HTTP：http上传文件的原理及java处理方法的介绍

素颜马尾好姑娘i 2024-03-24 23:23 35阅读 0赞

为了说明原理，以下提供一个可以上传多个文件的例子，html页面代码如下：

<!DOCTYPE html>
    <html>
    <head>
    <meta charset="UTF-8">
    <title>http upload file</title>
    </head>
    <body>
    	<form action="/TestWeb/upload" method="post" enctype="multipart/form-data">
    		<input type="text" name="uploadName1" id="uploadName1">
    		<p />
    		<input type="file" name="fileName1" id="file1">
    		<p />
    		<input type="text" name="uploadName2" id="uploadName2">
    		<p />
    		<input type="file" name="fileName2" id="file2">
    		<p />
    		<input type="submit" value="上传">
    	</form>
    </body>
    </html>

显示效果如下：

![83c54d340bc94c26a8a26f83585790ea.png][]

通过点“浏览”选择要上传的文件，并分别输入保存时使用的文件名：

![b312a2328a3c45879ed26e6591e1795b.png][]

我们使用spring来处理上传的文件，代码如下：

import java.io.IOException;
    
    import org.springframework.stereotype.Controller;
    import org.springframework.web.bind.annotation.PostMapping;
    import org.springframework.web.bind.annotation.RequestParam;
    import org.springframework.web.bind.annotation.RequestPart;
    import org.springframework.web.multipart.MultipartFile;
    
    @Controller
    public class FileUploadController {
    
    	@PostMapping("/upload")
    	public String handleFormUpload(//
    			@RequestParam("uploadName1") String uploadName1, //
    			@RequestPart("fileName1") MultipartFile file1, //
    			@RequestParam("uploadName2") String uploadName2, //
    			@RequestPart("fileName2") MultipartFile file2) throws IOException {
    
    		print(file1, uploadName1);
    
    		System.out.println("+++++++++++++++");
    		
    		print(file2, uploadName2);
    
    		return "redirect:upload";
    	}
    
    	private void print(MultipartFile file, String uploadName) throws IOException {
    		String contentType = file.getContentType();
    		String name = file.getName();
    		String originalFilename = file.getOriginalFilename();
    		long size = file.getSize();
    
    		byte[] bytes = file.getBytes();
    
    		System.out.println(uploadName);
    		System.out.println(contentType);
    		System.out.println(name);
    		System.out.println(originalFilename);
    		System.out.println(size);
    		System.out.println(bytes.length);
    	}
    }

为了能使以上代码正常运行，还要做一些配置。比如，如果使用servlet3.0作为底层处理组件，还需要使用如下代码做配置：

import javax.servlet.MultipartConfigElement;
    import javax.servlet.ServletRegistration;
    
    import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer;
    
    public class AppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
     
    
        @Override
        protected void customizeRegistration(ServletRegistration.Dynamic registration) {
    
            // Optionally also set maxFileSize, maxRequestSize, fileSizeThreshold
            registration.setMultipartConfig(new MultipartConfigElement("/tmp"));
        }
    
    	@Override
    	protected Class<?>[] getRootConfigClasses() {
    		return null;
    	}
    
    	@Override
    	protected Class<?>[] getServletConfigClasses() {
    		return null;
    	}
    
    	@Override
    	protected String[] getServletMappings() {
    		return null;
    	}
    }

点击“上传”，打印日志如下：

> report.txt  
> text/plain  
> fileName1  
> report.txt  
> 31  
> 31
> 
> \+++++++++++++++  
> temp.txt  
> text/plain  
> fileName2  
> temp.txt  
> 284  
> 284

如果使用拦截工具，可以获取到如下上传报文：

> POST /TestWeb/upload HTTP/1.1  
> Host: 127.0.0.1:9090  
> User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/112.0  
> Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,\*/\*;q=0.8  
> Accept-Language: zh-CN,zh;q=0.8,zh-TW;q=0.7,zh-HK;q=0.5,en-US;q=0.3,en;q=0.2  
> Accept-Encoding: gzip, deflate, br  
> Content-Type: multipart/form-data; boundary=\---------------------------38678334721585548371903973726  
> Content-Length: 951  
> Origin: http://127.0.0.1:9090  
> Connection: keep-alive  
> Referer: http://127.0.0.1:9090/TestWeb/index.html
> 
> \-----------------------------38678334721585548371903973726  
> Content-Disposition: form-data; name="uploadName1"
> 
> **report.txt**  
> \-----------------------------38678334721585548371903973726  
> Content-Disposition: form-data; name="fileName1"; filename="report.txt"  
> Content-Type: text/plain
> 
> 工作计划和工作总结
> 
>   
> \-----------------------------38678334721585548371903973726  
> Content-Disposition: form-data; name="uploadName2"
> 
> **temp.txt**  
> \-----------------------------38678334721585548371903973726  
> Content-Disposition: form-data; name="fileName2"; filename="temp.txt"  
> Content-Type: text/plain
> 
> java.lang.IncompatibleClassChangeError:Expected non-static field org.springframework.web.reactive.result.method.InvocableHandlerMethod.logger  
> at org.springframework.web.reactive.result.method.InvocableHandlerMethod.logArgumentErrorIfNecessary(InvocableHandlerMethod.java:207)  
> 
> 
> \-----------------------------38678334721585548371903973726--

其中，黄色表示分隔线，绿色是上传的文件内容，蓝色是额外上传的文件名，红色是实际文件名。

通过打印的日志和拦截的报文，结合代码，就可以知道整个上传的处理过程。

以上是通过html页面上传文件，其实也可以不用页面也可以实现html上传，比如使用postman或curl。下面使用cur可以实现与html页面相同的功能：

> curl -v http://127.0.0.1:9090/TestWeb/upload
> 
> \-F "fileName1=@/D/Temp/temp.txt"
> 
> \-F "uploadName1=temp.txt"
> 
> \-F "fileName2=@/D/Temp/report.txt"
> 
> \-F "uploadName2=report.txt"

[83c54d340bc94c26a8a26f83585790ea.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/13/5615bd33fa324870b3d367353db005d8.png
[b312a2328a3c45879ed26e6591e1795b.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/13/bb45b8e3a9034453b950f2704e0cc26a.png