The Loader Component

The Loader element represents the web application class loader that will be used to load Java classes and resources for your web application. Such a class loader must follow the requirements of the Servlet Specification, and load classes from the following locations:

From the /WEB-INF/classes directory inside your web application.
From JAR files in the /WEB-INF/lib directory inside your web application.
From resources made available by Catalina to all web applications globally.

A Loader element MAY be nested inside a Context component. If it is not included, a default Loader configuration will be created automatically, which is sufficient for most requirements.

For a more in-depth description of the class loader hierarchy that is implemented by Catalina, see the ClassLoader HowTo.

The description below uses the variable name $CATALINA_HOME to refer to the directory into which you have installed Tomcat 6, and is the base directory against which most relative paths are resolved. However, if you have configured Tomcat 6 for multiple instances by setting a CATALINA_BASE directory, you should use $CATALINA_BASE instead of $CATALINA_HOME for each of these references.

All implementations of Loader support the following attributes:

Java class name of the implementation to use. This class must implement the org.apache.catalina.Loader interface. If not specified, the standard value (defined below) will be used.

Set to true if you want the class loader to follow the standard Java2 delegation model, and attempt to load classes from parent class loaders before looking inside the web application. Set to false (the default) to have the class loader look inside the web application first, before asking parent class loaders to find requested classes or resources.

Set to true if you want Catalina to monitor classes in /WEB-INF/classes/ and /WEB-INF/lib for changes, and automatically reload the web application if a change is detected. This feature is very useful during application development, but it requires significant runtime overhead and is not recommended for use on deployed production applications. You can use the Manager web application, however, to trigger reloads of deployed applications on demand.

NOTE - The value for this property will be inherited from the reloadable attribute you set on the surrounding Context component, and any value you explicitly set here will be replaced.

The standard implementation of Loader is org.apache.catalina.loader.WebappLoader. It supports the following additional attributes (in addition to the common attributes listed above):

Java class name of the java.lang.ClassLoader implementation class to use. If not specified, the default value is org.apache.catalina.loader.WebappClassLoader.

An extension of the standard webapp loader. This extension, allows you to specify a classpath inside of your <Loader> element, or even read it from the webapps MANIFEST.MF file.

The virtual webapp loader extends the org.apache.catalina.loader.WebappLoader so all attributes are supported from the inherited implementation.

Java class name of the VirtualWebappLoader The value that must be specified is org.apache.catalina.loader.VirtualWebappLoader.

Class-Path string, separated by semi colon by default. Format is the same as a classpath for the JVM.
Example: /dir/classes:/somedir/somejar.jar
You can chose what separator should be used by using the separator attribute.

The separator of class path elements in the virtualClasspath element. Default value is semi colon ;.

If set to true, all repositories will be copied over to the java.io.tmpdir directory and used only by this webapp during runtime. During shutdown, the local copy will be removed. The default value is true and Tomcat will copy the libraries to the temp directory.

If set to true, the JAR files will be added as WebappClassLoader.addJar to prevent them from being locked during runtime. The default value is set to true.

If set to true, Tomcat will extract the Class-Path variable from the webapp's META-INF/MANIFEST.MF file and use that in addition to the virtualClasspath. The separator here is hardcoded to a space. Default value is true.