Polish usage of Collection in @ConfigurationProperties classes

1. It's safe to use immutable Collection object as default value of field.
2. It's unnecessary to create new Collection object in setter method.

Signed-off-by: Yanming Zhou <[email protected]>

Author: quaff

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/MetricsProperties.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -18,8 +18,6 @@
 
 import java.io.File;
 import java.time.Duration;
-import java.util.ArrayList;
-import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
@@ -202,7 +200,7 @@ public static class Diskspace {
 			/**
 			 * List of paths to report disk metrics for.
 			 */
-			private List<File> paths = new ArrayList<>(Collections.singletonList(new File(".")));
+			private List<File> paths = List.of(new File("."));
 
 			public List<File> getPaths() {
 				return this.paths;

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/web/exchanges/HttpExchangesProperties.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2022 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -16,7 +16,6 @@
 
 package org.springframework.boot.actuate.autoconfigure.web.exchanges;
 
-import java.util.HashSet;
 import java.util.Set;
 
 import org.springframework.boot.actuate.web.exchanges.Include;
@@ -53,7 +52,7 @@ public static class Recording {
 		 * (excluding Authorization and Cookie), response headers (excluding Set-Cookie),
 		 * and time taken.
 		 */
-		private Set<Include> include = new HashSet<>(Include.defaultIncludes());
+		private Set<Include> include = Include.defaultIncludes();
 
 		public Set<Include> getInclude() {
 			return this.include;

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/context/MessageSourceProperties.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -20,7 +20,6 @@
 import java.nio.charset.StandardCharsets;
 import java.time.Duration;
 import java.time.temporal.ChronoUnit;
-import java.util.ArrayList;
 import java.util.List;
 
 import org.springframework.boot.context.properties.ConfigurationProperties;
@@ -44,7 +43,7 @@ public class MessageSourceProperties {
 	 * locations. If it doesn't contain a package qualifier (such as "org.mypackage"), it
 	 * will be resolved from the classpath root.
 	 */
-	private List<String> basename = new ArrayList<>(List.of("messages"));
+	private List<String> basename = List.of("messages");
 
 	/**
 	 * List of locale-independent property file resources containing common messages.

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/elasticsearch/ElasticsearchProperties.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -17,8 +17,6 @@
 package org.springframework.boot.autoconfigure.elasticsearch;
 
 import java.time.Duration;
-import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 
 import org.springframework.boot.context.properties.ConfigurationProperties;
@@ -35,7 +33,7 @@ public class ElasticsearchProperties {
 	/**
 	 * List of the Elasticsearch instances to use.
 	 */
-	private List<String> uris = new ArrayList<>(Collections.singletonList("http://localhost:9200"));
+	private List<String> uris = List.of("http://localhost:9200");
 
 	/**
 	 * Username for authentication with Elasticsearch.

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/flyway/FlywayProperties.java

@@ -22,7 +22,6 @@
 import java.time.Duration;
 import java.time.temporal.ChronoUnit;
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -57,7 +56,7 @@ public class FlywayProperties {
 	 * Locations of migrations scripts. Can contain the special "{vendor}" placeholder to
 	 * use vendor-specific locations.
 	 */
-	private List<String> locations = new ArrayList<>(Collections.singletonList("classpath:db/migration"));
+	private List<String> locations = List.of("classpath:db/migration");
 
 	/**
 	 * Encoding of SQL migrations.
@@ -157,7 +156,7 @@ public class FlywayProperties {
 	/**
 	 * File name suffix for SQL migrations.
 	 */
-	private List<String> sqlMigrationSuffixes = new ArrayList<>(Collections.singleton(".sql"));
+	private List<String> sqlMigrationSuffixes = List.of(".sql");
 
 	/**
 	 * File name separator for SQL migrations.

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/kafka/KafkaProperties.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -19,8 +19,6 @@
 import java.io.IOException;
 import java.time.Duration;
 import java.time.temporal.ChronoUnit;
-import java.util.ArrayList;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Locale;
@@ -69,7 +67,7 @@ public class KafkaProperties {
 	 * List of host:port pairs to use for establishing the initial connections to the
 	 * Kafka cluster. Applies to all components unless overridden.
 	 */
-	private List<String> bootstrapServers = new ArrayList<>(Collections.singletonList("localhost:9092"));
+	private List<String> bootstrapServers = List.of("localhost:9092");
 
 	/**
 	 * ID to pass to the server when making requests. Used for server-side logging.

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/quartz/QuartzProperties.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2021 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -17,8 +17,6 @@
 package org.springframework.boot.autoconfigure.quartz;
 
 import java.time.Duration;
-import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -155,7 +153,7 @@ public static class Jdbc {
 		/**
 		 * Prefixes for single-line comments in SQL initialization scripts.
 		 */
-		private List<String> commentPrefix = new ArrayList<>(Arrays.asList("#", "--"));
+		private List<String> commentPrefix = List.of("#", "--");
 
 		public String getSchema() {
 			return this.schema;

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/security/SecurityProperties.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -146,7 +146,7 @@ public List<String> getRoles() {
 		}
 
 		public void setRoles(List<String> roles) {
-			this.roles = new ArrayList<>(roles);
+			this.roles = roles;
 		}
 
 		public boolean isPasswordGenerated() {

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/appendix/configurationmetadata/annotationprocessor/automaticmetadatageneration/MyMessagingProperties.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2021 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -16,16 +16,14 @@
 
 package org.springframework.boot.docs.appendix.configurationmetadata.annotationprocessor.automaticmetadatageneration;
 
-import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.List;
 
 import org.springframework.boot.context.properties.ConfigurationProperties;
 
 @ConfigurationProperties(prefix = "my.messaging")
 public class MyMessagingProperties {
 
-	private List<String> addresses = new ArrayList<>(Arrays.asList("a", "b"));
+	private List<String> addresses = List.of("a", "b");
 
 	private ContainerType containerType = ContainerType.SIMPLE;
 

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/features/externalconfig/typesafeconfigurationproperties/javabeanbinding/MyProperties.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2021 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -17,8 +17,6 @@
 package org.springframework.boot.docs.features.externalconfig.typesafeconfigurationproperties.javabeanbinding;
 
 import java.net.InetAddress;
-import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 
 import org.springframework.boot.context.properties.ConfigurationProperties;
@@ -60,7 +58,7 @@ public static class Security {
 
 		private String password;
 
-		private List<String> roles = new ArrayList<>(Collections.singleton("USER"));
+		private List<String> roles = List.of("USER");
 
 		// @fold:on // getters / setters...
 		public String getUsername() {