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From "Brus, Tom" <Tom.B...@nl.compuware.com>
Subject class loading speed can be improved in AntClassLoader.java
Date Wed, 25 Apr 2007 13:18:55 GMT
Hi,

We have a lot of classes that are loaded by the AntClassLoader. From
performance measurements I noticed that a lot of time was spend in
File.exists() during class loading. I checked the code and noticed that
in:

     InputStream getResourceStream  (File file, String resourceName);

and in

     URL         getResourceURL     (File file, String resourceName);

The following check is done first:

     if (!file.exists()) {
         return null;
     }

This seems smart, because if the file does not exist the answer is
clear. Unless of course 'exists()' is slow; which it turns out to be (on
Windows at least). A considerable improvement can be accomplished by
first checking the 'zipFiles' Hashtable: if "zipFiles.get(file)" returns
non-null we can be sure that the file exists and that it is not a
directory. Remember that most calls will be for a jar file that has
already been opened. So those expensive (compared to Hashtable.get())
tests on File can be skipped most of the time.

One of our test runs was reduced by 1/3 in runtime by a quick patch I
made (it loads thousands of classes...).

Has this issue ever been noticed/discussed?

Regards,
Tom Brus

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