add java doc to dubbo-config-api (#3103)

* add config-api javadoc

* add dubbo-config-api javadoc

* update javadoc

* add dubbo-config-api java doc

dubbo-config/dubbo-config-api/src/main/java/org/apache/dubbo/config/AbstractConfig.java

@@ -50,22 +50,55 @@ public abstract class AbstractConfig implements Serializable {
 
     protected static final Logger logger = LoggerFactory.getLogger(AbstractConfig.class);
     private static final long serialVersionUID = 4267533505537413570L;
+
+    /**
+     * The maximum length of a <b>parameter's value</b>
+     */
     private static final int MAX_LENGTH = 200;
 
+    /**
+     * The maximum length of a <b>path</b>
+     */
     private static final int MAX_PATH_LENGTH = 200;
 
+    /**
+     * The rule qualification for <b>name</b>
+     */
     private static final Pattern PATTERN_NAME = Pattern.compile("[\\-._0-9a-zA-Z]+");
 
+    /**
+     * The rule qualification for <b>multiply name</b>
+     */
     private static final Pattern PATTERN_MULTI_NAME = Pattern.compile("[,\\-._0-9a-zA-Z]+");
 
+    /**
+     * The rule qualification for <b>method names</b>
+     */
     private static final Pattern PATTERN_METHOD_NAME = Pattern.compile("[a-zA-Z][0-9a-zA-Z]*");
 
+    /**
+     * The rule qualification for <b>path</b>
+     */
     private static final Pattern PATTERN_PATH = Pattern.compile("[/\\-$._0-9a-zA-Z]+");
 
+    /**
+     * The pattern matches a value who has a symbol
+     */
     private static final Pattern PATTERN_NAME_HAS_SYMBOL = Pattern.compile("[:*,\\s/\\-._0-9a-zA-Z]+");
 
+    /**
+     * The pattern matches a property key
+     */
     private static final Pattern PATTERN_KEY = Pattern.compile("[*,\\-._0-9a-zA-Z]+");
+
+    /**
+     * The legacy properties container
+     */
     private static final Map<String, String> legacyProperties = new HashMap<String, String>();
+
+    /**
+     * The suffix container
+     */
     private static final String[] SUFFIXES = new String[]{"Config", "Bean"};
 
     static {
@@ -82,6 +115,9 @@ public abstract class AbstractConfig implements Serializable {
         DubboShutdownHook.getDubboShutdownHook().register();
     }
 
+    /**
+     * The config id
+     */
     protected String id;
     protected String prefix;
 
@@ -278,6 +314,14 @@ protected static void checkExtension(Class<?> type, String property, String valu
         }
     }
 
+    /**
+     * Check whether there is a <code>Extension</code> who's name (property) is <code>value</code> (special treatment is
+     * required)
+     *
+     * @param type The Extension type
+     * @param property The extension key
+     * @param value The Extension name
+     */
     protected static void checkMultiExtension(Class<?> type, String property, String value) {
         checkMultiName(property, value);
         if (StringUtils.isNotEmpty(value)) {