Improve array iterator (#19)

* Improve ArrayIterator performance.

For compact arrays, the old implementation was quadratic, resulting in absolutely terrible performance for large arrays.

* Prefer ArrayIterator over index based access when iterating arrays.

* Fix deserializeArray.

Author: mpoeter

src/main/java/com/arangodb/velocypack/ArrayIterator.java

@@ -35,17 +35,21 @@ public ArrayIterator(final VPackSlice slice) throws VPackValueTypeException {
 		if (!slice.isArray()) {
 			throw new VPackValueTypeException(ValueType.ARRAY);
 		}
+		if (size > 0) {
+			current = slice.getNth(0).getStart();
+		}
 	}
 
 	@Override
 	public VPackSlice next() {
-		final VPackSlice next;
 		if (hasNext()) {
-			next = slice.get((int) position++);
+			final VPackSlice next = getCurrent();
+			position++;
+			current += next.getByteSize();
+			return next;
 		} else {
 			throw new NoSuchElementException();
 		}
-		return next;
 	}
 
 	@Override

src/main/java/com/arangodb/velocypack/VPack.java

@@ -667,8 +667,9 @@ private <T> Object deserializeArray(final VPackSlice parent, final VPackSlice vp
         final int length = vpack.getLength();
         final Class<?> componentType = ((Class<?>) type).getComponentType();
         final Object value = Array.newInstance(componentType, length);
-        for (int i = 0; i < length; i++) {
-            Array.set(value, i, getValue(parent, vpack.get(i), componentType, null));
+        int i = 0;
+        for (final Iterator<VPackSlice> iterator = vpack.arrayIterator(); iterator.hasNext(); ) {
+            Array.set(value, i++, getValue(parent, iterator.next(), componentType, null));
         }
         return value;
     }

src/main/java/com/arangodb/velocypack/VPackParser.java

@@ -324,8 +324,8 @@ private void parseArray(final VPackSlice value, final StringBuilder json, final
 			throws VPackException {
 		json.append(ARRAY_OPEN);
 		int added = 0;
-		for (int i = 0; i < value.getLength(); i++) {
-			final VPackSlice valueAt = value.get(i);
+		for (final Iterator<VPackSlice> iterator = value.arrayIterator(); iterator.hasNext();) {
+			final VPackSlice valueAt = iterator.next();
 			if (!valueAt.isNull() || includeNullValues) {
 				if (added++ > 0) {
 					json.append(SEPARATOR);

src/main/java/com/arangodb/velocypack/VPackSlice.java

@@ -783,7 +783,7 @@ private VPackSlice getNthKey(final int index) {
 		return new VPackSlice(vpack, start + getNthOffset(index));
 	}
 
-	private VPackSlice getNth(final int index) {
+	public VPackSlice getNth(final int index) {
 		return new VPackSlice(vpack, start + getNthOffset(index));
 	}
 

src/test/java/com/arangodb/velocypack/VPackSliceTest.java

@@ -873,7 +873,7 @@ private void checkArray(final long[] expected, final byte[] vpack) throws VPackE
 	}
 
 	@Test
-	public void arrayIterator() throws VPackException {
+	public void arrayIteratorOnCompactArray() throws VPackException {
 		final Collection<String> expected = Arrays.asList("a", "b", "c", "d", "e", "f");
 		final VPackSlice slice = new VPackSlice(new byte[] { 0x13, 0x0f, 0x41, 0x61, 0x41, 0x62, 0x41, 0x63, 0x41, 0x64,
 				0x41, 0x65, 0x41, 0x66, 0x06 });
@@ -885,6 +885,18 @@ public void arrayIterator() throws VPackException {
 		}
 	}
 
+	@Test
+	public void arrayIteratorOnArrayWithIndexTable() throws VPackException {
+		final Collection<Integer> expected = Arrays.asList(1, 42, 3);
+		final VPackSlice slice = new VPackSlice(new byte[] { 0x06, 0x0a, 0x03, 0x31, 0x20, 0x2a, 0x33, 0x03, 0x04, 0x06 });
+		final Iterator<VPackSlice> iteratorSlice = slice.arrayIterator();
+		for (final Integer i : expected) {
+			final VPackSlice next = iteratorSlice.next();
+			assertThat(next.isInteger(), is(true));
+			assertThat(next.getAsInt(), is(i));
+		}
+	}
+
 	@Test
 	public void objectIterator() throws VPackException {
 		// {"a":"test","b":"test","c":"test"}