add getConverter method to expose converter for a given type

Signed-off-by: Erik Mattheis <[email protected]>

api/src/main/java/org/eclipse/microprofile/config/Config.java

@@ -37,6 +37,7 @@
 import java.util.Optional;
 
 import org.eclipse.microprofile.config.spi.ConfigSource;
+import org.eclipse.microprofile.config.spi.Converter;
 
 /**
  * <p>
@@ -144,7 +145,7 @@ public interface Config {
      * @return the configuration sources
      */
     Iterable<ConfigSource> getConfigSources();
-    
+
     /**
      * Convert an abritrary value to the specified type using the converters known to this instance
      * 
@@ -157,5 +158,20 @@ public interface Config {
      * @return the converted value
      * @throws java.lang.IllegalArgumentException if the value cannot be converted to the specified type.
      */
-    <T> T convert(String value, Class<T> type);
+    default <T> T convert(String value, Class<T> type) {        
+        return value == null ? null
+                             : getConverter(type).orElseThrow(() -> new IllegalArgumentException("no converter available for " + type))
+                                                 .convert(value);
+    }
+
+    /**
+     * Return the {@link Converter} used by this instance to produce instances of the specified type from string values. 
+     * 
+     * @param <T>
+     *             the conversion type
+     * @param forType
+     *             the type to be produced by the converter
+     * @return an {@link Optional} containing the converter, or empty if no converter is available for the specified type
+     */
+    <T> Optional<Converter<T>> getConverter(Class<T> forType);
 }