Apache Camel技巧之Servlet组件实现文件上传

╰半夏微凉° 2022-11-10 05:29 334阅读 0赞

> 一阵见血，直接上干货。

### 1. 前言 ###

本文解决Apache Camel提供Servlet服务时候，如何实现文件的上传。

### 2. 实现代码 ###

##### 2.1 作为服务端 #####

直接上代码。我们需要进行如下几步操作：

1.  使用SpringMVC的内置功能`StandardMultipartHttpServletRequest`实现上传文件的读取。
2.  借助Camel的 UoW特性，实现在请求处理结束时候确保资源被释放。
3.  抛弃Camel内置的Servlet配置，启用自定义的Servlet配置，使其支持文件上传。
4.  其它配置。主要是避免Camel在我们解析出上传文件前自行读取了request body里的内容。

// =================== 配置作为请求响应的服务端
    from("rest:get,post:receiveFile") //
      .routeId("receiveFile") //
      .tracing("false") // 避免Camel将request body中的流进行了读取, 导致之后无法读取到文件
      .process(new Processor() { 
    
    	  @Override
    	  public void process(Exchange exchange) throws Exception { 
    	      // 获取到源生的HttpServletRequest
    		  HttpServletRequest request = exchange.getIn().getHeader(Exchange.HTTP_SERVLET_REQUEST,
    				HttpServletRequest.class);
    		  // 借助SpringMVC提供的封装类, 完成附件文件的读取操作
    		  StandardMultipartHttpServletRequest standardMultipartHttpServletRequest = new StandardMultipartHttpServletRequest(
    				request, false);
    		  // 验证
    		  // Console.log(standardMultipartHttpServletRequest.getFileMap());
    		  MultipartFile file = standardMultipartHttpServletRequest.getFile("file");
    		  file.transferTo(FileUtil.file(FilenameUtil.concat(FilenameUtil.getDesktopLocation(), "xxx.txt")));
    
              // 获取前端传递来的其它参数
              Console.log(request.getParameter("name"));
    
    	  }
    
      })//
      .to("stream:err");
    
    // =================== 配置一
    public class TransactionCompensatingManager implements Synchronization { 
    
    	private static Logger LOG = LoggerFactory.getLogger(TransactionCompensatingManager.class);
    	
    	@Autowired
    	private ApplicationContext ac;
    	
    	@Autowired(required=false)
    	private MultipartResolver multipartResolver
    	
    	@Override
    	public void onComplete(Exchange exchange) { 
    		// 正常执行后的Message History日志
    		final String messageHistoryStacktrace = MessageHelper.dumpMessageHistoryStacktrace(exchange, //
    				CamelUtil.getDefaultExchangeFormatter(exchange.getContext())//
    				, false);
    
    		LOG.debug("当前Route[ {} ]执行的路径为:{}{}", exchange.getFromRouteId(), //
    				System.lineSeparator(), messageHistoryStacktrace);
    				
    		cleanupMultipart(exchange);
    	}
    
    	@Override
    	public void onFailure(Exchange exchange) { 
    		cleanupMultipart(exchange);
    	}
    	
    	// 确保非托管资源被回收, 借鉴自SpringMVC中的 DispatcherServlet.cleanupMultipart()
    	private void cleanupMultipart(Exchange exchange) { 
    	
    		if (this.multipartResolver != null) { 
    			MultipartHttpServletRequest multipartRequest =
    					exchange.getProperty(StandardMultipartHttpServletRequest.class.getName(), StandardMultipartHttpServletRequest.class);
    			if (multipartRequest != null) { 
    				this.multipartResolver.cleanupMultipart(multipartRequest);
    			}
    		}
    	} 
    }
    
    @Configuration
    public class GlobalCamelConfigurer { 
    	@Bean
    	public TransactionCompensatingManager transactionCompensatingManager() { 
    		return new TransactionCompensatingManager();
    	}
    }
    
    // =================== 配置二
    // 借鉴自 Camel中的同名类, 目的是实现对于文件上传的处理, 也就是注解@MultipartConfig
    @Configuration
    @AutoConfigureAfter(name = "org.apache.camel.spring.boot.CamelAutoConfiguration")
    @ConditionalOnWebApplication
    @EnableConfigurationProperties(ServletMappingConfiguration.class)
    public class ServletMappingAutoConfiguration { 
    
    	@Bean
    	ServletRegistrationBean<MyCamelHttpTransportServlet> servletRegistrationBean(ServletMappingConfiguration config,
    	      MultipartProperties multipartProperties) { 
    
    		ServletRegistrationBean<MyCamelHttpTransportServlet> mapping = new ServletRegistrationBean<>();
    		mapping.setServlet(new MyCamelHttpTransportServlet());
    		mapping.addUrlMappings(config.getContextPath());
    		mapping.setName(config.getServletName());
    		mapping.setLoadOnStartup(1);
    
    		return mapping;
    	}
    
    	@Bean
    	public DefaultHttpBinding binding(ServletComponent sc) { 
    		DefaultHttpBinding binding = new DefaultHttpBinding();
    		// 确保Camel不会提前解析request body, 导致后续无法解析到文件流
    		binding.setMapHttpMessageBody(false);
    		return binding;
    	}
    
    	@MultipartConfig
    	static class MyCamelHttpTransportServlet extends CamelHttpTransportServlet { 
    
    		/** * */
    		private static final long serialVersionUID = 1L;
    
    	}
    }
    
    # 承接上面,  application.yml文件
    camel:
      springboot:
        name: camelServlet
      component:
        # ServletComponentConfiguration
        servlet:      
          enabled: true
          # ServletMappingConfiguration
          mapping:
            # 只有禁用掉系统默认的ServletMappingAutoConfiguration, 才能启用我们自定义的ServletMappingAutoConfiguration
            enabled: false
    
    // 相关配置
    @Component
    public class GlobalCamelRouteRegister extends RouteBuilder{ 
    	@Override
    	public void configure() throws Exception { 
    	    // 配置一次就可以了
    		restConfiguration()//
    		      .bindingMode(RestBindingMode.json)//
    		      .endpointProperty("httpBinding", "binding")// 配置, 使用上面注册的HttpBinding 
    		      .host("0.0.0.0").component("servlet");		
    	}
    
    
    }

##### 2.1 作为客户端 #####

这一步在网上的相关资料角度，感兴趣的读者可以参见底部链接。

### 3. 背后原理 ###

1.  Servlet支持文件上传，主要是来自Servlet中的 `@MultipartConfig`注解。 SpringBoot正是借助内置的`DispatcherServletRegistrationBean`来实现配置的。另外SpringBoot还专门提供了相关的`MultipartAutoConfiguration`。
2.  Camel Servlet内置提供的`CamelServlet`是没有进行`@MultipartConfig`注解相关配置的，所以其默认是不支持的，这也是本文诞生的主要原因。
3.  Camel中有很多读取body的操作，而默认情况下 request body只允许读取一次，所以本文的场景下我们需要消除这种情况。

### 4. Links ###

1.  [Apache Camel源码研究之Rest][Apache Camel_Rest]
2.  [Apache Camel - Multipart File upload – 作为客户端][Apache Camel - Multipart File upload _]
3.  [Camel HTTP file upload with multipart/form-data][Camel HTTP file upload with multipart_form-data]

[Apache Camel_Rest]: https://blog.csdn.net/lqzkcx3/article/details/110318720
[Apache Camel - Multipart File upload _]: https://stackoverflow.com/questions/51218446/apache-camel-multipart-file-upload
[Camel HTTP file upload with multipart_form-data]: https://hilton.org.uk/blog/camel-multipart-form-data