Link.java cleaning : add some javadocs + rewrite serialize method.

leshan-core/src/main/java/org/eclipse/leshan/Link.java

@@ -16,6 +16,7 @@
 package org.eclipse.leshan;
 
 import java.io.Serializable;
+import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 import java.util.Collections;
 import java.util.HashMap;
@@ -27,15 +28,24 @@
 /**
  * A Link as defined in http://tools.ietf.org/html/rfc6690.
  */
-// TODO we should have a look at org.eclipse.californium.core.coap.LinkFormat
+// TODO this class has several problems :
+// 1) Parsing is too permissive...
+// e.g. it should not accept URI-Reference which are not between < >.
+// e.g URI-reference should be parsed to respect RFC3986.
+//
+// 2) we should have Parser/Serializer class instead of static method to allow custom implementation.
+// 3) attributes is not well named, it does not respect rfc naming : url => uriRef
+//
+// Maybe we could look at existing implementation :
+// https://github.com/google/coapblaster/blob/master/src/main/java/com/google/iot/coap/LinkFormat.java
+// https://github.com/eclipse/californium/blob/2.0.x/californium-core/src/main/java/org/eclipse/californium/core/coap/LinkFormat.java
+// https://github.com/ARMmbed/java-coap/blob/master/coap-core/src/main/java/com/mbed/coap/linkformat/LinkFormat.java
 public class Link implements Serializable {
 
     private static final long serialVersionUID = 1L;
 
     private final String url;
 
-    // TODO a map from String to Object could be a problem with serialization.
-    // TODO we are not able to make difference between string and quoted string.
     private final Map<String, Object> attributes;
 
     /**
@@ -100,6 +110,12 @@ public String toString() {
         return builder.toString();
     }
 
+    /**
+     * Parse a byte arrays representation of a {@code String} encoding with UTF_8 {@link Charset}.
+     * 
+     * @param a byte arrays representing {@code String} encoding with UTF_8 {@link Charset}.
+     * @return an array of {@code Link}
+     */
     public static Link[] parse(byte[] content) {
         if (content == null) {
             return new Link[] {};
@@ -143,22 +159,25 @@ public static Link[] parse(byte[] content) {
         return linksResult;
     }
 
-    public static final String INVALID_LINK_PAYLOAD = "<>";
     private static final String TRAILER = ", ";
 
+    /***
+     * Serialize severals {@code Link} to {@code String} as defined in http://tools.ietf.org/html/rfc6690.
+     * 
+     * @param linkObjects links to serialize.
+     * 
+     * @return a {@code String} representation like defined in http://tools.ietf.org/html/rfc6690. If LinkObjects is
+     *         empty return an empty {@code String};
+     */
     public static String serialize(Link... linkObjects) {
-        try {
-            StringBuilder builder = new StringBuilder();
-            for (Link link : linkObjects) {
-                builder.append(link.toString()).append(TRAILER);
+        StringBuilder builder = new StringBuilder();
+        if (linkObjects.length != 0) {
+            builder.append(linkObjects[0].toString());
+            for (int i = 1; i < linkObjects.length; i++) {
+                builder.append(TRAILER).append(linkObjects[i].toString());
             }
-
-            builder.delete(builder.length() - TRAILER.length(), builder.length());
-
-            return builder.toString();
-        } catch (Exception e) {
-            return null;
         }
+        return builder.toString();
     }
 
     @Override
@@ -191,4 +210,4 @@ public boolean equals(Object obj) {
             return false;
         return true;
     }
-}
+}