prefixexample.java

java实现正则表达式的代码

/*
 * $Id: prefixExample.java,v 1.7 2003/11/07 20:16:23 dfs Exp $
 *
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 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2000 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
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 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
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 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
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 */


package examples;

import org.apache.oro.text.regex.*;

/**
 * This is a test program demonstrating an application of the matchesPrefix()
 * methods introduced in OROMatcher v1.0.6.  This example program shows how
 * you might tokenize a stream of input using whitespace as a token
 * separator.  Don't forget to use quotes around the input on the command
 * line, e.g.
 *    java prefixExample "Test to see if 1.0 is real and 2 is an integer"
 *
 * If you don't need the power of a full blown lexer generator, you can
 * easily use regular expressions to create your own tokenization and
 * simple parsing classes using similar approaches.
 *
 * @version @version@
 */
public final class prefixExample {
  public static final int REAL        = 0;
  public static final int INTEGER     = 1;
  public static final int STRING      = 2;

  public static final String[] types = { "Real", "Integer", "String" };
  public static final String whitespace = "\\s+";
  public static final String[] tokens   = {
    "-?\\d*\\.\\d+(?:[eE][-+]-?\\d+)?(?=\\s|$)", "-?\\d+(?=\\s|$)", "\\S+"
  };
  public static final String tokens2 =
    "(-?\\d*\\.\\d+(?:[eE][-+]-?\\d+)?(?=\\s|$))|(-?\\d+(?=\\s|$))|(\\S+)";

  public static final void main(String args[]) {
    int token;
    PatternMatcherInput input;
    PatternMatcher matcher;
    PatternCompiler compiler;
    Pattern[] patterns;
    Pattern tokenSeparator = null, patterns2 = null;

    if(args.length < 1) {
      System.err.println("Usage: prefixExample <sample input>");
      System.exit(1);
    }

    input    = new PatternMatcherInput(args[0]);
    compiler = new Perl5Compiler();
    patterns = new Pattern[tokens.length];

    try {
      tokenSeparator = compiler.compile(whitespace);
      patterns2      = compiler.compile(tokens2);
      for(token=0; token < tokens.length; token++)
	patterns[token] = compiler.compile(tokens[token]);
    } catch(MalformedPatternException e) {
      System.err.println("Bad pattern.");
      e.printStackTrace();
      System.exit(1);
    }

    matcher  = new Perl5Matcher();

    System.out.println("\nOne approach.\n");

    do {
      for(token = 0; token < tokens.length; token++)
	if(matcher.matchesPrefix(input, patterns[token])) {
	  System.out.println(types[token] + ": " + matcher.getMatch());
	  break;
	}
    } while(matcher.contains(input, tokenSeparator));

    // An alternative approach using the tokens2 expression which
    // packs all the token patterns into one regular expression.
    // As in Perl, there's more than one way to do something in Java.
    System.out.println("\nAn equivalent alternative.\n");

    input.setCurrentOffset(input.getBeginOffset());
    do {
      if(matcher.matchesPrefix(input, patterns2)) {
	MatchResult result = matcher.getMatch();

	for(token = 1; token <= tokens.length; token++) {
	  if(result.group(token) != null) {
	    System.out.println(types[token - 1] + ": " + result);
	    break;
	  }
	}
      }
    } while(matcher.contains(input, tokenSeparator));

  }
}