java - 为什么在处理图像文件时会出现此错误？

Question

我正在学习一本有很多拼写错误/错误的书的教程。每当作者犯错误时，我都会通过检查和修复明显的错误来跟上它。

目前我陷入困境。我有一个上传图像文件的表单，当页面重新加载时(上传后)，图像应该显示在表单上方(上传前的空白图像)。 img src 属性是在上传后生成的，并由 Thymleaf 和 Controller 中的 URL (/uploadedPicture) 处理，但我的代码似乎在某个地方出错了，因为它不工作。我想继续写这本很棒的书。

此外，我不确定我是否导入了正确的路径，因为有一些可用的路径，并且本书没有像其他章节那样指定。

注意:上传图片后，当我在 Chrome 控制台上查看 /uploadedPicture 时，它抛出 500 错误并显示以下消息:

{
"timestamp":1454561252135,
"status":500,
"error":"Internal Server Error",
"exception":"org.springframework.beans.ConversionNotSupportedException",
"message":"Failed to convert value of type [org.springframework.core.io.FileSystemResource] to required type [java.nio.file.Path]; nested exception is java.lang.IllegalStateException: Cannot convert value of type [org.springframework.core.io.FileSystemResource] to required type [java.nio.file.Path]: no matching editors or conversion strategy found",
"path":"/uploadedPicture"
}

PictureUploadController.java

package masterSpringMvc.profile;

import masterSpringMvc.config.PictureUploadProperties;
import org.apache.tomcat.util.http.fileupload.IOUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.io.FileSystemResource;
import org.springframework.core.io.Resource;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.SessionAttributes;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.servlet.mvc.support.RedirectAttributes;

import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.net.URLConnection;
import java.nio.file.Path;

@Controller
@SessionAttributes("picturePath")
public class PictureUploadController {
    private final Resource picturesDir;
    private final Resource anonymousPicture;

    @Autowired
    public PictureUploadController(PictureUploadProperties uploadProperties) {
        picturesDir = uploadProperties.getUploadPath();
        anonymousPicture = uploadProperties.getAnonymousPicture();
    }

    @ModelAttribute("picturePath")
    public Resource picturePath() {
        return anonymousPicture;
    }

    @RequestMapping("/upload")
    public String uploadPage() {
        return "profile/uploadPage";
    }

    @RequestMapping(value = "/upload", method = RequestMethod.POST)
    public String onUpload(MultipartFile file,
                           RedirectAttributes redirectAttributes,
                           Model model) throws IOException {
        if (file.isEmpty() || !isImage(file)) {
            redirectAttributes.addFlashAttribute("error",
                    "Incorrect file. Please upload a picture.");
            return "redirect:/upload";
        }

        Resource picturePath = copyFileToPictures(file);
        model.addAttribute("picturePath", picturePath);

        return "profile/uploadPage";
    }

    @RequestMapping(value = "/uploadedPicture")
    public void getUploadedPicture(HttpServletResponse response,
                                   @ModelAttribute("picturePath") Path picturePath)
            throws IOException {
        response.setHeader("Content-Type", URLConnection
                .guessContentTypeFromName(picturePath.toString()));
        IOUtils.copy(anonymousPicture.getInputStream(), response.getOutputStream());
    }

    private Resource copyFileToPictures(MultipartFile file) throws IOException {
        String fileExtension = getFileExtension(file.getOriginalFilename());
        File tempFile = File.createTempFile("pic", fileExtension,
                picturesDir.getFile());

        try (InputStream in = file.getInputStream();
             OutputStream out = new FileOutputStream(tempFile)) {
            IOUtils.copy(in, out);
        }

        return new FileSystemResource(tempFile);
    }

    private boolean isImage(MultipartFile file) {
        return file.getContentType().startsWith("image");
    }

    private static String getFileExtension(String name) {
        return name.substring(name.lastIndexOf("."));
    }
}

uploadPage.html

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org"
      xmlns:layout="http://www.ultraq.net.nz/thymeleaf/layout"
      layout:decorator="layout/default">
<head lang="en">
    <title>Profile Picture Upload</title>
</head>
<body>
<div class="row" layout:fragment="content">
    <h2 class="indigo-text center">Upload</h2>

    <div class="col s12 center red-text" th:text="${error}" th:if="${error}">
        Error during upload
    </div>

    <div class="col m8 s12 offset-m2">
        <img th:src="@{/uploadedPicture}" width="100" height="100"/>
    </div>

    <form th:action="@{/upload}" method="post" enctype="multipart/form-data" class="col m8 s12 offset-m2">
        <div class="input-field col s6">
            <input type="file" id="file" name="file"/>
        </div>
        <div class="col s6 center">
            <button class="btn indigo waves-effect waves-light" type="submit" name="save" th:text="#{submit}">
                Submit<i class="mdi-content-send right"></i>
            </button>
        </div>
    </form>
</div>
</body>
</html>

Answer 1

注入(inject)Resource而不是Path，如下所示:

@RequestMapping(value = "/uploadedPicture")
public void getUploadedPicture(HttpServletResponse response, @ModelAttribute("picturePath") Resource picturePath) throws IOException  {
    response.setHeader("Content-Type", URLConnection.guessContentTypeFromName(picturePath.toString()));
    Path path = Paths.get(picturePath.getURI());
    Files.copy(path, response.getOutputStream());
}