Always obtain fresh PropertySources in ConfigurableEnvironmentPropertySource

Although it's unlikely that the implementation of getPropertySources() in a ConfigurableEnvironment would be overridden to return a different MutablePropertySources instance than the one that the ConfigurableEnvironment typically acts on, it is in fact possible. In light of that possibility, this commit refactors ConfigurableEnvironmentPropertySource so that it always obtains a fresh PropertySources reference. See spring-projectsgh-34861

Author: sbrannen

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

@@ -227,19 +227,15 @@ public PropertySources getAppliedPropertySources() throws IllegalStateException
  */
 private static class ConfigurableEnvironmentPropertySource extends PropertySource<ConfigurableEnvironment> {
 
-private final PropertySources propertySources;
-
-
 ConfigurableEnvironmentPropertySource(ConfigurableEnvironment environment) {
 super(ENVIRONMENT_PROPERTIES_PROPERTY_SOURCE_NAME, environment);
-this.propertySources = environment.getPropertySources();
 }
 
 
 @Override
 @Nullable
 public Object getProperty(String name) {
-for (PropertySource<?> propertySource : this.propertySources) {
+for (PropertySource<?> propertySource : super.source.getPropertySources()) {
 Object candidate = propertySource.getProperty(name);
 if (candidate != null) {
 return candidate;
@@ -250,7 +246,7 @@ public Object getProperty(String name) {
 
 @Override
 public boolean containsProperty(String name) {
-for (PropertySource<?> propertySource : this.propertySources) {
+for (PropertySource<?> propertySource : super.source.getPropertySources()) {
 if (propertySource.containsProperty(name)) {
 return true;
 }
@@ -260,7 +256,7 @@ public boolean containsProperty(String name) {
 
 @Override
 public String toString() {
-return "ConfigurableEnvironmentPropertySource {propertySources=" + this.propertySources + "}";
+return "ConfigurableEnvironmentPropertySource {propertySources=" + super.source.getPropertySources() + "}";
 }
 }