spring boot 圖片的上傳與顯示

首先描述一下問題，spring boot 使用的是內嵌的tomcat， 所以不清楚文件上傳到哪裏去了， 而且spring boot 把靜態的文件全部在啓動的時候都會加載到classpath的目錄下的，所以上傳的文件不知相對於應用目錄在哪，也不知怎麼寫訪問路徑合適，對於新手的自己真的一頭霧水。

後面想起了官方的例子，沒想到一開始被自己找到的官方例子，後面太依賴百度谷歌了，結果發現只有官方的例子能幫上忙，而且幫上大忙，直接上密碼的代碼

package hello;

import static org.springframework.hateoas.mvc.ControllerLinkBuilder.linkTo;
import static org.springframework.hateoas.mvc.ControllerLinkBuilder.methodOn;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.stream.Collectors;

import javax.servlet.http.HttpServletRequest;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.io.ResourceLoader;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.servlet.mvc.support.RedirectAttributes;

@Controller
public class FileUploadController {

	private static final Logger log = LoggerFactory.getLogger(FileUploadController.class);

	public static final String ROOT = "upload-dir";

	private final ResourceLoader resourceLoader;

	@Autowired
	public FileUploadController(ResourceLoader resourceLoader) {
		this.resourceLoader = resourceLoader;
	}

	@RequestMapping(method = RequestMethod.GET, value = "/")
	public String provideUploadInfo(Model model) throws IOException {

		model.addAttribute("files", Files.walk(Paths.get(ROOT))
				.filter(path -> !path.equals(Paths.get(ROOT)))
				.map(path -> Paths.get(ROOT).relativize(path))
				.map(path -> linkTo(methodOn(FileUploadController.class).getFile(path.toString())).withRel(path.toString()))
				.collect(Collectors.toList()));

		return "uploadForm";
	}

//顯示圖片的方法關鍵 匹配路徑像 localhost:8080/b7c76eb3-5a67-4d41-ae5c-1642af3f8746.png
	@RequestMapping(method = RequestMethod.GET, value = "/{filename:.+}")
	@ResponseBody
	public ResponseEntity<?> getFile(@PathVariable String filename) {

		try {
			return ResponseEntity.ok(resourceLoader.getResource("file:" + Paths.get(ROOT, filename).toString()));
		} catch (Exception e) {
			return ResponseEntity.notFound().build();
		}
	}

//上傳的方法
	@RequestMapping(method = RequestMethod.POST, value = "/")
	public String handleFileUpload(@RequestParam("file") MultipartFile file,
								   RedirectAttributes redirectAttributes, HttpServletRequest request) {
		System.out.println(request.getParameter("member"));
		if (!file.isEmpty()) {
			try {
				Files.copy(file.getInputStream(), Paths.get(ROOT, file.getOriginalFilename()));
				redirectAttributes.addFlashAttribute("message",
						"You successfully uploaded " + file.getOriginalFilename() + "!");
			} catch (IOException|RuntimeException e) {
				redirectAttributes.addFlashAttribute("message", "Failued to upload " + file.getOriginalFilename() + " => " + e.getMessage());
			}
		} else {
			redirectAttributes.addFlashAttribute("message", "Failed to upload " + file.getOriginalFilename() + " because it was empty");
		}

		return "redirect:/";
	}

}

看完上面的代碼可以理解到spring boot 的存取文件思路了，存的時候的路徑爲

Paths.get(ROOT, filename).toString()))

這個路徑會在本地的工程根目錄上創建，不應用部署裏的目錄，所以一般的訪問http訪問不可能 ，所以它提供了ResourceLoader,利於這個類可以加載非應用目錄的裏文件然後返回

所以就可以讀取文件，所以就要寫getFIle方法來顯示圖片