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java - Spring MVC - 文件上传 - etat HTTP 500 错误消息

转载 作者：太空宇宙 更新时间：2023-11-04 10:59:38 26 4
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尝试使用 spring mvc 上传文件时出现以下错误。“Etat HTTP 500 - 请求处理失败；嵌套异常为 java.lang.NullPointerException”。这是我第一次这样做。我知道原因，但到目前为止我还找不到解决方案。

感谢任何可以提供帮助的人。

FileModel.java

package com.model;

import org.springframework.web.multipart.MultipartFile;

public class FileModel {

    private MultipartFile file;

    public MultipartFile getFile() {
        return file;
    }

    public void setFile(MultipartFile file) {
        this.file = file;
    }
}

FileUploadController.java

package com.controller;

import java.io.File;
import java.io.IOException;

import javax.servlet.ServletContext;

import org.jboss.logging.Logger;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.util.FileCopyUtils;
import org.springframework.validation.BindingResult;
import org.springframework.validation.annotation.Validated;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.servlet.ModelAndView;

import com.model.FileModel;

@Controller
public class FileUploadController {

    public Logger logger = Logger.getLogger(FileUploadController.class);

    public FileUploadController(){
        System.out.println("FileUploadController");
    }

    @Autowired
    private ServletContext context;

    @RequestMapping(value = "/fileUploadPage", method = RequestMethod.GET)
    public ModelAndView fileUploadPage() {
        FileModel file = new FileModel();
        ModelAndView modelAndView = new ModelAndView("fileUpload", "command", file);
        return modelAndView;
    }

    @RequestMapping(value="/fileUploadPage", method = RequestMethod.POST)
    public String fileUpload(@Validated FileModel file, BindingResult result, ModelMap model) throws IOException {
        if (result.hasErrors()) {
            System.out.println("validation errors");
            return "fileUploadPage";
        } else {            
            System.out.println("Fetching file");

            MultipartFile multipartFile = file.getFile();

            System.out.println("Multipart "+multipartFile);

            String uploadPath = context.getRealPath("") + File.separator + "fichiers" + File.separator;
            System.out.println(uploadPath);         

            String fileName = multipartFile.getOriginalFilename();
            System.out.println(fileName);

            FileCopyUtils.copy(file.getFile().getBytes(), new File(uploadPath+file.getFile().getOriginalFilename()));           

            model.addAttribute("fileName", fileName);
            return "success";
        }
    }

}

FileUpload.jsp

<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1" isELIgnored="false"%>
<%@ taglib uri="http://www.springframework.org/tags/form" prefix="form"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
        <title>Upload</title>
    </head>
    <body>
        <form:form action="fileUploadPage" method = "POST" modelAttribute = "fileUpload" enctype = "multipart/form-data">
            Please select a file to upload : <input type = "file" name = "file" />
            <input type = "submit" value = "upload" />
        </form:form>
    </body>
</html>

控制台

GRAVE: Servlet.service() for servlet [spring] in context with path [/oracle_spring_user_test_project] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException
    at com.controller.FileUploadController.fileUpload(FileUploadController.java:56)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:137)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:777)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:706)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:943)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:868)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:962)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:445)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1115)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

最佳答案

您正在 JSP 表单中使用 modelAttribute = "fileUpload"。因此，您应该使用 @ModelAttribute spring 注释作为方法参数，以指示应从模型中检索的参数。尽管这是最佳实践，但这并不是必需的。

fileUpload 模型属性应使用提交到 fileUploadPage 端点的表单中的数据进行填充。因此，请尝试以下代码片段:

@RequestMapping(value="/fileUploadPage", method = RequestMethod.POST)
    public String fileUpload(@ModelAttribute("fileUpload") FileModel fileUpload, BindingResult result, ModelMap model) throws IOException {
        if (result.hasErrors()) {
            System.out.println("validation errors");
            return "fileUploadPage";
        } else {            
            System.out.println("Fetching file");

            MultipartFile file = fileUpload.getFile();
        ...

关于Spring documentation您可以阅读有关此注释的官方信息。

关于java - Spring MVC - 文件上传 - etat HTTP 500 错误消息，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/47030335/

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