formatparser.java

swing编写的库存管理程序。毕业设计类

/**
 * ========================================
 * JFreeReport : a free Java report library
 * ========================================
 *
 * Project Info:  http://www.jfree.org/jfreereport/index.html
 * Project Lead:  Thomas Morgner;
 *
 * (C) Copyright 2000-2002, by Simba Management Limited and Contributors.
 *
 * This library is free software; you can redistribute it and/or modify it under the terms
 * of the GNU Lesser General Public License as published by the Free Software Foundation;
 * either version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License along with this
 * library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 * -----------------
 * FormatParser.java
 * -----------------
 * (C)opyright 2000-2002, by Simba Management Limited.
 *
 * $Id: FormatParser.java,v 1.2 2003/08/24 15:13:22 taqua Exp $
 *
 * Changes
 * -------
 * 20-May-2002 : Initial version
 * 06-Jun-2002 : Updated Javadoc comments
 * 08-Jun-2002 : added isValidOutput for skipping the parsing when a valid (parsed) value is
 *               already read from the assigned datasource.
 * 03-Jul-2002 : Cloneable implemented
 */
package org.jfree.report.filter;

import java.io.Serializable;
import java.text.Format;
import java.text.ParseException;

/**
 * A format parser tries to parse a string into an object. If the value returned by the
 * datasource is no string, a string is formed using String.valueOf (Object). This string
 * is fed into the java.text.Format of this FormatParser and the parsed object is returned.
 * <p>
 * What class of object is returned, is determined by the given format. If parsing failed,
 * the defined NullValue is returned.
 *
 * @author Thomas Morgner
 */
public class FormatParser implements DataFilter, Serializable
{
  /** The format used to create the string representation of the data. */
  private Format format;

  /** The datasource from where the data is obtained. */
  private DataSource datasource;

  /** The object used to represent null. */
  private Object nullvalue;

  /**
   * DefaultConstructor.
   */
  public FormatParser()
  {
  }

  /**
   * Sets the format for the filter.
   *
   * @param format The format.
   * @throws NullPointerException if the given format is null
   */
  public void setFormatter(final Format format)
  {
    if (format == null)
    {
      throw new NullPointerException();
    }
    this.format = format;
  }

  /**
   * Returns the format for the filter.
   *
   * @return The format.
   */
  public Format getFormatter()
  {
    return this.format;
  }

  /**
   * Returns the parsed object. The value is read using the data source given
   * and parsed using the formatter of this object. The parsing is guaranteed to
   * completly form the target object or to return the defined NullValue.
   * <p>
   * If the given datasource does not return a string, the returned object is
   * transformed into a string using String.valueOf (Object) and then parsed.
   * <p>
   * If format, datasource or object are null, the NullValue is returned.
   *
   * @return The formatted value.
   */
  public Object getValue()
  {
    final Format f = getFormatter();
    if (f == null)
    {
      return getNullValue();
    }

    final DataSource ds = getDataSource();
    if (ds == null)
    {
      return getNullValue();
    }

    final Object o = ds.getValue();
    if (o == null)
    {
      return getNullValue();
    }

    if (isValidOutput(o))
    {
      return o;
    }

    try
    {
      return f.parseObject(String.valueOf(o));
    }
    catch (ParseException e)
    {
      return null;
    }
  }

  /**
   * Checks whether the given value is already a valid result. IF the datasource already returned
   * a valid value, and no parsing is required, a parser can skip the parsing process by returning
   * true in this function.
   *
   * @param o  the object to parse.
   *
   * @return false as this class does not know anything about the format of input or result objects.
   */
  protected boolean isValidOutput(final Object o)
  {
    return false;
  }

  /**
   * Returns the data source for the filter.
   *
   * @return The data source.
   */
  public DataSource getDataSource()
  {
    return datasource;
  }

  /**
   * Sets the data source.
   *
   * @param ds The data source.
   */
  public void setDataSource(final DataSource ds)
  {
    if (ds == null)
    {
      throw new NullPointerException();
    }
    this.datasource = ds;
  }

  /**
   * Sets the value that will be displayed if the data source supplies a null value.
   * The nullValue itself can be null to cover the case when no reasonable default value
   * can be defined.
   *
   * @param nullvalue The value returned when the parsing failed.
   */
  public void setNullValue(final Object nullvalue)
  {
    this.nullvalue = nullvalue;
  }

  /**
   * Returns the object representing a null value from the data source. This value will
   * also be returned when parsing failed or no parser or datasource is set at all.
   *
   * @return The value returned when the parsing failed.
   */
  public Object getNullValue()
  {
    return nullvalue;
  }

  /**
   * Clones the parser.
   *
   * @return a clone.
   *
   * @throws CloneNotSupportedException this should never happen.
   */
  public Object clone() throws CloneNotSupportedException
  {
    final FormatParser p = (FormatParser) super.clone();
    if (datasource != null)
    {
      p.datasource = (DataSource) datasource.clone();
    }
    if (format != null)
    {
      p.format = (Format) format.clone();
    }
    return p;
  }

}