Java servlet 无法接收 http post 多部分请求的各个部分

Question

首先，我问了这个问题What did I miss to send a http part post request看来我不理解从客户端发送多部分到服务器的逻辑。使用这篇文章https://developer.constantcontact.com/docs/mylibrary-files-api/file-add-multipart-post.html我无法看到每个部分中的必填字段。

我构建了我的请求并添加了所有必填字段，如您在此处看到的

HttpClient client = HttpClientBuilder.create().build();
        HttpPost httpPost = new HttpPost(
                "http://localhost:8080/ServletExample1/multipart1");
        httpPost.addHeader("Content-Type",
                "multipart/related; boundary=HereItGoes");
        httpPost.addHeader("Accept", MediaType.TEXT_PLAIN);
        MultipartEntityBuilder builder = MultipartEntityBuilder.create();
        FileBody bin = new FileBody(new File("./test.txt"));
        builder.addPart("source", new StringBody("MyComputer",
                ContentType.TEXT_PLAIN));
        builder.addPart("folder_id", new StringBody("-1",
                ContentType.TEXT_PLAIN));
        builder.addPart("file_type", new StringBody("txt",
                ContentType.TEXT_PLAIN));
        builder.addPart("file_name", new StringBody("test.txt",
                ContentType.TEXT_PLAIN));
        builder.addPart("description", new StringBody("The file to test",
                ContentType.TEXT_PLAIN));
        builder.addPart("data", bin);
        HttpEntity entity = builder.build();
        httpPost.setEntity(entity);
        HttpResponse response = client.execute(httpPost);
        String responseString = new BasicResponseHandler()
                .handleResponse(response);
        System.out.println(responseString);

我的问题出在服务器上，我不断收到零件数量为零的信息。对于某些人来说，服务器没有收到零件(注意我并不是说服务器中有异常(exception))

我这么说是因为在服务器(我的 servlet)上我这样做

Iterator<Part> partsIterator = request.getParts().iterator();
            System.out.println("The number of parts is :"
                    + request.getParts().size());

并且打印结果始终为零，始终

请问我缺少什么？

Answer 1

Servlet 的多部分配置需要 Content-Type 为 multipart/form-data。

这是在 javadoc of @MultipartConfig 等地方指定的。

Annotation that may be specified on a javax.servlet.Servlet class, indicating that instances of the Servlet expect requests that conform to the multipart/form-data MIME type.

您正在指定不同的内容类型

httpPost.addHeader("Content-Type", "multipart/related; boundary=HereItGoes");

摆脱这个。 MultipartEntityBuilder 已经使用适当的 header 构建了一个请求。只需添加

builder.setBoundary("HereItGoes")

边界。

示例Servlet

@WebServlet(loadOnStartup = 1, urlPatterns = "/multipart1")
@MultipartConfig()
public class MyServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("The number of parts is :" + request.getParts().size());
        Iterator<Part> partsIterator = request.getParts().iterator();
        while (partsIterator.hasNext()) {
            System.out.println(partsIterator.next().getName());
        }
    }
}

它将收到您发送的所有 6 个部分以及问题中的代码。