Apache Tomcat Configuration ReferenceThe Loader Component |  |
| Introduction |
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.
在下面的描述中使用变量名$CATALINA_HOME来代指Tomcat5所安装的目录地址,这是一个基础目录(base directory),其他的相关路径由它而派生。不过，如果你已经把Tomcat设置成多个体实例(multiple instances),并且设立了一个$CATALINA_BASE目录，那么你就应使用$CATALINA_BASE而不是$CATALINA_HOME作为参照。
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| Attributes |
| Common Attributes |
Loader的所有实现支持下列属性：
| Attribute | Description |
|---|
className |
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.
| delegate |
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.
| reloadable |
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.
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| Standard Implementation |
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):
| Attribute | Description |
|---|
backgroundProcesssorDelay |
The number of seconds between checks for modified classes and
resources, if reloadable has been set to
true.
See the general documentation for this parameter at Host Container.
| loaderClass |
Java class name of the java.lang.ClassLoader
implementation class to use. If not specified, the default value is
org.apache.catalina.loader.WebappClassLoader.
| useSystemClassLoaderAsParent |
If no parent classloader is specified, should the system
classloader be used? The default of true mantains
backwards compatibility with previous releases however most
users will want to set this to false to obtain
the parent classloader from the associated container.
This attribute will not be present in Tomcat 6 where the
Loader API has changed and the parent class loader is always
obtained from the associated container.
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