GH-570 Remove hard dependency on Gson for GCP

Resolves #570

spring-cloud-function-adapters/spring-cloud-function-adapter-gcp/src/main/java/org/springframework/cloud/function/adapter/gcp/FunctionInvoker.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020-2020 the original author or authors.
+ * Copyright 2020-2021 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.
@@ -66,7 +66,6 @@ public class FunctionInvoker extends AbstractSpringFunctionAdapterInitializer<Ht
 		if (System.getenv().containsKey("spring.cloud.function.definition")) {
 			this.functionName = System.getenv("spring.cloud.function.definition");
 		}
-		System.setProperty("spring.http.converters.preferred-json-mapper", "gson");
 		Thread.currentThread() // TODO: remove after upgrading to 1.0.0-alpha-2-rc5
 				.setContextClassLoader(FunctionInvoker.class.getClassLoader());
 		initialize(null);

spring-cloud-function-adapters/spring-cloud-function-adapter-gcp/src/test/java/org/springframework/cloud/function/adapter/gcp/FunctionInvokerBackgroundTests.java

@@ -245,24 +245,45 @@ public class FunctionInvokerBackgroundTests {
 
 	}
 
-	private static class IncomingRequest {
+	public static class IncomingRequest {
 
 		String message;
 
-		IncomingRequest(String message) {
+		public IncomingRequest(String message) {
 			this.message = message;
 		}
 
+		public IncomingRequest() {
+		}
+
+		public String getMessage() {
+			return message;
+		}
+
+		public void setMessage(String message) {
+			this.message = message;
+		}
 	}
 
-	private static class OutgoingResponse {
+	public static class OutgoingResponse {
 
 		String message;
 
+		public String getMessage() {
+			return message;
+		}
+
+		public void setMessage(String message) {
+			this.message = message;
+		}
+
 		OutgoingResponse(String message) {
 			this.message = message;
 		}
 
+		public OutgoingResponse() {
+		}
+
 	}
 
 }

spring-cloud-function-adapters/spring-cloud-function-adapter-gcp/src/test/java/org/springframework/cloud/function/adapter/gcp/FunctionInvokerHttpTests.java

@@ -145,24 +145,46 @@ public class FunctionInvokerHttpTests {
 
 	}
 
-	private static class IncomingRequest {
+	public static class IncomingRequest {
 
 		String message;
 
-		IncomingRequest(String message) {
+		public IncomingRequest(String message) {
 			this.message = message;
 		}
 
+		public IncomingRequest() {
+		}
+
+		public String getMessage() {
+			return message;
+		}
+
+		public void setMessage(String message) {
+			this.message = message;
+		}
 	}
 
-	private static class OutgoingResponse {
+	public static class OutgoingResponse {
 
 		String message;
 
+		public String getMessage() {
+			return message;
+		}
+
+		public void setMessage(String message) {
+			this.message = message;
+		}
+
 		OutgoingResponse(String message) {
 			this.message = message;
 		}
 
+		public OutgoingResponse() {
+		}
+
 	}
 
+
 }

spring-cloud-function-adapters/spring-cloud-function-adapter-gcp/src/test/java/org/springframework/cloud/function/adapter/gcp/integration/FunctionInvokerIntegrationTests.java

@@ -119,17 +119,28 @@ public class FunctionInvokerIntegrationTests {
 
 	}
 
-	private static class Foo {
+	public static class Foo {
 
 		String value;
 
+		public String getValue() {
+			return value;
+		}
+
+		public void setValue(String value) {
+			this.value = value;
+		}
+
+		public Foo() {
+		}
+
 		Foo(String value) {
 			this.value = value;
 		}
 
 	}
 
-	private static class Bar {
+	public static class Bar {
 
 		String value;
 
@@ -137,6 +148,16 @@ public class FunctionInvokerIntegrationTests {
 			this.value = value;
 		}
 
+		Bar() {
+		}
+
+		public String getValue() {
+			return value;
+		}
+
+		public void setValue(String value) {
+			this.value = value;
+		}
 	}
 
 }