• Introduction
• Attributes
  1. Common Attributes
  2. Standard Implementation
• Nested Components
• Special Features
  1. Logging
  2. Access Logs
  3. Lifecycle Listeners
  4. Request Filters

The Engine element represents the entire request processing machinery associated with a particular Catalina Service. It receives and processes all requests from one or more Connectors, and returns the completed response to the Connector for ultimate transmission back to the client.

Exactly one Engine element MUST be nested inside a Service element, following all of the corresponding Connector elements associated with this Service.

You can nest one or more Host elements inside this Engine element, each representing a different virtual host associated with this server. At least one Host is required, and one of the nested Hosts MUST have a name that matches the name specified for the defaultHost attribute, listed above.

You can nest at most one instance of the following utility components by nesting a corresponding element inside your Engine element:

• Realm - Configure a realm that will allow its database of users, and their associated roles, to be shared across all Hosts and Contexts nested inside this Engine, unless overridden by a Realm configuration at a lower level.

Logging

An engine is associated with the org.apache.catalina.core.ContainerBase.[enginename] log category. Note that the brackets are actually part of the name, don't omit them.

Access Logs

When you run a web server, one of the output files normally generated is an access log, which generates one line of information for each request processed by the server, in a standard format. Catalina includes an optional Valve implementation that can create access logs in the same standard format created by web servers, or in any number of custom formats.

You can ask Catalina to create an access log for all requests processed by an Engine, Host, or Context by nesting a Valve element like this:

<Engine name="Standalone" ...>
 ...
 <Valve className="org.apache.catalina.valves.AccessLogValve"
 prefix="catalina_access_log." suffix=".txt"
 pattern="common"/>
 ...
</Engine>

See Access Log Valve for more information on the configuration attributes that are supported.

Lifecycle Listeners

If you have implemented a Java object that needs to know when this Engine is started or stopped, you can declare it by nesting a Listener element inside this element. The class name you specify must implement the org.apache.catalina.LifecycleListener interface, and it will be notified about the occurrence of the corresponding lifecycle events. Configuration of such a listener looks like this:

<Engine name="Standalone" ...>
 ...
 <Listener className="com.mycompany.mypackage.MyListener" ... >
 ...
</Engine>

Note that a Listener can have any number of additional properties that may be configured from this element. Attribute names are matched to corresponding JavaBean property names using the standard property method naming patterns.

Request Filters

You can ask Catalina to check the IP address, or host name, on every incoming request directed to the surrounding Engine, Host, or Context element. The remote address or name will be checked against a configured list of "accept" and/or "deny" filters, which are defined using java.util.regex Regular Expression syntax. Requests that come from locations that are not accepted will be rejected with an HTTP "Forbidden" error. Example filter declarations:

<Engine name="Standalone" ...>
 ...
 <Valve className="org.apache.catalina.valves.RemoteHostValve"
 allow=".*\.mycompany\.com|www\.yourcompany\.com"/>
 <Valve className="org.apache.catalina.valves.RemoteAddrValve"
 deny="192\.168\.1\.\d+"/>
 ...
</Engine>

See Remote Address Filter and Remote Host Filter for more information about the configuration options that are supported.