如何最有效地将特定字节从二进制文件转换为字符串 [英] How to convert specific bytes from binary file into string most efficiently

问题描述

所以我有二进制FRX文件，我需要从中将字符串提取到Java中.
我是这样写到我的Java程序中的:

So I have binary FRX files, from which I need to extract strings into Java.
I wrote this into my Java program like so:

FileInputStream ReadFRX = null ;
FileOutputStream TempCapt = null ;
    try{                
        // refNum is hex number on end of VB form property converted to decimal, ex: $"frmResidency.frx":0134
        int refNum = Integer.parseInt(line.substring(line.length() - 4, line.length()), 16);

        // FRXtemp.txt is created, to temporarily write FRX captions onto to be read from. 
        PrintWriter writer = new PrintWriter("FRXtemp.txt", "UTF-8");
        writer.close();

        //opens corresponding FRX file to read into
        ReadFRX = new FileInputStream("FRXFiles\\"+curFrmName + ".frx");
        //aLittleEndian... must be used to match readInt() little-endianness
        LittleEndianDataInputStream ActReadFRX = new LittleEndianDataInputStream(ReadFRX);
        TempCapt = new FileOutputStream("FRXtemp.txt");

        ActReadFRX.skipBytes(refNum);
        int length = ActReadFRX.readInt();
        int c;

            for (c = 0; c < length; c++) {
                // first read byte and check for EOF
                TempCapt.write(ActReadFRX.read());
            }
        }
//If caption is not read properly (ie. possibly wrong bytes), EOF Exception will occur and designer will break
catch (EOFException e){

    System.out.println("ERROR : FRX Caption property was mishandled");
    break;
}

//Read data from FRXtemp.txt into string
String actCaption = "\"" + new Scanner(new File("FRXtemp.txt")).useDelimiter("\\A").next() + " \" ";

这很好用，但是我认为写一个临时文件非常必要，这样我就可以读出它了.

为什么我没想到更有效的方法:
我觉得更实用的方法是使用Byte[] Array，然后将其转换为字符串，但是我必须仅具有存储字符串的字节.研究使我相信RandomAccessFile才是必需的，这样我可以设置与ReadInt的偏移量以开始读取字节，但是RandomAccessFile假定为大端格式，而我为小端格式.我显然可以转换，但是到那时我当前的解决方案似乎同样可行.

This works perfectly, however I think writing to a temporary file so that I can read off of it must be highly unnecessary.

Why I can't think of a more efficient method:
I feel like a much more practical approach would be to use a Byte[] Array, and then convert that to a string, however I must only have the bytes in which the string are stored. Research led me to believe that RandomAccessFile was then necessary so that I could set an offset from ReadInt to begin reading bytes , however RandomAccessFile assumes big-endian format, whereas I have little-endian format. I can obviously convert, however at that point my current solution seems just as viable.

我的问题是 ，是否存在一种有效的方法来转换对应于4字节整数的特定字节部分(从具有Little-Endian格式的二进制文件中转换) )转换为Java中的字符串?

我觉得好像我必须忽略一些更简单的事情.谢谢:)

My question is, is there an efficient way to convert a specific section of bytes corresponding to a 4-byte integer (from a binary file with little-endian format) into a string in Java?

I feel as though I must be overlooking something much more simple. Thanks :)

推荐答案

您可以通过多种方式进行此操作，但是最简单的方法可能是

You can do this any number ways, however the simplest might be.

try (DataInputStream dis = new DataInputStream(new FileInputStream(file))) {
    dis.skip(bytesToSkip);
    int length = Integer.reverseBytes(dis.readInt());
    byte[] bytes = new bytes[length];
    dis.readFully(bytes);
    return new String(bytes, "UTF-8");
}

您可能一直在寻找的方法在Integer

The method you might have been looking for is in Integer

/**
 * Returns the value obtained by reversing the order of the bytes in the
 * two's complement representation of the specified {@code int} value.
 *
 * @param i the value whose bytes are to be reversed
 * @return the value obtained by reversing the bytes in the specified
 *     {@code int} value.
 * @since 1.5
 */
public static int reverseBytes(int i) {
    return ((i >>> 24)           ) |
           ((i >>   8) &   0xFF00) |
           ((i <<   8) & 0xFF0000) |
           ((i << 24));
}

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