JSF and File Downloads
Tuesday, April 04, 2006 |At IEC, we have an application used to report inventory counts. Part of the app creates an Excel spreadsheet using POI. The user selects a batch from a select/combo, click on the button, and the server sends them a spreadsheet. The basic work flow is this:
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Display the page
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User selects a batch and clicks the button
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JSF calls the specified action on the backing
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The backing bean creates the spreadsheet, then navigates to success.jsp, a plain ol' JSP
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The JSP pulls the backing bean from the session, gets the workbook reference from it, and streams that to the user using a ServletOutputStream.
This works well under Tomcat and JSF 1.1. Our goal, though, is to migrate to a full JEE 5 environment, hosted on GlassFish. GlassFish, though, ships with JSF 1.2, as JSF is now part of the JEE spec (starting with version 5). This poses a problem, though, as there has apparently been a good deal of work in view handling in 1.2 that breaks this behavior. Ed Burns has been nice enough to take a look for me, but, while waiting for him to get time to help me, I took a stab at fixing it. My tentative work around for it is as follows:
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Alter the form to use a "normal" (read as: non-JSF) form and submit to a servlet.
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Write a servlet that in effect duplicates the JSF lifecycle:
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Build/load the FacesContext
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Get a reference to the backing bean
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Pull the batch id from the request and set it on the backing bean.
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Call the action method.
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At this point, the servlet works the same as the JSP:
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Get the reference to the workbook
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Stream the workbook to the user.
This works, but is a pretty ugly hack. In fact, check out the code:
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public class ExcelServlet extends HttpServlet {
/**
* If you examine FacesContext, you'll find that the setFacesContextAsCurrentInstance method is protected.
*/
private abstract static class ProtectedFacesContext extends FacesContext {
protected static void setFacesContextAsCurrentInstance(FacesContext facesContext) {
FacesContext.setCurrentInstance(facesContext);
}
}
public ExcelServlet() {
super();
}
@Override
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
this.getFacesContext(request, response);
BatchAuditReportBean report = (BatchAuditReportBean) FacesUtils.getManagedBean("batchAuditReportBean");
report.performTask();
org.apache.poi.hssf.usermodel.HSSFWorkbook workBook = report
.getWorkBook();
ServletOutputStream sos;
try {
response.setHeader("Cache-Control", "max-age=1");
response.setHeader("Content-Disposition",
"attachment; filename=\"InventoryErrorReportServlet.xls\"");
response.setContentType("application/vnd.ms-excel");
sos = response.getOutputStream();
workBook.write(sos);
sos.flush();
} catch (IOException ioe) {
System.out.println("IO Exception: " + ioe.toString());
}
response.getOutputStream().close();
}
private FacesContext getFacesContext(ServletRequest req,
ServletResponse res) {
/** Try to get it first */
FacesContext facesContext = FacesContext.getCurrentInstance();
if (facesContext != null)
return facesContext;
// Use the FactoryFinder to grab the Lifecycle object
FacesContextFactory contextFactory = (FacesContextFactory)
FactoryFinder.getFactory(FactoryFinder.FACES_CONTEXT_FACTORY);
LifecycleFactory lifecycleFactory = (LifecycleFactory)
FactoryFinder.getFactory(FactoryFinder.LIFECYCLE_FACTORY);
Lifecycle lifecycle =
lifecycleFactory.getLifecycle(LifecycleFactory.DEFAULT_LIFECYCLE);
// Here's where the ProtectedFacesContext comes in
facesContext = contextFactory.getFacesContext(this.getServletContext(),
req, res, lifecycle);
ProtectedFacesContext.setFacesContextAsCurrentInstance(facesContext);
return facesContext;
}
}
This code doesn’t yet have the parameter fetching, but you can see how unattractive it is. Hopefully, Ed will have a nicer fix for me. Until then, I may have to put this monstrosity in production.
My name is Jason Lee. I am a software developer living in the middle of Oklahoma. I’ve been a professional developer since 1997,
using a variety of languages, including Java, Javascript, PHP, Python, Delphi, and even a bit of C#. I currently work for Red Hat
on the WildFly/EAP team, where, among other things, I maintain integrations for some MicroProfile specs, OpenTelemetry, Micrometer,
Jakarta Faces, and Bean Validation. (Full resume 