仅在匹配阈值字节时才在地图中填充字符串值 [英] Populate string value in a map only if matches the threshold bytes

问题描述

我有一个任务列表对象，我正在迭代并将每个任务对象附加到 StringBuilder 后跟新行如下所示。现在，我将继续在同一个字符串构建器中追加任务对象，直到达到60000字节的大小限制。一旦达到限制，我将把这个字符串填充为map中的值，key将是带有增量索引的文件名。然后我将重置字符串构建器和其他东西并再次重复此过程。

I have a tasks list object which I am iterating and appending each task object into StringBuilder followed by new line as shown below. Now I will keep appending task object in same string builder until it reaches a size limit of 60000 bytes. Once it reaches the limit, I will populate this string as a value in the map and key will be file name with incremental index. And then I will reset string builder and other thing and repeat this process again.

所以如果我有一个很大的任务对象，然后我将拆分成多个字符串对象，其大小应始终小于60000字节。

So if I have a big tasks object, then I will split into multiple string object whose size should always be less than 60000 bytes.

我得到了下面的代码，但我总是看到地图中的值有大小大于60000字节。我做错了什么？此外，我在两个不同的地方填充 HashMap - 一个达到限制，另一个如果未达到限制。

I got below code but I always see value in the map has size greater than 60000 bytes. Anything wrong I am doing? Also I am populating into HashMap at two different places - one if limit is reached and other is if limit is not reached.

  public void populate(final List<Task> tasks) {
    Map<String, String> holder = new HashMap<>();
    int size = 0;
    int index = 0;
    StringBuilder sb = new StringBuilder();
    for (Task task : tasks) {
      sb.append(task).append(System.getProperty("line.separator"));
      size = sb.toString().getBytes(StandardCharsets.UTF_8).length;
      if (size > 60000) {
        String fileName = "tasks_info_" + index + ".txt";
        holder.put(fileName, sb.toString());
        index++;
        sb = new StringBuilder();
        size = 0;
      }
    }
    // for cases where we don't reach the limit
    if(sb.toString().length > 0) {
        String fileName = "tasks_info_" + index + ".txt";
        holder.put(fileName, sb.toString());        
    }
    System.out.println(holder);
  }

注意：如果每个Task对象超过 60000字节，然后我会立即删除该对象并转到下一个条目。但实际上，它不会发生。

Note: If each Task object is more than 60000 bytes, then I will drop that object right away and move to next entry. But in real, its not gonna happen.

更新：

public void populate(final List<Task> tasks, final long timestamp) {
    Map<String, String> holder = new HashMap<>();
    int size = 0;
    int index = 0;
    int nl = System.getProperty("line.separator").getBytes(StandardCharsets.UTF_8).length;
    StringBuilder sb = new StringBuilder();
    // new change
    sb.append(timestamp).append(System.getProperty("line.separator"));
    for (Task task : tasks) {
        int ts = String.valueOf(task).getBytes(StandardCharsets.UTF_8).length;
        if (size + ts + nl > 60000) {
            String fileName = "tasks_info_" + index + ".txt";
            holder.put(fileName, sb.toString());
            index++;
            sb = new StringBuilder();
            // new change
            sb.append(timestamp).append(System.getProperty("line.separator"));          
            size = 0;
        }
        sb.append(task).append(System.getProperty("line.separator"));
        size += ts + nl;
    }
    // for cases where we don't reach the limit
    if (size > 0) { // size can only be 0 if you have 0 tasks
        String fileName = "tasks_info_" + index + ".txt";
        holder.put(fileName, sb.toString());        
    }
    System.out.println(holder);
}

推荐答案

之所以不是其他答案已经提到了工作（你已经超过限制后添加）。但我认为到目前为止没有一个实现是正确的，不仅因为新行的大小已被省略。

The reason why it is not working was already mentioned by other answers (you add after it already exceeded the limit). But I think none of the implementations is correct so far, not only because the size of the newline was ommitted.

public Map<String, String> populate(final List<Task> tasks) {
    Map<String, String> holder = new HashMap<>();
    if (tasks.size() == 0)
        return holder;
    int index = 0;
    int nl = System.getProperty("line.separator").getBytes(StandardCharsets.UTF_8).length;
    StringBuilder sb = new StringBuilder();
    sb.append(System.currentTimeMillis()).append(System.getProperty("line.separator"));
    int size = sb.toString().getBytes(StandardCharsets.UTF_8).length;
    for (Task task : tasks) {
        int ts = String.valueOf(task).getBytes(StandardCharsets.UTF_8).length;
        if (size + ts + nl > 60000) {
            String fileName = "tasks_info_" + index + ".txt";
            holder.put(fileName, sb.toString());
            index++;
            sb = new StringBuilder();
            sb.append(System.currentTimeMillis()).append(System.getProperty("line.separator"));
            size = sb.toString().getBytes(StandardCharsets.UTF_8).length;
        }
        sb.append(task).append(System.getProperty("line.separator"));
        size += ts + nl;
    }
    String fileName = "tasks_info_" + index + ".txt";
    holder.put(fileName, sb.toString());        
    return holder;
}

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