java/jsf 奇怪的错误：警告：StandardWrapperValve PWC1406：Servlet.service() ...抛出异常 java.lang.NullPointerException

Question

我有简单的 jsf 应用程序，带有用于动态图像的 servlet 和过滤器设置 utf8 编码。有时（1/10 请求）我会收到非常奇怪的错误：

WARNING: StandardWrapperValve[com.webapp.servlet.ImageServlet]: PWC1406: Servlet.service() for servlet com.webapp.servlet.ImageServlet threw exception
java.lang.NullPointerException
    at com.sun.enterprise.v3.services.impl.monitor.MonitorableSelectionKeyHandler$CloseHandler.notifyClosed(MonitorableSelectionKeyHandler.java:94)
    at com.sun.enterprise.v3.services.impl.monitor.MonitorableSelectionKeyHandler$CloseHandler.remotlyClosed(MonitorableSelectionKeyHandler.java:90)
    at com.sun.grizzly.BaseSelectionKeyHandler.notifyRemotlyClose(BaseSelectionKeyHandler.java:233)
    at com.sun.grizzly.util.OutputWriter.notifyRemotelyClosed(OutputWriter.java:353)
    at com.sun.grizzly.util.OutputWriter.flushChannel(OutputWriter.java:148)
    at com.sun.grizzly.util.OutputWriter.flushChannel(OutputWriter.java:76)
    at com.sun.grizzly.http.SocketChannelOutputBuffer.flushChannel(SocketChannelOutputBuffer.java:326)
    at com.sun.grizzly.http.SocketChannelOutputBuffer.flushBuffer(SocketChannelOutputBuffer.java:398)
    at com.sun.grizzly.http.SocketChannelOutputBuffer.flush(SocketChannelOutputBuffer.java:376)
    at com.sun.grizzly.http.ProcessorTask.action(ProcessorTask.java:1247)
    at com.sun.grizzly.tcp.Response.action(Response.java:268)
    at org.apache.catalina.connector.OutputBuffer.doFlush(OutputBuffer.java:380)
    at org.apache.catalina.connector.OutputBuffer.flush(OutputBuffer.java:353)
    at org.apache.catalina.connector.CoyoteOutputStream.flush(CoyoteOutputStream.java:175)
*   at com.webapp.servlet.ImageServlet.doGet(ImageServlet.java:35)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:734)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1539)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:343)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
    at com.ocpsoft.pretty.PrettyFilter.doFilter(PrettyFilter.java:118)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
*   at com.webapp.filter.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:32)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:279)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
    at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655)
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595)
    at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:98)
    at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:91)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:162)
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:330)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231)
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:174)
    at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:828)
    at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:725)
    at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1019)
    at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:225)
    at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
    at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
    at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
    at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
    at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
    at java.lang.Thread.run(Thread.java:722)

这是我的 servlet 和过滤器，我用星号标记了引用堆栈跟踪的行：

@WebServlet(urlPatterns = "/images/*")
public class ImageServlet extends HttpServlet {

  @Inject
  private FileService fileService;

  @Override
  public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
      byte[] img = fileService.getImage(request.getPathInfo());
      if (img != null) {
        response.setContentType("image/png");
        response.addHeader("Content-Length", String.valueOf(img.length));
        ServletOutputStream os = response.getOutputStream();
          os.write(img);
*         os.flush();
          os.close();
      } else {
        response.sendRedirect(request.getContextPath() + "/error");
      }
  }
}


@WebFilter(urlPatterns = "/*")
public class CharacterEncodingFilter implements Filter {

  @Override
  public void init(FilterConfig filterConfig) {
  }

  @Override
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    request.setCharacterEncoding("UTF-8");
    response.setCharacterEncoding("UTF-8");
*   chain.doFilter(request, response);
  }

  @Override
  public void destroy() {
  }
}

我完全不知道发生了什么...我正在使用 Glassfish 3.1.1 jdk7 的网络配置文件

Answer 1

当您关闭流时，刷新已经隐式完成。关闭已经由容器本身隐式完成。您实际上不需要需要自己做。然而，大多数 servlet 开发人员这样做是为了获得早期反馈，以防他们忽略了请求-响应链中的其他内容正在写入输出流，例如有问题的过滤器或响应包装器等。这将导致每次调用时出现 IOException，因为流已关闭。

无论如何，您有两种选择来处理 flush() 和 close()：

1. 将它们放在您忽略的 try-catch 中例外。
2. 删除那两行。无论如何，容器会为你做这件事。它也将忽略异常。

该异常只是客户端中止连接的标志。例如，在图像仍在流式传输时按 [Esc] 或关闭窗口/选项卡或导航到其他页面。

另请参阅：

• 我应该关闭 servlet 输出流吗？

Answer 2

at com.sun.grizzly.util.OutputWriter.notifyRemotelyClosed()

不知何故，在我看来，好像您正在刷新流的连接已被远程对等点（Web 浏览器？）中间关闭。

您可以尝试一下 response.flushBuffer() 吗？这也抛出异常吗？