Added Maps2.fromKeys

core/src/main/java/org/jclouds/util/Maps2.java

@@ -26,16 +26,17 @@ import static com.google.common.collect.Maps.filterKeys;
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.Set;
 
 import com.google.common.base.Function;
 import com.google.common.base.Supplier;
 import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.ImmutableMap.Builder;
 import com.google.common.collect.Maps;
 import com.google.common.collect.Multimap;
-import com.google.common.collect.ImmutableMap.Builder;
 
 /**
- * General utilities used in jclouds code for {@link Map}s.
+ * General utilities used in jclouds code for {@link Map Maps}.
  * 
  * @author Adrian Cole
  */
@@ -120,5 +121,25 @@ public class Maps2 {
          return toReturn;
       }
    }
+   
+   /**
+    * Constructs a map with the given keys where values are generated by the given function.
+    * Supports duplicate and {@code null} values, but {@code null} keys are <em>not</em> allowed.
+    * 
+    * @param <K>   the type of the keys
+    * @param <V>   the type of the values
+    * @param keys  the keys to be included in the map. Keys must be non-<code>null</code>
+    * @param valueFunction the function that produces values for the keys
+    * @return a map containing the keys from the given set with values which are generated from
+    *      the keys
+    * @see Maps#uniqueIndex(Iterable, Function)
+    */
+   public static <K, V> Map<K, V> fromKeys(Set<K> keys, Function<? super K, V> valueFunction) {
+       Map<K, V> result = Maps.newHashMapWithExpectedSize(keys.size());
+       for (K key : keys) {
+               result.put(checkNotNull(key), valueFunction.apply(key));
+       }
+       return result;
+   }
 
 }

core/src/test/java/org/jclouds/util/Maps2Test.java

@@ -18,7 +18,11 @@
  */
 package org.jclouds.util;
 
+import static com.google.common.base.Functions.constant;
+import static com.google.common.base.Functions.identity;
+import static com.google.common.collect.Sets.newHashSet;
 import static org.testng.Assert.assertEquals;
+import static org.testng.Assert.assertTrue;
 
 import java.util.Map;
 
@@ -26,6 +30,8 @@ import org.testng.annotations.Test;
 
 import com.google.common.base.Function;
 import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Maps;
 
 /**
  * @author Adrian Cole
@@ -54,4 +60,30 @@ public class Maps2Test {
       }), ImmutableMap.of("foo", "bar"));
    }
 
+   public void testFromKeysEmptyKeys() {
+       assertTrue(Maps2.fromKeys(ImmutableSet.of(), identity()).isEmpty(),
+               "Expected returned map to be empty");
+   }
+   
+   @Test(expectedExceptions = { NullPointerException.class })
+   public void testFromKeysNullKey() {
+       Maps2.fromKeys(newHashSet((Object) null), constant("const"));
+   }
+   
+   public void testFromKeys() {
+       // ImmutableMap doesn't support null values
+       Map<String, String> expected = Maps.newHashMap();
+       expected.put("foo", "foo");
+       expected.put("bar", "foo");
+       expected.put("baz", null);
+
+       assertEquals(Maps2.fromKeys(ImmutableSet.of("foo", "bar", "baz"),
+           new Function<String, String>() {
+                @Override
+                public String apply(String input) {
+                    return (input.equals("baz") ? null : "foo");
+                }
+            }), expected);
+   }
+   
 }