classloader.xtp

解压在c盘

<s1 title="Classloading and Compilation">

<summarylist/>

<s2 title="Where do I put my jars and classes?">

<p>Application classes belong in <var/WEB-INF/classes/>.  Jars belong
in <var/WEB-INF/lib/>.</p>

<p>Look at the standard installation and check the
HelloWorld example.  The HelloWorld source is in
<var/resin-2.1/doc/WEB-INF/classses/>.  Resin will automatically compile
that source when running the demo and put the class in the same directory.</p>

<p>If you change the app-dir to /usr/local/apache/htdocs, servlets and beans
will belong in /usr/local/apache/htdocs/WEB-INF/classes.</p>

<p>Until you get your first servlets working, don't try to create your
own web-apps.  When you do start working with web-apps, look at the
guest book examples to see where beans and servlets belong.</p>

<p>You can also change the default location with the
<var/&lt;classpath>/> directive.</p>

<p>Application jars belong in <var/WEB-INF/lib/> and standard libraries,
like JDBC drivers, belong in the global classpath.  In
general, you should put standard libraries in the global classpath.
Resin has several equivalent methods to add a jar to the classpath:</p>

<ol>
<li>Add the driver to the CLASSPATH environment variable.
<li>Start Resin with a -classpath argument including the driver.
<li>Put the jar file in resin1.1/lib.
<li>Put the classes in resin1.1/classes.
</ol>

<p>Only the last two will be automatically reloaded when the class or
jar changes.  For the first two, you'll need to restart Resin.</p>

<p>You can see Resin's global classpath by starting it with the
-verbose option:</p>

<example>
unix> httpd.sh -verbose
</example>

<p>You must restart Resin to pick up the new classpath.
When using the Win32 Resin, you must quit the Resin application.  Just
pressing the stop and start buttons will not suffice.</p>

</s2>

<s2 title="Where does Resin generate *.java and *.class files?">

<p>The &lt;work-dir>'<var/foo/>'&lt;/work-dir> attribute configures the
directory where generated *.java (for JSP) and *.class files go.  If
unassigned, they go into <var//tmp/caucho/> on Unix and <var/\temp\caucho/>
on Windows.</p>

</s2>

<s2 title="Resin doesn't update changed servlets and JSP pages">

<p>Resin has a delay for testing updated servlets and JSP pages.
The configuration variable for both is 'class-update-interval' in
resin.conf.  It's an application-level variable.  The default is 15
seconds.  So Resin will only check every 15 seconds for an updated
page.  You can set this value to 0 for development work.</p>

<example>
&lt;http-config class-update-interval='0'>
  ...
&lt;/http-config>
</example>

<p>If you want Resin to check servlets for updates every hour, your
resin.conf might look like:</p>

<example>
&lt;http-config class-update-interval='3600'>
  ...
&lt;/http-config>
</example>

</s2>

<s2 title="Servlets don't compile">

<example>
java.lang.NoClassDefFoundError: sun/tools/javac/Main
</example>

<p>The JRE does not contain a Java compiler.  You either need to get
the JDK or use another compiler.  To configure another compiler use:</p>

<example>
&lt;caucho.com>
  &lt;java compiler='/usr/local/bin/jikes'/>
  ...
&lt;/caucho.com>
</example>

</s2>

<s2 title="ClassNotFoundException for servlet or bean">

<p>First check that the class is in the right location.  In the standard
configuration, Java classes belong in <var/resin/doc/WEB-INF/classes/>.
If you're using Resin's autocompilation, the Java source file must be in the
same location.</p>

<p>If you're using the automatic compilation, check that the <var/package/>
in the *.java file matches its location.</p>

</s2>

<s2 title="How do I get the application class loader?">

<p>cyou can get the application classloader from a servlet
using the standard call <var/Thread.getContextClassLoader()/>.

</s2>

<s2 title="The application gets reloaded on each request">

<p>Other symptoms are that sessions are killed on each request.

<p>This may occur if your *.java files have a date in the future.
When the *.class is compiled, it will have an date before the *.java.
So Resin will think it's old and recompile on the next request.

<p>This may occur, for example, if you work on NT and use Linux as a
fileserver and the two clocks aren't properly synchronized.

<p>The only solution is to synchronize the clocks for both machines.

</s2>
<!--
<s2 title="Resin crashes on Windows when recompiling">

This appears to be a problem with the internal javac compiler for some
versions of the JDK.

<p/>To solve the problem, just use an external compiler, either javac or
jikes:

<example>
&lt;java compiler='javac'/>
</example>

</section>
-->

<s2 title='What is the classloader order?'>

<p>In Resin 2.1 the order is:</p>
<ol>
<li>The commandline classpath
<li>The resin/lib directory
<li>The envivonmental classpath
<li>An application's WEB-INF/lib and WEB-INF/classes
</ol>

</s2>
</s1>