Optimized Special Character Escaper vs Matcher/Pattern

Question

I need to escape special characters which are sent to Apache Lucene.

Since the code will run on a production server, I want the code to be the fastest possible.

I've seen multiple ways to do it:

• Using Pattern
• Using Replace
• Using Library

See: http://www.javalobby.org/java/forums/t86124.html

I'm wondering:

• For trivial cases such as this, should I use RegEx or custom?

• Can the below code be optimized further?

  /*
   * Lucene supports escaping special characters that are part of the
   * query syntax. The current list special characters are + - && || !
   * ( ) { } [ ] ^ " ~ * ? : \
   * 
   * To escape these character use the \ before the character.
   */
  String query = "http://This+*is||a&&test(whatever!!!!!!)";
  char[] queryCharArray = new char[query.length()*2];
  char c;
  int length = query.length();
  int currentIndex = 0;
  for (int i = 0; i < length; i++) 
  {
      c = query.charAt(i);
      switch (c) {                
      case ':':
      case '\\':
      case '?':
      case '+':
      case '-':
      case '!':
      case '(':
      case ')':
      case '{':
      case '}':
      case '[':
      case ']':
      case '^':
      case '"':
      case '~':
      case '*':
          queryCharArray[currentIndex++] = '\\'; 
          queryCharArray[currentIndex++] = c; 
      break;
  
      case '&':
      case '|':   
          if(i+1 < length && query.charAt(i+1) == c)
          {
              queryCharArray[currentIndex++] = '\\'; 
              queryCharArray[currentIndex++] = c; 
              queryCharArray[currentIndex++] = c; 
              i++;
          }
      break;
  
      default:
          queryCharArray[currentIndex++] = c;     
  
      }
  
  }
  
  query = new String(queryCharArray,0,currentIndex);
  
  System.out.println("TEST="+query);
  

Answer 1

I would use a boolean[65536] which flags if the character has to be escaped. I am quite confident that this is faster than the switch.

But only profiling can show if it is really faster.

String query = "http://This+*is||a&&test(whatever!!!!!!)";
char[] queryCharArray = new char[query.length()*2];
char c;
int length = query.length();
int currentIndex = 0;
for (int i = 0; i < length; i++) 
{
    c = query.charAt(i);
    if(mustBeEscaped[c]){        
      if('&'==c || '|'==c){
        if(i+1 < length && query.charAt(i+1) == c){
            queryCharArray[currentIndex++] = '\\'; 
            queryCharArray[currentIndex++] = c; 
            queryCharArray[currentIndex++] = c; 
            i++;
        }
      }    
      else{
        queryCharArray[currentIndex++] = '\\'; 
        queryCharArray[currentIndex++] = c; 
      }     
    }
    else{
        queryCharArray[currentIndex++] = c;     
    }
}

query = new String(queryCharArray,0,currentIndex);

System.out.println("TEST="+query);

---

private static final boolean[] mustBeEscaped = new boolean[65536];
static{
mustBeEscaped[':']=  //
  for(char c: "\\?+-!(){}[]^\"~*&|".toCharArray()){
     mustBeEscaped[c]=true; 
  }
}