SlackNotifier#setMessage should accept strings

spring-boot-admin-server/src/main/java/de/codecentric/boot/admin/notify/SlackNotifier.java

@@ -77,11 +77,11 @@ public class SlackNotifier extends AbstractStatusChangeNotifier {
 		this.username = username;
 	}
 
-	public void setMessage(Expression message) {
-		this.message = message;
+	public void setMessage(String message) {
+		this.message = parser.parseExpression(message, ParserContext.TEMPLATE_EXPRESSION);
 	}
 
-	private Object createMessage(ClientApplicationStatusChangedEvent event) {
+	protected Object createMessage(ClientApplicationStatusChangedEvent event) {
 		Map<String, Object> messageJson = new HashMap<>();
 		messageJson.put("username", username);
 		if (icon != null) {

spring-boot-admin-server/src/test/java/de/codecentric/boot/admin/notify/SlackNotifierTest.java

@@ -14,9 +14,6 @@ import javax.annotation.Nullable;
 
 import org.junit.Before;
 import org.junit.Test;
-import org.springframework.expression.Expression;
-import org.springframework.expression.ParserContext;
-import org.springframework.expression.spel.standard.SpelExpressionParser;
 import org.springframework.web.client.RestTemplate;
 
 import de.codecentric.boot.admin.event.ClientApplicationStatusChangedEvent;
@@ -93,9 +90,7 @@ public class SlackNotifierTest {
 		StatusInfo infoDown = StatusInfo.ofDown();
 		StatusInfo infoUp = StatusInfo.ofUp();
 
-		Expression expression = new SpelExpressionParser().parseExpression(message,
-				ParserContext.TEMPLATE_EXPRESSION);
-		notifier.setMessage(expression);
+		notifier.setMessage(message);
 		notifier.setChannel(channel);
 		notifier.setIcon(icon);
 		notifier.notify(getEvent(infoDown, infoUp));