Inserting strings in a RandomAccessFile at a particular location

Question

I wrote a java program to read and display the contents of RAF. It is working. Actually,I need to read a file and search for a string in it and if the string equals certain value, then i need to insert a line in the file at that location.
My problem is I am not able to insert any string in the RandomAccessFile(RAF) at a particular location, it always overwrites the already present string.
I have a file called SOE_Arrays2.js which needs to be read and its content has to be modified. I am searching for a string like "os = [" in it and inserting another line like "["64w","64-bit Windows"]," at that location.
the file looks like this:
os1 = [
["win","Windows"],
["unx","UNIX"],
["mvs","MVS"]
os2 = [
["alp","Alpha VMS"],
["lnx","Linux"]
var letter = [
["new","New"],
["addon","Add-on"],
["lsf","LSF"],
["renew","Renewal"]
The java program i wrote is here:
import java.io.*;
public class RAFtest
     public void writeTo()
          try
     String f = "C:\\webapps\\oncall\\soe\\SOE_Arrays2.js";
     File arrayfile = new File(f);
     RandomAccessFile raf = new RandomAccessFile(arrayfile, "rw");
     String s="",ss="";
     int i,j = 0,len;
     long fp;
while((s = raf.readLine()) != null)
          //System.out.println(s);
          int ptr = 0;
          ptr = s.indexOf("os2 = [");
          if(ptr != -1)
               System.out.println(s);
               System.out.println("The OS array is here:");
               ss = s;
               raf.writeBytes("\r\t");
               fp = raf.getFilePointer();
               raf.seek(fp-4);
          raf.writeBytes("[\"64w\",\"64-bit Windows\"],\r");
               break;
     raf.close();     
     catch(Exception e){e.printStackTrace(System.out);}      
     public static void main(String args[])
          RAFtest e = new RAFtest();
          e.writeTo();
After executing the code SOE_Arrays2.js looks like this:
os1 = [
["win","Windows"],
["unx","UNIX"],
["mvs","MVS"]
os2 = [["64w","64-bit Windows"],
lnx","Linux"]
var letter = [
["new","New"],
["addon","Add-on"],
["lsf","LSF"],
["renew","Renewal"]
you can see that RAF overwrites to the file at that particular location( after the line "os2 = [ ". What i need is to insert the text at a particular location, Is there a way to do this?
I tried to insert carriage return, etc and move the file ptr back a little and write, whatever it is, RAF overwrites it, is there a way to insert instead of overwrite?
Basically I want to get some string from the user from a web page and insert that string in my SOE_Arrays2.js file at a particular location depending on certain conditions.
Is there another way of doing this instead of RAF?
Please let me know how to do this.
Thanks,
Priyha.

Answer 1

Hi DrClap,
Thanks for the clarification. Everything works except the renameTo() . I am trying to rename the arrayfile2 to arrayfile1 , but the rename always return false. I am not sure why rename is not successful.
I checked for the permissions of the file, full permission is there. I closed the files before renaming.
Here's the code.
import java.io.*;
public class RAFtest
public void writeTo()
try
String f1 = "C:\\JAVA\\SOE_Arrays2.js";
String f2 = "C:\\JAVA\\SOE_Arrays3.js";
File arrayfile1 = new File(f1);
File arrayfile2 = new File(f2);
RandomAccessFile raf1 = new RandomAccessFile(arrayfile1, "rw");
RandomAccessFile raf2 = new RandomAccessFile(arrayfile2, "rw");
long fp1=0,fp2=0; // file pointers
String s="",ss="";
int i,j = 0,len;
boolean b= false;
raf2.seek(0);
while((s = raf1.readLine()) != null)
int ptr = 0;
raf2.writeBytes(s);
ptr = s.indexOf("var OS9.1_sol = [");
     if(ptr != -1)
          System.out.println(s);
          System.out.println("The OS array is here:");
          ss = s;
          fp1 = raf1.getFilePointer();
          raf2.writeBytes("[\"64w\",\"64-bit Windows\"],");
          fp2 = raf2.getFilePointer();
          break;
raf1.seek(fp1);
while((s = raf1.readLine()) != null)
     raf2.writeBytes(s);               
raf1.close();
raf2.close();
if(arrayfile2.exists()) System.out.println("file2 exists!");
try{
b = arrayfile2.renameTo(arrayfile1); //rename the file, why does it return false?
}catch(SecurityException se){se.printStackTrace(System.out);}
catch(NullPointerException ne){ne.printStackTrace(System.out);}
System.out.println("b: "+b);
catch(Exception e){e.printStackTrace(System.out);}
public static void main(String args[])
RAFtest e = new RAFtest();
e.writeTo();
here is the SOE_Arrays2.js
var OS9.1 = [
["win","Windows"],
["unx","UNIX"],
["mvs","MVS"]
var OS9.1_sol = [
["alp","Alpha VMS"],
["lnx","Linux"]
var letter = [
["new","New"],
["addon","Add-on"],
["lsf","LSF"],
["renew","Renewal"]
Please let me know whats wrong with the above code. I have no clue why renameTo returns false.
Thanks,
Priyha