How to remove line breaks from a file?

Source:

import java.io.*;

public class RemoveLineBreaks {

   public static void main(String[] args) {
      String content = "";
      try {
         FileInputStream is = new FileInputStream("file1.txt");
         BufferedReader br = new BufferedReader(new InputStreamReader(is));
         String str;
         while ((str = br.readLine()) != null)   {
            content = content + str + " ";
         }
         br.close();

         FileWriter fw = new FileWriter("file2.txt");
         BufferedWriter bw = new BufferedWriter(fw);
         bw.write(content);
         bw.close();

      } catch (Exception e) {
         System.out.println(e);
      }
   }
}

Output:

   $ cat file1.txt 
   First first line.
   Second first line.
   Third first line.

   $ cat file2.txt 
   First first line. Second first line. Third first line.