从Java中的二进制文件读取位字符串

Question

I have a string of bits with length 128 and I want to convert it to an byte array, then write it to a binary file and later read from the binary file and convert byte array to bit string. This is my code ( I use an input of length 16 for simplicity):

    String stest = "0001010010000010";
    //convert to byte array
    short a = Short.parseShort(stest, 2);
    ByteBuffer bytes = ByteBuffer.allocate(2).putShort(a);
    byte[] wbytes = bytes.array();

    System.out.println("Byte length: "+ wbytes.length);     
    System.out.println("Writing to binary file");
    try {
        FileOutputStream fos = new FileOutputStream("test.ai");
        fos.write(wbytes);
        fos.flush();
        fos.close();
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    System.out.println("Reading from binary file");

    File inputFile = new File("test.ai");
    byte[] rdata = new byte[(int) inputFile.length()];
    //byte[] rdata = new byte[2];
    FileInputStream fis;
    String readstr = "";
    try {
        fis = new FileInputStream(inputFile);
        fis.read(rdata, 0, rdata.length);
        fis.close();
        for(int i=0; i<rdata.length; i++){
            Byte cb = new Byte(rdata[i]);
            readstr += Integer.toBinaryString(cb.intValue());
        }
        System.out.println("Read data from file: " + readstr);
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

However the string that I read from the file is not equal to the original string. This is the output:

String: 0001010010000010
Byte length: 2
Writing to binary file
Reading from binary file
Read data from file: 1010011111111111111111111111110000010

Answer 1

I would start to choose data type I use for both scenario. Lets think about, you choose byte. So, writing it is pretty easy.

byte data[] = ... //your data
FileOutputStream fo = new FileOutputStream("test.ai");
fo.write(data);
fo.close();

now, lets read stringized data from the file. As you know, 1 byte is 8 bit. So, you need to just read 8 chars from the file, and convert it to a byte. So,

FileInputStream fi = new FileInputStream("test2.ai"); // I assume this is different file
StringBuffer buf = new StringBuffer();
int b = fi.read();
int counter = 0;
ByteArrayOutputStream dataBuf = new ByteArrayOutputStream();
while (b != -1){
  buf.append((char)b);
  b = fi.read();
  counter++;
  if (counter%8 == 0){
    int i = Integer.parseInt(buf.toString(),2);
    byte b = (byte)(i & 0xff);
    dataBuf.write(b);
    buf.clear(0,buf.length());
  }
}
byte data[] = dataBuf.toByteArray();

I think the problem in your code is converting string to byte. Your starting point is already wrong. You are converting your data to short that keeps only 2 byte. But, you say your file can keep 128 bit, that is 16 byte. So, you should not try to convert whole file to a data type, like short, integer or long. you have to convert every 8 bit to byte.