be handled when the jakarta.faces.FACELETS_BUFFER_SIZE is large enough so that the so far rendered response until the occurrence of the exception fits in there and can therefore safely be resetted.

    Error in error page itself

    When the rendering of the error page failed due to a bug in the error page itself, and the response can still be resetted, then the FullAjaxExceptionHandler will display a hardcoded error message in "plain text" informing the developer about the double mistake.

    Normal requests

    Note that the FullAjaxExceptionHandler does not deal with normal (non-ajax) requests at all. To properly handle Faces and EL exceptions on normal requests as well, you need an additional FacesExceptionFilter. This will extract the root cause from a wrapped FacesException and ELException before delegating the ServletException further to the container (the container will namely use the first root cause of ServletException to match an error page by exception in web.xml).

    Configuration

    By default only FacesException and ELException are unwrapped. You can supply a context parameter "org.omnifaces.EXCEPTION_TYPES_TO_UNWRAP" to specify additional exception types to unwrap. The context parameter value must be a commaseparated string of fully qualified names of additional exception types. Note that this also covers subclasses of specified exception types. 

     <context-param>
     <param-name>org.omnifaces.EXCEPTION_TYPES_TO_UNWRAP</param-name>
     <param-value>jakarta.ejb.EJBException,jakarta.persistence.RollbackException</param-value>
 </context-param>

    This context parameter will also be read and used by FacesExceptionFilter.

    By default all exceptions are logged. You can supply a context parameter "org.omnifaces.EXCEPTION_TYPES_TO_IGNORE_IN_LOGGING" to specify exception types to ignore from logging. The context parameter value must be a commaseparated string of fully qualified names of exception types. Note that this also covers subclasses of specified exception types. 

     <context-param>
     <param-name>org.omnifaces.EXCEPTION_TYPES_TO_IGNORE_IN_LOGGING</param-name>
     <param-value>jakarta.faces.application.ViewExpiredException</param-value>
 </context-param>

    This context parameter will also be read and used by FacesExceptionFilter.

    This context parameter will not suppress standard Faces and/or container builtin logging. This will only suppress org.omnifaces.exceptionhandler.FullAjaxExceptionHandler logging. So chances are that standard Faces and/or container will still log it. This may need to be configured separately.

    Customizing FullAjaxExceptionHandler

    If more fine grained control is desired for determining the root cause of the caught exception, or whether it should be handled, or determining the error page, or logging the exception, then the developer can opt to extend this FullAjaxExceptionHandler and override one or more of the following protected methods:

    Don't forget to create a custom ExceptionHandlerFactory for it as well, so that it could be registered in faces-config.xml. This does not necessarily need to extend from FullAjaxExceptionHandlerFactory.

    Author:
    Bauke Scholtz
    See Also:
    FullAjaxExceptionHandlerFactory, OmniPartialViewContext, OmniPartialViewContextFactory, WebXml, FacesExceptionFilter

    • Constructor Detail

      • FullAjaxExceptionHandler

        public FullAjaxExceptionHandler​(ExceptionHandler wrapped)
        Construct a new ajax exception handler around the given wrapped exception handler.
        Parameters:
        wrapped - The wrapped exception handler.

    • Method Detail

      • handle

        public void handle()
        Handle the ajax exception as follows, only and only if the current request is an ajax request with an uncommitted response and there is at least one unhandled exception: Any remaining unhandled exceptions will be swallowed. Only the first one is relevant.
        Overrides:
        handle in class ExceptionHandlerWrapper

      • shouldHandleExceptionRootCause

        protected boolean shouldHandleExceptionRootCause​(FacesContext context,
                                                 Throwable exception)
        Returns true if the FullAjaxExceptionHandler should handle this exception root cause. If this returns false, then the FullAjaxExceptionHandler will skip handling this exception and delegate it further to the wrapped exception handler. The default implementation just returns true.
        Parameters:
        context - The involved faces context.
        exception - The caught exception to determine the root cause for.
        Returns:
        true if the given exception should be handled by the FullAjaxExceptionHandler.
        Since:
        1.8

      • findErrorPageLocation

        protected String findErrorPageLocation​(FacesContext context,
                                       Throwable exception)
        Determine the error page location based on the given exception. The default implementation delegates to WebXml.findErrorPageLocation(Throwable).
        Parameters:
        context - The involved faces context.
        exception - The exception to determine the error page for.
        Returns:
        The location of the error page. It must start with / and be relative to the context path.
        Since:
        1.5

      • logException

        protected void logException​(FacesContext context,
                            Throwable exception,
                            String location,
                            String message,
                            Object... parameters)
        Log the thrown exception and determined error page location with the given message, optionally parameterized with the given parameters. The default implementation logs through java.util.logging as SEVERE when the thrown exception is not an instance of any type specified in context parameter "org.omnifaces.EXCEPTION_TYPES_TO_IGNORE_IN_LOGGING". Since version 3.2, the log message will be prepended with the UUID and IP address. The UUID is available in EL by #{requestScope['org.omnifaces.exception_uuid']}.
        Parameters:
        context - The involved faces context.
        exception - The exception to log.
        location - The error page location.
        message - The log message.
        parameters - The log message parameters, if any. They are formatted using Formatter.
        Since:
        1.6