Hi,
I use the Include tag quiet extensively in
the app I am building in order to "componentise" the pages. My
app is initially going to run on a virtual Linux server which has very
little memory so I am always concerned about optimising resources use
where I can. I was a bit worried about the implementation of the
IncludeTag which always caches its output in memory buffers. With a
heavily componentised page (hierarchical) I could end up with many copies
of the same jsp output in memory before the response is
complete.
I believe from previous discussions that the
only reason the IncludeTag caches the output is so that both
getOutputStream and getWriter may be called from the included page.
As far as I can tell this usually should not happen as you would only use
an OutputStream if you were writing binary data. However, the spec
states that either should be able to be called and some implementations
may use either.
I have altered the current IncludeTag which
was ported from WW1 to NOT buffer output. It wraps the Response and
merely writes directly to the JspWriter like so:
class
PageResponse extends HttpServletResponseWrapper
{
...
public PrintWriter
getWriter() throws IOException
{
return
new
PrintWriter(_context.getOut());
}
public
ServletOutputStream getOutputStream() throws
IOException
{
throw new
UnsupportedOperationException("Can't do
this!");
}
...
}
This works great in Tomcat but will not work on servers
which use getOutputStream(). I am looking at implementing a wrapper
that implements OutputStream but writes to the JspWriter. The
problem is in implementing the method write(int b) as some charsets
use more than one byte to represent a char. This seems to be
the reason that the current implementation buffers the entire output and
then uses:
out.write(
new String(bytes, encoding));
However, it would be possible to only buffer enough of the output in
order to convert a few bytes into a char which can then be written to the
JspWriter.
My current quick fix works great for me and reduces the memory overhead
of my web app. I can make a Jira issue with the code if anyone is
interested.
Feed back on the writer wrapper idea?
John.
