[Objectlabkit-svn] SF.net SVN: objectlabkit: [73] trunk/datecalc-jdk/src/main/java/net/ objectlab/kit/datecalc/jdk/ExcelDateUtil.java

[<be...@us...>]

Revision: 73
          http://svn.sourceforge.net/objectlabkit/?rev=73&view=rev
Author:   benoitx
Date:     2006-09-01 07:39:54 -0700 (Fri, 01 Sep 2006)

Log Message:
-----------
Added Excel converter to Java Date.

Added Paths:
-----------
    trunk/datecalc-jdk/src/main/java/net/objectlab/kit/datecalc/jdk/ExcelDateUtil.java

Added: trunk/datecalc-jdk/src/main/java/net/objectlab/kit/datecalc/jdk/ExcelDateUtil.java
===================================================================
--- trunk/datecalc-jdk/src/main/java/net/objectlab/kit/datecalc/jdk/ExcelDateUtil.java	                        (rev 0)
+++ trunk/datecalc-jdk/src/main/java/net/objectlab/kit/datecalc/jdk/ExcelDateUtil.java	2006-09-01 14:39:54 UTC (rev 73)
@@ -0,0 +1,93 @@
+/*
+ * $Id$
+ * 
+ * Copyright 2006 the original author or authors.
+ *
+ * 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 net.objectlab.kit.datecalc.jdk;
+
+import java.util.Date;
+import java.util.GregorianCalendar;
+
+/**
+ * Convert Excel Date to Java Date.
+ * @author Benoit Xhenseval
+ * @author $LastChangedBy$
+ * @version $Revision$ $Date$
+ *
+ */
+public final class ExcelDateUtil {
+    private ExcelDateUtil() {}
+    
+    private static final long DAY_MILLISECONDS = 24 * 60 * 60 * 1000;
+
+    /**
+     * Given an Excel date with either 1900 or 1904 date windowing, converts it
+     * to a java.util.Date.
+     * 
+     * NOTE: If the default <code>TimeZone</code> in Java uses Daylight Saving
+     * Time then the conversion back to an Excel date may not give the same
+     * value, that is the comparison <CODE>excelDate ==
+     * getExcelDate(getJavaDate(excelDate,false))</CODE> is not always true.
+     * For example if default timezone is <code>Europe/Copenhagen</code>, on
+     * 2004-03-28 the minute after 01:59 CET is 03:00 CEST, if the excel date
+     * represents a time between 02:00 and 03:00 then it is converted to past
+     * 03:00 summer time
+     * 
+     * @param date
+     *            The Excel date.
+     * @param use1904windowing
+     *            true if date uses 1904 windowing, or false if using 1900 date
+     *            windowing.
+     * @return Java representation of the date, or null if date is not a valid
+     *         Excel date
+     * @see java.util.TimeZone
+     */
+    public static Date getJavaDate(double date, boolean use1904windowing) {
+        if (isValidExcelDate(date)) {
+            int startYear = 1900;
+            int dayAdjust = -1; // Excel thinks 2/29/1900 is a valid date, which
+            // it isn't
+            int wholeDays = (int) Math.floor(date);
+            if (use1904windowing) {
+                startYear = 1904;
+                dayAdjust = 1; // 1904 date windowing uses 1/2/1904 as the
+                // first day
+            } else if (wholeDays < 61) {
+                // Date is prior to 3/1/1900, so adjust because Excel thinks
+                // 2/29/1900 exists
+                // If Excel date == 2/29/1900, will become 3/1/1900 in Java
+                // representation
+                dayAdjust = 0;
+            }
+            GregorianCalendar calendar = new GregorianCalendar(startYear, 0, wholeDays + dayAdjust);
+            int millisecondsInDay = (int) ((date - Math.floor(date)) * (double) DAY_MILLISECONDS + 0.5);
+            calendar.set(GregorianCalendar.MILLISECOND, millisecondsInDay);
+            return calendar.getTime();
+        } else {
+            return null;
+        }
+    }
+
+    /**
+     * Given a double, checks if it is a valid Excel date.
+     * 
+     * @return true if valid
+     * @param value
+     *            the double value
+     */
+    public static boolean isValidExcelDate(double value) {
+        return (value > -Double.MIN_VALUE);
+    }
+}


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