Overwriting texfile using BufferedWriter

Question

Hi. I have a simple servlet that reads values from a textfile into an array using a BufferedWriter and String Tokenizer, and checks one token against a user defined parameter in the web interface.
For example, if the user Id entered in the interface is "Bob", it checks each line in the array (the specific token) for "Bob" - if it is the same, it replaces the values in that row of the array with the user defined variables for Bob (password, home directory, etc.)
PROBLEM:
How do I write the array back to the textfile, OVERWRITING the entire file contents? I know I use BufferedWriter - I can append the modified data easily enough - maybe I should be deleting that row of the array and appending a new line to the end?
1) Is there an easier way to read in, compare, modify and write back out line by line?
2) By doing things this way, is there a danger that a maximum array size may be reached? It is a 2D array, fixed columns (6), probably 5000 rows at the very most.
Thanks!!! Geoff

Answer 1

Random access files work best when you know how long each data entry is. Then you can create a class like this {
class DataIO {
    public static String readFixedString(int size, DataInput in) throws IOException {
        StringBuffer b = new StringBuffer(size);
        int i = 0;
        boolean more = true;
        while(more && i < size) {
            char ch = in.readChar();
            i++;
            if (ch == 0) more = false;
            else b.append(ch);
        in.skipBytes(2 * (size - i));
        return b.toString();
    public static void writeFixedString(String s, int size, DataOutput out) throws IOException {
        int i;
        for (i = 0; i < size; i++) {
            char ch = 0;
            if (i < s.length()) ch = s.charAt(i);
            out.writeChar(ch);
}That class has two static methods that write and read Strings as Bytes of always equal lenth. Then your RandomAccessFile object could perform like this:
// open RandomAccessFile with "rw" for read and write
RandomAccessFile out = new RandomAccessFile("employee.dat", "rw");
// look for record number
int recordNum = 5
// write after recordNum
out.seek(recordNum * RECORD_SIZE) //The record size being defined by you
DataIO.writeFixedString("yourText", RECORD_SIZE, out);
out.close();