Recipe2.4.Using Multiple Struts Configuration Files

Recipe 2.4. Using Multiple Struts Configuration Files

Problem

You want to break apart a large struts-config.xml file into smaller files for improved organization and easier maintenance, particularly in a team environment.

Solution

Split your monolithic struts-config.xml into multiple configuration files. Each file must be well-formed and valid according to the struts-config XML DTD. Reference these files as the value for the config initialization parameter of the ActionServlet in the web.xml file as shown in Example 2-9.

Example 2-9. Multiple config files (single module)

<servlet>   <servlet-name>action</servlet-name>   <servlet-class>     org.apache.struts.action.ActionServlet   </servlet-class>   <init-param>     <param-name>config</param-name>     <param-value>       /WEB-INF/struts-config.xml,       /WEB-INF/struts-config-2.xml     </param-value>   </init-param>   <load-on-startup>1</load-on-startup> </servlet>

When the ActionServlet is loaded, Struts will merge the results of the specified configuration files into a single in-memory configuration.

Discussion

For anything other than the most trivial applications, the struts-config.xml file tends to get large and unwieldy. Many applications may have action elements numbering in the hundreds. Combine this with the use of a locking source control system, and soon you will have developers in constant contention for the same file.

Struts 1.1 introduced support for multiple configuration files. Each configuration file must be a valid XML file and conform to the struts-config XML Document Type Definition (DTD). You declare the set of files as the parameter value for the config ActionServlet initialization parameter in your web.xml file. You specify the files as a comma-separated list of file paths. At runtime, the files are merged in memory into a single configuration set. If duplicate elements existfor example, a form bean declaration with the same value for the name attributethe value read from the last configuration file listed takes precedence.

Just because you are using multiple configuration files doesn't necessarily mean that you're using Struts modules. In fact, you can have multiple configuration files for one individual module. In the Solution above, the param-name element value of config dictates to the ActionServlet the path to the Struts configuration files for the default module. Additional modules are indicated by using a param-name value of config/module-name. Example 2-10 shows a Struts ActionServlet declaration from a web.xml file with a default module and two additional modules. The default module uses two configuration files: module1 uses only one configuration file, and module2 uses three configuration files.

Example 2-10. Multiple config files (multiple modules)

<servlet>   <servlet-name>action</servlet-name>   <servlet-class>     org.apache.struts.action.ActionServlet   </servlet-class>   <init-param>     <param-name>config</param-name>     <param-value>       /WEB-INF/struts-default-config.xml,       /WEB-INF/struts-default-config-2.xml     </param-value>   </init-param>   <init-param>     <param-name>config/module1</param-name>     <param-value>       /WEB-INF/struts-module1-config.xml     </param-value>   </init-param>   <init-param>     <param-name>config/module2</param-name>     <param-value>       /WEB-INF/struts-module2-config.xml,       /WEB-INF/struts-module2-config-2.xml,       /WEB-INF/struts-module2-config-3.xml     </param-value>   </init-param>   <load-on-startup>1</load-on-startup> </servlet>

If you are doing team development, consider splitting your configuration files based on functional area, use cases, or user stories. Individual team members can focus on their areas of responsibility without bumping into the rest of the team.

Recipe2.4.Using Multiple Struts Configuration Files