Creates indents in the xml file

XmlIndenter.java

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.util.regex.Pattern;
import java.util.regex.Matcher;

/**
 * Main class of the application.
 *
 * <p>The application parses input files, seeks xml tags and creates valid hierarchy.</p>
 * <p> The amount of indent is 2 spaces.</p>
 * @author Gennadiy Zlobin <[email protected]>
 * @since 1.0
 */
public class XmlIndenter {

  /*
   * Entry method of the application.
   *
   * <p> The main method which executes the logic.
   * @param args Arguments of the application.
   */
  public static void main(String[] args) {
  
    boolean res = checkParams(args);
  
    File file = new File(args[0]);
    FileReader fr = null;
    FileWriter fw = null;
    BufferedReader br = null;
    
    try {
      fr = new FileReader(file);
      br = new BufferedReader(fr);

      String s;
      StringBuffer sb = new StringBuffer(); 
      int numOfSpaces = 0;

      Pattern p = Pattern.compile("\\<\\w");
      Matcher m;

      while ((s = br.readLine() ) != null) {
	m = p.matcher(s);
	if (! m.find(0)) { // Not open
          if (s.indexOf("</") != -1) // And close
            numOfSpaces -= 2;
        }

	String spaces = "";

	for (int i = 0; i < numOfSpaces; i++) {
          spaces += " ";
        }

        s = s.trim();
	sb.append(spaces).append(s).append("\n");

        if (m.find(0)) { // Open
          if (s.indexOf("</") == -1) // And not close
            numOfSpaces += 2;
        }
      }

      fr.close();

      fw = new FileWriter(file, false);
      fw.write(sb.toString());
      fw.close();      

      System.out.printf("The file '%s' is parsed successfully.\n", args[0]);

    } catch (FileNotFoundException fnfe) {
      System.out.println("File doesn't exist");
      System.exit(1);
    } catch (IOException ioe) {
      System.out.println("IO Exception appeared");
      System.exit(1);
    }
  }

  /**
   * Check param for validness.
   * 
   * <p>Stops the application if params are invalid.</p>
   * @param args Args of the application.
   * @return If the params are correct, returns true, otherwise false.
   */
  public static boolean checkParams(String[] args) {
       if (args.length == 0) {
         System.out.println("Usage: java XmlParser FILENAME");
         System.exit(1);
       }
       return true;
  }
}