原文链接：http://www.dubby.cn/detail.html?id=9043

1. 我们要做什么

使用Spring实现一个最基本的文件上传，文件下载的web应用。

2.你需要什么

• MySQL 5.6或者更高版本
• 大约15分钟
• 一个最爱的编辑器或者IDE
• JDK 1.8 +
• Maven 3.0+

3. 创建项目

3.1 项目依赖

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>cn.dubby</groupId>
    <artifactId>uploading-files</artifactId>
    <version>0.1.0</version>

    <!--原文链接：www.dubby.cn-->

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.8.RELEASE</version>
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

从依赖中看到加了spring-boot-starter-thymeleaf的starter，这里的目的是用thymeleaf渲染一个页面来上传文件和展示已上传的文件列表，真实使用时完全可以不用。

借鉴本文时，请注意根据实际情况来改造，比如，1. 你们可能不需要有下载的controller，因为完全可以把上传路径设为静态服务器目录下，比如css，png文件可以直接让前段请求URL来获取，毕竟静态资源服务器（如：Nginx）的处理效率肯定比Java更高效；2. 可以考虑使用很多云厂商的OSS或者CDN来代替本地文件系统，只需要自己实现存储的service；其他……

3.2 启动类

src/main/java/hello/Application.java

package hello;

import hello.storage.StorageProperties;
import hello.storage.StorageService;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
@EnableConfigurationProperties(StorageProperties.class)
public class Application {

    //原文链接：www.dubby.cn
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    CommandLineRunner init(StorageService storageService) {
        return (args) -> {
            storageService.deleteAll();
            storageService.init();
        };
    }
}

如果是传统的servlet项目，需要在web.xml里配置<multipart-config>来注册MultipartConfigElement。但是Spring帮我自动配置了。

3.3 controller

src/main/java/hello/FileUploadController.java

package hello;

import java.io.IOException;
import java.util.stream.Collectors;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.io.Resource;
import org.springframework.http.HttpHeaders;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
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.method.annotation.MvcUriComponentsBuilder;
import org.springframework.web.servlet.mvc.support.RedirectAttributes;

import hello.storage.StorageFileNotFoundException;
import hello.storage.StorageService;

@Controller
public class FileUploadController {

    private final StorageService storageService;

    @Autowired
    public FileUploadController(StorageService storageService) {
        this.storageService = storageService;
    }

    @GetMapping("/")
    public String listUploadedFiles(Model model) throws IOException {

        model.addAttribute("files", storageService.loadAll().map(
                path -> MvcUriComponentsBuilder.fromMethodName(FileUploadController.class,
                        "serveFile", path.getFileName().toString()).build().toString())
                .collect(Collectors.toList()));

        return "uploadForm";
    }

    @GetMapping("/files/{filename:.+}")
    @ResponseBody
    public ResponseEntity<Resource> serveFile(@PathVariable String filename) {

        Resource file = storageService.loadAsResource(filename);
        return ResponseEntity.ok().header(HttpHeaders.CONTENT_DISPOSITION,
                "attachment; filename=\"" + file.getFilename() + "\"").body(file);
    }

    @PostMapping("/")
    public String handleFileUpload(@RequestParam("file") MultipartFile file,
            RedirectAttributes redirectAttributes) {

        storageService.store(file);
        redirectAttributes.addFlashAttribute("message",
                "You successfully uploaded " + file.getOriginalFilename() + "!");

        return "redirect:/";
    }

    @ExceptionHandler(StorageFileNotFoundException.class)
    public ResponseEntity<?> handleStorageFileNotFound(StorageFileNotFoundException exc) {
        return ResponseEntity.notFound().build();
    }

}

这个例子，没有用@RestController，所以返回的并不是JSON。@GetMapping和@PostMapping的意义之前有介绍过，这里就不再赘述了，如果不清楚可以看之前的[Spring系列——RESTful的web项目](http://www.dubby.cn/detail.html?id=9040#3.3 controller)。

这个例子中，每个URI的意义分别是：

• GET /：显示一个页面，里面可以上传文件，还展示已经上传的文件的列表。
• GET /files/{filename}：如果文件存在的话，下载这个文件。注意使用了Content-Disposition这个Header。
• POST /：上传一个文件。

如果读者时初学者，可能对上面的代码还存有一点疑惑，我这里简单描述一下，1.@GetMapping("/files/{filename:.+}")这个时Spring MVC的一个URI匹配的方式，格式是PathVariable:正则表达式，用后面的正则来校验这个参数；2. @ExceptionHandler(StorageFileNotFoundException.class)这是Spring提供的异常处理器，如果请求发生指定的异常就会被捕获。

3.4 文件存储

这里定义一个接口，上面也提到了，文件存储不建议使用本地存储的方式，所以使用接口，读者可以随意替换成你需要的，只需要自己实现这个接口就可以了。

src/main/java/hello/storage/StorageService.java

package hello.storage;

import org.springframework.core.io.Resource;
import org.springframework.web.multipart.MultipartFile;

import java.nio.file.Path;
import java.util.stream.Stream;

public interface StorageService {

    void init();

    void store(MultipartFile file);

    Stream<Path> loadAll();

    Path load(String filename);

    Resource loadAsResource(String filename);

    void deleteAll();

}

这里给出本地存储服务的代码

src/main/java/hello/storage/FileSystemStorageService.java

package hello.storage;

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.util.StringUtils;
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.nio.file.StandardCopyOption;
import java.util.stream.Stream;

@Service
public class FileSystemStorageService implements StorageService {

    private final Path rootLocation;

    @Autowired
    public FileSystemStorageService(StorageProperties properties) {
        this.rootLocation = Paths.get(properties.getLocation());
    }

    @Override
    public void store(MultipartFile file) {
        String filename = StringUtils.cleanPath(file.getOriginalFilename());
        try {
            if (file.isEmpty()) {
                throw new StorageException("Failed to store empty file " + filename);
            }
            if (filename.contains("..")) {
                // This is a security check
                throw new StorageException(
                        "Cannot store file with relative path outside current directory "
                                + filename);
            }
            Files.copy(file.getInputStream(), this.rootLocation.resolve(filename),
                    StandardCopyOption.REPLACE_EXISTING);
        }
        catch (IOException e) {
            throw new StorageException("Failed to store file " + filename, e);
        }
    }

    @Override
    public Stream<Path> loadAll() {
        try {
            return Files.walk(this.rootLocation, 1)
                    .filter(path -> !path.equals(this.rootLocation))
                    .map(path -> this.rootLocation.relativize(path));
        }
        catch (IOException e) {
            throw new StorageException("Failed to read stored files", e);
        }

    }

    @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 {
                throw new StorageFileNotFoundException(
                        "Could not read file: " + filename);

            }
        }
        catch (MalformedURLException e) {
            throw new StorageFileNotFoundException("Could not read file: " + filename, e);
        }
    }

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

    @Override
    public void init() {
        try {
            Files.createDirectories(rootLocation);
        }
        catch (IOException e) {
            throw new StorageException("Could not initialize storage", e);
        }
    }
}

3.5 HTML模板

src/main/resources/templates/uploadForm.html

<html xmlns:th="http://www.thymeleaf.org">
<body>

    <div th:if="${message}">
        <h2 th:text="${message}"/>
    </div>

    <div>
        <form method="POST" enctype="multipart/form-data" action="/">
            <table>
                <tr><td>File to upload:</td><td><input type="file" name="file" /></td></tr>
                <tr><td></td><td><input type="submit" value="Upload" /></td></tr>
            </table>
        </form>
    </div>

    <div>
        <ul>
            <li th:each="file : ${files}">
                <a th:href="${file}" th:text="${file}" />
            </li>
        </ul>
    </div>

</body>
</html>

这个HTML模板有三个部分：

• 一个message的attribute展示信息。
• 一个表单，用来上传文件。
• 一个列表来展示已上传的文件列表。

3.6 文件的大小限制

src/main/resources/application.properties

spring.http.multipart.max-file-size=128KB
spring.http.multipart.max-request-size=128KB

这个配置的意思是：

• spring.http.multipart.max-file-size限制了文件的大小。
• spring.http.multipart.max-request-size限制了请求的大小。

4. 测试

4.1 动手测一测

4.2 单元测试

这里给一点测试代码

src/test/java/hello/storage/FileUploadTests.java

package hello;

import hello.storage.StorageFileNotFoundException;
import hello.storage.StorageService;
import org.hamcrest.Matchers;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.mock.mockito.MockBean;
import org.springframework.mock.web.MockMultipartFile;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.servlet.MockMvc;

import java.nio.file.Paths;
import java.util.stream.Stream;

import static org.mockito.BDDMockito.given;
import static org.mockito.BDDMockito.then;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.fileUpload;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;

@RunWith(SpringRunner.class)
@AutoConfigureMockMvc
@SpringBootTest
public class FileUploadTests {

    @Autowired
    private MockMvc mvc;

    @MockBean
    private StorageService storageService;

    @Test
    public void shouldListAllFiles() throws Exception {
        given(this.storageService.loadAll())
                .willReturn(Stream.of(Paths.get("first.txt"), Paths.get("second.txt")));

        this.mvc.perform(get("/")).andExpect(status().isOk())
                .andExpect(model().attribute("files",
                        Matchers.contains("http://localhost/files/first.txt",
                                "http://localhost/files/second.txt")));
    }

    @Test
    public void shouldSaveUploadedFile() throws Exception {
        MockMultipartFile multipartFile = new MockMultipartFile("file", "test.txt",
                "text/plain", "Spring Framework".getBytes());
        this.mvc.perform(fileUpload("/").file(multipartFile))
                .andExpect(status().isFound())
                .andExpect(header().string("Location", "/"));

        then(this.storageService).should().store(multipartFile);
    }

    @SuppressWarnings("unchecked")
    @Test
    public void should404WhenMissingFile() throws Exception {
        given(this.storageService.loadAsResource("test.txt"))
                .willThrow(StorageFileNotFoundException.class);

        this.mvc.perform(get("/files/test.txt")).andExpect(status().isNotFound());
    }

}

完整代码地址：https://github.com/dubby1994/spring-demo

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