Java文件上传实例并解决跨域问题

深藏阁楼爱情的钟 2021-09-25 14:46 405阅读 0赞

**Java文件上传实例并解决跨域问题**

**目录**

了解MultipartFile接口

文件上传业务代码

Controller类

Service类：写了具体的业务逻辑

修改nginx配置，将文件存储到文件服务器中

每次上传文件都会经过网关，必然会给网关带来很大的压力，那我们如何绕过网关呢？

1.在网关中配置白名单 ，这样也会走网关，只是压力少了一点点

2.在nginx做转发，当请求文件上传时，直接转到相应的服务

解决上传文件出现跨域问题

写配置类CorsFilter

在nginx配置中配置请求实体大小

--------------------

在Web应用系统开发中，文件上传和下载功能是非常常用的功能，今天来讲一下JavaWeb中的文件上传功能的实现。

# 了解MultipartFile接口 #

我们实现文件的上传用到了Spring-web框架中的 MultipartFile接口，MultipartFile接口的源码注释中说“MultipartFile接口是  在大部分请求中接收的上载文件的表示形式。”

> A representation of an uploaded file received in a multipart request.  
> The file contents are either stored in memory or temporarily on disk. In either case, the user is responsible for copying file contents to a session-level or persistent store as and if desired. The temporary storage will be cleared at the end of request processing.

常用方法如下表

<table> 
 <tbody> 
 <tr> 
 <th colspan="3">Method Summary</th> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;width:118px;"><code>&nbsp;byte[]</code></td> 
 <td style="width:143px;">获取文件的字节数组</td> 
 <td style="width:432px;"><code><a href="https://docs.spring.io/spring-framework/docs/1.2.x/javadoc-api/org/springframework/web/multipart/MultipartFile.html#getBytes%28%29" rel="nofollow">getBytes</a>()</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Return the contents of the file as an array of bytes.</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;width:118px;"><code>&nbsp;<a href="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/String.html" rel="nofollow">String</a></code></td> 
 <td style="width:143px;">获取文件的类型</td> 
 <td style="width:432px;"><code><a href="https://docs.spring.io/spring-framework/docs/1.2.x/javadoc-api/org/springframework/web/multipart/MultipartFile.html#getContentType%28%29" rel="nofollow">getContentType</a>()</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Return the content type of the file.</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;width:118px;"><code>&nbsp;<a href="http://java.sun.com/j2se/1.5.0/docs/api/java/io/InputStream.html" rel="nofollow">InputStream</a></code></td> 
 <td style="width:143px;">获取文件的输入流</td> 
 <td style="width:432px;"><code><a href="https://docs.spring.io/spring-framework/docs/1.2.x/javadoc-api/org/springframework/web/multipart/MultipartFile.html#getInputStream%28%29" rel="nofollow">getInputStream</a>()</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Return an InputStream to read the contents of the file from.</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;width:118px;"><code>&nbsp;<a href="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/String.html" rel="nofollow">String</a></code></td> 
 <td style="width:143px;">获取文件名</td> 
 <td style="width:432px;"><code><a href="https://docs.spring.io/spring-framework/docs/1.2.x/javadoc-api/org/springframework/web/multipart/MultipartFile.html#getName%28%29" rel="nofollow">getName</a>()</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Return the name of the parameter in the multipart form.</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;width:118px;"><code>&nbsp;<a href="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/String.html" rel="nofollow">String</a></code></td> 
 <td style="width:143px;">获取原始文件名（防止篡改文件类型）</td> 
 <td style="width:432px;"><code><a href="https://docs.spring.io/spring-framework/docs/1.2.x/javadoc-api/org/springframework/web/multipart/MultipartFile.html#getOriginalFilename%28%29" rel="nofollow">getOriginalFilename</a>()</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Return the original filename in the client's filesystem.</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;width:118px;"><code>&nbsp;long</code></td> 
 <td style="width:143px;">获取文件的大小，以字节的形式）</td> 
 <td style="width:432px;"><code><a href="https://docs.spring.io/spring-framework/docs/1.2.x/javadoc-api/org/springframework/web/multipart/MultipartFile.html#getSize%28%29" rel="nofollow">getSize</a>()</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Return the size of the file in bytes.</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;width:118px;"><code>&nbsp;boolean</code></td> 
 <td style="width:143px;">判断文件是否为空</td> 
 <td style="width:432px;"><code><a href="https://docs.spring.io/spring-framework/docs/1.2.x/javadoc-api/org/springframework/web/multipart/MultipartFile.html#isEmpty%28%29" rel="nofollow">isEmpty</a>()</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Return whether the uploaded file is empty, that is, either no file has been chosen in the multipart form or the chosen file has no content.</td> 
 </tr> 
 <tr> 
 <td style="vertical-align:top;width:118px;"><code>&nbsp;void</code></td> 
 <td style="width:143px;">将接收到的文件传输到给定的目标文件。</td> 
 <td style="width:432px;"><code><a href="https://docs.spring.io/spring-framework/docs/1.2.x/javadoc-api/org/springframework/web/multipart/MultipartFile.html#transferTo%28java.io.File%29" rel="nofollow">transferTo</a>(<a href="http://java.sun.com/j2se/1.5.0/docs/api/java/io/File.html" rel="nofollow">File</a>&nbsp;dest)</code> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Transfer the received file to the given destination file.</td> 
 </tr> 
 </tbody> 
</table>

# 文件上传业务代码 #

## Controller类 ##

/**
 * @Author: 小小张自由
 * @Date: 2021/7/6 - 20:56
 * @Description: 文件上传
 * @version： 1.0
 */
 @Controller
 @RequestMapping("upload")
 public class UploadController {
 
 @Autowired
 private UploadService uploadService;
 
 @PostMapping("image")
 public ResponseEntity<String> uploadImage(@RequestParam("file") MultipartFile file){
 String url= this.uploadService.uploadImage(file);
 if (StringUtils.isBlank(url)){
 return ResponseEntity.badRequest().build();
 }
 return ResponseEntity.status(HttpStatus.CREATED).body(url);
 }
 }

## Service类：写了具体的业务逻辑 ##

/**
 * @Author: 小小张自由
 * @Date: 2021/7/6 - 21:01
 * @Description: 文件上传
 * @version： 1.0
 */
 @Service
 public class UploadService {
 
 //用于判断文件的类型，暂时只判断了“image/gif","image/jpeg”
 private static final List<String> CONTENT_TYPES= Arrays.asList("image/gif","image/jpeg");
 
 private static final Logger LOGGER= LoggerFactory.getLogger(UploadService.class);
 
 /**
 * 业务逻辑代码
 * @param file 文件的存储的url
 * @return
 */
 public String uploadImage(MultipartFile file) {
 
 String originalFilename = file.getOriginalFilename();
 //校验文件类型
 //方法一:截取字符串
 String afterLast = StringUtils.substringAfterLast(".", originalFilename);
 //方法二：使用getContentType方法
 String contentType = file.getContentType();
 if (!CONTENT_TYPES.contains(contentType)){
 LOGGER.info("文件类型不合法："+originalFilename);
 return null;
 }
 //校验文件内容
 try {
 //获取文件流
 BufferedImage bufferedImage = ImageIO.read(file.getInputStream());
 if (bufferedImage==null){
 LOGGER.info("文件内容不合法：{}",originalFilename);
 return null;
 }
 //保存到服务器 E:\Leyou\image
 //将接收到的文件传输到给定的目标文件。
 file.transferTo(new File("E:\\Leyou\\Image\\"+originalFilename));
 
 //返回URL，进行回显
 //可以使用Nginx-图片服务器
 return "http://image.leyou.com/"+originalFilename;
 } catch (Exception e) {
 LOGGER.info("服务器内部错误："+originalFilename);
 e.printStackTrace();
 }
 return null;
 }
 }

# 修改nginx配置，将文件存储到文件服务器中 #

修改Nginx的配置文件nginx.conf，监听80端口，设置root的值为：E盘

> \- 图片不能保存在服务器内部，这样会对服务器产生额外的加载负担  
> \- 一般静态资源都应该使用独立域名，这样访问静态资源时不会携带一些不必要的cookie，减小请求的数据量

server {
            listen       80;
            server_name  image.leyou.com;
    
            proxy_set_header X-Forwarded-Host $host;
    		proxy_set_header X-Forwarded-Server $host;
    		proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    		
    		location / {
    			root E:\\Leyou\\image;
    		}
        }

## 每次上传文件都会经过网关，必然会给网关带来很大的压力，那我们如何绕过网关呢？ ##

## 1.在网关中配置白名单 ，这样也会走网关，只是压力少了一点点 ##

@Slf4j
 public class AuthorizeFilter implements GlobalFilter, Ordered {
 
 //白名单：存放放行的URL
 private List<String> allowPaths;
 
 
 @Override
 public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
 
 //获取请求的url路径
 String path = request.getURI().getPath();
 boolean flag=isAllowPath(path);
 if (flag) {
 log.info("请求在白名单中，leyou.filter: {}",path);
 //放行
 return chain.filter(exchange);
 } else {
 //写其他的业务逻辑
 ~~~~
 
 }
 }
 
 private boolean isAllowPath(String path) {
 
 //判断是否允许放行
 if (allowPaths.contains(path)){
 return true;
 }
 return false;
 
 }

## 2.在nginx做转发，当请求文件上传时，直接转到相应的服务 ##

本实例使用了方法二、需要增加配置

server {
            listen       80;
            server_name  api.leyou.com;
    
            proxy_set_header X-Forwarded-Host $host;
    		proxy_set_header X-Forwarded-Server $host;
    		proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    		# 新增加的配置，用于文件上传
    		location /api/upload {
    			proxy_pass http://127.0.0.1:8082;
    			proxy_connect_timeout 600;
    			proxy_read_timeout 600;
    			
    			rewrite "^/api/(.*)$" /$1 break;
    		}
    		# 网关的配置
    		location / {
    			proxy_pass http://127.0.0.1:10010;
    			proxy_connect_timeout 600;
    			proxy_read_timeout 600;
    		}
        }

当这样配置之后，文件上传就不会过网关，减少了网关的压力。但是有引来了一个新问题那就是跨域。

# 解决上传文件出现跨域问题 #

由于Nginx将文件上传的请求直接转发到了具体服务中，不再走gateway，所以gateway中的跨域配置，不再生效了。 需要在文件上传这个服务中单独配置跨域。

## 写配置类CorsFilter ##

/**
     * @Author: 小小张自由
     * @Date: 2021/6/15 - 11:12
     * @Description: 解决 跨域问题
     * @version： 1.0
     */
    @Configuration
    public class LeyouCorsConfiguration {
    
        @Bean
        public CorsFilter corsFilter(){
            //初始化配置对象
            CorsConfiguration configuration = new CorsConfiguration();
            //允许跨域访问的域名
            configuration.addAllowedOrigin("*");
           // configuration.setAllowCredentials(true);  //运行携带cookie
            configuration.addAllowedMethod("*"); //代表所有请求方法
            configuration.addAllowedHeader("*"); //允许携带任何头信息
    
            //初始化cors配置源对象
            UrlBasedCorsConfigurationSource configurationSource=new UrlBasedCorsConfigurationSource();
            configurationSource.registerCorsConfiguration("/**",configuration);
    
            //返回CorSfilter实例，参数
            return new CorsFilter(configurationSource);
        }
    
    }

到此应该就可以上传了，但是还是报跨域，我已经配置好了啊，为什么还是报跨域呢？

## 在nginx配置中配置请求实体大小 ##

我就想是不是Nginx的问题，然后我就一行一行的读配置，最后发现

**nginx配置中没有配置请求实体大小**

![image.png][]

加上这行配置就好了

client_max_body_size 1024m;

# **如果本篇博客对您有一定的帮助，大家记得留言\+点赞\+收藏哦。**  #

[image.png]: /images/20210923/298a212234c545c18126b9a7e1d0f1e2.png