abstractarrayconverter.java

apache beanutils开源项目源码

/*
 * Copyright 2001-2004 The Apache Software Foundation.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */ 


package org.apache.commons.beanutils.converters;


import java.io.IOException;
import java.io.StreamTokenizer;
import java.io.StringReader;
import java.util.ArrayList;
import java.util.List;
import org.apache.commons.beanutils.ConversionException;
import org.apache.commons.beanutils.Converter;



/**
 * <p>Convenience base class for converters that translate the String
 * representation of an array into a corresponding array of primitives
 * object.  This class encapsulates the functionality required to parse
 * the String into a list of String elements that can later be
 * individually converted to the appropriate primitive type.</p>
 *
 * <p>The input syntax accepted by the <code>parseElements()</code> method
 * is designed to be compatible with the syntax used to initialize arrays
 * in a Java source program, except that only String literal values are
 * supported.  For maximum flexibility, the surrounding '{' and '}'
 * characters are optional, and individual elements may be separated by
 * any combination of whitespace and comma characters.</p>
 *
 * @author Craig R. McClanahan
 * @version $Revision: 1.6 $ $Date: 2004/02/28 13:18:34 $
 * @since 1.4
 */

public abstract class AbstractArrayConverter implements Converter {


    // ----------------------------------------------------- Instance Variables


    /**
     * The default value specified to our Constructor, if any.
     */
    protected Object defaultValue = null;


    /**
     * <p>Model object for string arrays.</p>
     */
    protected static String strings[] = new String[0];


    /**
     * Should we return the default value on conversion errors?
     */
    protected boolean useDefault = true;


    // --------------------------------------------------------- Public Methods


    /**
     * Convert the specified input object into an output object of the
     * specified type.  This method must be implemented by a concrete
     * subclass.
     *
     * @param type Data type to which this value should be converted
     * @param value The input value to be converted
     *
     * @exception ConversionException if conversion cannot be performed
     *  successfully
     */
    public abstract Object convert(Class type, Object value);


    // ------------------------------------------------------ Protected Methods


    /**
     * <p>Parse an incoming String of the form similar to an array initializer
     * in the Java language into a <code>List</code> individual Strings
     * for each element, according to the following rules.</p>
     * <ul>
     * <li>The string must have matching '{' and '}' delimiters around
     *     a comma-delimited list of values.</li>
     * <li>Whitespace before and after each element is stripped.
     * <li>If an element is itself delimited by matching single or double
     *     quotes, the usual rules for interpreting a quoted String apply.</li>
     * </ul>
     *
     * @param svalue String value to be parsed
     *
     * @exception ConversionException if the syntax of <code>svalue</code>
     *  is not syntactically valid
     * @exception NullPointerException if <code>svalue</code>
     *  is <code>null</code>
     */
    protected List parseElements(String svalue) {

        // Validate the passed argument
        if (svalue == null) {
            throw new NullPointerException();
        }

        // Trim any matching '{' and '}' delimiters
        svalue = svalue.trim();
        if (svalue.startsWith("{") && svalue.endsWith("}")) {
            svalue = svalue.substring(1, svalue.length() - 1);
        }

        try {

            // Set up a StreamTokenizer on the characters in this String
            StreamTokenizer st =
                new StreamTokenizer(new StringReader(svalue));
            st.whitespaceChars(',',','); // Commas are delimiters
            st.ordinaryChars('0', '9');  // Needed to turn off numeric flag
            st.ordinaryChars('.', '.');
            st.ordinaryChars('-', '-');
            st.wordChars('0', '9');      // Needed to make part of tokens
            st.wordChars('.', '.');
            st.wordChars('-', '-');

            // Split comma-delimited tokens into a List
            ArrayList list = new ArrayList();
            while (true) {
                int ttype = st.nextToken();
                if ((ttype == StreamTokenizer.TT_WORD) ||
                    (ttype > 0)) {
                    list.add(st.sval);
                } else if (ttype == StreamTokenizer.TT_EOF) {
                    break;
                } else {
                    throw new ConversionException
                        ("Encountered token of type " + ttype);
                }
            }

            // Return the completed list
            return (list);

        } catch (IOException e) {

            throw new ConversionException(e);

        }



    }


}