是什么原因導致org.apache.catalina.connector.CoyoteWriter.flush（）中的該NPE？

Question

 private void respond(String response) {

    httpServletResponse.setContentType("application/json");
    httpServletResponse.setCharacterEncoding("UTF-8");

    try {
        PrintWriter out = httpServletResponse.getWriter();

        out.print(response);
        out.flush();

    } catch (IOException ex) {
        log.error("Error while writing response",ex);
    }

}

此代碼在out.flush（）處拋出空指針。 httpServletResponse是實例變量。 我已驗證響應不為空。 該函數是從Apache的aync http客戶端庫的CloseableHttpAsyncClient.execute.completed（）內部調用的。

LOG:

Caused by: java.lang.NullPointerException: null
    at org.apache.coyote.http11.InternalNioOutputBuffer.flushBuffer(InternalNioOutputBuffer.java:234) ~[tomcat-coyote.jar:8.0.14]
    at org.apache.coyote.http11.InternalNioOutputBuffer.addToBB(InternalNioOutputBuffer.java:189) ~[tomcat-coyote.jar:8.0.14]
    at org.apache.coyote.http11.InternalNioOutputBuffer.commit(InternalNioOutputBuffer.java:177) ~[tomcat-coyote.jar:8.0.14]
    at org.apache.coyote.http11.AbstractHttp11Processor.action(AbstractHttp11Processor.java:739) ~[tomcat-coyote.jar:8.0.14]
    at org.apache.coyote.Response.action(Response.java:179) ~[tomcat-coyote.jar:8.0.14]
    at org.apache.coyote.Response.sendHeaders(Response.java:341) ~[tomcat-coyote.jar:8.0.14]
    at org.apache.catalina.connector.OutputBuffer.doFlush(OutputBuffer.java:331) ~[catalina.jar:8.0.14]
    at org.apache.catalina.connector.OutputBuffer.flush(OutputBuffer.java:313) ~[catalina.jar:8.0.14]
    at org.apache.catalina.connector.CoyoteWriter.flush(CoyoteWriter.java:98) ~[catalina.jar:8.0.14]
    at com.thruport.aje.rotator.reward.async.RewardRequest.respond(RewardRequest.java:185) ~[output/:na]
    at com.thruport.aje.rotator.reward.async.RewardRequest.lambda$new$2(RewardRequest.java:131) ~[output/:na]
    at java.util.concurrent.CompletableFuture.uniApply(CompletableFuture.java:602) ~[na:1.8.0_121]
    ... 8 common frames omitted

Answer 1

事實證明，我不應該在此處進行沖洗，因為Servlet容器將在Servlet生命周期結束時進行處理，並且Buffer在此階段將不准備沖洗。 刷新ServletOutputStream時出現此Nullpointer異常，並且應該在HttpServletResponse.getOutputStream（）/。getWriter（）上調用.close（）嗎？ 答案有所幫助。