java - 显示 CSV 文件中的前 10 个单词

Question

我有 CSV 文件，已存储在 Google 云存储中。我正在阅读这个 CSV 文件，并为每个出现的单词构建一个树形图。有没有办法可以排序并仅显示文件中的前 10 个单词？

这是我的代码:

@SuppressWarnings("serial")
public class GoogleCloudStorageServlet extends HttpServlet {
   public static final String BUCKETNAME = "bigdata";
   public static final String FILENAME = "Railways.csv";

@SuppressWarnings({ "unchecked", "rawtypes" })

  @Override
  public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
    resp.setContentType("text/plain");
    resp.getWriter().println("Hello, world from java");
    GcsService gcsService = GcsServiceFactory.createGcsService();
    GcsFilename filename = new GcsFilename(BUCKETNAME, FILENAME);
    GcsFileOptions options = new GcsFileOptions.Builder()
        .mimeType("text/html")
        .acl("public-read")
        .addUserMetadata("myfield1", "my field value")
        .build();

    GcsOutputChannel writeChannel = gcsService.createOrReplace(filename, options);

    PrintWriter writer = new PrintWriter(Channels.newWriter(writeChannel, "UTF8"));

    GcsInputChannel readChannel = null;
    BufferedReader reader = null;

    String cvsSplitBy = ",";
    try {
      readChannel = gcsService.openReadChannel(filename, 0);
      reader = new BufferedReader(Channels.newReader(readChannel, "UTF8"));
      String line;
      TreeMap<String, Integer> map = new TreeMap<String, Integer>();
        while ((line = reader.readLine()) != null) {

          String[] post = line.split(cvsSplitBy);

          String[] words = post[1].split("[ \n\t\r.,;:!?(){}]");

          for (int counter = 0; counter < words.length; counter++) {
              String key = words[counter].toLowerCase(); // remove .toLowerCase for Case Sensitive result.
              if (key.length() > 0) {
                  if (map.get(key) == null) {
                      map.put(key, 1);
                  }
                  else {
                      int value = map.get(key).intValue();
                      value++;
                      map.put(key, value);
                  }
              }
           }

          //Display only top 10 words in the file
    }


    } finally {
      if (reader != null) { reader.close(); }
    }
  }
}

Answer 1

计算 CSV 文件中前 10 个单词的方式取决于文件的大小。

1. 小文件(可以存储在内存中)

   如果文件较小，您可以使用某种针对您的情况优化的集合(例如 Bill Lin 提到的 Multiset)或自行计算。

   Map<String, Integer> counts = new HashMap<String, Integer>();
       for (String word : words) {
       Integer count = counts.get(word);
       if (count == null) {
           counts.put(word, 1);
       } else {
          counts.put(word, count + 1);
       }
   }
   

   如果文件确实很小，这样的计算可以在单个请求的范围内处理。

2. 中/大尺寸文件

   如果是中型或大型文件，您可能会超出请求限制(60 秒)，并且可能会耗尽可用内存。效率也不会很高。您需要一种不同的方法。

   尝试查看MapReduce for App Engine .

   MapReduce is a programming model for processing large amounts of data in a parallel and distributed fashion. It is useful for large, long-running jobs that cannot be handled within the scope of a single request.

显示结果的方式取决于您的处理模式。

1. 同步

   如果您的计算是同步的，您可以通过传递的响应对象直接从 Servlet 显示结果。

   HttpServletResponse#getWriter()
   

2. 异步

   如果是异步计算，您需要将结果存储在某个地方(例如Datastore)并按需显示