Introduce LogAccessor and LogMessage as convenient logging utilities

Closes gh-22726

spring-core/src/test/java/org/springframework/core/log/LogSupportTests.java

@@ -0,0 +1,36 @@
+/*
+ * 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.
+ * 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.core.log;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+/**
+ * @author Juergen Hoeller
+ * @since 5.2
+ */
+public class LogSupportTests {
+
+	@Test
+	public void testLogMessage() {
+		LogMessage msg = new LogMessage(() -> new StringBuilder("a"));
+		assertEquals("a", msg.toString());
+		assertSame(msg.toString(), msg.toString());
+	}
+
+}