GH-752 Add support to stop caching functions in FunctionCatalog

Resolves #752

spring-cloud-function-context/src/main/java/org/springframework/cloud/function/context/catalog/SimpleFunctionRegistry.java

@@ -194,7 +194,6 @@ public class SimpleFunctionRegistry implements FunctionRegistry, FunctionInspect
 	@SuppressWarnings("unchecked")
 	<T> T doLookup(Class<?> type, String functionDefinition, String[] expectedOutputMimeTypes) {
 		FunctionInvocationWrapper function = this.wrappedFunctionDefinitions.get(functionDefinition);
-
 		if (function == null) {
 			function = this.compose(type, functionDefinition);
 		}
@@ -269,10 +268,18 @@ public class SimpleFunctionRegistry implements FunctionRegistry, FunctionInspect
 				.filter(fr -> fr.getNames().contains(functionName))
 				.findFirst()
 				.orElseGet(() -> null);
-		return functionRegistration != null
+		FunctionInvocationWrapper function = functionRegistration != null
 				? this.invocationWrapperInstance(functionName, functionRegistration.getTarget(), functionRegistration.getType().getType())
 				: null;
-
+		if (functionRegistration != null && functionRegistration.getProperties().containsKey("singleton")) {
+			try {
+				function.isSingleton = Boolean.parseBoolean(functionRegistration.getProperties().get("singleton"));
+			}
+			catch (Exception e) {
+				// ignore
+			}
+		}
+		return function;
 	}
 
 	/*
@@ -297,7 +304,9 @@ public class SimpleFunctionRegistry implements FunctionRegistry, FunctionInspect
 					composedFunction = (FunctionInvocationWrapper) composedFunction.andThen((Function<Object, Object>) andThenFunction);
 				}
 				composedFunction = this.enrichInputIfNecessary(composedFunction);
-				this.wrappedFunctionDefinitions.put(composedFunction.functionDefinition, composedFunction);
+				if (composedFunction.isSingleton) {
+					this.wrappedFunctionDefinitions.put(composedFunction.functionDefinition, composedFunction);
+				}
 			}
 		}
 		if (logger.isDebugEnabled()) {
@@ -370,6 +379,8 @@ public class SimpleFunctionRegistry implements FunctionRegistry, FunctionInspect
 
 		private boolean skipOutputConversion;
 
+		private boolean isSingleton = true;
+
 		/*
 		 * This is primarily to support Stream's ability to access
 		 * un-converted payload (e.g., to evaluate expression on some attribute of a payload)
@@ -389,9 +400,6 @@ public class SimpleFunctionRegistry implements FunctionRegistry, FunctionInspect
 		}
 
 		FunctionInvocationWrapper(String functionDefinition,  Object target, Type inputType, Type outputType) {
-//			if (functionAroundWrapper != null) {
-//				this.setSkipOutputConversion(true);
-//			}
 			this.target = target;
 			this.inputType = this.normalizeType(inputType);
 			this.outputType = this.normalizeType(outputType);
@@ -399,6 +407,10 @@ public class SimpleFunctionRegistry implements FunctionRegistry, FunctionInspect
 			this.message = this.inputType != null && FunctionTypeUtils.isMessage(this.inputType);
 		}
 
+		public boolean isPrototype() {
+			return this.isPrototype();
+		}
+
 		public void setSkipInputConversion(boolean skipInputConversion) {
 			if (logger.isDebugEnabled() && skipInputConversion) {
 				logger.debug("'skipInputConversion' was explicitely set to true. No input conversion will be attempted");

spring-cloud-function-context/src/test/java/org/springframework/cloud/function/context/catalog/SimpleFunctionRegistryTests.java

@@ -86,6 +86,39 @@ public class SimpleFunctionRegistryTests {
 		this.conversionService = new DefaultConversionService();
 	}
 
+	@Test
+	public void testCachingOfFunction() {
+		Echo function = new Echo();
+		FunctionRegistration<Echo> registration = new FunctionRegistration<>(
+				function, "echo").type(FunctionType.of(Echo.class));
+		SimpleFunctionRegistry catalog = new SimpleFunctionRegistry(this.conversionService, this.messageConverter,
+				new JacksonMapper(new ObjectMapper()));
+		catalog.register(registration);
+
+		FunctionInvocationWrapper instanceA = catalog.lookup("echo", "application/json");
+		FunctionInvocationWrapper instanceb = catalog.lookup("echo", "text/plain");
+		FunctionInvocationWrapper instanceC = catalog.lookup("echo", "foo/bar");
+
+		assertThat(instanceA).isSameAs(instanceb).isSameAs(instanceC);
+	}
+
+	@Test
+	public void testNoCachingOfFunction() {
+		Echo function = new Echo();
+		FunctionRegistration<Echo> registration = new FunctionRegistration<>(
+				function, "echo").type(FunctionType.of(Echo.class));
+		registration.getProperties().put("singleton", "false");
+		SimpleFunctionRegistry catalog = new SimpleFunctionRegistry(this.conversionService, this.messageConverter,
+				new JacksonMapper(new ObjectMapper()));
+		catalog.register(registration);
+
+		FunctionInvocationWrapper instanceA = catalog.lookup("echo", "application/json");
+		FunctionInvocationWrapper instanceb = catalog.lookup("echo", "text/plain");
+		FunctionInvocationWrapper instanceC = catalog.lookup("echo", "foo/bar");
+
+		assertThat(instanceA).isNotSameAs(instanceb).isNotSameAs(instanceC);
+	}
+
 	@Test
 	public void testSCF640() {
 		Echo function = new Echo();