Java getPart（）拋出空指針異常

當我嘗試使用getPart（）時出現空指針異常，我無法理解爲什麼拋出異常而不是僅僅返回null。這是我在JSP形式：Java getPart（）拋出空指針異常

<form onsubmit="return check()" method="post" enctype="multipart/form-data" action="/TrainingServlet"> 
    <input id="hotel_file" type="file" name="hotel_file" size="30"> 
</form>

然後在我的servlet中，我有以下代碼：

public void doPost(HttpServletRequest req, HttpServletResponse resp) { 
    try { 
      Part filePart = req.getPart("hotel_file"); //this line throws null pointer exception 
      getServletContext().getRequestDispatcher("/import.jsp").forward(req, resp); 

    } catch(Exception e) { 

      e.printStackTrace(); 
    } 
}

閱讀本SO post後，我加入了@MultipartConfig註釋的servlet類和我我仍然在req.getPart（）行中獲得NPE。此外，我正在JBoss 6上運行servlet。任何洞察讚賞！

這裏是堆棧跟蹤

16:50:15,227 ERROR [STDERR] java.lang.NullPointerException 
16:50:15,228 ERROR [STDERR] at org.apache.catalina.connector.Request.getPart(Request.java:3225) 
16:50:15,228 ERROR [STDERR] at org.apache.catalina.connector.RequestFacade.getPart(RequestFacade.java:1102) 
16:50:15,229 ERROR [STDERR] at com.lanyon.training.javaproj.servlets.TrainingServlet.doPost(TrainingServlet.java:96) 
16:50:15,229 ERROR [STDERR] at javax.servlet.http.HttpServlet.service(HttpServlet.java:754) 
16:50:15,230 ERROR [STDERR] at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) 
16:50:15,230 ERROR [STDERR] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:324) 
16:50:15,231 ERROR [STDERR] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:242) 
16:50:15,231 ERROR [STDERR] at com.lanyon.ghotel.common.pagination.web.PaginationFilter.doFilter(PaginationFilter.java:77) 
16:50:15,232 ERROR [STDERR] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:274) 
16:50:15,232 ERROR [STDERR] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:242) 
16:50:15,233 ERROR [STDERR] at com.lanyon.common.serverobjects.UTF8EncodingFilter.doFilter(UTF8EncodingFilter.java:33) 
16:50:15,233 ERROR [STDERR] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:274) 
16:50:15,234 ERROR [STDERR] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:242) 
16:50:15,235 ERROR [STDERR] at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:275) 
16:50:15,235 ERROR [STDERR] at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) 
16:50:15,236 ERROR [STDERR] at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:181) 
16:50:15,236 ERROR [STDERR] at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:88) 
16:50:15,236 ERROR [STDERR] at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.invoke(SecurityContextEstablishmentValve.java:100) 
16:50:15,237 ERROR [STDERR] at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) 
16:50:15,237 ERROR [STDERR] at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) 
16:50:15,238 ERROR [STDERR] at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:158) 
16:50:15,238 ERROR [STDERR] at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:567) 
16:50:15,239 ERROR [STDERR] at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) 
16:50:15,239 ERROR [STDERR] at org.jboss.web.tomcat.service.request.ActiveRequestResponseCacheValve.invoke(ActiveRequestResponseCacheValve.java:53) 
16:50:15,240 ERROR [STDERR] at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:362) 
16:50:15,240 ERROR [STDERR] at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:877) 
16:50:15,241 ERROR [STDERR] at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:654) 
16:50:15,241 ERROR [STDERR] at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:951) 
16:50:15,242 ERROR [STDERR] at java.lang.Thread.run(Thread.java:619)

來源

2014-11-21 homegrown

的transferTo（）方法@ PM77-1堆棧跟蹤發佈 – homegrown 2014-11-21 22:58:38

是線＃** 96 **'TrainingServlet.java'文件，您的評論行？ – 2014-11-21 23:06:37

是的，它是...... – homegrown 2014-11-21 23:08:30

多給你一個字節流。你必須將其轉換成文件。

您還可以使用多

來源

2014-11-22 17:54:41 prsutar

Java getPart（）拋出空指針異常

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