literal.java

实现了Jms的服务器源码,支持多种适配器,DB,FTP,支持多种数据库

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 */

package org.exolab.jms.selector;

import javax.jms.Message;


/**
 * This class implements a literal expression.
 *
 * @version     $Revision: 1.8 $ $Date: 2003/08/09 15:49:50 $
 * @author      <a href="mailto:[e-mail]">Tim Anderson</a>
 * @see         Expression
 */
class Literal implements Expression {

    /**
     * The literal value
     */
    private SObject _value = null;

    /**
     * Construct a new <code>Literal</code> expression
     *
     * @param value the value of the literal
     */
    protected Literal(final SObject value) {
        _value = value;
    }

    /**
     * Construct an approximate numeric literal expression
     *
     * @param text the literal text
     * @return an approximate numeric literal expression
     * @throws SelectorException if <code>text</code> is not a valid
     * approximate numeric literal
     */
    public static Literal approxNumericLiteral(final String text)
        throws SelectorException {
        SDouble value = null;
        try {
            value = new SDouble(Double.parseDouble(text));
        } catch (NumberFormatException exception) {
            throw new SelectorException("invalid float: " + text);
        }
        return new Literal(value);
    }

    /**
     * Construct an exact numeric literal expression
     *
     * @param text the literal text
     * @return an exact numeric literal expression
     * @throws SelectorException if <code>text</code> is not a valid exact
     * numeric literal
     */
    public static Literal exactNumericLiteral(final String text)
        throws SelectorException {
        SLong value = null;
        try {
            value = new SLong(Long.decode(text).longValue());
        } catch (NumberFormatException exception) {
            throw new SelectorException("invalid integer: " + text);
        }
        return new Literal(value);
    }

    /**
     * Construct a string literal expression
     *
     * @param text the literal text
     * @return a string literal expression
     */
    public static Literal stringLiteral(final String text) {
        return new Literal(new SString(text)) {

            public final String toString() {
                return "'" + this.getValue().toString() + "'";
            }
        };
    }

    /**
     * Construct a boolean literal expression
     *
     * @param value the boolean literal value
     * @return a boolean literal expression
     */
    public static Literal booleanLiteral(final boolean value) {
        SBool bool = SBool.FALSE;
        if (value) {
            bool = SBool.TRUE;
        }
        return new Literal(bool);
    }

    /**
     * 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
     */
    public final SObject evaluate(final Message msg) {
        return _value;
    }

    /**
     * Return a string representation of the literal
     *
     * @return a string representation of the literal
     */
    public String toString() {
        return getValue().toString();
    }

    /**
     * Returns the value of the literal
     *
     * @return the value of the literal
     */
    protected final SObject getValue() {
        return _value;
    }

} //-- Literal