Fix UnsupportedOperationException in DubboDefaultPropertiesEnvironmentPostProcessor.addOrReplace on immutable property source (#16268)

dubbo-spring-boot-project/dubbo-spring-boot/src/main/java/org/apache/dubbo/spring/boot/env/DubboDefaultPropertiesEnvironmentPostProcessor.java

@@ -127,13 +127,17 @@ private void addOrReplace(MutablePropertySources propertySources, Map<String, Ob
         if (propertySources.contains(PROPERTY_SOURCE_NAME)) {
             PropertySource<?> source = propertySources.get(PROPERTY_SOURCE_NAME);
             if (source instanceof MapPropertySource) {
-                target = (MapPropertySource) source;
+                // The existing backing map may be immutable, so copy into a mutable map and replace the
+                // source instead of mutating it in place. See dubbo#16268.
+                Map<String, Object> merged = new HashMap<>(((MapPropertySource) source).getSource());
                 for (Map.Entry<String, Object> entry : map.entrySet()) {
                     String key = entry.getKey();
-                    if (!target.containsProperty(key)) {
-                        target.getSource().put(key, entry.getValue());
+                    if (!merged.containsKey(key)) {
+                        merged.put(key, entry.getValue());
                     }
                 }
+                target = new MapPropertySource(PROPERTY_SOURCE_NAME, merged);
+                propertySources.replace(PROPERTY_SOURCE_NAME, target);
             }
         }
         if (target == null) {

dubbo-spring-boot-project/dubbo-spring-boot/src/test/java/org/apache/dubbo/spring/boot/env/DubboDefaultPropertiesEnvironmentPostProcessorTest.java

@@ -16,7 +16,9 @@
  */
 package org.apache.dubbo.spring.boot.env;
 
+import java.util.Collections;
 import java.util.HashMap;
+import java.util.Map;
 
 import org.junit.jupiter.api.Test;
 import org.springframework.boot.SpringApplication;
@@ -26,6 +28,7 @@
 import org.springframework.core.env.PropertySource;
 import org.springframework.mock.env.MockEnvironment;
 
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 
@@ -106,4 +109,35 @@ void testPostProcessEnvironment() {
         assertNotNull(defaultPropertySource);
         assertEquals("virtual", defaultPropertySource.getProperty("dubbo.protocol.threadpool"));
     }
+
+    /** #16268: addOrReplace must not fail when "defaultProperties" is backed by an immutable map. */
+    @Test
+    void testPostProcessEnvironmentOnImmutableDefaultProperties() {
+        MockEnvironment environment = new MockEnvironment();
+        MutablePropertySources propertySources = environment.getPropertySources();
+        propertySources.addLast(
+                new MapPropertySource("defaultProperties", Collections.unmodifiableMap(new HashMap<String, Object>())));
+
+        instance.postProcessEnvironment(environment, springApplication);
+
+        PropertySource<?> defaultPropertySource = propertySources.get("defaultProperties");
+        assertNotNull(defaultPropertySource);
+        assertEquals("true", defaultPropertySource.getProperty("dubbo.config.multiple"));
+    }
+
+    /** #16268: on an immutable "defaultProperties", Dubbo's default must not override an existing key. */
+    @Test
+    void testImmutableDefaultPropertiesDoesNotOverrideExistingKey() {
+        MockEnvironment environment = new MockEnvironment();
+        MutablePropertySources propertySources = environment.getPropertySources();
+        Map<String, Object> existing = new HashMap<>();
+        existing.put("dubbo.config.multiple", "false");
+        propertySources.addLast(new MapPropertySource("defaultProperties", Collections.unmodifiableMap(existing)));
+
+        assertDoesNotThrow(() -> instance.postProcessEnvironment(environment, springApplication));
+
+        PropertySource<?> defaultPropertySource = propertySources.get("defaultProperties");
+        assertNotNull(defaultPropertySource);
+        assertEquals("false", defaultPropertySource.getProperty("dubbo.config.multiple"));
+    }
 }