当使用okhttp发送发布请求时，服务器接收到的请求主体为null。可能是什么问题？

Question

这是代码，它将参数fname，selectedFile（byteArray）作为发布请求主体的一部分从android发送到Tomcat服务器。

    public void uploadFile(){
        EditText filename=findViewById(R.id.fileName);
        //content://
        try {
            InputStream inputStream=getContentResolver().openInputStream(filePath);
            selectedFile= IOUtils.toByteArray(inputStream);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        String purl="http://192.168.1.11:8080/placement/V2TryUploadFile";

        RequestBody requestBody=new MultipartBody.Builder()
                .setType(MultipartBody.FORM)
                .addFormDataPart("fname",filename.getText().toString())
                .addFormDataPart("selectedFile",filename.getText().toString(),RequestBody.create(MediaType.parse("application/pdf"),selectedFile))
                .build();
        Request request=new Request.Builder()
                .url(purl)
                .post(requestBody)
                .build();

        Toast.makeText(MainActivity.this,filename.getText().toString(),Toast.LENGTH_SHORT).show();
        Toast.makeText(MainActivity.this,selectedFile.length+":",Toast.LENGTH_SHORT).show();
        OkHttpClient okHttpClient=new OkHttpClient();
        okHttpClient.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                call.cancel();
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        Toast.makeText(MainActivity.this,"Failed to Upload",Toast.LENGTH_SHORT).show();
                    }
                });
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                final String responseString=response.body().string();
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        Toast.makeText(MainActivity.this,responseString,Toast.LENGTH_SHORT).show();
                    }
                });
            }
        });

Servlet代码（在tomcat服务器上运行）以处理从android add发送的发布请求

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        String fname=request.getParameter("fname")+".pdf";
        Part selectedFile=request.getPart("selectedFile");
        System.out.println(fname);
        System.out.println(selectedFile+"");
        InputStream filecontent = selectedFile.getInputStream();

        byte[] fileAsByteArray = IOUtils.toByteArray(filecontent);

        FileOutputStream imageOutFile = new FileOutputStream("C:\\Users\\VAISHAK`\\placeWorkSpace\\placement\\ResumeUploads\\" + fname);
        imageOutFile.write(fileAsByteArray);
        imageOutFile.close();
        doGet(request, response);
    }

问题是fname和selectedFile在android应用程序中未显示为null，但在tomcat服务器控制台中都显示为null。

也下面是Eclipse中的tomcat服务器登录

null.pdf
null
Apr 13, 2020 11:56:20 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [trial.V2TryUploadFile] in context with path [/placement] threw exception
java.lang.NullPointerException
    at trial.V2TryUploadFile.doPost(V2TryUploadFile.java:49)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
    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:52)
    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:199)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:543)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:688)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:615)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:818)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1623)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)

Answer 1

我终于找到了解决方案

默认情况下，Servlet不处理

MutipartBody FORM

因此，为了支持它，我们需要将以下注释添加到servlet中

@MultipartConfig