Add support for converting to/from SYSTEMTIME dates

git-svn-id: https://svn.apache.org/repos/asf/jakarta/poi/trunk@381143 13f79535-47bb-0310-9956-ffa450edef68

diff --git a/src/scratchpad/src/org/apache/poi/hslf/util/SystemTimeUtils.java b/src/scratchpad/src/org/apache/poi/hslf/util/SystemTimeUtils.java
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+++ b/src/scratchpad/src/org/apache/poi/hslf/util/SystemTimeUtils.java
@@ -0,0 +1,88 @@
+/* ====================================================================
+   Copyright 2002-2004   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.poi.hslf.util;
+
+import java.util.Calendar;
+import java.util.Date;
+import java.util.GregorianCalendar;
+
+import org.apache.poi.util.LittleEndian;
+
+/**
+ * A helper class for dealing with SystemTime Structs, as defined at
+ * http://msdn.microsoft.com/library/en-us/sysinfo/base/systemtime_str.asp .
+ * 
+ * Discrepancies between Calendar and SYSTEMTIME:
+ *  - that January = 1 in SYSTEMTIME, 0 in Calendar.
+ *  - that the day of the week (0) starts on Sunday in SYSTEMTIME, and Monday in Calendar
+ * It is also the case that this does not store the timezone, and no... it is not
+ * stored as UTC either, but rather the local system time (yuck.)
+ *
+ * @author Daniel Noll
+ * @author Nick Burch
+ */
+public class SystemTimeUtils {
+       /**
+        * Get the date found in the byte array, as a java Data object
+        */
+       public static Date getDate(byte[] data) {
+               return getDate(data,0);
+       }
+       /**
+        * Get the date found in the byte array, as a java Data object
+        */
+       public static Date getDate(byte[] data, int offset) {
+        Calendar cal = new GregorianCalendar();
+        
+        cal.set(Calendar.YEAR,         LittleEndian.getShort(data,offset));
+        cal.set(Calendar.MONTH,        LittleEndian.getShort(data,offset+2)-1);
+        // Not actually needed 0 - can be found from day of month 
+        //cal.set(Calendar.DAY_OF_WEEK,  LittleEndian.getShort(data,offset+4)+1);
+        cal.set(Calendar.DAY_OF_MONTH, LittleEndian.getShort(data,offset+6));
+        cal.set(Calendar.HOUR,         LittleEndian.getShort(data,offset+8));
+        cal.set(Calendar.MINUTE,       LittleEndian.getShort(data,offset+10));
+        cal.set(Calendar.SECOND,       LittleEndian.getShort(data,offset+12));
+        cal.set(Calendar.MILLISECOND,  LittleEndian.getShort(data,offset+14));
+
+        return cal.getTime();
+       }
+       
+       /**
+        * Convert the supplied java Date into a SystemTime struct, and write it
+        *  into the supplied byte array. 
+        */
+       public static void storeDate(Date date, byte[] dest) {
+               storeDate(date, dest, 0);
+       }
+       /**
+        * Convert the supplied java Date into a SystemTime struct, and write it
+        *  into the supplied byte array. 
+        */
+       public static void storeDate(Date date, byte[] dest, int offset) {
+        Calendar cal = new GregorianCalendar();
+        cal.setTime(date);
+
+        LittleEndian.putShort(dest, offset + 0, (short) cal.get(Calendar.YEAR));
+        LittleEndian.putShort(dest, offset + 2, (short)(cal.get(Calendar.MONTH) + 1));
+        LittleEndian.putShort(dest, offset + 4, (short)(cal.get(Calendar.DAY_OF_WEEK)-1));
+        LittleEndian.putShort(dest, offset + 6, (short) cal.get(Calendar.DAY_OF_MONTH));
+        LittleEndian.putShort(dest, offset + 8, (short) cal.get(Calendar.HOUR));
+        LittleEndian.putShort(dest, offset + 10,(short) cal.get(Calendar.MINUTE));
+        LittleEndian.putShort(dest, offset + 12,(short) cal.get(Calendar.SECOND));
+        LittleEndian.putShort(dest, offset + 14,(short) cal.get(Calendar.MILLISECOND));
+       }
+}