HADOOP-7350. Use ServiceLoader to discover compression codec classes.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1328083 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -360,6 +360,9 @@ Release 2.0.0 - UNRELEASED
     HADOOP-8282. start-all.sh refers incorrectly start-dfs.sh
     existence for starting start-yarn.sh. (Devaraj K via eli)
 
+    HADOOP-7350. Use ServiceLoader to discover compression codec classes.
+    (tomwhite)
+
   BREAKDOWN OF HADOOP-7454 SUBTASKS
 
     HADOOP-7455. HA: Introduce HA Service Protocol Interface. (suresh)

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/CompressionCodecFactory.java

@@ -37,6 +37,9 @@ public class CompressionCodecFactory {
   public static final Log LOG =
     LogFactory.getLog(CompressionCodecFactory.class.getName());
   
+  private static final ServiceLoader<CompressionCodec> CODEC_PROVIDERS =
+    ServiceLoader.load(CompressionCodec.class);
+
   /**
    * A map from the reversed filename suffixes to the codecs.
    * This is probably overkill, because the maps should be small, but it 
@@ -95,16 +98,23 @@ public class CompressionCodecFactory {
   }
 
   /**
-   * Get the list of codecs listed in the configuration
+   * Get the list of codecs discovered via a Java ServiceLoader, or
+   * listed in the configuration. Codecs specified in configuration come
+   * later in the returned list, and are considered to override those
+   * from the ServiceLoader.
    * @param conf the configuration to look in
-   * @return a list of the Configuration classes or null if the attribute
+   * @return a list of the {@link CompressionCodec} classes
-   *         was not set
    */
   public static List<Class<? extends CompressionCodec>> getCodecClasses(Configuration conf) {
+    List<Class<? extends CompressionCodec>> result
+      = new ArrayList<Class<? extends CompressionCodec>>();
+    // Add codec classes discovered via service loading
+    for (CompressionCodec codec : CODEC_PROVIDERS) {
+      result.add(codec.getClass());
+    }
+    // Add codec classes from configuration
     String codecsString = conf.get("io.compression.codecs");
     if (codecsString != null) {
-      List<Class<? extends CompressionCodec>> result
-        = new ArrayList<Class<? extends CompressionCodec>>();
       StringTokenizer codecSplit = new StringTokenizer(codecsString, ",");
       while (codecSplit.hasMoreElements()) {
         String codecSubstring = codecSplit.nextToken();
@@ -123,14 +133,14 @@ public class CompressionCodecFactory {
           }
         }
       }
-      return result;
-    } else {
-      return null;
     }
+    return result;
   }
   
   /**
-   * Sets a list of codec classes in the configuration.
+   * Sets a list of codec classes in the configuration. In addition to any
+   * classes specified using this method, {@link CompressionCodec} classes on
+   * the classpath are discovered using a Java ServiceLoader.
    * @param conf the configuration to modify
    * @param classes the list of classes to set
    */
@@ -151,21 +161,19 @@ public class CompressionCodecFactory {
   
   /**
    * Find the codecs specified in the config value io.compression.codecs 
-   * and register them. Defaults to gzip and zip.
+   * and register them. Defaults to gzip and deflate.
    */
   public CompressionCodecFactory(Configuration conf) {
     codecs = new TreeMap<String, CompressionCodec>();
     codecsByClassName = new HashMap<String, CompressionCodec>();
     codecsByName = new HashMap<String, CompressionCodec>();
     List<Class<? extends CompressionCodec>> codecClasses = getCodecClasses(conf);
-    if (codecClasses == null) {
+    if (codecClasses == null || codecClasses.isEmpty()) {
       addCodec(new GzipCodec());
       addCodec(new DefaultCodec());      
     } else {
-      Iterator<Class<? extends CompressionCodec>> itr = codecClasses.iterator();
+      for (Class<? extends CompressionCodec> codecClass : codecClasses) {
-      while (itr.hasNext()) {
+        addCodec(ReflectionUtils.newInstance(codecClass, conf));
-        CompressionCodec codec = ReflectionUtils.newInstance(itr.next(), conf);
-        addCodec(codec);     
       }
     }
   }

hadoop-common-project/hadoop-common/src/main/resources/META-INF/services/org.apache.hadoop.io.compress.CompressionCodec

@@ -0,0 +1,20 @@
+#
+#   Licensed under the Apache License, Version 2.0 (the "License");
+#   you may not use this file except in compliance with the License.
+#   You may obtain a copy of the License at
+#
+#       http://www.apache.org/licenses/LICENSE-2.0
+#
+#   Unless required by applicable law or agreed to in writing, software
+#   distributed under the License is distributed on an "AS IS" BASIS,
+#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#   See the License for the specific language governing permissions and
+#   limitations under the License.
+#
+org.apache.hadoop.io.compress.BZip2Codec
+org.apache.hadoop.io.compress.DefaultCodec
+org.apache.hadoop.io.compress.DeflateCodec
+org.apache.hadoop.io.compress.GzipCodec
+org.apache.hadoop.io.compress.Lz4Codec
+org.apache.hadoop.io.compress.SnappyCodec
+

hadoop-common-project/hadoop-common/src/main/resources/core-default.xml

@@ -268,9 +268,11 @@
 
 <property>
   <name>io.compression.codecs</name>
-  <value>org.apache.hadoop.io.compress.DefaultCodec,org.apache.hadoop.io.compress.GzipCodec,org.apache.hadoop.io.compress.BZip2Codec,org.apache.hadoop.io.compress.DeflateCodec,org.apache.hadoop.io.compress.SnappyCodec,org.apache.hadoop.io.compress.Lz4Codec</value>
+  <value></value>
-  <description>A list of the compression codec classes that can be used 
+  <description>A comma-separated list of the compression codec classes that can
-               for compression/decompression.</description>
+  be used for compression/decompression. In addition to any classes specified
+  with this property (which take precedence), codec classes on the classpath
+  are discovered using a Java ServiceLoader.</description>
 </property>
 
 <property>

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/compress/TestCodecFactory.java

@@ -101,6 +101,12 @@ public class TestCodecFactory extends TestCase {
     }
   }
   
+  private static class NewGzipCodec extends BaseCodec {
+    public String getDefaultExtension() {
+      return ".gz";
+    }
+  }
+  
   /**
    * Returns a factory for a given set of codecs
    * @param classes the codec classes to include
@@ -167,32 +173,43 @@ public class TestCodecFactory extends TestCase {
     checkCodec("default factory for deflate codec", DeflateCodec.class, codec);
 
     factory = setClasses(new Class[0]);
+    // gz, bz2, snappy, lz4 are picked up by service loader, but bar isn't
     codec = factory.getCodec(new Path("/tmp/foo.bar"));
-    assertEquals("empty codec bar codec", null, codec);
+    assertEquals("empty factory bar codec", null, codec);
     codec = factory.getCodecByClassName(BarCodec.class.getCanonicalName());
-    assertEquals("empty codec bar codec", null, codec);
+    assertEquals("empty factory bar codec", null, codec);
     
     codec = factory.getCodec(new Path("/tmp/foo.gz"));
-    assertEquals("empty codec gz codec", null, codec);
+    checkCodec("empty factory gz codec", GzipCodec.class, codec);
     codec = factory.getCodecByClassName(GzipCodec.class.getCanonicalName());
-    assertEquals("empty codec gz codec", null, codec);
+    checkCodec("empty factory gz codec", GzipCodec.class, codec);
     
     codec = factory.getCodec(new Path("/tmp/foo.bz2"));
-    assertEquals("empty factory for .bz2", null, codec);
+    checkCodec("empty factory for .bz2", BZip2Codec.class, codec);
     codec = factory.getCodecByClassName(BZip2Codec.class.getCanonicalName());
-    assertEquals("empty factory for bzip2 codec", null, codec);
+    checkCodec("empty factory for bzip2 codec", BZip2Codec.class, codec);
+    
+    codec = factory.getCodec(new Path("/tmp/foo.snappy"));
+    checkCodec("empty factory snappy codec", SnappyCodec.class, codec);
+    codec = factory.getCodecByClassName(SnappyCodec.class.getCanonicalName());
+    checkCodec("empty factory snappy codec", SnappyCodec.class, codec);
+    
+    codec = factory.getCodec(new Path("/tmp/foo.lz4"));
+    checkCodec("empty factory lz4 codec", Lz4Codec.class, codec);
+    codec = factory.getCodecByClassName(Lz4Codec.class.getCanonicalName());
+    checkCodec("empty factory lz4 codec", Lz4Codec.class, codec);
     
     factory = setClasses(new Class[]{BarCodec.class, FooCodec.class, 
                                      FooBarCodec.class});
     codec = factory.getCodec(new Path("/tmp/.foo.bar.gz"));
-    assertEquals("full factory gz codec", null, codec);
+    checkCodec("full factory gz codec", GzipCodec.class, codec);
     codec = factory.getCodecByClassName(GzipCodec.class.getCanonicalName());
-    assertEquals("full codec gz codec", null, codec);
+    checkCodec("full codec gz codec", GzipCodec.class, codec);
      
     codec = factory.getCodec(new Path("/tmp/foo.bz2"));
-    assertEquals("full factory for .bz2", null, codec);
+    checkCodec("full factory for .bz2", BZip2Codec.class, codec);
     codec = factory.getCodecByClassName(BZip2Codec.class.getCanonicalName());
-    assertEquals("full codec bzip2 codec", null, codec);
+    checkCodec("full codec bzip2 codec", BZip2Codec.class, codec);
 
     codec = factory.getCodec(new Path("/tmp/foo.bar"));
     checkCodec("full factory bar codec", BarCodec.class, codec);
@@ -220,5 +237,11 @@ public class TestCodecFactory extends TestCase {
     checkCodec("full factory foo codec", FooCodec.class, codec);
     codec = factory.getCodecByName("FOO");
     checkCodec("full factory foo codec", FooCodec.class, codec);
+    
+    factory = setClasses(new Class[]{NewGzipCodec.class});
+    codec = factory.getCodec(new Path("/tmp/foo.gz"));
+    checkCodec("overridden factory for .gz", NewGzipCodec.class, codec);
+    codec = factory.getCodecByClassName(NewGzipCodec.class.getCanonicalName());
+    checkCodec("overridden factory for gzip codec", NewGzipCodec.class, codec);
   }
 }