java.lang.NullPointerException:未设置FileItemFactory

尝试使用流式API实现文件上载时，我遇到一个错误，如下所述： 当我从网页上得知“传统的FileItemFactory完全被忽略”时，我想知道我做错了什么。因此，我定义了一个基本方法，如下所示：

/**
 * 
 * @param
 * @return
 */
public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {

    // Check that we have a file upload request
    boolean isMultipart = ServletFileUpload.isMultipartContent(request);

    if (isMultipart) {

        ServletFileUpload upload = new ServletFileUpload();                 // Create a new file upload handler

            // Parse the request
            try {
Line 39 -->         List items = upload.parseRequest(request);                      // FileItem
            Iterator iter = items.iterator();
            while (iter.hasNext()) {
                FileItemStream item = (FileItemStream) iter.next();

                if (!item.isFormField()) {
                    this.processFITSFile(item);
                }
            }
        } catch (FileUploadException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }       
    }
}

但这导致了以下错误：

SEVERE: Servlet.service() for servlet FitsFileProcessorServlet threw exception
java.lang.NullPointerException: No FileItemFactory has been set.
    at org.apache.commons.fileupload.FileUploadBase.parseRequest(FileUploadBase.java:353)
    at org.apache.commons.fileupload.servlet.ServletFileUpload.parseRequest(ServletFileUpload.java:126)
    at controller.FITSFileProcessor.doPost(FITSFileProcessor.java:39)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:849)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:454)
    at java.lang.Thread.run(Unknown Source)

---

新建ServletFileUpload（）

创建未初始化的实例。它的文件说：

构造未初始化的实例 这个班的学生。工厂必须是 配置，使用 setFileItemFactory（），在 正在尝试分析请求

因此，您需要使用

setFileItemFactory（）

或使用另一个构造函数，该构造函数将工厂作为参数。像这样：

// Create a factory for disk-based file items
FileItemFactory factory = new DiskFileItemFactory();

// Create a new file upload handler
ServletFileUpload upload = new ServletFileUpload(factory);

有关详细信息，请参阅。这个例子也来自那里

或者，您可以使用，但需要以不同的方式获取迭代器：

ServletFileUpload upload = new ServletFileUpload();
FileItemIterator iter = upload.getItemIterator(request);
while (iter.hasNext()) {
    FileItemStream item = iter.next();
    ...
}

---

您能在代码中标记导致错误的那一行吗？（第39行，我猜）第39行应该是

List items=upload.parseRequest（request）是的，没错。编辑代码，但这样做会产生：java.lang.ClassCastException:org.apache.commons.fileupload.disk.DiskFileItem不能强制转换为org.apache.commons.fileupload.FileItemStream controller.FITSFileProcessor.doPost（FITSFileProcessor.java:46）javax.servlet.http.HttpServlet.service（HttpServlet.java:637）javax.servlet.http.HttpServlet.service（HttpServlet.java:717）如果要使用流式API，需要执行
upload.getItemIterator（请求）
，请参阅