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.
