Resolve nested placeholders if value is CharSequence

Fix GH-34195

Author: quaff

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/source/ConfigurationPropertySourcesPropertyResolver.java

@@ -27,6 +27,7 @@
  * underlying sources if the name is a value {@link ConfigurationPropertyName}.
  *
  * @author Phillip Webb
+ * @author Yanming Zhou
  */
 class ConfigurationPropertySourcesPropertyResolver extends AbstractPropertyResolver {
 
@@ -76,8 +77,8 @@ private <T> T getProperty(String key, Class<T> targetValueType, boolean resolveN
 		if (value == null) {
 			return null;
 		}
-		if (resolveNestedPlaceholders && value instanceof String string) {
-			value = resolveNestedPlaceholders(string);
+		if (resolveNestedPlaceholders && value instanceof CharSequence cs) {
+			value = resolveNestedPlaceholders(cs.toString());
 		}
 		return convertValueIfNecessary(value, targetValueType);
 	}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/ConfigurationPropertySourcesPropertyResolverTests.java

@@ -33,6 +33,7 @@
  * Tests for {@link ConfigurationPropertySourcesPropertyResolver}.
  *
  * @author Phillip Webb
+ * @author Yanming Zhou
  */
 class ConfigurationPropertySourcesPropertyResolverTests {
 
@@ -113,6 +114,40 @@ void getPropertyAsTypeWhenHasPlaceholder() {
 		assertThat(environment.getProperty("v2", Integer.class)).isOne();
 	}
 
+	@Test // gh-34195
+	void resolveNestedPlaceholdersIfValueIsCharSequence() {
+		ResolverEnvironment environment = new ResolverEnvironment();
+		MockPropertySource propertySource = new MockPropertySource();
+		propertySource.withProperty("v1", "1");
+		propertySource.withProperty("v2", new CharSequence() {
+
+			static final String underlying = "${v1}";
+
+			@Override
+			public int length() {
+				return underlying.length();
+			}
+
+			@Override
+			public char charAt(int index) {
+				return underlying.charAt(index);
+			}
+
+			@Override
+			public CharSequence subSequence(int start, int end) {
+				return underlying.subSequence(start, end);
+			}
+
+			@Override
+			public String toString() {
+				return underlying;
+			}
+		});
+		environment.getPropertySources().addFirst(propertySource);
+		assertThat(environment.getProperty("v2")).isEqualTo("1");
+		assertThat(environment.getProperty("v2", Integer.class)).isOne();
+	}
+
 	private CountingMockPropertySource createMockPropertySource(StandardEnvironment environment, boolean attach) {
 		CountingMockPropertySource propertySource = new CountingMockPropertySource();
 		propertySource.withProperty("spring", "boot");