HttpClient 是JDK11提供的一個全新HTTP客戶端Api，超級好用。

Multipart 請求

HttpClient 并沒有提供 Multipart 請求體的構(gòu)建Api。但是可以使用apache的開源httpmime庫來進行構(gòu)建。

<!-- https://mvnrepository.com/artifact/org.apache.httpcomponents/httpmime -->
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpmime</artifactId>
    <version>4.5.13</version>
</dependency>

構(gòu)建一個 MultipartBody

// 構(gòu)建Multipart請求
HttpEntity httpEntity = MultipartEntityBuilder.create()
		// 表單數(shù)據(jù)
		.addPart("name", new StringBody(UriUtils.encode("SpringBoot中文社區(qū)", StandardCharsets.UTF_8), ContentType.APPLICATION_FORM_URLENCODED))
		// JSON數(shù)據(jù)
		.addPart("info", new StringBody("{"site": "https://springboot.io", "now": 2021}", ContentType.APPLICATION_JSON))
		// 文件數(shù)據(jù)
		.addBinaryBody("file", file, ContentType.APPLICATION_OCTET_STREAM, "eclipse-jee-2019-12-R-win32-x86_64.zip")
		.build();

ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream((int) httpEntity.getContentLength());

// 把body寫入到內(nèi)存
httpEntity.writeTo(byteArrayOutputStream);

Multipart 請求可以一次性post多個子body，通常用來上傳本地磁盤上的文件。所以這種請求體可能會異常龐大。甚至內(nèi)存不能完整的存入整個請求體。那么這個時候有2種辦法可以解決。

1. 先把構(gòu)建好的Body數(shù)據(jù)寫入到磁盤，再通過IO磁盤數(shù)據(jù)，提交給服務(wù)器
2. 使用管道流，在讀取磁盤數(shù)據(jù)進行body構(gòu)建的時候，直接通過管道提交到遠程服務(wù)器

管道流

管道流，顧名思義，可以往一邊寫，從另一邊讀。

// 創(chuàng)建讀取流
PipedInputStream pipedInputStream = new PipedInputStream();
// 創(chuàng)建寫入流
PipedOutputStream pipedOutputStream = new PipedOutputStream();
// 連接寫入和讀取流
pipedInputStream.connect(pipedOutputStream);

通過往pipedOutputStream寫入數(shù)據(jù)，就可以在pipedInputStream 讀取。

不能使用單線程既讀又寫，因為讀寫都是阻塞方法。任何一方阻塞住了了，另一方就會一直處于等待狀態(tài)，導(dǎo)致死鎖

完整Demo

客戶端

package io.springcloud.test;

import java.io.IOException;
import java.io.InputStream;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpRequest.BodyPublishers;
import java.net.http.HttpResponse;
import java.net.http.HttpResponse.BodyHandlers;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;

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.util.UriUtils;

public class MainTest {


	public static void main(String[] args) throws Exception {
		
		// 管道流
		PipedInputStream pipedInputStream = new PipedInputStream();
		PipedOutputStream pipedOutputStream = new PipedOutputStream();
		pipedInputStream.connect(pipedOutputStream);
		
		// 本地文件
		InputStream file =  Files.newInputStream(Paths.get("D:\eclipse-jee-2019-12-R-win32-x86_64.zip"));
		
		// 構(gòu)建Multipart請求
		HttpEntity httpEntity = MultipartEntityBuilder.create()
				// 表單數(shù)據(jù)
				.addPart("name", new StringBody(UriUtils.encode("SpringBoot中文社區(qū)", StandardCharsets.UTF_8), ContentType.APPLICATION_FORM_URLENCODED))
				// JSON數(shù)據(jù)
				.addPart("info", new StringBody("{"site": "https://springboot.io", "now": 2021}", ContentType.APPLICATION_JSON))
				// 文件數(shù)據(jù)
				.addBinaryBody("file", file, ContentType.APPLICATION_OCTET_STREAM, "eclipse-jee-2019-12-R-win32-x86_64.zip")
				.build();
		
		// 異步寫入數(shù)據(jù)到管道流
		new Thread(() -> {
			try (file; pipedOutputStream){
				httpEntity.writeTo(pipedOutputStream);
			} catch (IOException e) {
				e.printStackTrace();
			}
		}).start();
		
		HttpClient httpClient = HttpClient.newHttpClient();
		
		try (pipedInputStream){
			// 創(chuàng)建請求和請求體
			HttpRequest request = HttpRequest
						.newBuilder(new URI("http://localhost/upload"))
						// 設(shè)置ContentType
						.header("Content-Type", httpEntity.getContentType().getValue())
						.header("Accept", "text/plain")   
						// 從管道流讀取數(shù)據(jù)，提交給服務(wù)器
						.POST(BodyPublishers.ofInputStream(() -> pipedInputStream))
						.build();
			
			// 執(zhí)行請求，獲取響應(yīng)
			HttpResponse<String> responseBody = httpClient.send(request, BodyHandlers.ofString(StandardCharsets.UTF_8));
			
			System.out.println(responseBody.body());
		}
	}
}

服務(wù)端

package io.springcloud.web.controller;

import java.nio.charset.StandardCharsets;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestPart;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.util.UriUtils;

import com.google.gson.JsonObject;


@RestController
@RequestMapping("/upload")
public class UploadController {
	
	private static final Logger LOGGER = LoggerFactory.getLogger(UploadController.class);
	
	@PostMapping
	public Object upload (@RequestPart("file") MultipartFile file,
						@RequestPart("info") JsonObject info,
						@RequestPart("name") String name) {
		
		LOGGER.info("file: name={}, size={}", file.getOriginalFilename(), file.getSize());
		LOGGER.info("info: {}", info.toString());
		LOGGER.info("name: {}", UriUtils.decode(name, StandardCharsets.UTF_8));
		
		return ResponseEntity.ok("success");
	}
}

啟動服務(wù)端后，執(zhí)行客戶端請求，服務(wù)端日志輸出

2021-09-24 13:38:15.067  INFO 2660 --- [  XNIO-1 task-1] i.s.web.controller.UploadController      : file: name=eclipse-jee-2019-12-R-win32-x86_64.zip, size=369653147
2021-09-24 13:38:15.067  INFO 2660 --- [  XNIO-1 task-1] i.s.web.controller.UploadController      : info: {"site":"https://springboot.io","now":2021}
2021-09-24 13:38:15.067  INFO 2660 --- [  XNIO-1 task-1] i.s.web.controller.UploadController      : name: SpringBoot中文社區(qū)

首發(fā)：https://springboot.io/t/topic/4185