Context attributes as enumeration

Signed-off-by: Fabio José <fabiojose@gmail.com>

api/src/main/java/io/cloudevents/v03/ContextAttributes.java

@@ -0,0 +1,30 @@
+package io.cloudevents.v03;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+
+/**
+ * The specification reserved words: the context attributes
+ * 
+ * @author fabiojose
+ *
+ */
+public enum ContextAttributes {
+
+	id,
+	source,
+	specversion,
+	type,
+	time,
+	schemaurl,
+	datacontenttype,
+	datacontentencoding,
+	subject;
+	
+	public static final List<String> VALUES = 
+		Arrays.asList(ContextAttributes.values())
+		.stream()
+		.map(Enum::name)
+		.collect(Collectors.toList());
+}