Merge pull request apache#3096, code review config center.

* polish javadoc

* git rid of template class for apollo

* get rid of template class for NopDynamicConfiguration

* get rid of tempate class for ZookeeperDynamicConfiguration

* get rid of AbstractDynamicConfiguration

* get rid of AbstractConfiguration

* fix compilation error

* fix compilation error

* polish code

dubbo-common/src/main/java/org/apache/dubbo/common/config/AbstractPrefixConfiguration.java

@@ -21,7 +21,7 @@
 /**
  * This is an abstraction specially customized for the sequence Dubbo retrieves properties.
  */
-public abstract class AbstractPrefixConfiguration extends AbstractConfiguration {
+public abstract class AbstractPrefixConfiguration implements Configuration {
     protected String id;
     protected String prefix;
 
@@ -44,9 +44,10 @@ public Object getProperty(String key, Object defaultValue) {
         if (value == null && StringUtils.isNotEmpty(prefix)) {
             value = getInternalProperty(prefix + key);
         }
+
         if (value == null) {
-            value = super.getProperty(key, defaultValue);
+            value = getInternalProperty(key);
         }
-        return value;
+        return value != null ? value : defaultValue;
     }
 }

dubbo-common/src/main/java/org/apache/dubbo/common/config/CompositeConfiguration.java

@@ -16,14 +16,18 @@
  */
 package org.apache.dubbo.common.config;
 
+import org.apache.dubbo.common.logger.Logger;
+import org.apache.dubbo.common.logger.LoggerFactory;
+
 import java.util.Arrays;
 import java.util.LinkedList;
 import java.util.List;
 
 /**
  *
  */
-public class CompositeConfiguration extends AbstractConfiguration {
+public class CompositeConfiguration implements Configuration {
+    private Logger logger = LoggerFactory.getLogger(CompositeConfiguration.class);
 
     /**
      * List holding all the configuration
@@ -56,7 +60,7 @@ public void addConfiguration(int pos, Configuration configuration) {
     }
 
     @Override
-    protected Object getInternalProperty(String key) {
+    public Object getInternalProperty(String key) {
         Configuration firstMatchingConfiguration = null;
         for (Configuration config : configList) {
             try {
@@ -65,7 +69,7 @@ protected Object getInternalProperty(String key) {
                     break;
                 }
             } catch (Exception e) {
-                e.printStackTrace();
+                logger.error("Error when trying to get value for key " + key + " from " + config + ", will continue to try the next one.");
             }
         }
         if (firstMatchingConfiguration != null) {

dubbo-common/src/main/java/org/apache/dubbo/common/config/Configuration.java

@@ -26,7 +26,9 @@ public interface Configuration {
      * @param key The configuration key.
      * @return The associated string.
      */
-    String getString(String key);
+    default String getString(String key) {
+        return convert(String.class, key, null);
+    }
 
     /**
      * Get a string associated with the given configuration key.
@@ -38,7 +40,9 @@ public interface Configuration {
      * @return The associated string if key is found and has valid
      * format, default value otherwise.
      */
-    String getString(String key, String defaultValue);
+    default String getString(String key, String defaultValue) {
+        return convert(String.class, key, defaultValue);
+    }
 
     /**
      * Gets a property from the configuration. This is the most basic get
@@ -56,7 +60,9 @@ public interface Configuration {
      * @return the value to which this configuration maps the specified key, or
      * null if the configuration contains no mapping for this key.
      */
-    Object getProperty(String key);
+    default Object getProperty(String key) {
+        return getProperty(key, null);
+    }
 
     /**
      * Gets a property from the configuration. The default value will return if the configuration doesn't contain
@@ -67,7 +73,12 @@ public interface Configuration {
      * @return the value to which this configuration maps the specified key, or default value if the configuration
      * contains no mapping for this key.
      */
-    Object getProperty(String key, Object defaultValue);
+    default Object getProperty(String key, Object defaultValue) {
+        Object value = getInternalProperty(key);
+        return value != null ? value : defaultValue;
+    }
+
+    Object getInternalProperty(String key);
 
     /**
      * Check if the configuration contains the specified key.
@@ -76,7 +87,50 @@ public interface Configuration {
      * @return {@code true} if the configuration contains a value for this
      * key, {@code false} otherwise
      */
-    boolean containsKey(String key);
+    default boolean containsKey(String key) {
+        return getProperty(key) != null;
+    }
+
+
+    default <T> T convert(Class<T> cls, String key, T defaultValue) {
+        // we only process String properties for now
+        String value = (String) getProperty(key);
+
+        if (value == null) {
+            return defaultValue;
+        }
+
+        Object obj = value;
+        if (cls.isInstance(value)) {
+            return cls.cast(value);
+        }
+
+        if (String.class.equals(cls)) {
+            return cls.cast(value);
+        }
+
+        if (Boolean.class.equals(cls) || Boolean.TYPE.equals(cls)) {
+            obj = Boolean.valueOf(value);
+        } else if (Number.class.isAssignableFrom(cls) || cls.isPrimitive()) {
+            if (Integer.class.equals(cls) || Integer.TYPE.equals(cls)) {
+                obj = Integer.valueOf(value);
+            } else if (Long.class.equals(cls) || Long.TYPE.equals(cls)) {
+                obj = Long.valueOf(value);
+            } else if (Byte.class.equals(cls) || Byte.TYPE.equals(cls)) {
+                obj = Byte.valueOf(value);
+            } else if (Short.class.equals(cls) || Short.TYPE.equals(cls)) {
+                obj = Short.valueOf(value);
+            } else if (Float.class.equals(cls) || Float.TYPE.equals(cls)) {
+                obj = Float.valueOf(value);
+            } else if (Double.class.equals(cls) || Double.TYPE.equals(cls)) {
+                obj = Double.valueOf(value);
+            }
+        } else if (cls.isEnum()) {
+            obj = Enum.valueOf(cls.asSubclass(Enum.class), value);
+        }
+
+        return cls.cast(obj);
+    }
 
 
 }

dubbo-common/src/main/java/org/apache/dubbo/common/config/EnvironmentConfiguration.java

@@ -30,7 +30,7 @@ public EnvironmentConfiguration() {
     }
 
     @Override
-    protected Object getInternalProperty(String key) {
+    public Object getInternalProperty(String key) {
         return System.getenv(key);
     }
 

dubbo-common/src/main/java/org/apache/dubbo/common/config/InmemoryConfiguration.java

@@ -36,7 +36,7 @@ public InmemoryConfiguration() {
     }
 
     @Override
-    protected Object getInternalProperty(String key) {
+    public Object getInternalProperty(String key) {
         return store.get(key);
     }
 

dubbo-common/src/main/java/org/apache/dubbo/common/config/PropertiesConfiguration.java

@@ -35,7 +35,7 @@ public PropertiesConfiguration() {
     }
 
     @Override
-    protected Object getInternalProperty(String key) {
+    public Object getInternalProperty(String key) {
         return ConfigUtils.getProperty(key);
     }
 }

dubbo-common/src/main/java/org/apache/dubbo/common/config/SystemConfiguration.java

@@ -33,7 +33,7 @@ public SystemConfiguration() {
     }
 
     @Override
-    protected Object getInternalProperty(String key) {
+    public Object getInternalProperty(String key) {
         return System.getProperty(key);
     }