Chapter 4: Tomcat Architecture host name requested, and
Chapter 4: Tomcat Architecture host name requested, and so on) and any cookies sent with the request. Response dumping logs the response headers and cookies (if set) to a file. Valves are typically reusable components, and can therefore be added and removed from the request path according to need. Their inclusion is transparent to Web applications, although the response time will increase if a valve is added. An application that wishes to intercept requests for pre-processing and responses for post-processing should use the filters that are a part of the Servlet specifications. A Valve may intercept a request between an Engine and a Host/Context, between a Host and a Context, and between a Context and a resource within the Web application. You may have one or more Valves at its particular parent, and the Valves are typically chained in the order that they were added to the parent. This means that you may have Valves that depend on previous Valves as long as they are added in a specific order. The server.xml file will install the Valves in the order that they are found in this file. The Loggers Loggers report on the internal state of a component. They can be set for components from top-level containers downward, except for the Context. Logging behavior is inherited, so a Logger set at the Engine level is assigned to every child object unless overridden by the child. The configuration of Loggers at this level can be a convenient way to decide the default logging behavior for the server. This establishes a convenient destination for all logging events for those components that are not specially configured to generate their own logs. The Host A Host mimics the popular Apache virtual host functionality. In Apache, this enables multiple servers to be used on the same machine, and to be differentiated by their IP address or by their host name. In Tomcat, the virtual hosts are differentiated by a fully qualified host name. Thus, the Web sites www.example.comand www.example.net can both reside in the same server, with requests for each routed to different groups of Web applications. Configuring a Host includes setting the name of the host. The majority of clients can be depended on to send both the IP address of the server and the host name they used to resolve the IP address. The host name is provided as an HTTP header that an Engine inspects to determine the Host to which a request should be passed. The Host is a child of the Engine. The Engine may contain one or more host objects that will represent a default host and zero or more virtual host objects. The Engine has a setting to designate one of the host objects as the default. This is so it can dispatch requests to a host if it is unable to resolve who it is intended for. The Context Finally, there is the Web application, also known as a Context. Configuration of a Web application includes informing the Engine/Hosts of the location of the root folder of the application. Dynamic reloading can also be enabled so that any classes that have been changed are reloaded into memory. However, this is resource-intensive, and is not recommended for deployment scenarios.
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