1900_6789 2021-12-05 22:19 采纳率: 53.8%
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已结题

用ssm框架写一个博客项目，后端用@RequestParam获取form表单中input元素的值，获取不到值

问题遇到的现象和发生背景

问题发生的现象：
后端用@RequestParam通过input元素的name属性 获取input中输入的值，获取不到值。
详情：项目运行后，通过点击头像跳转到editHeadImg.html，在其中输入用户名及选择本地图片后，点击上传按钮，会跳到UserController中的/uploadHeadImg位置，执行uploadHeadImg方法，该方法通过@RequestParam(value = "name", required = false)获取editHeadImg.html中的name属性值，运行至此报错！

发生问题的背景：
用ssm框架编写博客项目，想写一个上传头像的功能。

问题相关代码，请勿粘贴截图

问题相关代码：
editHeadImg.html：

<form action="/uploadHeadImg" method="post" enctype="multipart/form-data">
    上传人：<input id="name" type="text" name="name"><br>
    请选择文件：<input id="file" type="file" name="uploadfile" multiple="multiple"><br>
    <input type="submit" value="上传">
</form>

UserControllerjava：

@RequestMapping("/uploadHeadImg")
    public String uploadHeadImg(@RequestParam(value = "name", required = false) String name,
                                @RequestParam(value = "uploadfile", required = false) MultipartFile headImg,
                                HttpServletRequest request) {
        System.out.println("\n\n************\n\n" + name + headImg);
        String filename = headImg.getOriginalFilename();
        if ("".equals(filename)) {
            return "error";
        }
        // 获取上传文件的原始名称
        String originalFilename = headImg.getOriginalFilename();
        // 设置上传文件的保存地址目录
        String dirPath =
                request.getServletContext().getRealPath("/uploadheadimg");
        File filePath = new File(dirPath);
        // 如果保存文件的地址不存在，就先创建目录
        if (!filePath.exists()) {
            filePath.mkdirs();
        }
        System.out.println("文件保存路径为："+filePath);
        // 使用UUID重新命名上传的文件名称(上传人_uuid_原始文件名称)
        newFilename = name+ "_"+ UUID.randomUUID() +
                "_"+originalFilename;
        try {
            // 使用MultipartFile接口的方法完成文件上传到指定位置
            headImg.transferTo(new File(dirPath + newFilename));
        } catch (Exception e) {
            e.printStackTrace();
            return "error";
        }
        return "editHeadImg";
    }
运行结果及报错内容

运行结果及报错内容：
浏览器中：

HTTP状态 500 - 内部服务器错误
类型 异常报告

消息 Request processing failed; nested exception is java.lang.NullPointerException

描述 服务器遇到一个意外的情况，阻止它完成请求。

例外情况

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.NullPointerException
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:986)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:881)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:652)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:855)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
根本原因。

java.lang.NullPointerException
    com.xxx.blog.controller.UserController.uploadHeadImg(UserController.java:83)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    java.lang.reflect.Method.invoke(Method.java:498)
    org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:209)
    org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136)
    org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:871)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:777)
    org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:991)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:978)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:881)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:652)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:855)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
):注意 主要问题的全部 stack 信息可以在 server logs 里查看

Apache Tomcat/9.0.37

idea控制台中：



************

nullnull
22:03:21.849 [http-nio-7080-exec-2] DEBUG org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver - Resolving exception from handler [public java.lang.String com.xxx.blog.controller.UserController.uploadHeadImg(java.lang.String,org.springframework.web.multipart.MultipartFile,javax.servlet.http.HttpServletRequest)]: java.lang.NullPointerException
22:03:21.849 [http-nio-7080-exec-2] DEBUG org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver - Resolving exception from handler [public java.lang.String com.xxx.blog.controller.UserController.uploadHeadImg(java.lang.String,org.springframework.web.multipart.MultipartFile,javax.servlet.http.HttpServletRequest)]: java.lang.NullPointerException
22:03:21.849 [http-nio-7080-exec-2] DEBUG org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver - Resolving exception from handler [public java.lang.String com.xxx.blog.controller.UserController.uploadHeadImg(java.lang.String,org.springframework.web.multipart.MultipartFile,javax.servlet.http.HttpServletRequest)]: java.lang.NullPointerException
22:03:21.849 [http-nio-7080-exec-2] DEBUG org.springframework.web.servlet.DispatcherServlet - Could not complete request
java.lang.NullPointerException: null
    at com.xxx.blog.controller.UserController.uploadHeadImg(UserController.java:83)
    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:498)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:209)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:871)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:777)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:991)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:978)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:881)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:652)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:855)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1589)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:748)
我的解答思路和尝试过的方法

尝试过的方法：
百度说添加required = false，但是我已经添加了这个属性。该方法不使用我。

我想要达到的结果

望各位友友帮忙指点一下 > ~ <

  • 写回答

3条回答 默认 最新

  • 可以睡觉但是没必要 2021-12-06 09:43
    关注

    看看是不是缓存的原因，我复制你的代码去运行是能获取到值的(上传的一个图片)

    img

    本回答被题主选为最佳回答 , 对您是否有帮助呢?
    评论
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  • 系统已结题 12月14日
  • 已采纳回答 12月6日
  • 创建了问题 12月5日

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