适用场景： 网络绝对路径的URL文件或图片，不存储到本地，转换成stream,直接使用HTTPClient传送到SpringBoot的服务端，将文件存储下来，并返回一个文件地址。目前分层架构的系统越来越多这种需求，所以记录下来以备不时之需。 

1、调用端 

首先引入httpclient所需包

<dependency>
        <groupId>org.apache.httpcomponents</groupId>
        <artifactId>httpclient</artifactId>
        <version>4.4</version>
    </dependency>
    <dependency>
        <groupId>org.apache.httpcomponents</groupId>
        <artifactId>httpmime</artifactId>
        <version>4.4</version>
    </dependency>

调用代码：  

package test.http;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONArray;
import com.alibaba.fastjson.JSONObject;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

import java.io.*;
import java.net.URL;
import java.nio.charset.Charset;

/**
 * 文件传送
 * 发送文件流到服务器端
 * 服务器端使用SpringBoot的MultipartFile接收
 *
 * 适用场景：
 * 绝对路径的URL文件，不存储到本地，转换成stream,直接使用HTTPClient传送到SpringBoot
 *
 */
public class TestUpload {

    public static void main(String[] args) {
        //文件URL，此处取豆瓣上的一个图片
        String fileUrl ="https://img1.doubanio.com/view/photo/l/public/p2537149328.webp";
        try {
            //提取到文件名
            String fileName = fileUrl.substring(fileUrl.lastIndexOf("/")+1);
            //转换成文件流
            InputStream is = new URL(fileUrl).openStream();

            //接收文件的服务器地址
            String uploadURL = "http://localhost:8003/fileupload";

            //创建HttpClient
            CloseableHttpClient httpClient = HttpClients.createDefault();
            HttpPost httpPost = new HttpPost(uploadURL);
            MultipartEntityBuilder builder = MultipartEntityBuilder.create();
            /*绑定文件参数，传入文件流和contenttype，此处也可以继续添加其他formdata参数*/
            builder.addBinaryBody("file",is, ContentType.MULTIPART_FORM_DATA,fileName);
            HttpEntity entity = builder.build();
            httpPost.setEntity(entity);

            //执行提交
            HttpResponse response = httpClient.execute(httpPost);
            HttpEntity responseEntity = response.getEntity();
            if(responseEntity != null){
                //将响应的内容转换成字符串
                String result = EntityUtils.toString(responseEntity, Charset.forName("UTF-8"));

                //此处根据服务器返回的参数转换，这里返回的是JSON格式
                JSONObject output = JSON.parseobject(result);
                JSONArray body = output.getJSONArray("body");
                String resUrl = body.get(0)+"";

                System.out.println(resUrl);
            }
        }catch (Exception ex){
            ex.printStackTrace();
        }

    }
}

2、服务端

服务端直接使用MultipartFile接收即可

/**
     * 上传文件
     * 
     * @throws BusinessException
     */
    @PostMapping("")
    public String upload(@RequestParam(defaultValue = "", required = false) String prefix,
            @RequestParam("file") MultipartFile... files) throws BusinessException {
        ResultView<List<String>> resultView = new ResultView<>();
        List<String> list = new ArrayList<>();
        for (MultipartFile file : files) {
            if (file.isEmpty()) {
                log.warn("have empty upload file,you need check is right?");
                continue;
            }
            String filepath = storageService.store(file, prefix);
            list.add(fileServerAddress + filepath.replaceAll("\\\\", "/"));
        }

        resultView.setBody(list);
        log.info(JSONObject.toJSONString(resultView));
        return JSONObject.toJSONString(resultView);
    }

具体如何存储如何返回，因人而异，我这里返回的是JSON字符串。

其他：本文参考了博友Vincent-Li的博文，表示感谢：https://www.cnblogs.com/lyxy/p/5629151.html

来自：https://www.cnblogs.com/tobeymarshall/p/10215101.html

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