struts2 handle static resource

在web.xml中作如下配置：

    <filter>
        <filter-name>struts2</filter-name>
        <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
        <init-param>
         <param-name>packages</param-name>
         <param-value>net.zdsoft.eis.template</param-value>
        </init-param>
    </filter>

  <filter-mapping>
  <filter-name>struts2</filter-name>
  <url-pattern>*.action</url-pattern>
 </filter-mapping> <filter-mapping>
  <filter-name>struts2</filter-name>
  <url-pattern>/static/*</url-pattern>
 </filter-mapping>

用于处理静态资源（css、js、图片之类），启动后正常。但当修改了struts配置文件，并且struts.configuration.xml.reload=true时，再次加载静态资源时会出错如下错误：

java.lang.NullPointerException at org.apache.struts2.dispatcher.DefaultStaticContentLoader.findStaticResource(DefaultStaticContentLoader.java:164)
 at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeStaticResourceRequest(ExecuteOperations.java:62)
 at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:86)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
 
原因：重新加载配置文件时，静态资源的处理类DefaultStaticContentLoader的setHostConfig(HostConfig filterConfig)方法没调用，导致pathPrefixes为空。

解决方案：

1、继承StrutsPrepareOperations类，构造方法中传入参数FilterConfig。createActionContext方法中如果oldContext为空，则重新初始化静态资源配置。完整代码如下：

public class StrutsPrepareOperations extends PrepareOperations {
    private ServletContext servletContext;
    private Dispatcher dispatcher;
    private FilterHostConfig config;

    public StrutsPrepareOperations(ServletContext servletContext, Dispatcher dispatcher,
            FilterConfig filterConfig) {
        super(servletContext, dispatcher);
        this.dispatcher = dispatcher;
        this.servletContext = servletContext;
        this.config = new FilterHostConfig(filterConfig);
    }

    // 重写doFilter，由于在struts配置文件重新加载后，静态资源有问题
    /**
     * Creates the action context and initializes the thread local
     */
    public ActionContext createActionContext(HttpServletRequest request,
            HttpServletResponse response) {
        ActionContext ctx;
        Integer counter = 1;
        Integer oldCounter = (Integer) request.getAttribute(CLEANUP_RECURSION_COUNTER);
        if (oldCounter != null) {
            counter = oldCounter + 1;
        }

        ActionContext oldContext = ActionContext.getContext();
        if (oldContext != null) {
            // detected existing context, so we are probably in a forward
            ctx = new ActionContext(new HashMap<String, Object>(oldContext.getContextMap()));
        } else {
            ValueStack stack = dispatcher.getContainer().getInstance(ValueStackFactory.class)
                    .createValueStack();
            stack.getContext().putAll(
                    dispatcher.createContextMap(request, response, null, servletContext));
            ctx = new ActionContext(stack.getContext());

            // add by zhaosf
            StaticContentLoader staticResourceLoader = dispatcher.getContainer().getInstance(
                    StaticContentLoader.class);
            staticResourceLoader.setHostConfig(config);
        }
        request.setAttribute(CLEANUP_RECURSION_COUNTER, counter);
        ActionContext.setContext(ctx);
        return ctx;
    }

2、继承org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter时，重写init方法，如下：

public class StrutsFilter extends StrutsPrepareAndExecuteFilter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        InitOperations init = new InitOperations();
        try {
            FilterHostConfig config = new FilterHostConfig(filterConfig);
            init.initLogging(config);
            Dispatcher dispatcher = init.initDispatcher(config);
            init.initStaticContentLoader(config, dispatcher);

            prepare = new StrutsPrepareOperations(filterConfig.getServletContext(), dispatcher,
                    filterConfig);
            execute = new ExecuteOperations(filterConfig.getServletContext(), dispatcher);
            this.excludedPatterns = init.buildExcludedPatternsList(dispatcher);

            postInit(dispatcher, filterConfig);
        } finally {
            init.cleanup();
        }
    }