svn merge -c 1352689 from trunk. Backport HADOOP-8524 to branch-2. (harsh)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1352693 13f79535-47bb-0310-9956-ffa450edef68

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -44,6 +44,9 @@ Release 2.0.1-alpha - UNRELEASED
 
     HADOOP-8368. Use CMake rather than autotools to build native code (ccccabe via tucu)
 
+    HADOOP-8524. Allow users to get source of a Configuration
+    parameter (harsh)
+
   BUG FIXES
 
     HADOOP-8372. NetUtils.normalizeHostName() incorrectly handles hostname

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/Configuration.java

@@ -1034,6 +1034,38 @@ public class Configuration implements Iterable<Map.Entry<String,String>>,
     }
   }
 
+  /**
+   * Gets the absolute path to the resource object (file, URL, etc.), for a given
+   * property name.
+   *
+   * @param name - The property name to get the source of.
+   * @return null - If the property or its source wasn't found or if the property
+   * was defined in code (i.e. in a Configuration instance, not from a physical
+   * resource). Otherwise, returns the absolute path of the resource that loaded
+   * the property name, as a String.
+   */
+  @InterfaceStability.Unstable
+  public synchronized String getPropertySource(String name) {
+    if (properties == null) {
+      // If properties is null, it means a resource was newly added
+      // but the props were cleared so as to load it upon future
+      // requests. So lets force a load by asking a properties list.
+      getProps();
+    }
+    // Return a null right away if our properties still
+    // haven't loaded or the resource mapping isn't defined
+    if (properties == null || updatingResource == null) {
+      return null;
+    } else {
+      String source = updatingResource.get(name);
+      if (source == null || source.equals(UNKNOWN_RESOURCE)) {
+        return null;
+      } else {
+        return source;
+      }
+    }
+  }
+
   /**
    * A class that represents a set of positive integer ranges. It parses 
    * strings of the form: "2-3,5,7-" where ranges are separated by comma and 

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/conf/TestConfiguration.java

@@ -640,6 +640,26 @@ public class TestConfiguration extends TestCase {
                  conf.getPattern("test.pattern3", defaultPattern).pattern());
   }
 
+  public void testPropertySource() throws IOException {
+    out = new BufferedWriter(new FileWriter(CONFIG));
+    startConfig();
+    appendProperty("test.foo", "bar");
+    endConfig();
+    Path fileResource = new Path(CONFIG);
+    conf.addResource(fileResource);
+    conf.set("fs.defaultFS", "value");
+    assertEquals(
+        "Resource string returned for a file-loaded property" +
+        " must be a proper absolute path",
+        fileResource,
+        new Path(conf.getPropertySource("test.foo")));
+    assertEquals("Resource string returned for a set() property must be null",
+        null,
+        conf.getPropertySource("fs.defaultFS"));
+    assertEquals("Resource string returned for an unset property must be null",
+        null, conf.getPropertySource("fs.defaultFoo"));
+  }
+
   public void testSocketAddress() throws IOException {
     Configuration conf = new Configuration();
     final String defaultAddr = "host:1";