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java.lang.Object classpathhelper.tomcat.listener.TomcatClassLoaderService classpathhelper.tomcat.listener.VersionFourTomcatClassLoaderService
Instance of the ITomcatClassLoaderService
that
mimics the version 4 classloading properties of Apache's
Tomcat. The following is an excerp directly from the
4.0 documentation.
Like many server applications, Tomcat 4 installs a variety of class loaders (that is, classes that implement java.lang.ClassLoader) to allow different portions of the container, and the web applications running on the container, to have access to different repositories of available classes and resources. This mechanism is used to provide the functionality defined in the Servlet Specification, version 2.3 -- in particular, Sections 9.4 and 9.6.
In a Java 2 (that is, JDK 1.2 or later) environment, class loaders are arranged in a parent-child tree. Normally, when a class loader is asked to load a particular class or resource, it delegates the request to a parent class loader first, and then looks in its own repositories only if the parent class loader(s) cannot find the requested class or resource. The model for web application class loaders differs slightly from this, as discussed below, but the main principles are the same.
When Tomcat 4 is started, it creates a set of class loaders that are organized into the following parent-child relationships, where the parent class loader is above the child class loader:
Bootstrap
|
System
|
Common
/ \
Catalina Shared
/ \
Webapp1 Webapp2 ...
The characteristics of each of these class loaders,
including the source of classes and resources that they make
visible, are discussed in detail in the following section.
As indicated in the diagram above, Tomcat 4 creates the
following class loaders as it is initialized:
($JAVA_HOME/jre/lib/ext)
. NOTE - Some JVMs may
implement this as more than one class loader, or it may not be
visible (as a class loader) at all.CLASSPATH
environment variable. All
such classes are visible to both Tomcat internal classes, and to
web applications. However, the standard Tomcat 4 startup scripts
($CATALINA_HOME/bin/catalina.sh
or
%CATALINA_HOME%\bin\catalina.bat)
totally ignore the
contents of the CLASSPATH
environment variable
itself, and instead build the System class loader from the
following repositories:
$CATALINA_HOME/bin/bootstrap.jar
- Contains the
main() method that is used to initialize the Tomcat 4 server, and
the class loader implementation classes it depends on.$JAVA_HOME/lib/tools.jar
- Contains the "javac"
compiler used to convert JSP pages into servlet classes.$CATALINA_HOME/common/classes
, as well as classes
and resources in JAR files under the
$CATALINA_HOME/commons/endorsed
and
$CATALINA_HOME/common/lib directories
, are made
visible through this class loader. By default, that includes the
following:
/WEB-INF/lib
.$CATALINA_HOME/server/classes
, as well as classes
and resources in JAR files under
$CATALINA_HOME/server/lib
, are made visible through
this class loader. By default, that includes the following:
$CATALINA_BASE/shared/classes
, as well as classes
and resources in JAR files under
$CATALINA_BASE/shared/lib
, are made visible through
this class loader. By default, that includes the following:
/WEB-INF/classes
directory of your web application archive, plus classes and
resources in JAR files under the /WEB-INF/lib
directory of your web application archive, are made visible to
the containing web application, but to no others.
As mentioned above, the web application class loader diverges from the default Java 2 delegation model (in accordance with the recommendations in the Servlet Specification, version 2.3, section 9.6). When a request to load a class from the web application's WebappX class loader is processed, this class loader will look in the local repositories first, instead of delegating before looking. All other class loaders in Tomcat 4 follow the usual delegation pattern.
Therefore, from the perspective of a web application, class
or resource loading looks in the following repositories, in this
order:
/WEB-INF/classes
of your web application/WEB-INF/lib/*.jar
of your web application$CATALINA_HOME/common/classes
$CATALINA_HOME/common/endorsed/*.jar
$CATALINA_HOME/common/lib/*.jar
$CATALINA_BASE/shared/classes
$CATALINA_BASE/shared/lib/*.jar
Field Summary |
Fields inherited from class classpathhelper.tomcat.listener.TomcatClassLoaderService |
properties |
Constructor Summary | |
protected |
VersionFourTomcatClassLoaderService(TomcatProperties theProperties)
Basic constructor, not called directly, instances of this class are provided via TomcatClassLoaderService.getService(TomcatProperties) . |
Method Summary | |
protected static java.lang.String |
convertPathsToPath(java.util.List paths)
Internal method that takes a list of File
and File[] objects and appends them to
a string in a classic classpath format. |
CGClassLoader |
createClassLoader(java.lang.String appName,
CGClassLoaderFilter filter,
FileChangeMonitor fileMonitor)
Method that creates the appropriate class loader hierarchy consistent with the associated instance of Tomcat and the supplied application. |
protected static java.io.File[] |
enumerateJars(java.io.File root)
Internal method that enumerates the jar files at the path supplied. |
java.lang.String[] |
getAppNames()
Returns an array of application names in the associated Tomcat instance. |
Methods inherited from class classpathhelper.tomcat.listener.TomcatClassLoaderService |
getService |
Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
protected VersionFourTomcatClassLoaderService(TomcatProperties theProperties)
TomcatClassLoaderService.getService(TomcatProperties)
.
theProperties
- The properties associate with this instance
of Tomcat.Method Detail |
protected static java.io.File[] enumerateJars(java.io.File root)
root
- The root dir to look up files in.
.jar
or .zip
protected static java.lang.String convertPathsToPath(java.util.List paths)
File
and File[]
objects and appends them to
a string in a classic classpath format.
paths
- The list of files and file arrays.
public java.lang.String[] getAppNames()
ITomcatClassLoaderService
ITomcatClassLoaderService.createClassLoader(java.lang.String, classpathhelper.CGClassLoaderFilter, classpathhelper.filechangelistener.FileChangeMonitor)
.public CGClassLoader createClassLoader(java.lang.String appName, CGClassLoaderFilter filter, FileChangeMonitor fileMonitor)
ITomcatClassLoaderService
appName
- The application name, should be
a value from ITomcatClassLoaderService.getAppNames()
.filter
- The filter for the class loader.fileMonitor
- An optional (may be null) file monitor
that will be populated with the files to monitor related
to this classloader.
null
if
the application name is invalid.
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