Batik and FindBugs

[Robert Gurol <ro...@signavio.com>]

Hi,

quite some time ago on the batik dev mailing list, a suggestion was made to
use the Java Byte Code checker FindBugs (http://findbugs.sourceforge.net)
to assist development for Batik.

I recently investigated an issue with the software I work on, running
FindBugs on batik as well. I think you may find the results interesting - I
will attach them as both a browseable html file (zipped, its browser URL is
referred to as <HTML_FILE> in the following for fragment addressing) and
FindBugs 2.0.2 project files (in case you want to use the (free) FindBugs
GUI software, cf. http://findbugs.sourceforge.net/downloads.html).

To mention a few issues that are found, let me give you some I noticed
among the ones output by FindBugs:
* In many places, String or Integer comparisons are done using the ==
operator where the equals(...) method may be more appropriate
(<HTML_FILE>#ES_COMPARING_STRINGS_WITH_EQ). Even if constants are used
throughout the code, the assumption that the variable will not get re-boxed
etc should not be made.

* this piece of code in org.apache.batik.util.Service may throw unexpected
NPEs (first if should use "!=") (<HTML_FILE>#NP_LOAD_OF_KNOWN_NULL_VALUE)
if ( br == null ){
    try{
        br.close();
    } catch ( IOException ignored ){}
    br = null;
}

* many static fields are not final (potentially dangerous issue with regard
to multiple instances of a class running)
(<HTML_FILE>#MS_SHOULD_BE_FINAL)

* MacRenderer, where there was some synchronization issue in the past, may
cause trouble as the synchronization variable may get re-assigned (Only
shows up in my IDE FindBugs plugin output somehow, sorry.
MacRenderer.workImg field,
http://findbugs.sourceforge.net/bugDescriptions.html#ML_SYNC_ON_FIELD_TO_GUARD_CHANGING_THAT_FIELD;
similar AbstractDocument.elementsById
http://findbugs.sourceforge.net/bugDescriptions.html#ML_SYNC_ON_UPDATED_FIELD
)

Of course, the FindBugs GUI (or, alternatively, its Eclipse IDE plugin
equivalent) provides a much better breakdown, and provides functionality
for sorting, searching and classifying the issues found by different
criteria; the HTML is just there to give you a zero-threshold impression.
Filtering may also filter issues by severity, in case you are upset by the
sheer number of "mostly harmless" issues reported.

I'll gladly answer any FindBugs questions that may come up.

If any of the issues seem relevant for my own Batik use case (cf. users
mailing list), I'll gladly write a fix and submit a patch.

Best regards,

Robert



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Robert Gurol
Software Developer
robert.gurol@signavio.com
T +49 30 488 172 50
F +49 30 250 43 747

Signavio GmbH
Goethestr. 2-3
10623 Berlin

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