直接貼代碼吧

package com.wjs.controller;

import lombok.extern.slf4j.Slf4j;
import org.activiti.engine.RepositoryService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLEncoder;

/**
 * 獲取流程圖
 */
@Slf4j
@RequestMapping("/image")
@RestController
public class ImageController {
    @Autowired
    private RepositoryService repositoryService;

    @RequestMapping(value = "/getImg",method = RequestMethod.GET)
    public void getImg(@RequestParam String deploymentId, @RequestParam String resourceName, HttpServletRequest request, HttpServletResponse response){
        log.info("deploymentId:{},resourceName:{}",deploymentId,resourceName);

        response.setCharacterEncoding(request.getCharacterEncoding());
        response.setContentType("application/octet-stream");
        InputStream is = null;
        is = repositoryService.getResourceAsStream(deploymentId, resourceName);
        response.setHeader("Content-Disposition","attachment; filename=" + URLEncoder.encode("流程圖.png"));
        OutputStream os = null;
        try {
            // 這兩行代碼可以代替42-48行的代碼。
//            IOUtils.copy(is,response.getOutputStream());
//            response.flushBuffer();
            os = response.getOutputStream();
            byte[] b = new byte[1024];
            int len;
            while ((len = is.read(b)) != -1) {
                os.write(b,0,len);
            }
            response.flushBuffer();
        } catch (IOException e) {
            e.printStackTrace();
            log.error("圖片下載失敗....");
        }finally {
            if (null != is) {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}