On 17.06.2010 16:37, Konstantin Kolinko wrote:
2010/6/16<peter_f...@blm.gov>:
Looking at section 10 of the 6.0 user guide, which describes classloading,
the text makes perfect sense and matches the way I understand things work.
However the summary at the end of the section "Class Loader Definitions"
looks wrong; it basically says that the search order is...
Bootstrap
$CLASSPATH
WEB-INF/classes
WEB-INF/lib/*.jar
$CATALINA_HOME/lib
$CATALINA_HOME/lib/*.jar
...when my understanding is it should be...
WEB-INF/classes
WEB-INF/lib/*.jar
Bootstrap
$CLASSPATH
$CATALINA_HOME/lib
$CATALINA_HOME/lib/*.jar
So, is the documentation just wrong, or have I misunderstood something?
The order is
Bootstrap
$CLASSPATH
WEB-INF/classes
WEB-INF/lib/*.jar
$CATALINA_BASE/lib
$CATALINA_BASE/lib/*.jar
$CATALINA_HOME/lib
$CATALINA_HOME/lib/*.jar
as documented.
Note, that many Bootstrap and $CLASSPATH classes are loaded at early
stages of Tomcat startup sequence, that is before classloading
hierarchy itself is created. It would be a mess if those classes
were ignored.
That is why people should not play with $CLASSPATH, unless in certain
very rare cases.
If you have some documentation changes in your mind, the patches are
welcome. The sources are in webapps/docs/*.xml . Create a Bugzilla
issue and attach a diff file there (svn diff or an 'Unified diff'
(diff -u)).
I guess part of the confusion comes from the terminology "parent" and
"delegating".
The classloader used by the webapps is derived from the usual
URLClassloader as an extension. In Tomcat land it's parent is the
classloader that loads from the common lib directory.
The webapp classloader is "not delegating first" in the sense that it
first tries to find classes via it's own super URLClassloader, before
asking the parent common loader.
The URLClassloader in turn is the one, that first goes down to bootstrap
and system/CLASSPATH before checking the configured URLs (WEB-INF). So
in Tomcat terminology it's true, that the webapp classloader does only
delegate (to common) if it can't find the class, but the webapp loader
itself does delegate to bootstrap and system first.
(hope that's true and not too confusing ...)
Regards,
Rainer
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