Implement a minimal SimpleDateFormat

For the moment, this class can only handle dates of the form
"yyyy-MM-dd'T'HH:mm:ss".

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

classpath/java/text/SimpleDateFormat.java

@@ -0,0 +1,98 @@
+/* Copyright (c) 2008-2013, Avian Contributors
+
+   Permission to use, copy, modify, and/or distribute this software
+   for any purpose with or without fee is hereby granted, provided
+   that the above copyright notice and this permission notice appear
+   in all copies.
+
+   There is NO WARRANTY for this software.  See license.txt for
+   details. */
+
+package java.text;
+
+import java.util.Calendar;
+import java.util.Date;
+
+public class SimpleDateFormat {
+  private String pattern;
+
+  public SimpleDateFormat(String pattern) {
+    this.pattern = pattern;
+    if (! "yyyy-MM-dd'T'HH:mm:ss".equals(pattern)) {
+      throw new UnsupportedOperationException("Unsupported pattern: " + pattern);
+    }
+  }
+
+  public StringBuffer format(Date date, StringBuffer buffer, FieldPosition position) {
+    Calendar calendar = Calendar.getInstance();
+    calendar.setTime(date);
+    pad(buffer, calendar.get(Calendar.YEAR), 4);
+    buffer.append('-');
+    pad(buffer, calendar.get(Calendar.MONTH) + 1, 2);
+    buffer.append('-');
+    pad(buffer, calendar.get(Calendar.DAY_OF_MONTH), 2);
+    buffer.append("T");
+    pad(buffer, calendar.get(Calendar.HOUR_OF_DAY), 2);
+    buffer.append(':');
+    pad(buffer, calendar.get(Calendar.MINUTE), 2);
+    buffer.append(':');
+    pad(buffer, calendar.get(Calendar.SECOND), 2);
+    return buffer;
+  }
+
+  public Date parse(String text) {
+    return parse(text, new ParsePosition(0));
+  }
+
+  public Date parse(String text, ParsePosition position) {
+    int index = position.getIndex();
+    try {
+      Calendar calendar = Calendar.getInstance();
+      index = parseField(text, index, 4, calendar, Calendar.YEAR, 0);
+      index = expectPrefix(text, index, "-");
+      index = parseField(text, index, 2, calendar, Calendar.MONTH, -1);
+      index = expectPrefix(text, index, "-");
+      index = parseField(text, index, 2, calendar, Calendar.DAY_OF_MONTH, 0);
+      index = expectPrefix(text, index, "T");
+      index = parseField(text, index, 2, calendar, Calendar.HOUR_OF_DAY, 0);
+      index = expectPrefix(text, index, ":");
+      index = parseField(text, index, 2, calendar, Calendar.MINUTE, 0);
+      index = expectPrefix(text, index, ":");
+      index = parseField(text, index, 2, calendar, Calendar.SECOND, 0);
+      position.setIndex(index);
+      return calendar.getTime();
+    } catch (ParseException e) {
+      position.setErrorIndex(index);
+      return null;
+    }
+  }
+
+  private static void pad(StringBuffer buffer, int value, int digits) {
+    int i = value == 0 ? 1 : value;
+    while (i > 0) {
+      i /= 10;
+      --digits;
+    }
+    while (digits-- > 0) {
+      buffer.append('0');
+    }
+    buffer.append(value);
+  }
+
+  private static int parseField(String text, int offset, int length, Calendar calendar, int field, int adjustment) throws ParseException {
+    if (text.length() < offset + length) throw new ParseException("Short date: " + text, offset);
+    try {
+      int value = Integer.parseInt(text.substring(offset, offset + length), 10);
+      calendar.set(field, value + adjustment);
+    } catch (NumberFormatException e) {
+      throw new ParseException("Not a number: " + text, offset);
+    }
+    return offset + length;
+  }
+
+  private static int expectPrefix(String text, int offset, String prefix) throws ParseException {
+    if (text.length() <= offset) throw new ParseException("Short date: " + text, offset);
+    if (! text.substring(offset).startsWith(prefix)) throw new ParseException("Parse error: " + text, offset);
+    return offset + prefix.length();
+  }
+}