如何刷新 DeflaterOutputStream 中的缓冲区数据答案

【问题标题】：How do I flush the buffered data in a DeflatorOutputStream如何刷新 DeflaterOutputStream 中的缓冲区数据
【发布时间】：2013-09-12 12:50:05
【问题描述】：

我希望能够刷新 DeflaterOutputStream 中的任何待处理数据并在 InflaterInputStream 中读取它。但是，flush() 似乎并没有这样做。还有其他方法吗？

ByteArrayOutputStream baos = new ByteArrayOutputStream();
DeflaterOutputStream dos = new DeflaterOutputStream(baos);

for(char ch = 'a';ch <= 'z';ch ++) {
    dos.write(ch);
    dos.flush();
    System.out.println("compressed size = "+baos.toByteArray().length);
}
dos.close();
System.out.println("After close, compressed size = "+baos.toByteArray().length);

我希望看到每次刷新时大小都会增加，因为它会刷新任何挂起/缓冲的数据。然而，事实并非如此。它只是停留在缓冲区中，直到我关闭流。

compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
compressed size = 2
After close, compressed size = 34

如果 DeflaterOutputStream 不支持这一点，是否有压缩流支持？

我查看了 Apache Commons Compress，唯一刷新数据的流是 XZCompressorInputStream，但在这样做时，数据比不压缩大约大 50%。

ByteArrayOutputStream baos = new ByteArrayOutputStream();
ByteArrayOutputStream baos2 = new ByteArrayOutputStream();
XZCompressorOutputStream dos = new XZCompressorOutputStream(baos);

for (char ch = 'a'; ch <= 'z'; ch++) {
    dos.write(("Hello world").getBytes());
    baos2.write(("Hello world").getBytes());
    dos.flush();
    System.out.println("compressed size = " + baos.toByteArray().length);
}
dos.close();
System.out.println("After close, compressed size = " + baos.toByteArray().length);
System.out.println("uncompressed size = " + baos2.toByteArray().length);

终于打印出来了

compressed size = 388
After close, compressed size = 424
uncompressed size = 286

【问题讨论】：

标签： java flush deflate

【解决方案1】：

我应该阅读 Javadoc。构造函数syncFlush 有一个选项，如果为true，则给出我想要的行为。

ByteArrayOutputStream baos = new ByteArrayOutputStream();
ByteArrayOutputStream baos2 = new ByteArrayOutputStream();
DeflaterOutputStream dos = new DeflaterOutputStream(baos, true);

for (char ch = 'a'; ch <= 'z'; ch++) {
    dos.write(("Hello world").getBytes());
    baos2.write(("Hello world").getBytes());
    dos.flush();
    System.out.println("compressed size = " + baos.toByteArray().length);
}
dos.close();
System.out.println("After close, compressed size = " + baos.toByteArray().length);
System.out.println("uncompressed size = " + baos2.toByteArray().length);

终于打印出来了

compressed size = 212
compressed size = 220
After close, compressed size = 226
uncompressed size = 286

注意：这只是在 Java 7 中添加的，我正在查看 Java 6。

【讨论】：

遇到同样的问题。该死的 Java 6 兼容性！