Use ConversionService from Environment in PropertySourcesPlaceholderConfigurer

This commit fixes a regression in PropertySourcesPlaceholderConfigurer
that was introduced in Spring Framework 6.2.7.

Specifically, this commit reinstates automatic String-conversion of
values from PropertySources in the Environment using the
ConversionService configured in the Environment.

See gh-34861
Closes gh-34936

Author: sbrannen

spring-context/src/main/java/org/springframework/context/support/PropertySourcesPlaceholderConfigurer.java

@@ -24,6 +24,8 @@
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
 import org.springframework.beans.factory.config.PlaceholderConfigurerSupport;
 import org.springframework.context.EnvironmentAware;
+import org.springframework.core.convert.ConversionService;
+import org.springframework.core.convert.support.DefaultConversionService;
 import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.env.ConfigurablePropertyResolver;
 import org.springframework.core.env.Environment;
@@ -243,16 +245,38 @@ public boolean containsProperty(String name) {
 
 		@Override
 		@Nullable
-		public Object getProperty(String name) {
+		// Declare String as covariant return type, since a String is actually required.
+		public String getProperty(String name) {
 			for (PropertySource<?> propertySource : super.source.getPropertySources()) {
 				Object candidate = propertySource.getProperty(name);
 				if (candidate != null) {
-					return candidate;
+					return convertToString(candidate);
 				}
 			}
 			return null;
 		}
 
+		/**
+		 * Convert the supplied value to a {@link String} using the {@link ConversionService}
+		 * from the {@link Environment}.
+		 * <p>This is a modified version of
+		 * {@link org.springframework.core.env.AbstractPropertyResolver#convertValueIfNecessary(Object, Class)}.
+		 * @param value the value to convert
+		 * @return the converted value, or the original value if no conversion is necessary
+		 * @since 6.2.8
+		 */
+		@Nullable
+		private String convertToString(Object value) {
+			if (value instanceof String string) {
+				return string;
+			}
+			ConversionService conversionService = super.source.getConversionService();
+			if (conversionService == null) {
+				conversionService = DefaultConversionService.getSharedInstance();
+			}
+			return conversionService.convert(value, String.class);
+		}
+
 		@Override
 		public String toString() {
 			return "ConfigurableEnvironmentPropertySource {propertySources=" + super.source.getPropertySources() + "}";
@@ -279,7 +303,8 @@ public boolean containsProperty(String name) {
 
 		@Override
 		@Nullable
-		public Object getProperty(String name) {
+		// Declare String as covariant return type, since a String is actually required.
+		public String getProperty(String name) {
 			return super.source.getProperty(name);
 		}
 

spring-context/src/test/java/org/springframework/context/support/PropertySourcesPlaceholderConfigurerTests.java

@@ -25,7 +25,6 @@
 
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.BeforeEach;
-import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
@@ -98,7 +97,6 @@ void replacementFromEnvironmentProperties() {
 	 * used by the {@code Environment} is applied during placeholder resolution
 	 * against a {@link PropertySource} registered in the {@code Environment}.
 	 */
-	@Disabled("Disabled until gh-34936 is resolved")
 	@Test  // gh-34936
 	void replacementFromEnvironmentPropertiesWithConversion() {
 		DefaultListableBeanFactory bf = new DefaultListableBeanFactory();