需求描述

為了能方便快速的獲取HDFS中的文件，簡單的搭建一個web服務提供下載很方便快速，而且在web服務器端不留臨時文件，只做stream中轉，效率相當高！
使用的框架是SpringMVC+HDFS API

關鍵代碼

@Controller
@RequestMapping("/file")
public class FileDownloadController {
     
     private static final String BASE_DIR = "/user/app/dump/";
    @RequestMapping(value = "/download/{filename}", method = RequestMethod.GET)
    @ResponseBody
    public void fileDownload(@PathVariable("filename") String fileName, HttpServletRequest request, HttpServletResponse response) {
        try {
            response.setContentType("application/octet-stream; charset=utf-8");
            response.addHeader("Content-Disposition", "attachment; filename=" + URLEncoder.encode(fileName + ".csv", "UTF-8"));
            String path = BASE_DIR + fileName;
            HdfsUtils.copyFileAsStream(path, response.getOutputStream());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
 

• 加載要下載的文件都在 /user/app/dump/這個目錄下
• 下載路徑 http://ip:port/file/download/xxxfile

HdfsUtils.copyFileAsStream 實現

public class HdfsUtils {
    private static FileSystem hdfs = null;
    static {
        URL.setURLStreamHandlerFactory(new FsUrlStreamHandlerFactory());
        Configuration conf=new Configuration();
        try {
            hdfs = FileSystem.get(URI.create("hdfs://xxxxxxx"), conf, "app");
        } catch (Exception e) {
            e.printStackTrace();
        } 
    }

    public static void copyFileAsStream(String fpath, OutputStream out) throws IOException, InterruptedException {
        org.apache.hadoop.fs.Path path = new org.apache.hadoop.fs.Path(fpath);
        FSDataInputStream fsInput = hdfs.open(path);
        IOUtils.copyBytes(fsInput, out, 4096, false);
        fsInput.close();
        out.flush();
    }
}
 

是不是非常簡單？ HDFS的文件流沒落在web服務上，而是直接copy到了瀏覽器的OutputStream上

更進一步提升性能，壓縮

修改 web端的代碼, 用zip進行壓縮，默認的壓縮比例是1：5，大大減少了流在網絡上傳輸量

@Controller
@RequestMapping("/file")
public class FileDownloadController {
     private static final String BASE_DIR = "/user/app/dump/";
    
    @RequestMapping(value = "/download/zip/{filename}", method = RequestMethod.GET)
    @ResponseBody
    public void hdfsDownload2(@PathVariable("filename") String fileName, HttpServletRequest request, HttpServletResponse response) {
        try {
            response.setContentType("application/octet-stream; charset=utf-8");
            response.setHeader("Content-Disposition", "attachment; filename=" + URLEncoder.encode(fileName + ".zip", "UTF-8"));

            ZipOutputStream zipOut = null;
            try {
                zipOut = new ZipOutputStream(new BufferedOutputStream(response.getOutputStream()));
                zipOut.putNextEntry(new ZipEntry(fileName + ".csv"));
            } catch (Exception e) {
                e.printStackTrace();
            }
            String path = BASE_DIR + fileName;
            HdfsUtils.copyFileAsStream(path, zipOut);
            zipOut.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
 

一些用的主要jar版本

<properties>
    <spring.version>4.2.5.RELEASE</spring.version>
    <hadoop.version>2.7.0</hadoop.version>
</properties>

<dependencies>
  <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-web</artifactId>
      <version>${spring.version}</version>
  </dependency>
  <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-webmvc</artifactId>
      <version>${spring.version}</version>
  </dependency>
  <dependency>
      <groupId>org.apache.hadoop</groupId>
      <artifactId>hadoop-client</artifactId>
      <version>${hadoop.version}</version>
  </dependency>
  <dependency>
      <groupId>org.apache.hadoop</groupId>
      <artifactId>hadoop-common</artifactId>
      <version>${hadoop.version}</version>
  </dependency>
</dependencies>

搭建一個web服務下載HDFS的文件