源码分析：Struts 2配置文件加载顺序

org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter

    public void init(FilterConfig filterConfig) throws ServletException {

        InitOperations init = new InitOperations();

        Dispatcher dispatcher = null;

        try {

            FilterHostConfig config = new FilterHostConfig(filterConfig);

            init.initLogging(config);

            dispatcher = init.initDispatcher(config);

            init.initStaticContentLoader(config, dispatcher);

            prepare = new PrepareOperations(filterConfig.getServletContext(), dispatcher);

            execute = new ExecuteOperations(filterConfig.getServletContext(), dispatcher);

            this.excludedPatterns = init.buildExcludedPatternsList(dispatcher);

            postInit(dispatcher, filterConfig);

        } finally {

            if (dispatcher != null) {

                dispatcher.cleanUpAfterInit();

            }

            init.cleanup();

        }

    }

    /**

     * Creates and initializes the dispatcher

     */

    public Dispatcher initDispatcher( HostConfig filterConfig ) {

        Dispatcher dispatcher = createDispatcher(filterConfig);

        dispatcher.init();

        return dispatcher;

    }

    /**

     * Load configurations, including both XML and zero-configuration strategies,

     * and update optional settings, including whether to reload configurations and resource files.

     */

    public void init() {

         if (configurationManager == null) {

              configurationManager = createConfigurationManager(DefaultBeanSelectionProvider.DEFAULT_BEAN_NAME);

         }

        try {

            init_FileManager();

            init_DefaultProperties(); // [1]

            init_TraditionalXmlConfigurations(); // [2]

            init_LegacyStrutsProperties(); // [3]

            init_CustomConfigurationProviders(); // [5]

            init_FilterInitParameters() ; // [6]

            init_AliasStandardObjects() ; // [7]

            Container container = init_PreloadConfiguration();

            container.inject(this);

            init_CheckWebLogicWorkaround(container);

            if (!dispatcherListeners.isEmpty()) {

                for (DispatcherListener l : dispatcherListeners) {

                    l.dispatcherInitialized(this);

                }

            }

        } catch (Exception ex) {

            if (LOG.isErrorEnabled())

                LOG.error("Dispatcher initialization failed", ex);

            throw new StrutsException(ex);

        }

    }

    private void init_DefaultProperties() {

        configurationManager.addContainerProvider(new DefaultPropertiesProvider());

    }

/**

* Loads the default properties, separate from the usual struts.properties loading

*/

public class DefaultPropertiesProvider extends PropertiesConfigurationProvider {

    public void destroy() {

    }

    public void init(Configuration configuration) throws ConfigurationException {

    }

    public void register(ContainerBuilder builder, LocatableProperties props) throws ConfigurationException {

        try {

            PropertiesSettings defaultSettings = new PropertiesSettings("org/apache/struts2/default");

            loadSettings(props, defaultSettings);

        } catch (Exception e) {

            throw new ConfigurationException("Could not find or error in org/apache/struts2/default.properties", e);

        }

    }

}

    private void init_TraditionalXmlConfigurations() {

        String configPaths = initParams.get("config");

        if (configPaths == null) {

            configPaths = DEFAULT_CONFIGURATION_PATHS;

        }

        String[] files = configPaths.split("\\s*[,]\\s*");

        for (String file : files) {

            if (file.endsWith(".xml")) {

                if ("xwork.xml".equals(file)) {

                    configurationManager.addContainerProvider(createXmlConfigurationProvider(file, false));

                } else {

                    configurationManager.addContainerProvider(createStrutsXmlConfigurationProvider(file, false, servletContext));

                }

            } else {

                throw new IllegalArgumentException("Invalid configuration file name");

            }

        }

    }

    /**

     * Provide list of default configuration files.

     */

    private static final String DEFAULT_CONFIGURATION_PATHS = "struts-default.xml,struts-plugin.xml,struts.xml";

    private void init_LegacyStrutsProperties() {

        configurationManager.addContainerProvider(new PropertiesConfigurationProvider());

    }

    public void register(ContainerBuilder builder, LocatableProperties props) throws ConfigurationException {

        final DefaultSettings settings = new DefaultSettings();

        loadSettings(props, settings);

    }

    /**

     * Constructs an instance by loading the standard property files,

     * any custom property files (<code>struts.custom.properties</code>),

     * and any custom message resources ().

     * <p>

     * Since this constructor  combines Settings from multiple resources,

     * it utilizes a {@link DelegatingSettings} instance,

     * and all API calls are handled by that instance.

     */

    public DefaultSettings() {

        ArrayList<Settings> list = new ArrayList<Settings>();

        // stuts.properties, default.properties

        try {

            list.add(new PropertiesSettings("struts"));

        } catch (Exception e) {

            LOG.warn("DefaultSettings: Could not find or error in struts.properties", e);

        }

        delegate = new DelegatingSettings(list);

        // struts.custom.properties

        String files = delegate.get(StrutsConstants.STRUTS_CUSTOM_PROPERTIES);

        if (files != null) {

            StringTokenizer customProperties = new StringTokenizer(files, ",");

            while (customProperties.hasMoreTokens()) {

                String name = customProperties.nextToken();

                try {

                    list.add(new PropertiesSettings(name));

                } catch (Exception e) {

                    LOG.error("DefaultSettings: Could not find " + name + ".properties. Skipping.");

                }

            }

            delegate = new DelegatingSettings(list);

        }

    }

<filter>

   <filter-name> struts2 </filter-name>

   <filter-class> org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter </filter-class>

    <init-param>

          <param-name> config </param-name>

          <param-value>struts-default.xml,struts-plugin.xml,META-INF/config/struts/struts.xml </param-value>

   </init-param>

</filter>