更改索引定位于为InputStream [英] changing the index positioning in InputStream

问题描述

我有一个二进制文件，其中包含密钥和之后每键有与之相关联的图像。我想跳下去不同的密钥，但没有找到任何这改变了指数定位于输入流的方法。我已经看到了标记（）方法，但它不能在不同的地方往下跳。

I have a binary file which contains keys and after every key there is an image associated with it. I want to jump off different keys but could not find any method which changes the index positioning in input stream. I have seen the mark() method but it does not jump on different places.

没有任何人有任何想法如何做到这一点？

Does anybody have any idea how to do that?

推荐答案

有一个的 长跳（N久） ，你可能能够使用方法：

There's a long skip(long n) method that you may be able to use:

跳过和放弃从输入流中数据的n 字节。该跳方法，可由于种种原因，最终跳过的字节一些数量较少，可能是 0 。这可能是由于任意数量的条件; 前N到达文件结尾字节被跳过只是一种可能性。的实际字节数目返回跳过。如果 N 为负，则不跳过任何字节。

Skips over and discards n bytes of data from this input stream. The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly 0. This may result from any of a number of conditions; reaching end of file before n bytes have been skipped is only one possibility. The actual number of bytes skipped is returned. If n is negative, no bytes are skipped.

由于记录的，你不能保证 N 字节将被跳过，所以总是doublecheck返回值。请注意，这不会让你快退，但如果它的 的markSupported（） ，你可以的 复位（） 第一和那么的跳前进到一个较早的位置，如果你必须这样做。

As documented, you're not guaranteed that n bytes will be skipped, so doublecheck the returned value always. Note that this does not allow you to "skip backward", but if it's markSupported(), you can reset() first and then skip forward to an earlier position if you must.

您也可以使用 java.io.RandomAccessFile中的 ，该顾名思义，允许其的 求（长POS） 的方法。

You may also use java.io.RandomAccessFile, which as the name implies, permits random access with its seek(long pos) method.

您提到的图像，因此，如果您使用的是 Java高级图像，另一种可能的选择是<一个href="http://download.oracle.com/docs/cd/E17802_01/products/products/java-media/jai/forDevelopers/jai-apidocs/com/sun/media/jai/$c$cc/FileSeekableStream.html"相对=nofollow> com.sun.media.jai。codec.FileSeekableStream ，这是一个<一个href="http://download.oracle.com/docs/cd/E17802_01/products/products/java-media/jai/forDevelopers/jai-apidocs/com/sun/media/jai/$c$cc/SeekableStream.html"相对=nofollow> SeekableStream 这需要从文件或 RandomAccessFile的。注意，这个类不是JAI API的承诺的一部分。它可能会被删除或JAI的未来版本中改变。

You mentioned images, so if you are using Java Advanced Imaging, another possible option is com.sun.media.jai.codec.FileSeekableStream, which is a SeekableStream that takes its input from a File or RandomAccessFile. Note that this class is not a committed part of the JAI API. It may be removed or changed in future releases of JAI.

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