From the spring forum post:
===============

General introduction:
---------------------------------
For our project, we are using the combination of spring 2.0 and jasper reports 2.0.2 for reporting. We rendered our report via an AbstractController and set the cacheSeconds property to zero (we know that for excel/pdf due to a bug in IE6 we need to set the cacheSeconds to -1, but say for now we are only interested about the HTML report without caching). But the problem is when the user logged out from our application and clicked the back button s/he can see the report from cache, but there should be no cache. (FYI: In other pages of our application we use the cacheSeconds property to prevent caching and it worked fine). Then we investigate bit further by using an application WebScarab to intercept the response and watched that in the report response only "Pragma" header is set, where as cacheSeconds instructs to set three headers in default settings - "Pragma", "Cache-Control" and "Expires".

We have manually setup those three headers in the view (JasperReportsMultiFormatView) in controller and it works fine. So where is the problem? why setting cacheSeconds is not sufficient to set those headers? Does Jasper overwrite/reset headers which are already set by spring or is it a spring-jasper integration code problem?

Detailed analysis:
---------------------------
I debugged the spring code to see where the response cache headers got lost after set via the WebContentGenerator. In WebContentGenerator the following method adds the cache prevention headers to response:

Code:

protected final void preventCaching(HttpServletResponse response) {
response.setHeader(HEADER_PRAGMA, "No-cache");
if (this.useExpiresHeader) {
// HTTP 1.0 header
response.setDateHeader(HEADER_EXPIRES, 1L);
}
if (this.useCacheControlHeader) {
// HTTP 1.1 header: "no-cache" is the standard value,
// "no-store" is necessary to prevent caching on FireFox.
response.setHeader(HEADER_CACHE_CONTROL, "no-cache");
response.addHeader(HEADER_CACHE_CONTROL, "no-store");
}
}

But in the AbstractJasperReportsView the response is reset and the headers are populated again in the following way in renderMergedOutputModel method:

Code:

protected void renderMergedOutputModel(Map model, HttpServletRequest request, HttpServletResponse response)
throws Exception {

if (this.subReports != null) {
// Expose sub-reports as model attributes.
model.putAll(this.subReports);

// Transform any collections etc into JRDataSources for sub reports.
if (this.subReportDataKeys != null) {
for (int i = 0; i < this.subReportDataKeys.length; i++) {
String key = this.subReportDataKeys[i];
model.put(key, convertReportData(model.get(key)));
}
}
}

// Expose Spring-managed Locale and MessageSource.
exposeLocalizationContext(model, request);

// Fill the report.
JasperPrint filledReport = fillReport(model);
postProcessReport(filledReport, model);

// Prepare response and render report.
response.reset();
populateHeaders(response);
renderReport(filledReport, model, response);
}

I don't understand actually why do we need to call the reset method? The reset method call clears all the previous headers in the response (which includes the cache headers set previously in WebContentGenerator). Setting the headers manually in the view cause no problem as after the reset call, in the populateHeaders method headers are added from view's headers property (so the cache headers are set again if you add those to headers property prior).

Code:

private void populateHeaders(HttpServletResponse response) {
// Apply the headers to the response.
for (Enumeration en = this.headers.propertyNames(); en.hasMoreElements();) {
String key = (String) en.nextElement();
response.addHeader(key, this.headers.getProperty(key));
}
}


Rob, Juergen - Is this a problem? Is the reset call necessary? If it's necessary then shouldn't we check the cache headers before resetting the response and keep somewhere to add again later?