typemapper.java

OpenJMS是一个开源的Java Message Service API 1.0.2 规范的实现,它包含有以下特性： *. 它既支持点到点（point-to-point）（PTP）模型和发布/订

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 * Copyright 2001-2005 (C) Exoffice Technologies Inc. All Rights Reserved.
 *
 * $Id: TypeMapper.java,v 1.2 2005/09/04 07:17:05 tanderson Exp $
 */
package org.exolab.jms.tools.db;

import java.sql.Types;
import java.util.HashMap;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;


/**
 * A helper class for mapping between SQL types.
 * <p/>
 * NOTE: this mapping is not complete, only reflecting those types required
 * by OpenJMS
 *
 * @version     $Revision: 1.2 $ $Date: 2005/09/04 07:17:05 $
 * @author      <a href="mailto:[e-mail]">Tim Anderson</a>
 */
class TypeMapper {

    /**
     * The set of types supported by the RDBMS.
     */
    private final TypeSet _set;

    /**
     * A mapping of SQL type identifiers to their corresponding alternative
     * types. The alternatives are represented as an array of Type
     */
    private final HashMap _mappings = new HashMap();

    /**
     * The logger.
     */
    private static final Log _log = LogFactory.getLog(TypeMapper.class);


    /**
     * Construct the type mapper with the set of types supported by the
     * RDBMS.
     */
    public TypeMapper(TypeSet set) {
        _set = set;

        // alternatives for the Types.BINARY type
        Type[] binaries = {new Type(Types.VARBINARY, 0, true),
                           new Type(Types.LONGVARBINARY, 0, true)};
        add(Types.BINARY, binaries);

        // alternatives for the Types.VARBINARY type
        Type[] varbinaries = {new Type(Types.LONGVARBINARY, 0, true)};
        add(Types.VARBINARY, varbinaries);

        // alternatives for the Types.BIT type
        Type[] bits = {new Type(Types.CHAR, 0, false),
                       new Type(Types.TINYINT, 0, false),
                       new Type(Types.SMALLINT, 0, false),
                       new Type(Types.INTEGER, 0, false),
                       new Type(Types.NUMERIC, 1, true)};
        add(Types.BIT, bits);

        // alternatives for the Types.TINYINT type
        Type[] tinyints = {new Type(Types.SMALLINT, 0, false),
                           new Type(Types.INTEGER, 0, false),
                           new Type(Types.NUMERIC, 0, true)};
        add(Types.TINYINT, tinyints);

        // alternatives for the Types.DECIMAL type
        Type[] decimals = {new Type(Types.NUMERIC, 0, false)};
        add(Types.DECIMAL, decimals);

        // alternatives for the Types.DATE type
        Type[] dates = {new Type(Types.TIMESTAMP, 0, false)};
        add(Types.DATE, dates);

        // alternatives for the Types.BIGINT type
        long precision = Long.toString(Long.MAX_VALUE).length();
        Type[] bigints = {new Type(Types.NUMERIC, precision, true)};
        add(Types.BIGINT, bigints);
    }

    public Type getType(int type, long precision) {
        // check if type set supports the requested type directly
        Type result = _set.getType(type, precision);
        if (result == null) {
            // type not supported so return the mapping, if one is available
            result = (Type) _mappings.get(new Integer(type));
        }
        return result;
    }

    private void add(int type, Type[] mappings) {
        for (int i = 0; i < mappings.length; ++i) {
            Type requested = mappings[i];
            Type supported = _set.getType(requested.getType(),
                requested.getPrecision());
            if (supported == null) {
                _log.debug(
                    "TypeMapper: alternative mapping for type=" +
                    Descriptor.getDescriptor(type).getName() +
                    " is not supported by the database");
            } else {
                long precision = requested.getPrecision();
                long maxPrecision = supported.getPrecision();
                _log.debug(
                    "TypeMapper: alternative mapping for type=" +
                    Descriptor.getDescriptor(type).getName() +
                    ", precision=" + precision +
                    ", is supported by the database as " + supported);
                if (type == supported.getType() &&
                    ((precision > 0) && (precision < maxPrecision))) {
                    // if the requested type is supported by the database, and
                    // has a smaller precision, override the maximum precision
                    // defined by the supported type
                    supported = new Type(
                        supported.getType(), supported.getName(),
                        precision, supported.getParameters());
                }
                _mappings.put(new Integer(type), supported);
                break;
            }
        }
    }

}