以Spring Boot的方式显示图片或下载文件到浏览器的示例代码

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

import java.io.File;
import java.io.IOException;

@Configuration
public class ImageShow implements WebMvcConfigurer {

 @Override
 public void addResourceHandlers(ResourceHandlerRegistry registry) {
  File directory = new File("image");
  String path = null;
  try {
   path = directory.getCanonicalPath();
  }catch (IOException e){
   e.printStackTrace();
  }
  registry.addResourceHandler("/image/**").addResourceLocations("file:"+path+"/");
 }

}

@GetMapping(value = "v1/returnGroupCode",produces = MediaType.IMAGE_JPEG_VALUE)
  public byte[] returnGroupCode(@RequestParam("seriesUniqueCode") String seriesUniqueCode){
    URL url = null;
            InputStream is = null;
            ByteArrayOutputStream outStream = null;
            HttpURLConnection httpUrl = null;
            try{
              url = new URL(pdGroupcodeSeriesInfo.getQrCodeUrl());
              httpUrl = (HttpURLConnection) url.openConnection();
              httpUrl.connect();
              httpUrl.getInputStream();
              is = httpUrl.getInputStream();
              outStream = new ByteArrayOutputStream();
              //创建一个Buffer字符串
              byte[] buffer = new byte[1024];
              //每次读取的字符串长度，如果为-1，代表全部读取完毕
              int len = 0;
              //使用一个输入流从buffer里把数据读取出来
              while( (len=is.read(buffer)) != -1 ){
                //用输出流往buffer里写入数据，中间参数代表从哪个位置开始读，len代表读取的长度
                outStream.write(buffer, 0, len);
              }
              byte[] temp = outStream.toByteArray();
              return temp;
  }