likeexpression.java

来自「OpenJMS是一个开源的Java Message Service API 1.」· Java 代码 · 共 182 行

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 */

package org.exolab.jms.selector;

import javax.jms.Message;

import org.apache.oro.text.regex.Pattern;
import org.apache.oro.text.regex.PatternMatcher;
import org.apache.oro.text.regex.Perl5Matcher;


/**
 * This class implements a 'like' expression.
 * This is an expression that returns true if a identifier's value matches
 * a pattern
 *
 * @version     $Revision: 1.1 $ $Date: 2004/11/26 01:50:44 $
 * @author      <a href="mailto:[e-mail]">Tim Anderson</a>
 * @see         Identifier
 * @see         IdentifierExpression
 * @see         RegexpFactory
 */
class LikeExpression extends IdentifierExpression {

    /**
     * The regular expression
     */
    private final Pattern _regexp;

    /**
     * The pattern matcher
     */
    private final PatternMatcher _matcher;

    /**
     * The pattern
     */
    private final String _pattern;

    /**
     * The escape character. May be null.
     */
    private final String _escape;


    /**
     * Construct a new <code>LikeExpression</code>
     *
     * @param identifier the identifier
     * @param pattern the pattern
     * @param escape the escape character. May be null.
     * @throws SelectorException if <code>pattern</code> or <code>escape</code>
     * are invalid
     */
    public LikeExpression(final Identifier identifier, final String pattern,
                          final String escape) throws SelectorException {
        super(identifier);
        _pattern = pattern;
        _escape = escape;
        _regexp = getRegexp(_pattern, _escape);
        _matcher = new Perl5Matcher();
    }

    /**
     * Evaluate the expression
     *
     * @param msg the message to use to obtain any header identifier and
     * property values
     * @return the evaluated result, or <code>null</code> if the value of the
     * expression is unknown
     * @throws TypeMismatchException if the expression tries to evaluate
     * mismatched types.
     */
    public final SObject evaluate(final Message msg)
        throws TypeMismatchException {
        SBool result = null;
        SString value = TypeCaster.castToString(identifier().evaluate(msg),
            "like expression");
        if (value != null) {
            if (_matcher.matches((String) value.getObject(), _regexp)) {
                result = SBool.TRUE;
            } else {
                result = SBool.FALSE;
            }
        }
        return result;
    }

    /**
     * Return a string representation of this expression.
     *
     * @return a string representation of this expression
     */
    public final String toString() {
        StringBuffer result = new StringBuffer();
        result.append('(');
        result.append(identifier().toString());
        result.append(" like '");
        result.append(_pattern);
        result.append('\'');
        if (_escape != null) {
            result.append(" escape '");
            result.append(_escape);
            result.append('\'');
        }
        result.append(')');
        return result.toString();
    }

    /**
     * Converts the pattern and escape to an ORO <code>Pattern</code>
     *
     * @param pattern the pattern
     * @param escape the escape character. May be null
     * @return an ORO <code>Pattern</code> corresponding to
     * <code>pattern</code> and <code>escape</code>
     * @throws SelectorException if <code>pattern</code> or <code>escape</code>
     * are invalid
     */
    private Pattern getRegexp(final String pattern, final String escape)
        throws SelectorException {
        Pattern result = null;
        Character esc = null;

        if (escape != null) {
            if (escape.length() != 1) {
                throw new SelectorException("Invalid escape: " + escape);
            }
            esc = new Character(escape.charAt(0));
        }

        try {
            result = RegexpFactory.create(pattern, esc);
        } catch (InvalidRegexpException err) {
            throw new SelectorException("Invalid pattern: " + pattern);
        }
        return result;
    }

} //-- LikeExpression