diff --git a/wsclient/src/main/java/com/google/gson/webservice/client/RestClient.java b/wsclient/src/main/java/com/google/gson/webservice/client/RestClient.java
index a6567b21..54a8d9a3 100644
--- a/wsclient/src/main/java/com/google/gson/webservice/client/RestClient.java
+++ b/wsclient/src/main/java/com/google/gson/webservice/client/RestClient.java
@@ -27,6 +27,7 @@ import com.google.gson.GsonBuilder;
 import com.google.gson.webservice.definition.WebServiceSystemException;
 import com.google.gson.webservice.definition.rest.RestCallSpec;
 import com.google.gson.webservice.definition.rest.RestRequest;
+import com.google.gson.webservice.definition.rest.RestResource;
 import com.google.gson.webservice.definition.rest.RestResponse;
 
 /**
@@ -49,7 +50,7 @@ public class RestClient {
     this.logLevel = logLevel;
   }
   
-  private URL getWebServiceUrl(RestCallSpec<?> callSpec) {
+  private URL getWebServiceUrl(RestCallSpec callSpec) {
     String url = config.getServiceBaseUrl() + callSpec.getPath().get();
     try {
       return new URL(url);
@@ -58,13 +59,14 @@ public class RestClient {
     }
   }
   
-  public <R> RestResponse<R> getResponse(RestCallSpec<R> callSpec, RestRequest<R> request) {
+  public <R extends RestResource<R>> RestResponse<R> getResponse(
+      RestCallSpec callSpec, RestRequest<R> request) {
     Gson gson = new GsonBuilder().create();
     return getResponse(callSpec, request, gson);
   }
 
-  public <R> RestResponse<R> getResponse(
-      RestCallSpec<R> callSpec, RestRequest<R> request, Gson gson) {
+  public <R extends RestResource<R>> RestResponse<R> getResponse(
+      RestCallSpec callSpec, RestRequest<R> request, Gson gson) {
     HttpURLConnection conn = null;
     try {
       URL webServiceUrl = getWebServiceUrl(callSpec);
@@ -84,8 +86,8 @@ public class RestClient {
    * Use this method if you want to mange the HTTP Connection yourself. This is useful when you
    * want to use HTTP pipelining.
    */
-  public <R> RestResponse<R> getResponse(
-      RestCallSpec<R> callSpec, RestRequest<R> request, Gson gson, HttpURLConnection conn) {
+  public <R extends RestResource<R>> RestResponse<R> getResponse(
+      RestCallSpec callSpec, RestRequest<R> request, Gson gson, HttpURLConnection conn) {
     try {
       if (logger != null) {
         URL webServiceUrl = getWebServiceUrl(callSpec);
diff --git a/wsclient/src/main/java/com/google/gson/webservice/client/RestRequestSender.java b/wsclient/src/main/java/com/google/gson/webservice/client/RestRequestSender.java
index 6c432691..3a90272f 100644
--- a/wsclient/src/main/java/com/google/gson/webservice/client/RestRequestSender.java
+++ b/wsclient/src/main/java/com/google/gson/webservice/client/RestRequestSender.java
@@ -27,6 +27,7 @@ import com.google.gson.webservice.definition.HeaderMap;
 import com.google.gson.webservice.definition.HeaderMapSpec;
 import com.google.gson.webservice.definition.WebServiceSystemException;
 import com.google.gson.webservice.definition.rest.RestRequest;
+import com.google.gson.webservice.definition.rest.RestResource;
 
 /**
  * Class to send Web service requests on a {@link HttpURLConnection}.
@@ -48,7 +49,7 @@ public final class RestRequestSender {
     this.logLevel = logLevel;
   }
   
-  public <R> void send(HttpURLConnection conn, RestRequest<R> request) {    
+  public <R extends RestResource<R>> void send(HttpURLConnection conn, RestRequest<R> request) {    
     try {
       conn.setRequestMethod(request.getHttpMethod().toString());
       setHeader(conn, "Content-Type", request.getContentType(), true);
@@ -63,7 +64,7 @@ public final class RestRequestSender {
       // Android Java VM ignore Content-Length if setDoOutput is not set
       conn.setDoOutput(true);
       if (requestBody != null) {
-        requestBodyContents = gson.toJson(requestBody);
+        requestBodyContents = gson.toJson(requestBody, request.getSpec().getResourceType());
       }
       String contentLength = String.valueOf(requestBodyContents.length());
       setHeader(conn, "Content-Length", contentLength, true);
diff --git a/wsclient/src/main/java/com/google/gson/webservice/client/RestResponseReceiver.java b/wsclient/src/main/java/com/google/gson/webservice/client/RestResponseReceiver.java
index f2d2a4cf..a178800e 100644
--- a/wsclient/src/main/java/com/google/gson/webservice/client/RestResponseReceiver.java
+++ b/wsclient/src/main/java/com/google/gson/webservice/client/RestResponseReceiver.java
@@ -30,6 +30,7 @@ import com.google.gson.webservice.definition.ContentBodySpec;
 import com.google.gson.webservice.definition.HeaderMap;
 import com.google.gson.webservice.definition.HeaderMapSpec;
 import com.google.gson.webservice.definition.WebServiceSystemException;
+import com.google.gson.webservice.definition.rest.RestResource;
 import com.google.gson.webservice.definition.rest.RestResponse;
 import com.google.gson.webservice.definition.rest.RestResponseSpec;
 
@@ -38,16 +39,16 @@ import com.google.gson.webservice.definition.rest.RestResponseSpec;
  * 
  * @author inder
  */
-public final class RestResponseReceiver<R> {
+public final class RestResponseReceiver<R extends RestResource<R>> {
   private final Gson gson;
-  private final RestResponseSpec<R> spec;
+  private final RestResponseSpec spec;
   private final Logger logger;
   private final Level logLevel;
 
-  public RestResponseReceiver(Gson gson, RestResponseSpec<R> spec) {
+  public RestResponseReceiver(Gson gson, RestResponseSpec spec) {
     this(gson, spec, null);
   }
-  public RestResponseReceiver(Gson gson, RestResponseSpec<R> spec, Level logLevel) {
+  public RestResponseReceiver(Gson gson, RestResponseSpec spec, Level logLevel) {
     this.gson = gson;
     this.spec = spec;
     this.logger = logLevel == null ? null : Logger.getLogger(RestResponseReceiver.class.getName());
@@ -57,11 +58,11 @@ public final class RestResponseReceiver<R> {
   public RestResponse<R> receive(HttpURLConnection conn) {
     try {
       HeaderMapSpec paramSpec = spec.getHeadersSpec();
-      Class<R> bodySpec = spec.getResourceClass();
+      Type bodyType = spec.getResourceType();
       // read response
       HeaderMap responseParams = readResponseHeaders(conn, paramSpec);
-      R responseBody = readResponseBody(conn, bodySpec);
-      return new RestResponse<R>(responseParams, responseBody);
+      R responseBody = readResponseBody(conn, bodyType);
+      return new RestResponse<R>(responseParams, responseBody, bodyType);
     } catch (IOException e) {
       throw new WebServiceSystemException(e);
     }
@@ -84,11 +85,13 @@ public final class RestResponseReceiver<R> {
     return paramsBuilder.build();
   }
 
-  private R readResponseBody(HttpURLConnection conn, Class<R> resourceClass) throws IOException {
+  @SuppressWarnings("unchecked")
+  private R readResponseBody(
+      HttpURLConnection conn, Type resourceType) throws IOException {
     String connContentType = conn.getContentType();
     Preconditions.checkArgument(connContentType.contains(ContentBodySpec.JSON_CONTENT_TYPE), conn);
     Reader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
-    R body = gson.fromJson(reader, resourceClass);
+    R body = (R) gson.fromJson(reader, resourceType);
     return body;
   }
 }
diff --git a/wsdef/src/main/java/com/google/gson/webservice/definition/rest/HasId.java b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/HasId.java
new file mode 100644
index 00000000..3bd9ad42
--- /dev/null
+++ b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/HasId.java
@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2010 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.gson.webservice.definition.rest;
+
+/**
+ * An interface to indicate that an object has an Id
+ *
+ * @author inder
+ *
+ * @param <T> type of object
+ */
+public interface HasId<R> {
+  public Id<R> getId();
+  public void setId(Id<R> id);
+  public boolean hasId();
+}
diff --git a/wsdef/src/main/java/com/google/gson/webservice/definition/rest/Id.java b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/Id.java
new file mode 100644
index 00000000..20b3349d
--- /dev/null
+++ b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/Id.java
@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2010 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.gson.webservice.definition.rest;
+
+import java.lang.reflect.Type;
+
+/**
+ * An id for a rest resource
+ *
+ * @author inder
+ *
+ * @param <R> type variable for the rest resource
+ */
+public final class Id<R> {
+  private final long value;
+  private final Type typeOfId;
+
+  private Id(long value, Type typeOfId) {
+    this.value = value;
+    this.typeOfId = typeOfId;
+  }
+
+  public long getValue() {
+    return value;
+  }
+
+  public Type getTypeOfId() {
+    return typeOfId;
+  }
+
+  @Override
+  public int hashCode() {
+    final int prime = 31;
+    int result = 1;
+    result = prime * result + ((typeOfId == null) ? 0 : typeOfId.hashCode());
+    result = prime * result + (int)(value ^ (value >>> 32));
+    return result;
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (this == obj) return true;
+    if (obj == null) return false;
+    if (getClass() != obj.getClass()) return false;
+    @SuppressWarnings("unchecked")
+    Id<R> other = (Id<R>)obj;
+    if (typeOfId == null) {
+      if (other.typeOfId != null) return false;
+    } else if (!typeOfId.equals(other.typeOfId)) return false;
+    if (value != other.value) return false;
+    return true;
+  }
+
+  public static <RS> Id<RS> get(long value, Type typeOfId) {
+    return new Id<RS>(value, typeOfId);
+  }
+
+  @Override
+  public String toString() {
+    return String.format("{value:%s,type:%s}", value, typeOfId);
+  }
+}
diff --git a/wsdef/src/main/java/com/google/gson/webservice/definition/rest/ResourceMap.java b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/ResourceMap.java
index 920eb615..db2fcd4e 100644
--- a/wsdef/src/main/java/com/google/gson/webservice/definition/rest/ResourceMap.java
+++ b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/ResourceMap.java
@@ -28,10 +28,11 @@ import com.google.gson.webservice.definition.CallPath;
 public final class ResourceMap {
 
   public static final class Builder {
-    private final Map<CallPath, RestCallSpec<?>> resources =
-      new HashMap<CallPath, RestCallSpec<?>>();
+    private final Map<CallPath, RestCallSpec> resources =
+      new HashMap<CallPath, RestCallSpec>();
     
-    public <R> Builder set(CallPath callPath, RestCallSpec<R> spec) {
+    public Builder set(CallPath callPath, RestCallSpec spec) {
+      Preconditions.checkArgument(resources.get(callPath) == null);
       resources.put(callPath, spec);
       return this;
     }
@@ -41,15 +42,13 @@ public final class ResourceMap {
     }
   }
 
-  private final Map<CallPath, RestCallSpec<?>> resources;
+  private final Map<CallPath, RestCallSpec> resources;
 
-  public ResourceMap(Map<CallPath, RestCallSpec<?>> resources) {
+  public ResourceMap(Map<CallPath, RestCallSpec> resources) {
     this.resources = resources;
   }
 
-  public <T> RestCallSpec<T> get(CallPath callPath) {
-    @SuppressWarnings("unchecked")
-    RestCallSpec<T> restCallSpec = (RestCallSpec<T>)resources.get(callPath);
-    return restCallSpec;
+  public RestCallSpec get(CallPath callPath) {
+    return (RestCallSpec)resources.get(callPath);
   }
 }
diff --git a/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestCall.java b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestCall.java
index 9af43f5c..6d6b0acd 100644
--- a/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestCall.java
+++ b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestCall.java
@@ -21,19 +21,19 @@ package com.google.gson.webservice.definition.rest;
  * 
  * @author inder
  */
-public final class RestCall<R> {
+public final class RestCall<R extends RestResource<R>> {
   
-  private final RestCallSpec<R> callSpec;
+  private final RestCallSpec callSpec;
   private final RestRequest<R> request;
   private final RestResponse<R> response;
   
-  public RestCall(RestCallSpec<R> callSpec, RestRequest<R> request, RestResponse<R> response) {
+  public RestCall(RestCallSpec callSpec, RestRequest<R> request, RestResponse<R> response) {
     this.callSpec = callSpec;
     this.request = request;
     this.response = response;
   }
 
-  public RestCallSpec<R> getSpec() {
+  public RestCallSpec getSpec() {
     return callSpec;
   }
   
diff --git a/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestCallSpec.java b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestCallSpec.java
index 1d567ada..c7163459 100644
--- a/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestCallSpec.java
+++ b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestCallSpec.java
@@ -15,6 +15,7 @@
  */
 package com.google.gson.webservice.definition.rest;
 
+import java.lang.reflect.Type;
 import java.util.Arrays;
 import java.util.LinkedHashSet;
 import java.util.Set;
@@ -29,61 +30,64 @@ import com.google.gson.webservice.definition.TypedKey;
  *
  * @author inder
  */
-public final class RestCallSpec<R> {
-  public static class Builder<R> {
+public final class RestCallSpec {
+  public static class Builder {
     private final CallPath callPath;
     private final Set<HttpMethod> supportedHttpMethods = new LinkedHashSet<HttpMethod>();
     private final HeaderMapSpec.Builder reqParamsSpecBuilder = new HeaderMapSpec.Builder();
     private final HeaderMapSpec.Builder resParamsSpecBuilder = new HeaderMapSpec.Builder();
-    private final Class<R> resourceClass;
+    private final Type resourceType;
     
-    public Builder(CallPath callPath, Class<R> resourceClass) {
+    public Builder(CallPath callPath, Type resourceType) {
       this.callPath = callPath;
       supportedHttpMethods.addAll(HttpMethod.ALL_METHODS);
-      this.resourceClass = resourceClass;
+      this.resourceType = resourceType;
     }
 
-    public Builder<R> disableHttpMethod(HttpMethod httpMethod) {
+    public Builder disableHttpMethod(HttpMethod httpMethod) {
       supportedHttpMethods.remove(httpMethod);
       return this;
     }
     
-    public <T> Builder<R> addRequestParam(TypedKey<T> param) {
+    public <T> Builder addRequestParam(TypedKey<T> param) {
       reqParamsSpecBuilder.put(param.getName(), param.getClassOfT());
       return this;
     }
 
-    public <T> Builder<R> addResponseParam(TypedKey<T> param) {
+    public <T> Builder addResponseParam(TypedKey<T> param) {
       resParamsSpecBuilder.put(param.getName(), param.getClassOfT());
       return this;
     }
 
-    public RestCallSpec<R> build() {
+    public RestCallSpec build() {
       if (supportedHttpMethods.isEmpty()) {
         supportedHttpMethods.addAll(Arrays.asList(HttpMethod.values()));
       }
-      RestRequestSpec<R> requestSpec = 
-        new RestRequestSpec<R>(reqParamsSpecBuilder.build(), resourceClass);
-      RestResponseSpec<R> responseSpec =
-        new RestResponseSpec<R>(resParamsSpecBuilder.build(), resourceClass);
-      return new RestCallSpec<R>(supportedHttpMethods, callPath, 
-          requestSpec, responseSpec);
+      RestRequestSpec requestSpec = 
+        new RestRequestSpec(reqParamsSpecBuilder.build(), resourceType);
+      RestResponseSpec responseSpec =
+        new RestResponseSpec(resParamsSpecBuilder.build(), resourceType);
+      return new RestCallSpec(supportedHttpMethods, callPath, 
+          requestSpec, responseSpec, resourceType);
     }
   }
 
   private final Set<HttpMethod> supportedHttpMethods;
   private final CallPath path;
-  private final RestRequestSpec<R> requestSpec;
-  private final RestResponseSpec<R> responseSpec;
+  private final RestRequestSpec requestSpec;
+  private final RestResponseSpec responseSpec;
+  private final Type resourceType;
 
   private RestCallSpec(Set<HttpMethod> supportedHttpMethods, CallPath path,
-      RestRequestSpec<R> requestSpec, RestResponseSpec<R> responseSpec) {
+      RestRequestSpec requestSpec, RestResponseSpec responseSpec,
+      Type resourceType) {
     Preconditions.checkArgument(!supportedHttpMethods.isEmpty());
     Preconditions.checkNotNull(path);
     this.supportedHttpMethods = supportedHttpMethods;
     this.path = path;
     this.requestSpec = requestSpec;
     this.responseSpec = responseSpec;
+    this.resourceType = resourceType;
   }
 
   public CallPath getPath() {
@@ -94,11 +98,15 @@ public final class RestCallSpec<R> {
     return supportedHttpMethods;
   }
 
-  public RestResponseSpec<R> getResponseSpec() {
+  public RestResponseSpec getResponseSpec() {
     return responseSpec;
   }
   
-  public RestRequestSpec<R> getRequestSpec() {
+  public RestRequestSpec getRequestSpec() {
     return requestSpec;
   }
+
+  public Type getResourceType() {
+    return resourceType;
+  }
 }
diff --git a/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestRequest.java b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestRequest.java
index d354b88a..41a39a25 100644
--- a/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestRequest.java
+++ b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestRequest.java
@@ -15,6 +15,8 @@
  */
 package com.google.gson.webservice.definition.rest;
 
+import java.lang.reflect.Type;
+
 import com.google.gson.webservice.definition.ContentBodySpec;
 import com.google.gson.webservice.definition.HeaderMap;
 import com.google.gson.webservice.definition.HttpMethod;
@@ -27,25 +29,29 @@ import com.google.gson.webservice.definition.TypedKey;
  * 
  * @author inder
  */
-public final class RestRequest<R> {
+public final class RestRequest<R extends RestResource<R>> {
   private final HttpMethod method;
   private final HeaderMap headers;
   private final R body;
-  private final RestRequestSpec<R> spec;
+  private final RestRequestSpec spec;
   
   public RestRequest(HttpMethod method, HeaderMap requestHeaders,
-      R requestBody, Class<R> resourceClass) {
+      R requestBody, Type resourceType) {
     this.method = method;
     this.body = requestBody;
     this.headers = requestHeaders;
-    this.spec = new RestRequestSpec<R>(requestHeaders.getSpec(), resourceClass);
+    this.spec = new RestRequestSpec(requestHeaders.getSpec(), resourceType);
+  }
+
+  public Id<R> getId() {
+    return body.getId();
   }
 
   public HttpMethod getMethod() {
     return method;
   }
 
-  public RestRequestSpec<R> getSpec() {
+  public RestRequestSpec getSpec() {
     return spec;
   }
 
diff --git a/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestRequestSpec.java b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestRequestSpec.java
index 4595fb36..9fba1053 100644
--- a/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestRequestSpec.java
+++ b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestRequestSpec.java
@@ -15,6 +15,8 @@
  */
 package com.google.gson.webservice.definition.rest;
 
+import java.lang.reflect.Type;
+
 import com.google.gson.webservice.definition.HeaderMapSpec;
 
 /**
@@ -22,17 +24,17 @@ import com.google.gson.webservice.definition.HeaderMapSpec;
  * 
  * @author inder
  */
-public final class RestRequestSpec<R> {
+public final class RestRequestSpec {
   private final HeaderMapSpec headersSpec;
-  private final Class<R> resourceClass;
+  private final Type resourceType;
 
-  public RestRequestSpec(HeaderMapSpec headersSpec, Class<R> resourceClass) {
+  public RestRequestSpec(HeaderMapSpec headersSpec, Type resourceClass) {
     this.headersSpec = headersSpec;
-    this.resourceClass = resourceClass;
+    this.resourceType = resourceClass;
   }
 
-  public Class<R> getResourceClass() {
-    return resourceClass;
+  public Type getResourceType() {
+    return resourceType;
   }
 
   public HeaderMapSpec getHeadersSpec() {
@@ -41,6 +43,6 @@ public final class RestRequestSpec<R> {
   
   @Override
   public String toString() {
-    return String.format("{headersSpec:%s,resourceClass:%s}", headersSpec, resourceClass);
+    return String.format("{headersSpec:%s,resourceType:%s}", headersSpec, resourceType);
   }
 }
diff --git a/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestResource.java b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestResource.java
new file mode 100644
index 00000000..ed414095
--- /dev/null
+++ b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestResource.java
@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2010 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.gson.webservice.definition.rest;
+
+/**
+ * An interface implemented by an object that is intended to be a rest resource
+ *
+ * @author inder
+ *
+ * @param <R> the rest resource type
+ */
+public interface RestResource<R> extends HasId<R> {
+
+}
diff --git a/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestResponse.java b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestResponse.java
index e32829b8..e5d92b73 100644
--- a/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestResponse.java
+++ b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestResponse.java
@@ -15,6 +15,8 @@
  */
 package com.google.gson.webservice.definition.rest;
 
+import java.lang.reflect.Type;
+
 import com.google.gson.webservice.definition.HeaderMap;
 import com.google.gson.webservice.definition.TypedKey;
 
@@ -24,52 +26,50 @@ import com.google.gson.webservice.definition.TypedKey;
  * 
  * @author inder
  */
-public final class RestResponse<R> {
+public final class RestResponse<R extends RestResource<R>> {
   
   private final HeaderMap headers;
   private final R body;
-  private final RestResponseSpec<R> spec;
+  private final RestResponseSpec spec;
   
-  public static class Builder<R> {
+  public static class Builder<RS extends RestResource<RS>> {
     private final HeaderMap.Builder headers;
-    private R body;
-    private final RestResponseSpec<R> spec;
+    private RS body;
+    private final RestResponseSpec spec;
     
-    public Builder(RestResponseSpec<R> spec) {
+    public Builder(RestResponseSpec spec) {
       this.spec = spec;
       headers = new HeaderMap.Builder(spec.getHeadersSpec());
     }
     
-    public <T> Builder<R> putHeader(TypedKey<T> paramName, T content) {
+    public <T> Builder<RS> putHeader(TypedKey<T> paramName, T content) {
       headers.put(paramName.getName(), content, paramName.getClassOfT());
       return this;
     }
     
-    public Builder<R> setBody(R body) {
+    public Builder<RS> setBody(RS body) {
       this.body = body;
       return this;
     }
 
-    public RestResponse<R> build() {
-      return new RestResponse<R>(spec, headers.build(), body);
+    public RestResponse<RS> build() {
+      return new RestResponse<RS>(spec, headers.build(), body);
     }
   }
   
-  private RestResponse(RestResponseSpec<R> spec, HeaderMap headers, R body) {
+  private RestResponse(RestResponseSpec spec, HeaderMap headers, R body) {
     this.spec = spec;
     this.headers = headers;
     this.body = body;
   }
   
-  @SuppressWarnings("unchecked")
-  public RestResponse(HeaderMap responseHeaders, R responseBody) {
-    this.spec = new RestResponseSpec<R>(responseHeaders.getSpec(),
-        (Class<R>)responseBody.getClass());
+  public RestResponse(HeaderMap responseHeaders, R responseBody, Type responseBodyType) {
+    this.spec = new RestResponseSpec(responseHeaders.getSpec(), responseBodyType);
     this.headers = responseHeaders;
     this.body = responseBody;
   }
 
-  public RestResponseSpec<R> getSpec() {
+  public RestResponseSpec getSpec() {
     return spec;
   }
 
diff --git a/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestResponseSpec.java b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestResponseSpec.java
index 679bc3fd..2ce01aea 100644
--- a/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestResponseSpec.java
+++ b/wsdef/src/main/java/com/google/gson/webservice/definition/rest/RestResponseSpec.java
@@ -15,6 +15,8 @@
  */
 package com.google.gson.webservice.definition.rest;
 
+import java.lang.reflect.Type;
+
 import com.google.gson.webservice.definition.HeaderMapSpec;
 
 /**
@@ -22,17 +24,17 @@ import com.google.gson.webservice.definition.HeaderMapSpec;
  * 
  * @author inder
  */
-public final class RestResponseSpec<R> {
+public final class RestResponseSpec {
   private final HeaderMapSpec headersSpec;
-  private final Class<R> resourceClass;
+  private final Type resourceType;
 
-  public RestResponseSpec(HeaderMapSpec headersSpec, Class<R> resourceClass) {
+  public RestResponseSpec(HeaderMapSpec headersSpec, Type resourceType) {
     this.headersSpec = headersSpec;
-    this.resourceClass = resourceClass;
+    this.resourceType = resourceType;
   }
 
-  public Class<R> getResourceClass() {
-    return resourceClass;
+  public Type getResourceType() {
+    return resourceType;
   }
 
   public HeaderMapSpec getHeadersSpec() {
@@ -41,6 +43,6 @@ public final class RestResponseSpec<R> {
   
   @Override
   public String toString() {
-    return String.format("{headersSpec:%s,resourceClass:%s}", headersSpec, resourceClass);
+    return String.format("{headersSpec:%s,resourceType:%s}", headersSpec, resourceType);
   }
 }
diff --git a/wsf/pom.xml b/wsf/pom.xml
index 2fac729c..31c67b7d 100755
--- a/wsf/pom.xml
+++ b/wsf/pom.xml
@@ -69,12 +69,6 @@
       <version>0.1</version>
       <scope>compile</scope>
     </dependency>
-    <dependency>
-      <groupId>com.google.code.gson</groupId>
-      <artifactId>wsclient</artifactId>
-      <version>0.1</version>
-      <scope>compile</scope>
-    </dependency>
 
     <!-- Guice: Dependency injection -->
     <dependency>
diff --git a/wsf/src/main/java/com/google/gson/wsf/server/rest/IdMap.java b/wsf/src/main/java/com/google/gson/wsf/server/rest/IdMap.java
new file mode 100644
index 00000000..d04f61ae
--- /dev/null
+++ b/wsf/src/main/java/com/google/gson/wsf/server/rest/IdMap.java
@@ -0,0 +1,77 @@
+/*
+ * Copyright (C) 2010 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.gson.wsf.server.rest;
+
+import java.lang.reflect.Type;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+import com.google.gson.webservice.definition.rest.HasId;
+import com.google.gson.webservice.definition.rest.Id;
+
+/**
+ * This class provides a type-safe map to access values associated with Ids
+ *
+ * @author inder
+ *
+ * @param <T> the type of the objects being kept in the map
+ */
+public class IdMap<T extends HasId<T>> {
+  public static final Logger LOG = Logger.getLogger(IdMap.class.getName());
+  protected final Map<Id<T>, T> map;
+  private volatile long nextAvailableId;
+  private final Type typeOfId;
+
+  /**
+   * Use {@link #create(Class)} instead of constructor
+   */
+  protected IdMap(Type typeOfId) {
+    this.typeOfId = typeOfId;
+    map = new ConcurrentHashMap<Id<T>, T>();
+    nextAvailableId = 0;
+  }
+
+  public T get(Id<T> id) {
+    return map.get(id);
+  }
+
+  public T put(T obj) {
+    map.put(obj.getId(), obj);
+    return obj;
+  }
+
+  public void delete(Id<T> id) {
+    T removed = map.remove(id);
+    if (removed == null) {
+      LOG.log(Level.WARNING, "Attempted to delete non-existent id: {0}", id);
+    }
+  }
+
+  public boolean exists(Id<T> id) {
+    return map.containsKey(id);
+  }
+
+  public synchronized Id<T> getNextId() {
+    long id = nextAvailableId++;
+    return Id.get(id, typeOfId);
+  }
+
+  public static <S extends HasId<S>> IdMap<S> create(Type typeOfId) {
+    return new IdMap<S>(typeOfId);
+  }
+}
diff --git a/wsf/src/main/java/com/google/gson/wsf/server/rest/MetaData.java b/wsf/src/main/java/com/google/gson/wsf/server/rest/MetaData.java
new file mode 100644
index 00000000..4b23a0f8
--- /dev/null
+++ b/wsf/src/main/java/com/google/gson/wsf/server/rest/MetaData.java
@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2010 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.gson.wsf.server.rest;
+
+import com.google.gson.webservice.definition.rest.RestResource;
+
+/**
+ * Metadata associated with a repository for a rest resource
+ *
+ * @author inder
+ *
+ * @param <R> The resource
+ */
+public final class MetaData<R extends RestResource<R>> {
+
+  final boolean freshlyAssignedId;
+
+  public MetaData(boolean freshlyAssignedId) {
+    this.freshlyAssignedId = freshlyAssignedId;
+  }
+
+  public boolean isFreshlyAssignedId() {
+    return freshlyAssignedId;
+  }
+}
\ No newline at end of file
diff --git a/wsf/src/main/java/com/google/gson/wsf/server/rest/Repository.java b/wsf/src/main/java/com/google/gson/wsf/server/rest/Repository.java
new file mode 100644
index 00000000..15951fcd
--- /dev/null
+++ b/wsf/src/main/java/com/google/gson/wsf/server/rest/Repository.java
@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2010 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.gson.wsf.server.rest;
+
+import com.google.gson.webservice.definition.rest.HasId;
+import com.google.gson.webservice.definition.rest.Id;
+
+/**
+ * An interface for a repository of rest resources. Meant for abstracting the server-side
+ * storage of rest resources.
+ *
+ * @author inder
+ *
+ * @param <R> the type of rest resource
+ */
+public interface Repository<R extends HasId<R>> {
+  public R get(Id<R> resourceId);
+
+  /**
+   * if resource.getId() == null, inserts the resource after assigning it a new id.
+   * Otherwise, updates the resource ensuring that it pre-exists.
+   */
+  public R put(R resource);
+
+  public void delete(Id<R> resourceId);
+  
+  public boolean exists(Id<R> resourceId);
+
+  /**
+   * Ensures that the specified resource has a valid id that will be used when it is saved
+   */
+  public Id<R> assignId(R resource);
+
+  public Id<R> getNextId();
+}
diff --git a/wsf/src/main/java/com/google/gson/wsf/server/rest/RepositoryInMemory.java b/wsf/src/main/java/com/google/gson/wsf/server/rest/RepositoryInMemory.java
new file mode 100644
index 00000000..9ccd7156
--- /dev/null
+++ b/wsf/src/main/java/com/google/gson/wsf/server/rest/RepositoryInMemory.java
@@ -0,0 +1,95 @@
+/*
+ * Copyright (C) 2010 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.gson.wsf.server.rest;
+
+import java.util.Map;
+
+import com.google.gson.webservice.definition.rest.Id;
+import com.google.gson.webservice.definition.rest.RestResource;
+import com.google.inject.internal.Maps;
+import com.google.inject.internal.Preconditions;
+
+/**
+ * An in-memory map of rest resources
+ *
+ * @author inder
+ *
+ * @param <R> Type variable for the resource
+ */
+public class RepositoryInMemory<R extends RestResource<R>> implements Repository<R> {
+  private final IdMap<R> resources;
+  private final Map<Id<R>, MetaData<R>> metaDataMap;
+
+  public RepositoryInMemory(Class<? super R> classOfResource) {
+    this.resources = IdMap.create(classOfResource);
+    this.metaDataMap = Maps.newHashMap();
+  }
+
+  @Override
+  public R get(Id<R> resourceId) {
+    return resources.get(resourceId);
+  }
+
+  public boolean isFreshlyAssignedId(Id<R> resourceId) {
+    MetaData<R> metaData = metaDataMap.get(resourceId);
+    if (metaData == null) {
+      return false;
+    }
+    return metaData.isFreshlyAssignedId();
+  }
+
+  @Override
+  public R put(R resource) {
+    if (!resource.hasId()) {
+      // insert semantics
+      assignId(resource);
+    } else {
+      Id<R> id = resource.getId();
+      if (!isFreshlyAssignedId(id)) {
+        // update semantics
+        Preconditions.checkState(resources.exists(resource.getId()));
+      }
+    }
+    resource = resources.put(resource);
+    metaDataMap.remove(resource.getId());
+    return resource;
+  }
+
+  @Override
+  public void delete(Id<R> resourceId) {
+    resources.delete(resourceId);
+  }
+
+  @Override
+  public boolean exists(Id<R> resourceId) {
+    return resources.exists(resourceId);
+  }
+
+  @Override
+  public Id<R> getNextId() {
+    return resources.getNextId();
+  }
+
+  @Override
+  public Id<R> assignId(R resource) {
+    if (resource.getId() == null) {
+      Id<R> id = resources.getNextId();
+      resource.setId(id);
+      metaDataMap.put(id, new MetaData<R>(true));
+    }
+    return resource.getId();
+  }
+}
diff --git a/wsf/src/main/java/com/google/gson/wsf/server/rest/RestRequestReceiver.java b/wsf/src/main/java/com/google/gson/wsf/server/rest/RestRequestReceiver.java
index 196ef5da..d9adcf89 100644
--- a/wsf/src/main/java/com/google/gson/wsf/server/rest/RestRequestReceiver.java
+++ b/wsf/src/main/java/com/google/gson/wsf/server/rest/RestRequestReceiver.java
@@ -32,18 +32,19 @@ import com.google.gson.webservice.definition.HttpMethod;
 import com.google.gson.webservice.definition.WebServiceSystemException;
 import com.google.gson.webservice.definition.rest.RestRequest;
 import com.google.gson.webservice.definition.rest.RestRequestSpec;
+import com.google.gson.webservice.definition.rest.RestResource;
 
 /**
  * Receives and parses a request at the server side on a {@link HttpServletRequest}.  
  * 
  * @author inder
  */
-public final class RestRequestReceiver<R> {
+public final class RestRequestReceiver<R extends RestResource<R>> {
 
   private final Gson gson;
-  private final RestRequestSpec<R> spec;
+  private final RestRequestSpec spec;
 
-  public RestRequestReceiver(Gson gson, RestRequestSpec<R> spec) {
+  public RestRequestReceiver(Gson gson, RestRequestSpec spec) {
     this.gson = gson;
     this.spec = spec;
   }
@@ -54,7 +55,7 @@ public final class RestRequestReceiver<R> {
       R requestBody = buildRequestBody(request);
       
       HttpMethod method = HttpMethod.getMethod(request.getMethod());
-      return new RestRequest<R>(method, requestParams, requestBody, spec.getResourceClass());
+      return new RestRequest<R>(method, requestParams, requestBody, spec.getResourceType());
     } catch (IOException e) {
       throw new WebServiceSystemException(e);
     } catch (JsonParseException e) {
@@ -83,9 +84,8 @@ public final class RestRequestReceiver<R> {
   }
   
   private R buildRequestBody(HttpServletRequest request) throws IOException {
-    Class<R> resourceClass = spec.getResourceClass();
     Reader reader = new BufferedReader(new InputStreamReader(request.getInputStream()));
-    R requestBody = gson.fromJson(reader, resourceClass);
+    R requestBody = gson.fromJson(reader, spec.getResourceType());
     return requestBody;
   }
 }
diff --git a/wsf/src/main/java/com/google/gson/wsf/server/rest/RestResponseBuilder.java b/wsf/src/main/java/com/google/gson/wsf/server/rest/RestResponseBuilder.java
index 65aeb9bd..c8a41306 100644
--- a/wsf/src/main/java/com/google/gson/wsf/server/rest/RestResponseBuilder.java
+++ b/wsf/src/main/java/com/google/gson/wsf/server/rest/RestResponseBuilder.java
@@ -15,11 +15,54 @@
  */
 package com.google.gson.wsf.server.rest;
 
-import com.google.gson.webservice.definition.rest.RestRequest;
-import com.google.gson.webservice.definition.rest.RestResponse;
+import com.google.gson.webservice.definition.HttpMethod;
+import com.google.gson.webservice.definition.rest.Id;
 import com.google.gson.webservice.definition.rest.RestCallSpec;
+import com.google.gson.webservice.definition.rest.RestRequest;
+import com.google.gson.webservice.definition.rest.RestResource;
+import com.google.gson.webservice.definition.rest.RestResponse;
 
-public interface RestResponseBuilder<R> {
-  public void buildResponse(RestCallSpec<R> callSpec, RestRequest<R> request,
-      RestResponse.Builder<R> responseBuilder); 
+public abstract class RestResponseBuilder<R extends RestResource<R>> {
+  protected final Repository<R> resources;
+
+  public RestResponseBuilder(Repository<R> resources) {
+    this.resources = resources;
+  }
+
+  public void buildResponse(RestCallSpec callSpec, RestRequest<R> request,
+      RestResponse.Builder<R> responseBuilder) {
+    HttpMethod method = request.getMethod();
+    R responseBody = null;
+    switch (method) {
+      case GET:
+        responseBody = get(request.getId());
+        break;
+      case POST:
+        responseBody = post(request.getBody());
+        break;
+      case DELETE:
+        delete(request.getId());
+        break;
+      case PUT:
+      default:
+        throw new IllegalStateException("Unexpected method: " + method);
+    }
+    responseBuilder.setBody(responseBody);
+  }
+
+  public R get(Id<R> resourceId) {
+    return resources.get(resourceId);
+  }
+
+  public R post(R resource) {
+    return resources.put(resource);
+  }
+
+  public void delete(Id<R> resourceId) {
+    resources.delete(resourceId);
+  }
+
+  public R put(R resource) {
+    return resources.put(resource);
+  }
 }
diff --git a/wsf/src/main/java/com/google/gson/wsf/server/rest/RestResponseSender.java b/wsf/src/main/java/com/google/gson/wsf/server/rest/RestResponseSender.java
index cad49138..edfa5f31 100644
--- a/wsf/src/main/java/com/google/gson/wsf/server/rest/RestResponseSender.java
+++ b/wsf/src/main/java/com/google/gson/wsf/server/rest/RestResponseSender.java
@@ -26,6 +26,7 @@ import com.google.gson.Gson;
 import com.google.gson.webservice.definition.ContentBodySpec;
 import com.google.gson.webservice.definition.HeaderMap;
 import com.google.gson.webservice.definition.HeaderMapSpec;
+import com.google.gson.webservice.definition.rest.RestResource;
 import com.google.gson.webservice.definition.rest.RestResponse;
 
 /**
@@ -33,7 +34,7 @@ import com.google.gson.webservice.definition.rest.RestResponse;
  * 
  * @author inder
  */
-public final class RestResponseSender<R> {
+public final class RestResponseSender<R extends RestResource<R>> {
   private static final Logger logger = Logger.getLogger(RestResponseSender.class.getCanonicalName());
 
   private Gson gson;