Fix Compiled SpEL Test

Several problems:

- Setting the system property is not enough since the `static` parser already has its configuration
- Changing the ParametersWrapper to `private` makes property accessing not compilable (the method and class must be public).
- The expression...

    #target.messageAndHeader(message, headers['number'] != null ? headers['number'] : T(org.springframework.util.Assert).isTrue(false, 'required header not available: number'))

...is not compilable anyway because the right arguent to the `!=` is not compilable because the `TypeReference.exitTypeDescriptor` is `null`.

This commit addresses the first two.

Polishing

Use a compilable method.

* Simple polishing

spring-integration-core/src/main/java/org/springframework/integration/util/MessagingMethodInvokerHelper.java

@@ -785,10 +785,6 @@ public class MessagingMethodInvokerHelper<T> extends AbstractExpressionEvaluator
 			return (T) this.invocableHandlerMethod.invoke(message);
 		}
 
-		public Expression getExpression() {
-			return this.expression;
-		}
-
 		Class<?> getTargetParameterType() {
 			return this.targetParameterType;
 		}
@@ -979,7 +975,7 @@ public class MessagingMethodInvokerHelper<T> extends AbstractExpressionEvaluator
 		}
 	}
 
-	private static class ParametersWrapper {
+	public static class ParametersWrapper {
 
 		private final Object payload;
 

spring-integration-core/src/test/java/org/springframework/integration/handler/MethodInvokingMessageProcessorTests.java

@@ -40,13 +40,16 @@ import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
 
+import org.springframework.beans.DirectFieldAccessor;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.expression.spel.SpelCompilerMode;
 import org.springframework.expression.spel.SpelEvaluationException;
+import org.springframework.expression.spel.SpelParserConfiguration;
 import org.springframework.integration.annotation.ServiceActivator;
 import org.springframework.integration.gateway.GatewayProxyFactoryBean;
 import org.springframework.integration.gateway.RequestReplyExchanger;
 import org.springframework.integration.support.MessageBuilder;
+import org.springframework.integration.test.util.TestUtils;
 import org.springframework.integration.util.MessagingMethodInvokerHelper;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageHandlingException;
@@ -573,17 +576,19 @@ public class MethodInvokingMessageProcessorTests {
 	@Test
 	public void testPerformanceSpelVersusInvocable() throws Exception {
 		AnnotatedTestService service = new AnnotatedTestService();
-		Method method = service.getClass().getMethod("messageAndHeader", Message.class, Integer.class);
+		Method method = service.getClass().getMethod("integerMethod", Integer.class);
 
 		MethodInvokingMessageProcessor processor = new MethodInvokingMessageProcessor(service, method);
 		processor.setUseSpelInvoker(true);
 
-		Message<String> message = MessageBuilder.withPayload("foo").setHeader("number", 42).build();
+		Message<Integer> message = MessageBuilder.withPayload(42).build();
 
 		StopWatch stopWatch = new StopWatch("SpEL vs Invocable Performance");
 
+		int count = 20_000;
+
 		stopWatch.start("SpEL");
-		for (int i = 0; i < 10000; i++) {
+		for (int i = 0; i < count; i++) {
 			processor.processMessage(message);
 		}
 		stopWatch.stop();
@@ -591,24 +596,25 @@ public class MethodInvokingMessageProcessorTests {
 		processor = new MethodInvokingMessageProcessor(service, method);
 
 		stopWatch.start("Invocable");
-		for (int i = 0; i < 10000; i++) {
+		for (int i = 0; i < count; i++) {
 			processor.processMessage(message);
 		}
 		stopWatch.stop();
 
+		// Update the parser configuration compiler mode
+		SpelParserConfiguration config = TestUtils.getPropertyValue(processor,
+				"delegate.handlerMethod.EXPRESSION_PARSER.configuration", SpelParserConfiguration.class);
+		new DirectFieldAccessor(config).setPropertyValue("compilerMode", SpelCompilerMode.IMMEDIATE);
 
-		System.setProperty("spring.expression.compiler.mode", SpelCompilerMode.IMMEDIATE.name());
 		processor = new MethodInvokingMessageProcessor(service, method);
 		processor.setUseSpelInvoker(true);
 
 		stopWatch.start("Compiled SpEL");
-		for (int i = 0; i < 10000; i++) {
+		for (int i = 0; i < count; i++) {
 			processor.processMessage(message);
 		}
 		stopWatch.stop();
 
-		System.clearProperty("spring.expression.compiler.mode");
-
 		logger.warn(stopWatch.prettyPrint());
 	}
 
@@ -720,8 +726,7 @@ public class MethodInvokingMessageProcessorTests {
 
 	}
 
-	@SuppressWarnings("unused")
-	private static class AnnotatedTestService {
+	public static class AnnotatedTestService {
 
 		AnnotatedTestService() {
 			super();