Test coverage using API from Java, entry in README, more correct over…

…flow handling

README.md

@@ -253,3 +253,34 @@ public class StreamConvertersExample {
   }
 }
 ```
+
+## Converters between `scala.concurrent.duration.FiniteDuration` and `java.time.Duration`
+
+Interconversion between Java's standard `java.time.Duration` type 
+and the `scala.concurrent.duration.FiniteDuration` types. The Java `Duration` does 
+not contain a time unit, so when converting from `FiniteDuration` the time unit used 
+to create it is lost. 
+
+For the opposite conversion a `Duration` can potentially express a larger time span than
+a `FiniteDuration`, for such cases an exception is thrown.
+
+Example of conversions from the Java type ways: 
+
+```scala
+import scala.concurrent.duration._
+import scala.compat.java8.DurationConverters
+
+val javaDuration: java.time.Duration = 5.seconds.toJava
+val finiteDuration: FiniteDuration = javaDuration.toScala
+```
+
+From Java:
+```java
+import scala.compat.java8.DurationConverters;
+import scala.concurrent.duration.FiniteDuration;
+
+DurationConverters.toScala(Duration.of(5, ChronoUnit.SECONDS));
+DurationConverters.toJava(FiniteDuration.create(5, TimeUnit.SECONDS));
+```
+
+

src/main/scala/scala/compat/java8/DurationConverters.scala

@@ -23,29 +23,33 @@ object DurationConverters {
    * unit of nanoseconds.
    *
    * @throws IllegalArgumentException If the given Java Duration is out of bounds of what can be expressed with the
-   *                                  Scala Durations.
+   *                                  Scala FiniteDuration.
    */
-  final def toScala(duration: java.time.Duration): scala.concurrent.duration.Duration = {
-    if (duration.getNano == 0) {
-      if (duration.getSeconds == 0) ScalaDuration.Zero
-      else FiniteDuration(duration.getSeconds, TimeUnit.SECONDS)
+  final def toScala(duration: java.time.Duration): scala.concurrent.duration.FiniteDuration = {
+    val originalSeconds = duration.getSeconds
+    val originalNanos = duration.getNano
+    if (originalNanos == 0) {
+      if (originalSeconds == 0) ScalaDuration.Zero
+      else FiniteDuration(originalSeconds, TimeUnit.SECONDS)
+    } else if (originalSeconds == 0) {
+      FiniteDuration(originalNanos, TimeUnit.NANOSECONDS)
     } else {
-      FiniteDuration(
-        duration.getSeconds * 1000000000 + duration.getNano,
-        TimeUnit.NANOSECONDS
-      )
+      try {
+        val secondsAsNanos = Math.multiplyExact(originalSeconds, 1000000000)
+        val totalNanos = secondsAsNanos + originalNanos
+        if ((totalNanos < 0 && secondsAsNanos < 0) || (totalNanos > 0 && secondsAsNanos > 0)) FiniteDuration(totalNanos, TimeUnit.NANOSECONDS)
+        else throw new ArithmeticException()
+      } catch {
+        case _: ArithmeticException => throw new IllegalArgumentException(s"Java duration $duration cannot be expressed as a Scala duration")
+      }
     }
   }
 
   /**
-   * Transform a Scala duration into a Java duration. Note that the Scala duration keeps the time unit it was created
+   * Transform a Scala FiniteDuration into a Java duration. Note that the Scala duration keeps the time unit it was created
    * with while a Java duration always is a pair of seconds and nanos, so the unit it lost.
-   *
-   * @throws IllegalArgumentException If the Scala duration express a amount of time for the time unit that
-   *                                  a Java Duration can not express (infinite durations and undefined durations)
    */
-  final def toJava(duration: scala.concurrent.duration.Duration): java.time.Duration = {
-    require(duration.isFinite(), s"Got [$duration] but only finite Scala durations can be expressed as a Java Durations")
+  final def toJava(duration: scala.concurrent.duration.FiniteDuration): java.time.Duration = {
     if (duration.length == 0) JavaDuration.ZERO
     else duration.unit match {
       case TimeUnit.NANOSECONDS => JavaDuration.ofNanos(duration.length)
@@ -58,4 +62,18 @@ object DurationConverters {
     }
   }
 
+  implicit final class DurationOps(val duration: java.time.Duration) extends AnyVal {
+    /**
+     * See [[DurationConverters.toScala]]
+     */
+    def toScala: scala.concurrent.duration.FiniteDuration = DurationConverters.toScala(duration)
+  }
+
+  implicit final class FiniteDurationops(val duration: scala.concurrent.duration.FiniteDuration) extends AnyVal {
+    /**
+     * See [[DurationConverters.toJava]]
+     */
+    def toJava: java.time.Duration = DurationConverters.toJava(duration)
+  }
+
 }

src/test/java/scala/compat/java8/DurationConvertersJavaTest.java

@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2012-2018 Lightbend Inc. <http://www.lightbend.com>
+ */
+package scala.compat.java8;
+
+import org.junit.Test;
+import scala.concurrent.duration.FiniteDuration;
+import scala.runtime.java8.*;
+
+import java.time.Duration;
+import java.time.temporal.ChronoUnit;
+import java.util.concurrent.TimeUnit;
+
+public class DurationConvertersJavaTest {
+
+  @Test
+  public void apiAccessibleFromJava() {
+    DurationConverters.toScala(Duration.of(5, ChronoUnit.SECONDS));
+    DurationConverters.toJava(FiniteDuration.create(5, TimeUnit.SECONDS));
+  }
+
+}

src/test/scala/scala/compat/java8/DurationConvertersTest.scala

@@ -3,10 +3,11 @@
  */
 package scala.compat.java8
 
-import org.junit.Test
-import org.junit.Assert._
 import java.time.{Duration => JavaDuration}
 
+import org.junit.Assert._
+import org.junit.Test
+
 import scala.util.Try
 
 class DurationConvertersTest {
@@ -25,7 +26,7 @@ class DurationConvertersTest {
       1000000001L         -> (1,1),
       Long.MaxValue       -> (9223372036L, 854775807)
     ).foreach { case (n, (expSecs, expNanos)) =>
-      val result = toJava(n.nanos)
+      val result = n.nanos.toJava
       assertEquals(s"toJava($n nanos) -> $expSecs s)", expSecs, result.getSeconds)
       assertEquals(s"toJava($n nanos) -> $expNanos n)", expNanos, result.getNano)
     }
@@ -40,7 +41,7 @@ class DurationConvertersTest {
       1L              -> (0L,  1000000),
       9223372036854L  -> (9223372036L, 854000000)
     ).foreach { case (n, (expSecs, expNanos)) =>
-      val result = toJava(n.millis)
+      val result = n.millis.toJava
       assertEquals(s"toJava($n millis) -> $expSecs s)", expSecs, result.getSeconds)
       assertEquals(s"toJava($n millis) -> $expNanos n)", expNanos, result.getNano)
     }
@@ -55,7 +56,7 @@ class DurationConvertersTest {
       1L                 -> (0L,  1000),
       9223372036854775L  -> (9223372036L, 854775000)
     ).foreach { case (n, (expSecs, expNanos)) =>
-      val result = toJava(n.micros)
+      val result = n.micros.toJava
       assertEquals(s"toJava($n micros) -> $expSecs s)", expSecs, result.getSeconds)
       assertEquals(s"toJava($n micros) -> $expNanos n)", expNanos, result.getNano)
     }
@@ -70,7 +71,7 @@ class DurationConvertersTest {
       1L           -> (1L,  0),
       9223372036L  -> (9223372036L, 0)
     ).foreach { case (n, (expSecs, expNanos)) =>
-      val result = toJava(n.seconds)
+      val result = n.seconds.toJava
       assertEquals(expSecs, result.getSeconds)
       assertEquals(expNanos, result.getNano)
     }
@@ -87,19 +88,12 @@ class DurationConvertersTest {
 
   @Test
   def javaNanosPartToScalaDuration(): Unit = {
-    Seq[Long](Long.MinValue + 1L, -1L, 0L, 1L, Long.MaxValue).foreach { n =>
+    val nanosPerSecond = 1000000000L
+    Seq[Long](-nanosPerSecond - 1L, 0L, 1L, nanosPerSecond - 1L).foreach { n =>
       assertEquals(n, toScala(JavaDuration.ofNanos(n)).toNanos)
     }
   }
 
-  @Test
-  def unsupportedScalaDurationThrows(): Unit = {
-    Seq(Duration.Inf, Duration.MinusInf, Duration.Undefined).foreach { d =>
-      val res = Try { toJava(d) }
-      assertTrue(s"Expected exception for $d but got success", res.isFailure)
-    }
-  }
-
   @Test
   def unsupportedJavaDurationThrows(): Unit = {
     Seq(JavaDuration.ofSeconds(-9223372037L), JavaDuration.ofSeconds(9223372037L)).foreach { d =>