GH-2699: Make expressions cache concurrent

Fixes #2699

* [GH-2699] Match style

* [GH-2699] Shorten test line length

**Cherry-pick to 5.0.x**

(cherry picked from commit cd8cbaa)

Author: Cameronjmayfield

spring-integration-core/src/main/java/org/springframework/integration/aop/MethodAnnotationPublisherMetadataSource.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -22,6 +22,7 @@
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.stream.Collectors;
 
 import org.springframework.core.LocalVariableTableParameterNameDiscoverer;
@@ -42,18 +43,19 @@
  * @author Mark Fisher
  * @author Artem Bilan
  * @author Gareth Chapman
+ * @author Cameron Mayfield
  *
  * @since 2.0
  */
 public class MethodAnnotationPublisherMetadataSource implements PublisherMetadataSource {
 
 	private final ParameterNameDiscoverer parameterNameDiscoverer = new LocalVariableTableParameterNameDiscoverer();
 
-	private final Map<Method, String> channels = new HashMap<>();
+	private final Map<Method, String> channels = new ConcurrentHashMap<>();
 
-	private final Map<Method, Expression> payloadExpressions = new HashMap<>();
+	private final Map<Method, Expression> payloadExpressions = new ConcurrentHashMap<>();
 
-	private final Map<Method, Map<String, Expression>> headersExpressions = new HashMap<>();
+	private final Map<Method, Map<String, Expression>> headersExpressions = new ConcurrentHashMap<>();
 
 	private final Set<Class<? extends Annotation>> annotationTypes;
 

spring-integration-core/src/test/java/org/springframework/integration/aop/MethodAnnotationPublisherMetadataSourceTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -16,13 +16,16 @@
 
 package org.springframework.integration.aop;
 
+import static org.hamcrest.Matchers.instanceOf;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertThat;
 
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.reflect.Method;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 import org.junit.Test;
 
@@ -31,18 +34,19 @@
 import org.springframework.integration.annotation.Publisher;
 import org.springframework.messaging.handler.annotation.Header;
 import org.springframework.messaging.handler.annotation.Payload;
+import org.springframework.test.util.ReflectionTestUtils;
 
 /**
  * @author Mark Fisher
  * @author Artem Bilan
+ * @author Cameron Mayfield
  *
  * @since 2.0
  */
 public class MethodAnnotationPublisherMetadataSourceTests {
 
 	private final MethodAnnotationPublisherMetadataSource source = new MethodAnnotationPublisherMetadataSource();
 
-
 	@Test
 	public void channelNameAndExplicitReturnValuePayload() {
 		Method method = getMethod("methodWithChannelAndExplicitReturnAsPayload");
@@ -83,6 +87,16 @@ public void payloadAndHeaders() {
 		assertEquals("#args[2]", headerMap.get("bar").getExpressionString());
 	}
 
+	@Test
+	public void expressionsAreConcurrentHashMap() {
+		assertThat("Expressions should be concurrent to allow startup",
+				ReflectionTestUtils.getField(source, "channels"), instanceOf(ConcurrentHashMap.class));
+		assertThat("Expressions should be concurrent to allow startup",
+				ReflectionTestUtils.getField(source, "payloadExpressions"), instanceOf(ConcurrentHashMap.class));
+		assertThat("Expressions should be concurrent to allow startup",
+				ReflectionTestUtils.getField(source, "headersExpressions"), instanceOf(ConcurrentHashMap.class));
+	}
+
 	@Test
 	public void voidReturnWithValidPayloadExpression() {
 		Method method = getMethod("methodWithVoidReturnAndMethodNameAsPayload");
@@ -142,7 +156,6 @@ private static Method getMethodFromClass(Class<?> sourceClass, String name, Clas
 		}
 	}
 
-
 	@Publisher
 	@Payload("testExpression1")
 	public void methodWithPayloadAnnotation(String arg1, int arg2) {
@@ -160,7 +173,6 @@ public String methodWithChannelAndEmptyPayloadAnnotation() {
 		return "hello";
 	}
 
-
 	@Publisher(channel = "foo")
 	@Payload("#method")
 	public void methodWithVoidReturnAndMethodNameAsPayload() {