当前 MultipartFile 的 java.io.FileNotFoundException

Question

我正在处理有关 MultipartFile 的奇怪行为。

我的项目是一个接收文本文件的 Spring Boot 后端。该文本文件作为 MultipartFile 出现。我想将此文件发送到辅助 Spring Boot 后端，该后端将在我的主后端读取该文件之前向该文件添加一些内容。这些内容更改不是强制性的，如果它们不存在，程序也不会崩溃。

要将 MultipartFile 发送到另一个后端，我必须将 MultipartFile 转换为 java.io.File。在执行此操作时，MultipartFile 会被破坏。

创建 java.io.File 后，BufferedReader 无法读取原始 MultipartFile。

重度编辑：

我的项目规格发生了变化，额外的后端被取消了。不过我仍然很好奇这里发生了什么。以下代码重现了我遇到的异常：

@CrossOrigin
@RestController
@RequestMapping("/dragon")
public class TestController {

    @PostMapping("/killFile")
    public String sendInFileHere(@Valid @RequestBody MultipartFile multipartFile) {
        if (multipartFile == null) {
            throw new IllegalArgumentException("File has to be Present");
        }
        File file = new File(multipartFile.getOriginalFilename());
        try {
            multipartFile.transferTo(file);
        } catch (IOException e) {
            e.printStackTrace();
        }
        BufferedReader reader;
        try {
            InputStream is = multipartFile.getInputStream(); //exception is thrown here
            reader = new BufferedReader(new InputStreamReader(is));
            return reader.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return "something went wrong";
    }
}

抛出的异常如下：

java.io.FileNotFoundException: C:\Users\lucas.kahler\AppData\Local\Temp\tomcat.1947057742180166642.8080\work\Tomcat\localhost\ROOT\upload_51753fdf_0308_49d4_800c_bd95bd7760f3_00000001.tmp (Das System kann die angegebene Datei nicht finden)
    at java.base/java.io.FileInputStream.open0(Native Method)
    at java.base/java.io.FileInputStream.open(FileInputStream.java:213)
    at java.base/java.io.FileInputStream.<init>(FileInputStream.java:155)
    at org.apache.tomcat.util.http.fileupload.disk.DiskFileItem.getInputStream(DiskFileItem.java:194)
    at org.apache.catalina.core.ApplicationPart.getInputStream(ApplicationPart.java:100)
    at org.springframework.web.multipart.support.StandardMultipartHttpServletRequest$StandardMultipartFile.getInputStream(StandardMultipartHttpServletRequest.java:251)
    at eu.molit.dragon.text.Test.sendInFileHere(Test.java:34)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:567)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:888)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:793)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    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.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    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.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    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:201)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    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:526)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    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:367)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:860)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1591)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.base/java.lang.Thread.run(Thread.java:835)

当我注释掉该文件从 MultipartFile 接收内容的部分时，它完美地工作：

@CrossOrigin
@RestController
@RequestMapping("/dragon")
public class TestController {

    @PostMapping("/killFile")
    public String sendInFileHere(@Valid @RequestBody MultipartFile multipartFile) {
        if (multipartFile == null) {
            throw new IllegalArgumentException("File has to be Present");
        }
        File file = new File(multipartFile.getOriginalFilename());
//        try {
//            multipartFile.transferTo(file);
//        } catch (IOException e) {
//            e.printStackTrace();
//        }
        BufferedReader reader;
        try {
            InputStream is = multipartFile.getInputStream(); 
            reader = new BufferedReader(new InputStreamReader(is));
            return reader.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return "something went wrong";
    }
}

在上面的示例中，返回发送的文本文件的第一行。这表明在从 MultipartFile 到 File 的转换过程中发生了一些事情。

有任何想法吗？

Answer 1

这是正常行为。

对的调用会transferTo消耗关联的InputStream。结果，您无法重复使用它。

如果您想重新读取数据，则必须针对新创建（和写入）的数据File打开一个流来执行此操作。