From 6aabae46957f9e2b9c94e71792ccad380e29dc33 Mon Sep 17 00:00:00 2001
From: =?utf8?q?S=C3=A9bastien=20Lesaint?=
 <sebastien.lesaint@sonarsource.com>
Date: Tue, 26 May 2015 09:45:29 +0200
Subject: [PATCH] SONAR-6590 add factory methods for empty CloseableIterator
 and from Iterator

---
 .../sonar/server/util/CloseableIterator.java  | 66 +++++++++++++++++--
 .../server/util/CloseableIteratorTest.java    | 34 +++++++++-
 2 files changed, 93 insertions(+), 7 deletions(-)

diff --git a/server/sonar-server/src/main/java/org/sonar/server/util/CloseableIterator.java b/server/sonar-server/src/main/java/org/sonar/server/util/CloseableIterator.java
index c8244454baa..b63a332be9c 100644
--- a/server/sonar-server/src/main/java/org/sonar/server/util/CloseableIterator.java
+++ b/server/sonar-server/src/main/java/org/sonar/server/util/CloseableIterator.java
@@ -20,18 +20,74 @@
 package org.sonar.server.util;
 
 import com.google.common.base.Throwables;
-
-import javax.annotation.CheckForNull;
-
 import java.util.Iterator;
 import java.util.NoSuchElementException;
+import javax.annotation.CheckForNull;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static java.util.Objects.requireNonNull;
 
 public abstract class CloseableIterator<O> implements Iterator<O>, AutoCloseable {
+  private static final CloseableIterator<?> EMPTY_CLOSEABLE_ITERATOR = new CloseableIterator<Object>() {
+    @Override
+    public boolean hasNext() {
+      return false;
+    }
+
+    @Override
+    protected Object doNext() {
+      // never called anyway
+      throw new NoSuchElementException("Empty closeable Iterator has no element");
+    }
+
+    @Override
+    protected void doClose() throws Exception {
+      // do nothing
+    }
+  };
+
+  @SuppressWarnings("unchecked")
+  public static <T> CloseableIterator<T> emptyCloseableIterator() {
+    return (CloseableIterator<T>) EMPTY_CLOSEABLE_ITERATOR;
+  }
+
+  /**
+   * Creates a CloseableIterator from a regular {@link Iterator}.
+   *
+   * @throws IllegalArgumentException if the specified {@link Iterator} is a CloseableIterator
+   */
+  public static <T> CloseableIterator<T> from(final Iterator<T> iterator) {
+    // early fail
+    requireNonNull(iterator);
+    checkArgument(!(iterator instanceof CloseableIterator), "This method does not support creating a CloseableIterator from a CloseableIterator");
+    return new CloseableIterator<T>() {
+      @Override
+      public boolean hasNext() {
+        return iterator.hasNext();
+      }
+
+      @Override
+      public T next() {
+        return iterator.next();
+      }
+
+      @Override
+      protected T doNext() {
+        throw new UnsupportedOperationException("hasNext has been override, doNext is never called");
+      }
+
+      @Override
+      protected void doClose() throws Exception {
+        // do nothing
+      }
+    };
+  }
+
   private O nextObject = null;
   boolean isClosed = false;
 
   @Override
-  public final boolean hasNext() {
+  public boolean hasNext() {
     // Optimization to not call bufferNext() when already closed
     if (isClosed) {
       return false;
@@ -59,7 +115,7 @@ public abstract class CloseableIterator<O> implements Iterator<O>, AutoCloseable
   protected abstract O doNext();
 
   @Override
-  public final O next() {
+  public O next() {
     if (!hasNext()) {
       throw new NoSuchElementException();
     }
diff --git a/server/sonar-server/src/test/java/org/sonar/server/util/CloseableIteratorTest.java b/server/sonar-server/src/test/java/org/sonar/server/util/CloseableIteratorTest.java
index 4cfb6efb50e..83f06bf385b 100644
--- a/server/sonar-server/src/test/java/org/sonar/server/util/CloseableIteratorTest.java
+++ b/server/sonar-server/src/test/java/org/sonar/server/util/CloseableIteratorTest.java
@@ -19,9 +19,9 @@
  */
 package org.sonar.server.util;
 
-import org.junit.Test;
-
+import java.util.Collections;
 import java.util.NoSuchElementException;
+import org.junit.Test;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.Assert.fail;
@@ -111,6 +111,36 @@ public class CloseableIteratorTest {
     it.hasNext();
   }
 
+  @Test
+  public void emptyIterator_has_next_is_false() {
+    assertThat(CloseableIterator.emptyCloseableIterator().hasNext()).isFalse();
+  }
+
+  @Test(expected = NoSuchElementException.class)
+  public void emptyIterator_next_throws_NoSuchElemetException() {
+    CloseableIterator.emptyCloseableIterator().next();
+  }
+
+  @Test(expected = NullPointerException.class)
+  public void from_iterator_throws_early_NPE_if_arg_is_null() {
+    CloseableIterator.from(null);
+  }
+
+  @Test(expected = IllegalArgumentException.class)
+  public void from_iterator_throws_IAE_if_arg_is_a_CloseableIterator() {
+    CloseableIterator.from(new SimpleCloseableIterator());
+  }
+
+  @Test
+  public void verify_has_next_from_iterator_with_empty_iterator() {
+    assertThat(CloseableIterator.from(Collections.<String>emptyList().iterator()).hasNext()).isFalse();
+  }
+
+  @Test(expected = NoSuchElementException.class)
+  public void verify_next_from_iterator_with_empty_iterator() {
+    CloseableIterator.from(Collections.<String>emptyList().iterator()).next();
+  }
+
   static class SimpleCloseableIterator extends CloseableIterator {
     int count = 0;
     boolean isClosed = false;
-- 
2.39.5