typecaster.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;


/**
 * Utility class for casting from an SObject to a derived class,
 * raising a TypeMismatchException if the operation is invalid.
 *
 * @version     $Revision: 1.4 $ $Date: 2003/08/09 15:49:50 $
 * @author      <a href="mailto:[e-mail]">Tim Anderson</a>
 * @see         Expression
 * @see         SBool
 * @see         SNumber
 * @see         SString
 * @see         TypeMismatchException
 */
final class TypeCaster {

    /**
     * Private constructor
     */
    private TypeCaster() {
    }

    /**
     * Cast an object to boolean
     *
     * @param obj the object to cast
     * @param context the context where the object was created
     * @return the cast object
     * @throws TypeMismatchException if <code>obj</code> can't be cast
     */
    public static SBool castToBool(final SObject obj, final String context)
        throws TypeMismatchException {

        SBool result = null;
        if (obj instanceof SBool) {
            result = (SBool) obj;
        } else if (obj != null) {
            typeMismatch(Type.BOOLEAN, obj, context);
        }
        return result;
    }

    /**
     * Cast an object to numeric
     *
     * @param obj the object to cast
     * @param context the context where the object was created
     * @return the cast object
     * @throws TypeMismatchException if <code>obj</code> can't be cast
     */
    public static SNumber castToNumber(final SObject obj, final String context)
        throws TypeMismatchException {

        SNumber result = null;
        if (obj instanceof SNumber) {
            result = (SNumber) obj;
        } else if (obj != null) {
            typeMismatch(Type.NUMERIC, obj, context);
        }
        return result;
    }

    /**
     * Cast an object to string
     *
     * @param obj the object to cast
     * @param context the context where the object was created
     * @return the cast object
     * @throws TypeMismatchException if <code>obj</code> can't be cast
     */
    public static SString castToString(final SObject obj, final String context)
        throws TypeMismatchException {

        SString result = null;
        if (obj instanceof SString) {
            result = (SString) obj;
        } else if (obj != null) {
            typeMismatch(Type.STRING, obj, context);
        }
        return result;
    }

    /**
     * Raises a type mismatch exception
     *
     * @param expected the expected type
     * @param value the actual value
     * @param context the context where <code>value</code> was created
     * @throws TypeMismatchException corresponding to the expected and actual
     * values
     */
    private static void typeMismatch(final Type expected, final SObject value,
                                     final String context)
        throws TypeMismatchException {

        StringBuffer msg = new StringBuffer();
        msg.append("expecting a ");
        msg.append(expected);
        msg.append(" expression");
        if (context != null) {
            msg.append(" for ");
            msg.append(context);
        }
        msg.append(", found a ");
        msg.append(value.type());
        throw new TypeMismatchException(msg.toString());
    }

} //-- TypeCaster