GAE 上的 Struts 2：无法在拦截器内设置会话值

我正在编写一个 Struts 2 拦截器，在其中检查用户是否有效。如果无效，用户将被重定向到登录页面。但在此之前，我尝试检索用户访问此处的 URL，并将其放入会话变量中，以便在登录完成后我可以将他重定向回那里。但是当我尝试在会话中放入一个值时，它会抛出以下异常：

java.lang.NoClassDefFoundError: Could not initialize class freemarker.template.Configuration
    at org.apache.struts2.views.freemarker.FreemarkerManager.createConfiguration(FreemarkerManager.java:322)
    at org.apache.struts2.views.freemarker.FreemarkerManager.init(FreemarkerManager.java:273)
    at org.apache.struts2.views.freemarker.FreemarkerManager.getConfiguration(FreemarkerManager.java:260)
    at org.apache.struts2.dispatcher.Dispatcher.sendError(Dispatcher.java:865)
    at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:574)
    at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
    at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:99)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.api.socket.dev.DevSocketFilter.doFilter(DevSocketFilter.java:74)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.tools.development.ResponseRewriterFilter.doFilter(ResponseRewriterFilter.java:123)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:34)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:63)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:125)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.tools.development.DevAppServerModulesFilter.doDirectRequest(DevAppServerModulesFilter.java:368)
    at com.google.appengine.tools.development.DevAppServerModulesFilter.doDirectModuleRequest(DevAppServerModulesFilter.java:351)
    at com.google.appengine.tools.development.DevAppServerModulesFilter.doFilter(DevAppServerModulesFilter.java:116)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
    at org.mortbay.jetty.handler.ContextHandler.__handle(ContextHandler.java:765)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
    at com.google.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:97)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:485)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
    at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:547)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:212)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)

注意：它说找不到类，但我可以在构建路径的库列表中看到配置类。 拦截器的代码片段：

public String intercept(ActionInvocation actionInvocation)
        throws Exception {
    System.out.println("inside auth interceptor");
    //just to make sure session is created the first time
    HttpSession session = ServletActionContext.getRequest().getSession(true);
    Map<String, Object> sessionAttributes = ActionContext.getContext().getSession();

    User user = (User) sessionAttributes.get("user");

    ActionProxy proxy = actionInvocation.getProxy();
    String namespace =  proxy.getNamespace();
    String actionName = proxy.getActionName();

    sessionAttributes.put("returnUrl",  namespace+(actionName == null || actionName.equals("/") ?"":("/"+actionName)));
    //even tried this, but getting same error : 
    //session.setAttribute("returnUrl",  namespace+(actionName == null || actionName.equals("/") ?"":("/"+actionName)));
    System.out.println(namespace+(actionName == null || actionName.equals("/") ?"":("/"+actionName)));

    if(user == null){
        //no user exist. redirect to Login page
        return Action.LOGIN;

    }else
        return actionInvocation.invoke();
}

正如你所看到的，我什至尝试过session.setAttribute()得到同样的错误。无需将任何内容放入会话变量中，代码就会按预期运行。那么我做错了什么？

Update 1: 我有需要的freemarker-2.3.19 in web-inf/lib并将其添加到构建路径中。

部署项目时，jar 文件需要位于类路径上，其中应包含错误类中提到的内容。为了确保该文件已部署，您可以将其放置在web-inf/lib作为临时措施。您还可以将文件组装到 war 存档中以进行整体部署。我所说的库文件是

freemarker-2.3.19.jar

如果您使用的是 Maven，那么您的项目中需要以下依赖项pom.xml

<dependency>
    <groupId>org.apache.struts</groupId>
    <artifactId>struts2-core</artifactId>
    <version>2.3.16</version>
</dependency>

<dependency>
    <groupId>org.freemarker</groupId>
    <artifactId>freemarker</artifactId>
    <version>2.3.19</version>
</dependency>