我正在尝试使用 GWT 和 GAE/J（带有 Java 的 Google AppEngine）编写应用程序。对于我的应用程序，我需要使用 DTO。为了将 Pojo 转换为 JDO 实体，我想使用Dozer library。因此，当我尝试转换对象时，出现以下错误：
Jun 23, 2009 7:12:30 PM com.google.appengine.tools.development.ApiProxyLocalImpl log
SEVERE: [1245784350843000] javax.servlet.ServletContext log: Exception while dispatching incoming RPC call
com.google.gwt.user.server.rpc.UnexpectedException: Service method 'public abstract com.athena.client.entities.Person com.athena.client.GreetingService.getPerson(com.athena.client.entities.Person)' threw an unexpected exception: java.lang.NoClassDefFoundError: org/dozer/DozerBeanMapper
at com.google.gwt.user.server.rpc.RPC.encodeResponseForFailure(RPC.java:360)
at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:546)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:166)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.doPost(RemoteServiceServlet.java:86)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:713)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:806)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1093)
at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1084)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:360)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:712)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405)
at com.google.apphosting.utils.jetty.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:54)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:139)
at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:306)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:139)
at org.mortbay.jetty.Server.handle(Server.java:313)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:506)
at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:844)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:644)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:205)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:381)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:396)
at org.mortbay.thread.BoundedThreadPool$PoolThread.run(BoundedThreadPool.java:442)
Caused by: java.lang.NoClassDefFoundError: org/dozer/DozerBeanMapper
at com.athena.server.GreetingServiceImpl.getPerson(GreetingServiceImpl.java:38)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:527)
... 25 more
当我试图在服务器内实例化映射器对象时出现错误：
Mapper mapper = new DozerBeanMapper();
我该如何解决这个问题？