从Java中的二进制文件读取字符串

Question

I have read any page I found on the web, but non of them work for me.

I have a binary file which is created with a C code. I also have the C reader for this binary file. I need to write the java reader for this binary file.

In C code, the following command reads one string of size 'b * max_w' and a character.

fscanf(f, "%s%c", &vocab[b * max_w], &ch);

In java I read the binary file,

FileInputStream fis = new FileInputStream(filename);  
BufferedInputStream bin = new BufferedInputStream(fis);

And then read Bytes and convert it into string.

for(int j = 0; j < 200; j++) {
     int size = 2; // char is 2 bytes  
     byte[] tempId3 = new byte[size];
     bin.read(tempId3, 0, size); 
     String id3 = new String ( tempId3 ); 
     System.out.println( " id = " + id3 );                
}

But the output is a bunch of nonsense. Am I doing something wrong? Can I do better?

Edit: The working C snippet from here from is :

fscanf(f, "%lld", &words);
  fscanf(f, "%lld", &size);
  vocab = (char *)malloc((long long)words * max_w * sizeof(char));
  for (a = 0; a < N; a++) bestw[a] = (char *)malloc(max_size * sizeof(char));

Here is what I have:

FileInputStream fis = new FileInputStream(filename);  
BufferedInputStream bin = new BufferedInputStream(fis);

int length = 1; 

System.out.println("1st: "); 
byte[] tempId = new byte[8];
bin.read(tempId, 0, 8); 
String id = new String ( tempId, "US-ASCII" ); 
System.out.println( " out = " + id ); 

System.out.println("2nd: "); 
int size1 = 8; 
byte[] tempId2 = new byte[size1];
bin.read(tempId2, 0, size1); 
String id2 = new String ( tempId2, "US-ASCII"); 
System.out.println( " out = " + id2 ); 



for(int j = 0; j < 20; j++) {
     int size = 2; 
     byte[] tempId3 = new byte[size];
     bin.read(tempId3, 0, size); 
     String id3 = new String ( tempId3, "US-ASCII" ); 
     System.out.println( " out = " + id3 );                  
}

The output that I see is the following; except the first two 'long' numbers, the rest is nonsense (expected to be characters ).

PS. The C code is here (line 44-60 is the part which reads the binary file)

Answer 1

May be using Reader you can get what you need? Using InputStream you are reading binary data, Readers are for strings.

Answer 2

You can try to use a constructor like this one , and try different charset. Because a java string is encoded in UTF-16, so one character is encoded in 2 bytes, it could be why it doesn't work. Try with US-ASCII for example.

Answer 3

String is in unicode in Java. You have to take care of that. What is the encoding you use in your binary file?

Answer 4

  String id3 =   new String(tempId3, "US-ASCII");

Answer 5

As it was said in other comments try to use a String constructor with character encoding. That is:

String id3 = new String(tempId3, Charsets.US_ASCII);

Or:

String id3 = new String(tempId3, "US_ASCII");

Other lines may remain untouched.

In the C code you have posted there is no actual reading of characters. There is only memory allocation for further scanning process.