上载MultipartFile并将数据提交到对象，不存在所需的请求部分“文件”

Question

如您所见，用户正在创建一本包含数据字段和文件的新书。

我能够在开始添加此文件上载内容之前创建一本新书，所以我知道只是该模型无法将文件正确地返回到.store（file）

这是我的表格：

<form  method="post" action="#" th:action="@{__${T(com.potatospy.bookcatalog.util.Mappings).ADD_BOOK}__}" enctype="multipart/form-data" th:object="${book}">

        <p>Title: <input type="text" th:field="*{bookTitle}" th:text="${book.bookTitle}"/></p>
        <p>Published Date: <input type="date" th:field="*{publishedDate}" th:text="${book.publishedDate}"/></p>
        <p>File location: <input type="file" th:field="*{fileLoc}" name="file" ></p>
        <p>Authors: <input type="text" th:field="*{authors}" th:text="${book.authors}"/></p>

        <p><input type="submit" value="Submit"/></p>


    </form>

这是Spring.io的代码如何上传文件。我只编辑了日志记录和异常处理：

package com.potatospy.bookcatalog.filesystem;

// This code is from https://spring.io/guides/gs/uploading-files/
// Modified and re-distributed under the ASLv2 license
// https://www.apache.org/licenses/LICENSE-2.0

import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.io.Resource;
import org.springframework.core.io.UrlResource;
import org.springframework.stereotype.Service;
import org.springframework.util.FileSystemUtils;
import org.springframework.web.multipart.MultipartFile;

import java.io.IOException;
import java.net.MalformedURLException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.stream.Stream;

@Slf4j
@Service
public class StorageServiceImpl implements StorageService {


    private Path rootLocation;

    @Autowired
    private FileSystemProperties fsProperties;

    @Autowired
    public StorageServiceImpl(FileSystemProperties fsProperties) {
        this.fsProperties = fsProperties;
        log.info("fsProperties.getBookDirectory() " + fsProperties.getBookDirectory());
        this.rootLocation = Paths.get(fsProperties.getBookDirectory().toString());
    }


    @Override
    public void store(MultipartFile file) {
        try {
            if (file.isEmpty()) {
                log.info("Failed to store empty file " + file.getOriginalFilename());
            }
            Files.copy(file.getInputStream(), this.rootLocation.resolve(file.getOriginalFilename()));
        } catch (IOException e) {
            log.info("Failed to store file " + file.getOriginalFilename(), e);
        }
    }

    // Get relative paths to all files in rootLocation
    @Override
    public Stream<Path> loadAll() {
        log.info("\n\n\nloadAll() ");
        try {
            return Files.walk(this.rootLocation, 1)
                    .filter(path -> !path.equals(this.rootLocation))
                    .map(path -> this.rootLocation.relativize(path));
        } catch (IOException e) {
            log.info("Failed to read stored files: {}", e);
        }
        return null;// Todo Original did not return anything, it called super from RuntimeException
    }

    @Override
    public Path load(String filename) {
        return rootLocation.resolve(filename);
    }

    @Override
    public Resource loadAsResource(String filename) {
        try {
            Path file = load(filename);
            Resource resource = new UrlResource(file.toUri());
            if(resource.exists() || resource.isReadable()) {
                return resource;
            }
            else {
                log.info("Could not read file: " + filename);

            }
        } catch (MalformedURLException e) {
            log.info("Could not read file: " + filename, e);
        }

        return null;// Todo Original did not return anything, it called super from RuntimeException
    }

    @Override
    public void deleteAll() {
        FileSystemUtils.deleteRecursively(rootLocation.toFile());
    }
}

这是我控制器的相关行：

 // Add Book View
    @GetMapping(Mappings.ADD_BOOK)
    public String addBook(Model model){

        log.info("addBook method called");

        Book newBook = new Book();

        // Add the new Book (with no id) to the model
        model.addAttribute(AttributeNames.BOOK, newBook);


        return ViewNames.ADD_BOOK;
    }
    // Add Book post mapping
    @PostMapping(Mappings.ADD_BOOK)
    public String addBookSubmit(
            @RequestParam("file") MultipartFile file,
            @ModelAttribute Book newBook){

        log.info("addBookSubmit called. Got postmapping to new book: {}", newBook.toString());


        bookService.addBook(newBook);

        storageService.store(file);

        bookService.updateBook(newBook);

        return "redirect:/" + Mappings.CATALOG_DETAIL;
    }