Question

Take the following static method:

public static String fileToString(String filename) throws Exception {
        FileInputStream fis = new FileInputStream(filename);
        byte[] buffer = new byte[8192];
        StringBuffer sb = new StringBuffer();   
        int bytesRead; // unused? weird compiler messages...
        while((bytesRead = fis.read(buffer)) != -1) { // InputStream.read() returns -1 at EOF
            sb.append(new String(buffer));
        }
        return new String(sb);
    } 

As you can see everything looks okay, and it is perfect for small text files. But once you get to big files with thousands of lines, you encounter problems with repeating text. Based on my intuition, I thoughtbyte[] buffer was “unclean”, so to speak. So I added the following line to the method:

buffer = new byte[8192];

So that it is now:

public static String fileToString(String filename) throws Exception {
    FileInputStream fis = new FileInputStream(filename);
    byte[] buffer = new byte[8192];
    StringBuffer sb = new StringBuffer();   
    int bytesRead; // unused? weird compiler messages...
    while((bytesRead = fis.read(buffer)) != -1) { // InputStream.read() returns -1 at EOF
        sb.append(new String(buffer));
        buffer = new byte[8192]; // added new line here
    }
    return new String(sb);
} 

And it’s perfect, except for the fact that at the end of the String that the static method returns, I get a lot of null characters (depends on the buffer size). What’s going on here?

Answer 1

actually: // unused? weird compiler messages...

is not weird. You never read this.

how could sb.append(new String(buffer)); know how many bytes are written to the buffer.

Exactly, this is where bytesRead comes into play.

So you need new String(bytes, offset, length)

public static String fileToString(String filename) throws Exception {
    FileInputStream fis = new FileInputStream(filename);
    byte[] buffer = new byte[8192];
    StringBuffer sb = new StringBuffer();   
    int bytesRead; // unused? weird compiler messages...
    while((bytesRead = fis.read(buffer)) != -1) { // InputStream.read() returns -1 at EOF
        sb.append(new String(buffer,0,bytesRead));
        buffer = new byte[8192];
        bytesRead=0;
    }
    return new String(sb);
} 

might work