HDDS-4158. Provide a class type for Java based configuration

hadoop-hdds/common/src/test/java/org/apache/hadoop/hdds/conf/SimpleConfiguration.java

@@ -47,6 +47,11 @@ public class SimpleConfiguration extends SimpleConfigurationParent {
       + "test TIME config type)", tags = ConfigTag.MANAGEMENT)
   private long waitTime;
 
+  @Config(key = "class", type = ConfigType.CLASS,
+      defaultValue = "java.lang.Object", description = "",
+      tags = ConfigTag.OZONE)
+  private Class<?> myClass = Object.class;
+
   @PostConstruct
   public void validate() {
     if (port < 0) {
@@ -93,4 +98,12 @@ public int getPort() {
   public long getWaitTime() {
     return waitTime;
   }
+
+  public Class<? extends Object> getMyClass() {
+    return myClass;
+  }
+
+  public void setMyClass(Class<?> aClass) {
+    this.myClass = aClass;
+  }
 }

hadoop-hdds/common/src/test/java/org/apache/hadoop/hdds/conf/TestOzoneConfiguration.java

@@ -106,6 +106,7 @@ public void getConfigurationObject() {
     ozoneConfig.setBoolean("test.scm.client.enabled", true);
     ozoneConfig.setInt("test.scm.client.port", 5555);
     ozoneConfig.setTimeDuration("test.scm.client.wait", 10, TimeUnit.MINUTES);
+    ozoneConfig.set("test.scm.client.class", Integer.class.getName());
 
     SimpleConfiguration configuration =
         ozoneConfig.getObject(SimpleConfiguration.class);
@@ -115,6 +116,7 @@ public void getConfigurationObject() {
     Assert.assertTrue(configuration.isEnabled());
     Assert.assertEquals(5555, configuration.getPort());
     Assert.assertEquals(600, configuration.getWaitTime());
+    Assert.assertEquals(Integer.class, configuration.getMyClass());
   }
 
   @Test
@@ -126,6 +128,7 @@ public void getConfigurationObjectWithDefault() {
 
     Assert.assertTrue(configuration.isEnabled());
     Assert.assertEquals(9878, configuration.getPort());
+    Assert.assertEquals(Object.class, configuration.getMyClass());
   }
 
   @Test
@@ -137,6 +140,7 @@ public void setConfigFromObject() {
     object.setEnabled(true);
     object.setPort(5555);
     object.setWaitTime(600);
+    object.setMyClass(this.getClass());
 
     OzoneConfiguration subject = new OzoneConfiguration();
 
@@ -154,6 +158,8 @@ public void setConfigFromObject() {
         subject.getInt("test.scm.client.port", 0));
     Assert.assertEquals(TimeUnit.SECONDS.toMinutes(object.getWaitTime()),
         subject.getTimeDuration("test.scm.client.wait", 0, TimeUnit.MINUTES));
+    Assert.assertEquals(this.getClass(),
+        subject.getClass("test.scm.client.class", null));
   }
 
   @Test
@@ -208,7 +214,6 @@ public void postConstructValidation() {
     ozoneConfiguration.getObject(SimpleConfiguration.class);
   }
 
-
   private void appendProperty(BufferedWriter out, String name, String val)
       throws IOException {
     this.appendProperty(out, name, val, false);

hadoop-hdds/config/src/main/java/org/apache/hadoop/hdds/conf/ConfigType.java

@@ -30,5 +30,6 @@ public enum ConfigType {
   INT,
   LONG,
   TIME,
-  SIZE
+  SIZE,
+  CLASS
 }

hadoop-hdds/config/src/main/java/org/apache/hadoop/hdds/conf/ConfigurationReflectionUtil.java

@@ -92,6 +92,10 @@ public static <T> void injectConfigurationToObject(ConfigurationSource from,
             forcedFieldSet(field, configuration,
                 from.getTimeDuration(key, "0s", configAnnotation.timeUnit()));
             break;
+          case CLASS:
+            forcedFieldSet(field, configuration,
+                from.getClass(key, Object.class));
+            break;
           default:
             throw new ConfigurationException(
                 "Unsupported ConfigType " + type + " on " + fieldLocation);
@@ -133,6 +137,8 @@ private static ConfigType detectConfigType(Class<?> parameterType,
     } else if (parameterType == Boolean.class
         || parameterType == boolean.class) {
       type = ConfigType.BOOLEAN;
+    } else if (parameterType == Class.class) {
+      type = ConfigType.CLASS;
     } else {
       throw new ConfigurationException(
           "Unsupported configuration type " + parameterType + " in "
@@ -225,6 +231,12 @@ private static <T> void updateConfigurationFromObject(
             config.setTimeDuration(key, field.getLong(configObject),
                 configAnnotation.timeUnit());
             break;
+          case CLASS:
+            Object valueClass = field.get(configObject);
+            if (valueClass instanceof Class<?>) {
+              config.set(key, ((Class<?>) valueClass).getName());
+            }
+            break;
           default:
             throw new ConfigurationException(
                 "Unsupported ConfigType " + type + " on " + fieldLocation);