Added TemporalAdjuster for rounding to nearest part of an hour

src/main/java/org/threeten/extra/RoundingMode.java

@@ -0,0 +1,17 @@
+package org.threeten.extra;
+
+/**
+ * A time clock rounding mode.
+ * <p>
+ * {@code RoundingMode} specifies a time clock rounding strategy.
+ * <p>
+ * Rounding mode defines the following strategies:
+ * <li> DOWN - rounds the time towards the start of a fraction
+ * <li> HALF_UP - rounds towards the "nearest neighbor". UP, if the distance is of equal length
+ * <li> UP - rounds the time towards the end of a fraction
+ */
+public enum RoundingMode {
+    DOWN,
+    HALF_UP,
+    UP
+}

src/main/java/org/threeten/extra/Temporals.java

@@ -32,12 +32,16 @@
 package org.threeten.extra;
 
 import static java.time.temporal.ChronoField.DAY_OF_WEEK;
+import static java.time.temporal.ChronoField.MINUTE_OF_HOUR;
+import static java.time.temporal.ChronoField.SECOND_OF_MINUTE;
+import static java.time.temporal.ChronoField.NANO_OF_SECOND;
 import static java.time.temporal.ChronoUnit.DAYS;
 import static java.time.temporal.ChronoUnit.ERAS;
 import static java.time.temporal.ChronoUnit.FOREVER;
 import static java.time.temporal.ChronoUnit.WEEKS;
 
 import java.text.ParsePosition;
+import java.time.Duration;
 import java.time.DateTimeException;
 import java.time.format.DateTimeFormatter;
 import java.time.format.DateTimeParseException;
@@ -59,6 +63,7 @@
  * <li>adjusters that ignore Saturday/Sunday weekends
  * <li>conversion between {@code TimeUnit} and {@code ChronoUnit}
  * <li>converting an amount to another unit
+ * <li>adjusters that round time
  * </ul>
  *
  * <h3>Implementation Requirements:</h3>
@@ -126,6 +131,66 @@ public static TemporalAdjuster previousWorkingDayOrSame() {
         return Adjuster.PREVIOUS_WORKING_OR_SAME;
     }
 
+    /**
+     * Returns an adjuster that offers time clock rounding.
+     * <p>
+     * Time clock rounding divides the minutes of the hour into equal fractions of the same length. Every fraction has
+     * a start-inclusive and end-exclusive minute of the hour. A rounded result is either at the lower or upper end of
+     * one of these fractions.
+     * <p>
+     * Time clock rounding views time as hour-minute. Therefore it always truncates to minutes.
+     *
+     * @param duration  the fraction of the hour, must be a divisor of 60
+     * @param roundingMode  the time clock rounding mode
+     * @return time rounded to a fraction of the hour
+     */
+    public static TemporalAdjuster roundTime(Duration duration, RoundingMode roundingMode) {
+        Objects.requireNonNull(duration, "duration");
+        Objects.requireNonNull(roundingMode, "mode");
+
+        long minutes = duration.toMinutes();
+        if (minutes < 1 || 60 % minutes != 0) {
+            throw new DateTimeException("duration is not a divisor of 60");
+        }
+
+        int divisor = (int) minutes;
+
+        return temporal -> {
+            int minuteOfHour = temporal.get(MINUTE_OF_HOUR);
+
+            temporal = temporal.with(SECOND_OF_MINUTE, 0)
+                               .with(NANO_OF_SECOND, 0);
+
+            if (minuteOfHour % divisor == 0) {
+                return temporal;
+            }
+
+            int down = minuteOfHour / divisor * divisor;
+            int up = down + divisor;
+            RoundingMode mode = roundingMode;
+
+            if (roundingMode == RoundingMode.HALF_UP) {
+                mode = (minuteOfHour - down) < (up - minuteOfHour) ? RoundingMode.DOWN : RoundingMode.UP;
+            }
+
+            if (mode == RoundingMode.DOWN) {
+                temporal = temporal.with(MINUTE_OF_HOUR, down);
+            }
+
+            if (mode == RoundingMode.UP) {
+                if (up == 60) {
+                    if (temporal.isSupported(ChronoUnit.HOURS)) {
+                        temporal = temporal.plus(1, ChronoUnit.HOURS);
+                    }
+                    up = 0;
+                }
+                temporal = temporal.with(MINUTE_OF_HOUR, up);
+            }
+
+            return temporal;
+        };
+    }
+
     //-----------------------------------------------------------------------
     /**
      * Enum implementing the adjusters.

src/test/java/org/threeten/extra/TestTemporals.java

@@ -65,7 +65,9 @@
 import java.io.ObjectOutputStream;
 import java.io.Serializable;
 import java.time.DateTimeException;
+import java.time.LocalTime;
 import java.time.LocalDate;
+import java.time.Duration;
 import java.time.Month;
 import java.time.format.DateTimeFormatter;
 import java.time.format.DateTimeParseException;
@@ -670,4 +672,53 @@ public void test_convertAmountInvalidUnsupported(TemporalUnit fromUnit, Temporal
         assertThrows(UnsupportedTemporalTypeException.class, () -> Temporals.convertAmount(1, fromUnit, resultUnit));
     }
 
+
+    //-----------------------------------------------------------------------
+    // roundTime()
+    //-----------------------------------------------------------------------
+    @Test
+    public void test_roundTime_dateTimeException() {
+        assertThrows(DateTimeException.class, () -> Temporals.roundTime(Duration.ofMinutes(7), RoundingMode.DOWN));
+    }
+
+    @Test
+    public void test_roundTime_down_localTime() {
+        TemporalAdjuster down = Temporals.roundTime(Duration.ofMinutes(6), RoundingMode.DOWN);
+
+        assertEquals(LocalTime.of(14, 12), LocalTime.of(14, 12).with(down));
+        assertEquals(LocalTime.of(14, 12), LocalTime.of(14, 13).with(down));
+        assertEquals(LocalTime.of(14, 12), LocalTime.of(14, 14).with(down));
+        assertEquals(LocalTime.of(14, 12), LocalTime.of(14, 15).with(down));
+        assertEquals(LocalTime.of(14, 12), LocalTime.of(14, 16).with(down));
+        assertEquals(LocalTime.of(14, 12), LocalTime.of(14, 17).with(down));
+        assertEquals(LocalTime.of(14, 18), LocalTime.of(14, 18).with(down));
+
+    }
+
+    @Test
+    public void test_roundTime_up_localTime() {
+        TemporalAdjuster up = Temporals.roundTime(Duration.ofMinutes(6), RoundingMode.UP);
+
+        assertEquals(LocalTime.of(14, 12), LocalTime.of(14, 12, 7, 1).with(up));
+        assertEquals(LocalTime.of(14, 18), LocalTime.of(14, 13, 7, 1).with(up));
+        assertEquals(LocalTime.of(14, 18), LocalTime.of(14, 14).with(up));
+        assertEquals(LocalTime.of(14, 18), LocalTime.of(14, 15).with(up));
+        assertEquals(LocalTime.of(14, 18), LocalTime.of(14, 16).with(up));
+        assertEquals(LocalTime.of(14, 18), LocalTime.of(14, 17).with(up));
+        assertEquals(LocalTime.of(14, 18), LocalTime.of(14, 18).with(up));
+    }
+
+    @Test
+    public void test_roundTime_halfUp_localTime() {
+        TemporalAdjuster halfUp = Temporals.roundTime(Duration.ofMinutes(6), RoundingMode.HALF_UP);
+
+        assertEquals(LocalTime.of(14, 54), LocalTime.of(14, 54, 7, 1).with(halfUp));
+        assertEquals(LocalTime.of(14, 54), LocalTime.of(14, 55, 7, 1).with(halfUp));
+        assertEquals(LocalTime.of(14, 54), LocalTime.of(14, 56).with(halfUp));
+        assertEquals(LocalTime.of(15, 0), LocalTime.of(14, 57).with(halfUp));
+        assertEquals(LocalTime.of(15, 0), LocalTime.of(14, 58).with(halfUp));
+        assertEquals(LocalTime.of(15, 0), LocalTime.of(14, 59).with(halfUp));
+        assertEquals(LocalTime.of(15, 0), LocalTime.of(15, 0).with(halfUp));
+    }
+
 }