Messaging polyglot support (#1472)

added support for AMQP, KAFKA and standalone options

specs/spring-cloud-contract-spec-java/src/main/java/org/springframework/cloud/contract/spec/ContractConverter.java

@@ -27,7 +27,7 @@ import java.util.Collection;
  * @author Marcin Grzejszczak
  * @since 1.1.0
  */
-public interface ContractConverter<T> extends ContractStorer<T> {
+public interface ContractConverter<T> extends ContractStorer<T>, ContractReader<T> {
 
 	/**
 	 * Should this file be accepted by the converter. Can use the file extension to check

specs/spring-cloud-contract-spec-java/src/main/java/org/springframework/cloud/contract/spec/ContractReader.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2013-2020 the original author or authors.
+ *
+ * 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
+ *
+ *      https://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 org.springframework.cloud.contract.spec;
+
+/**
+ * Defines how to read converted contracts from a byte array representation back to
+ * contracts.
+ *
+ * @param <T> contracts type
+ * @author Marcin Grzejszczak
+ * @since 3.0.0
+ */
+public interface ContractReader<T> {
+
+	/**
+	 * Reads contracts from bytes.
+	 * @param bytes - byte representation of contracts
+	 * @return contracts
+	 */
+	default T read(byte[] bytes) {
+		throw new UnsupportedOperationException("Can't read contract from bytes");
+	}
+
+}