Fix incorrect rest response header and demo double path error

dubbo-demo/dubbo-demo-interface/src/main/java/org/apache/dubbo/demo/RestDemoService.java

@@ -65,7 +65,7 @@ public interface RestDemoService {
     Boolean testBody2(Boolean b);
 
     @POST
-    @Path("/testBody3")
+    @Path("/testBody4")
     @Consumes({MediaType.TEXT_PLAIN})
     TestPO testBody2(TestPO b);
 

dubbo-rpc/dubbo-rpc-rest/src/main/java/org/apache/dubbo/rpc/protocol/rest/extension/resteasy/ResteasyContext.java

@@ -169,10 +169,13 @@ default void addResponseHeaders(NettyHttpResponse response, MultivaluedMap<Strin
         for (Map.Entry<String, List<Object>> entry : headers.entrySet()) {
 
             String key = entry.getKey();
-            if (entry.getValue() == null) {
+            List<Object> value = entry.getValue();
+            if (value == null || value.isEmpty()) {
                 continue;
             }
-            response.addOutputHeaders(key, entry.getValue().toString());
+            for (Object tmp : value) {
+                response.addOutputHeaders(key, tmp.toString());
+            }
         }
     }
 

dubbo-rpc/dubbo-rpc-rest/src/main/java/org/apache/dubbo/rpc/protocol/rest/extension/resteasy/filter/ResteasyNettyHttpResponse.java

@@ -42,7 +42,14 @@ public ResteasyNettyHttpResponse(NettyHttpResponse response) {
         for (Map.Entry<String, List<String>> headers : outputHeaders.entrySet()) {
             String key = headers.getKey();
             List<String> value = headers.getValue();
-            multivaluedMap.add(key, value);
+
+            if (value == null || value.isEmpty()) {
+                continue;
+            }
+
+            for (String val : value) {
+                multivaluedMap.add(key, val);
+            }
         }
     }
 

dubbo-rpc/dubbo-rpc-rest/src/main/java/org/apache/dubbo/rpc/protocol/rest/message/codec/JsonCodec.java

@@ -33,13 +33,12 @@
 /**
  * body is json
  */
-@Activate("json")
+@Activate(value = "json", order = 100)
 public class JsonCodec implements HttpMessageCodec<byte[], OutputStream> {
     private static final Set<Class> unSupportClasses = new HashSet<>();
 
     static {
         unSupportClasses.add(byte[].class);
-        unSupportClasses.add(String.class);
     }
 
     public static void addUnSupportClass(Class<?> unSupportClass) {

dubbo-rpc/dubbo-rpc-rest/src/main/java/org/apache/dubbo/rpc/protocol/rest/message/codec/StringCodec.java

@@ -28,7 +28,7 @@
 /**
  *  body is string
  */
-@Activate("string")
+@Activate(value = "string", order = 200)
 public class StringCodec implements HttpMessageCodec<byte[], OutputStream> {
 
     @Override

dubbo-rpc/dubbo-rpc-rest/src/main/java/org/apache/dubbo/rpc/protocol/rest/netty/NettyHttpResponse.java

@@ -190,6 +190,10 @@ public void addOutputHeaders(String name, String value) {
             outputHeaders.put(name, values);
         }
 
+        if (values.contains(value)) {
+            return;
+        }
+
         values.add(value);
     }