Format Raw XML to Be Pretty

import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.io.Reader;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Formats raw XML to look prettier (i.e., easier to read).
 *
 * @author RedTeaHacker
 */
public class RawXmlFormatter {
  public static final Pattern PATTERN = Pattern.compile("(<!--[^(\\Q-->\\E)]*-->)|(<((\"[^\"]*\")|('[^']*')|[^\"'>])*>)|([^<]+)",Pattern.DOTALL);

  public static final Pattern COMMENT_TAG_PATTERN = Pattern.compile("<!--.+",Pattern.DOTALL);
  public static final Pattern DECLARATION_TAG_PATTERN = Pattern.compile("<\\?.+",Pattern.DOTALL);
  public static final Pattern END_TAG_PATTERN = Pattern.compile("<\\s*/.+",Pattern.DOTALL);
  public static final Pattern START_TAG_PATTERN = Pattern.compile("<((\"[^\"]*\")|('[^']*')|[^\"'/])+",Pattern.DOTALL);

  public static final int BUFFER_SIZE = 1024;
  public static final String NEWLINE = "\n";
  public static final String TAB = "\t";

  public static String formatRawXml(CharSequence rawXml) {
    return formatRawXml(rawXml,NEWLINE,TAB);
  }

  public static String formatRawXml(CharSequence rawXml,String newline) {
    return formatRawXml(rawXml,newline,TAB);
  }

  public static String formatRawXml(CharSequence rawXml,String newline,String tab) {
    Matcher matcher = PATTERN.matcher(rawXml);
    StringBuilder result = new StringBuilder();
    int tabCount = 0;

    while(matcher.find()) {
      String group = matcher.group();
      boolean isTag = group.length() > 0 && group.charAt(0) == '<'
        && !COMMENT_TAG_PATTERN.matcher(group).matches()
        && !DECLARATION_TAG_PATTERN.matcher(group).matches();

      if(isTag && tabCount > 0 && END_TAG_PATTERN.matcher(group).matches()) {
        --tabCount;
      }

      for(int i = 0; i < tabCount; ++i) {
        result.append(tab);
      }
      result.append(group);
      result.append(newline);

      if(isTag && START_TAG_PATTERN.matcher(group).matches()) {
        ++tabCount;
      }
    }
    return result.toString();
  }

  public static StringBuilder consumeFile(File file) {
    BufferedReader reader = null;
    try {
      reader = new BufferedReader(new FileReader(file));
      return consumeStream(reader);
    }
    catch(FileNotFoundException ex) {
      ex.printStackTrace();
    }
    finally {
      if(reader != null) {
        try { reader.close(); }
        catch(IOException ex) { ex.printStackTrace(); }
      }
    }
    return null;
  }

  public static StringBuilder consumeInput() {
    BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
    return consumeStream(reader);
  }

  public static StringBuilder consumeStream(Reader reader) {
    char[] buffer = new char[BUFFER_SIZE];
    int readCount = 0;
    StringBuilder result = new StringBuilder();
    try {
      while((readCount = reader.read(buffer)) >= 0) {
        result.append(buffer,0,readCount);
      }
    }
    catch(IOException ex) {
      ex.printStackTrace();
    }
    return result;
  }

  public static void main(String[] args) {
    String xmlString = null;
    StringBuilder xmlStringBuilder = null;

    // Piped in (e.g., echo 'example' | java RawXmlFormatter)
    if(args.length < 1) {
      xmlStringBuilder = consumeInput();
    }
    else {
      // Pathname
      File file = new File(args[0]);
      if(file.isFile() && file.exists() && file.canRead()) {
        xmlStringBuilder = consumeFile(file);
      }
      // String
      else {
        xmlString = args[0];
      }
    }

    if(xmlString != null) {
      System.out.print(formatRawXml(xmlString));
    }
    else if(xmlStringBuilder != null) {
      System.out.print(formatRawXml(xmlStringBuilder));
    }
    else {
      System.out.println("No input.");
    }
  }
}