客户端解析服务器响应的multipart/form-data数据

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multipart/form-data,多部件请求体。这个请求体比较特殊,它可以拆分为多个部件,每个部件都有自己的headerbody,最常用的地方就是:客户端文件上传,因为有多个部件,在上传文件的时候,还可以在body中添加其他的数据。jsonform。。。

一般来说,都是客户端发起multipart/form-data请求 ,服务器进行解析。而且这种东西的编码解码工作一般都是由底层的容器/框架完成。开发根本不必关心。但是我最近遇到了一个需求:

服务器响应multipart/form-data(包含了一个二进制文件和其他的文本数据),客户端来解析

意味着,需要自己完成2个东西

  1. 在服务端完成multipart/form-data的数据编码,并且响应给客户端
  2. 在客户端获取到响应后,进行数据的解码

multipart/form-data的请求体,看起来像这样(省略了部分 header)

POST /foo HTTP/1.1
Content-Length: 68137
Content-Type: multipart/form-data; boundary=---------------------------974767299852498929531610575

---------------------------974767299852498929531610575
Content-Disposition: form-data; name="description" 

some text
---------------------------974767299852498929531610575
Content-Disposition: form-data; name="myFile"; filename="foo.txt" 
Content-Type: text/plain 

(content of the uploaded file foo.txt)
---------------------------974767299852498929531610575

服务端的编码

使用 org.apache.httpcomponents 库进行编码

<!-- https://mvnrepository.com/artifact/org.apache.httpcomponents/httpmime -->
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpmime</artifactId>
    <version>4.5.12</version>
</dependency>

Controller

通过 MultipartEntityBuilder, 添加多个部件,每个部件有自己的名字,类型。构建出一个 HttpEntity 对象。可以从这个对象中获取到编码后的IO流以及ContentType,直接响应给 客户端就完事儿,比较简单。

import java.io.File;
import java.nio.charset.StandardCharsets;

import javax.servlet.http.HttpServletResponse;

import org.apache.http.HttpEntity;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.entity.mime.content.StringBody;
import org.springframework.web.bind.annotation.GetMapping;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.util.UriUtils;

@RestController
@RequestMapping("/test")
public class TestController {
	
	@GetMapping
	public void test (HttpServletResponse response) throws Exception {
		
		HttpEntity httpEntity = MultipartEntityBuilder.create()
					// 表单 => (部件名称,数据,类型),要注意uri编码
					.addPart("name", new StringBody(UriUtils.encode("SpringBoot中文社区", StandardCharsets.UTF_8), ContentType.APPLICATION_FORM_URLENCODED))
					// JSON => (部件名称,JSON,类型)
					.addPart("info", new StringBody("{\"site\": \"https://springboot.io\", \"year\": 2019}", ContentType.APPLICATION_JSON))
					// 文件 => ( 部件名称,文件,类型,文件名称)
					.addBinaryBody("logo", new File("D:\\logo.png"), ContentType.IMAGE_PNG, "logo.png")
					.build();
		
		// 设置ContentType
		response.setContentType(httpEntity.getContentType().getValue());
		
		// 响应客户端
		httpEntity.writeTo(response.getOutputStream());
	}
}

客户端的解码

使用commons-fileupload 库进行解码

<!-- https://mvnrepository.com/artifact/commons-fileupload/commons-fileupload -->
<dependency>
    <groupId>commons-fileupload</groupId>
    <artifactId>commons-fileupload</artifactId>
    <version>1.4</version>
</dependency>

MultipartTest

看这个代码,会觉得似曾相识。不错,在Servlet3.0以前,HttpServletRequest还没有getPart方法的时候 ,大家都是通过 commons-fileupload来从multipart/form-data请求中解析出数据的。


import java.io.IOException;
import java.io.InputStream;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.Iterator;
import java.util.List;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
import org.apache.commons.fileupload.FileItemHeaders;
import org.apache.commons.fileupload.FileUploadBase;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.RequestContext;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.portlet.PortletFileUpload;
import org.springframework.core.io.Resource;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.web.client.RestTemplate;

/**
 * 自己定义一个RequestContext的实现
 */
class SimpleRequestContext implements RequestContext {
	private final Charset charset;			// 编码
	private final MediaType contentType;	// contentType
	private final InputStream content;		// 数据
	public SimpleRequestContext(Charset charset, MediaType contentType, InputStream content) {
		this.charset = charset;
		this.contentType = contentType;
		this.content = content;
	}
	@Override
	public String getCharacterEncoding() {
		return this.charset.displayName();
	}
	@Override
	public String getContentType() {
		return this.contentType.toString();
	}
	@Override
	public int getContentLength() {
		try {
			return this.content.available();
		} catch (IOException e) {
		}
		return 0;
	}
	@Override
	public InputStream getInputStream() throws IOException {
		return this.content;
	}
}

public class MultipartTest {
	public static void main(String[] args) throws IOException, FileUploadException {

		// 获取服务器响应的IO流
		RestTemplate restTemplate = new RestTemplate();
		ResponseEntity<Resource> responseEntity = restTemplate.getForEntity("http://localhost:8081/test", Resource.class);
		
		// 创建RequestContext对象
		RequestContext requestContext = new SimpleRequestContext(StandardCharsets.UTF_8, responseEntity.getHeaders().getContentType(), 
						responseEntity.getBody().getInputStream());
		
		// 解析器创建
		FileUploadBase fileUploadBase = new PortletFileUpload();
		FileItemFactory fileItemFactory = new DiskFileItemFactory();
		fileUploadBase.setFileItemFactory(fileItemFactory);
		fileUploadBase.setHeaderEncoding(StandardCharsets.UTF_8.displayName());
		
		// 解析出所有的部件
		List<FileItem> fileItems = fileUploadBase.parseRequest(requestContext);
		
		for (FileItem fileItem : fileItems) {
			// 请求头
			System.out.println("headers:==========================");
			FileItemHeaders fileItemHeaders = fileItem.getHeaders();
			Iterator<String> headerNamesIterator = fileItemHeaders.getHeaderNames();
			while (headerNamesIterator.hasNext()) { // 迭代name
				String headerName = headerNamesIterator.next();
				Iterator<String> headerValueIterator =  fileItemHeaders.getHeaders(headerName);
				while (headerValueIterator.hasNext()) {	// 迭代value
					String headerValue = headerValueIterator.next();
					System.out.println(headerName + ":" +  headerValue);
				}
			}
			
			// 请求体
			System.out.println("body:==========================");
			if(fileItem.isFormField()) { // 是普通表单项
				byte[] data = fileItem.get();
				System.out.println(new String(data, StandardCharsets.UTF_8));
			} else {			// 是文件表单项
				String fileName = fileItem.getName();	// 文件的原始名称
				InputStream inputStream = fileItem.getInputStream();	// 文件的IO流
				System.out.println("fileName=" + fileName + ", size=" +  inputStream.available());
			}
			System.out.println();
		}
	}
}

完整的日志输出

17:18:55.384 [main] DEBUG org.springframework.web.client.RestTemplate - HTTP GET http://localhost:8081/test
17:18:55.449 [main] DEBUG org.springframework.web.client.RestTemplate - Accept=[application/json, application/*+json, */*]
17:18:56.426 [main] DEBUG org.springframework.web.client.RestTemplate - Response 200 OK
17:18:56.461 [main] DEBUG org.springframework.web.client.RestTemplate - Reading to [org.springframework.core.io.Resource] as "multipart/form-data;boundary=0W40KHiHJTyo5H_n1EIL68aM4tNRhPa-7Vp"
headers:==========================
content-disposition:form-data; name="name"
content-type:application/x-www-form-urlencoded; charset=ISO-8859-1
content-transfer-encoding:8bit
body:==========================
SpringBoot%E4%B8%AD%E6%96%87%E7%A4%BE%E5%8C%BA

headers:==========================
content-disposition:form-data; name="info"
content-type:application/json; charset=UTF-8
content-transfer-encoding:8bit
body:==========================
{"site": "https://springboot.io", "year": 2019}

headers:==========================
content-disposition:form-data; name="logo"; filename="logo.png"
content-type:image/png
content-transfer-encoding:binary
body:==========================
fileName=logo.png, size=2423

客户端准确的解析出了服务器响应的 multipart/form-data 数据。


同步发布:springboot.io/t/topic/255…