Add auto-trimming support to configtree sources

Update `ConfigTreePropertySource` with an option to automatically trim
trailing new-line characters.

Closes gh-23826

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigTreeConfigDataLoader.java

@@ -21,6 +21,7 @@ import java.nio.file.Path;
 import java.util.Collections;
 
 import org.springframework.boot.env.ConfigTreePropertySource;
+import org.springframework.boot.env.ConfigTreePropertySource.Option;
 
 /**
  * {@link ConfigDataLoader} for config tree locations.
@@ -37,7 +38,7 @@ public class ConfigTreeConfigDataLoader implements ConfigDataLoader<ConfigTreeCo
 		Path path = resource.getPath();
 		ConfigDataResourceNotFoundException.throwIfDoesNotExist(resource, path);
 		String name = "Config tree '" + path + "'";
-		ConfigTreePropertySource source = new ConfigTreePropertySource(name, path);
+		ConfigTreePropertySource source = new ConfigTreePropertySource(name, path, Option.AUTO_TRIM_TRAILING_NEW_LINE);
 		return new ConfigData(Collections.singletonList(source));
 	}
 

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/env/ConfigTreePropertySource.java

@@ -145,7 +145,12 @@ public class ConfigTreePropertySource extends EnumerablePropertySource<Path> imp
 		/**
 		 * Convert file and directory names to lowercase.
 		 */
-		USE_LOWERCASE_NAMES
+		USE_LOWERCASE_NAMES,
+
+		/**
+		 * Automatically attempt trim trailing new-line characters.
+		 */
+		AUTO_TRIM_TRAILING_NEW_LINE
 
 	}
 
@@ -173,17 +178,22 @@ public class ConfigTreePropertySource extends EnumerablePropertySource<Path> imp
 
 		private final PropertyFileContent cachedContent;
 
+		private final boolean autoTrimTrailingNewLine;
+
 		private PropertyFile(Path path, Set<Option> options) {
 			this.path = path;
 			this.resource = new PathResource(path);
 			this.origin = new TextResourceOrigin(this.resource, START_OF_FILE);
+			this.autoTrimTrailingNewLine = options.contains(Option.AUTO_TRIM_TRAILING_NEW_LINE);
 			this.cachedContent = options.contains(Option.ALWAYS_READ) ? null
-					: new PropertyFileContent(path, this.resource, this.origin, true);
+					: new PropertyFileContent(path, this.resource, this.origin, true, this.autoTrimTrailingNewLine);
 		}
 
 		PropertyFileContent getContent() {
-			return (this.cachedContent != null) ? this.cachedContent
-					: new PropertyFileContent(this.path, this.resource, this.origin, false);
+			if (this.cachedContent != null) {
+				return this.cachedContent;
+			}
+			return new PropertyFileContent(this.path, this.resource, this.origin, false, this.autoTrimTrailingNewLine);
 		}
 
 		Origin getOrigin() {
@@ -247,17 +257,21 @@ public class ConfigTreePropertySource extends EnumerablePropertySource<Path> imp
 
 		private final Resource resource;
 
+		private final Origin origin;
+
 		private final boolean cacheContent;
 
+		private final boolean autoTrimTrailingNewLine;
+
 		private volatile byte[] content;
 
-		private final Origin origin;
-
-		private PropertyFileContent(Path path, Resource resource, Origin origin, boolean cacheContent) {
+		private PropertyFileContent(Path path, Resource resource, Origin origin, boolean cacheContent,
+				boolean autoTrimTrailingNewLine) {
 			this.path = path;
 			this.resource = resource;
 			this.origin = origin;
 			this.cacheContent = cacheContent;
+			this.autoTrimTrailingNewLine = autoTrimTrailingNewLine;
 		}
 
 		@Override
@@ -282,7 +296,28 @@ public class ConfigTreePropertySource extends EnumerablePropertySource<Path> imp
 
 		@Override
 		public String toString() {
-			return new String(getBytes());
+			String string = new String(getBytes());
+			if (this.autoTrimTrailingNewLine) {
+				string = autoTrimTrailingNewLine(string);
+			}
+			return string;
+		}
+
+		private String autoTrimTrailingNewLine(String string) {
+			if (!string.endsWith("\n")) {
+				return string;
+			}
+			int numberOfLines = 0;
+			for (char ch : string.toCharArray()) {
+				if (ch == '\n') {
+					numberOfLines++;
+				}
+			}
+			if (numberOfLines > 1) {
+				return string;
+			}
+			return (string.endsWith("\r\n")) ? string.substring(0, string.length() - 2)
+					: string.substring(0, string.length() - 1);
 		}
 
 		@Override

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/config/ConfigTreeConfigDataLoaderTests.java

@@ -50,7 +50,7 @@ public class ConfigTreeConfigDataLoaderTests {
 	void loadReturnsConfigDataWithPropertySource() throws IOException {
 		File file = this.directory.resolve("hello").toFile();
 		file.getParentFile().mkdirs();
-		FileCopyUtils.copy("world".getBytes(StandardCharsets.UTF_8), file);
+		FileCopyUtils.copy("world\n".getBytes(StandardCharsets.UTF_8), file);
 		ConfigTreeConfigDataResource location = new ConfigTreeConfigDataResource(this.directory.toString());
 		ConfigData configData = this.loader.load(this.loaderContext, location);
 		assertThat(configData.getPropertySources().size()).isEqualTo(1);

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/env/ConfigTreePropertySourceTests.java

@@ -199,6 +199,30 @@ class ConfigTreePropertySourceTests {
 		assertThat(propertySource.getProperty("spring")).hasToString("boot");
 	}
 
+	@Test
+	void getPropertyAsStringWhenMultiLinePropertyReturnsNonTrimmed() throws Exception {
+		addProperty("a", "a\nb\n");
+		ConfigTreePropertySource propertySource = new ConfigTreePropertySource("test", this.directory,
+				Option.AUTO_TRIM_TRAILING_NEW_LINE);
+		assertThat(propertySource.getProperty("a").toString()).isEqualTo("a\nb\n");
+	}
+
+	@Test
+	void getPropertyAsStringWhenPropertyEndsWithNewLineReturnsTrimmed() throws Exception {
+		addProperty("a", "a\n");
+		ConfigTreePropertySource propertySource = new ConfigTreePropertySource("test", this.directory,
+				Option.AUTO_TRIM_TRAILING_NEW_LINE);
+		assertThat(propertySource.getProperty("a").toString()).isEqualTo("a");
+	}
+
+	@Test
+	void getPropertyAsStringWhenPropertyEndsWithWindowsNewLineReturnsTrimmed() throws Exception {
+		addProperty("a", "a\r\n");
+		ConfigTreePropertySource propertySource = new ConfigTreePropertySource("test", this.directory,
+				Option.AUTO_TRIM_TRAILING_NEW_LINE);
+		assertThat(propertySource.getProperty("a").toString()).isEqualTo("a");
+	}
+
 	private ConfigTreePropertySource getFlatPropertySource() throws IOException {
 		addProperty("a", "A");
 		addProperty("b", "B");