java：在运行时跟踪文件大小？

Question

我编写了一个将压缩对象写入文件的代码，我的问题是：有没有一种方法可以跟踪写入对象时文件大小的增量？这是我的代码：

public static void storeCompressedObjs(File outFile, ArrayList<Object[]> obj) {
    FileOutputStream fos = null;
    GZIPOutputStream gz = null;
    ObjectOutputStream oos = null;
    try {
        fos = new FileOutputStream(outFile);
        gz = new GZIPOutputStream(fos);
        oos = new ObjectOutputStream(gz);
        for (Object str : obj) {
            oos.writeObject(str);
            oos.flush();
            //I was hoping to print outFile.length() here, but it doesn't work
        }

    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        oos.close();
        gz.close();
        fos.close();
    }
}

我尝试在每个oos.writeObject(str); 之后使用flush，然后使用outFile.length() 获取文件大小，但是无论我刷新多少，文件大小都保持不变，直到最后一次跳转到最终大小。无论如何我可以解决它？谢谢

Answer 1

Apache Commons 项目提供了一个类CountingOutputStream，您可以将其放入OutputStreams 链中。您甚至可以拥有其中两个：

package so5997784;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.util.zip.GZIPOutputStream;

import org.apache.commons.io.output.CountingOutputStream;

public class CountBytes {

  private static void dump(File outFile, Object... objs) throws IOException {
    FileOutputStream fos = new FileOutputStream(outFile);
    try {
      CountingOutputStream compressedCounter = new CountingOutputStream(fos);
      OutputStream gz = new GZIPOutputStream(compressedCounter);
      CountingOutputStream uncompressedCounter = new CountingOutputStream(gz);
      ObjectOutputStream oos = new ObjectOutputStream(uncompressedCounter);

      for (Object obj : objs) {
        oos.writeObject(obj);
        oos.flush();
        System.out.println(uncompressedCounter.getByteCount() + " -> " + compressedCounter.getByteCount());
      }
      oos.close();
      System.out.println(uncompressedCounter.getByteCount() + " -> " + compressedCounter.getByteCount());

    } finally {
      fos.close();
    }
  }

  public static void main(String[] args) throws IOException {
    File outFile = new File("objects.out.gz");
    dump(outFile, "a", "b", "cde", "hello", "world");
  }

}