ICU-23309 Add ClassLoader to caching key in ResourceBundleWrapper

icu4j/main/core/src/main/java/com/ibm/icu/impl/ResourceBundleWrapper.java

@@ -17,6 +17,7 @@
 import java.util.Enumeration;
 import java.util.List;
 import java.util.MissingResourceException;
+import java.util.Objects;
 import java.util.PropertyResourceBundle;
 import java.util.ResourceBundle;
 
@@ -36,10 +37,39 @@ private abstract static class Loader {
         abstract ResourceBundleWrapper load();
     }
 
-    private static CacheBase<String, ResourceBundleWrapper, Loader> BUNDLE_CACHE =
-            new SoftCache<String, ResourceBundleWrapper, Loader>() {
+    private static class BundleCacheKey {
+        public final String baseName;
+        public final ClassLoader classLoader;
+
+        private BundleCacheKey(String baseName, ClassLoader classLoader) {
+            this.baseName = baseName;
+            this.classLoader = classLoader;
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) {
+                return true;
+            }
+            if (o == null || getClass() != o.getClass()) {
+                return false;
+            }
+            BundleCacheKey that = (BundleCacheKey) o;
+            return Objects.equals(baseName, that.baseName)
+                    && Objects.equals(classLoader, that.classLoader);
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(baseName, classLoader);
+        }
+    }
+
+    private static CacheBase<BundleCacheKey, ResourceBundleWrapper, Loader> BUNDLE_CACHE =
+            new SoftCache<BundleCacheKey, ResourceBundleWrapper, Loader>() {
                 @Override
-                protected ResourceBundleWrapper createInstance(String unusedKey, Loader loader) {
+                protected ResourceBundleWrapper createInstance(
+                        BundleCacheKey unusedKey, Loader loader) {
                     return loader.load();
                 }
             };
@@ -153,7 +183,8 @@ private static ResourceBundleWrapper instantiateBundle(
             final ClassLoader root,
             final boolean disableFallback) {
         final String name = localeID.isEmpty() ? baseName : baseName + '_' + localeID;
-        String cacheKey = disableFallback ? name : name + '#' + defaultID;
+        BundleCacheKey cacheKey =
+                new BundleCacheKey(disableFallback ? name : name + '#' + defaultID, root);
         return BUNDLE_CACHE.getInstance(
                 cacheKey,
                 new Loader() {

icu4j/main/core/src/test/java/com/ibm/icu/dev/test/impl/ResourceBundleWrapperCachingTest.java

@@ -0,0 +1,71 @@
+// © 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
+
+package com.ibm.icu.dev.test.impl;
+
+import static org.junit.Assert.*;
+
+import com.ibm.icu.util.ULocale;
+import com.ibm.icu.util.UResourceBundle;
+import java.io.IOException;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.util.MissingResourceException;
+import org.junit.Test;
+
+public class ResourceBundleWrapperCachingTest {
+    @Test
+    public void testCacheOnDifferentClassloaders() {
+        // Loading first bundle
+        try (var firstCL =
+                new URLClassLoader(
+                        new URL[] {getClass().getResource("/com/ibm/icu/dev/test/locale/first/")},
+                        null)) {
+            // Making sure that resources are available
+            assertNotNull(firstCL.getResource("localization.properties"));
+            assertNotNull(firstCL.getResource("localization_de.properties"));
+
+            // Getting the bundle. Since RootType here will be JAVA,
+            // ResourceBundleWrapper is chosen by UResourceBundle#instantiateBundle as
+            // implementation
+            // Passed locale here should not matter
+            var bundle = UResourceBundle.getBundleInstance("localization", ULocale.GERMAN, firstCL);
+
+            // Only 'First' should be present
+            assertEquals("Dies ist eine erste Zeile", bundle.getString("First"));
+            // 'Second' is not in the first bundle
+            assertThrows(MissingResourceException.class, () -> bundle.getString("Second"));
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+
+        // Loading second bundle
+        try (var secondFL =
+                new URLClassLoader(
+                        new URL[] {getClass().getResource("/com/ibm/icu/dev/test/locale/second/")},
+                        null)) {
+            // Making sure that resources are available
+            assertNotNull(secondFL.getResource("localization.properties"));
+            assertNotNull(secondFL.getResource("localization_de.properties"));
+
+            // Making sure that second bundle has `Second` in the localization file (unlike the
+            // first one)
+            assertTrue(
+                    new String(
+                                    secondFL.getResourceAsStream("localization.properties")
+                                            .readAllBytes())
+                            .contains("Second=This is a second line"));
+
+            // Getting the bundle, same as the first one
+            var bundle =
+                    UResourceBundle.getBundleInstance("localization", ULocale.GERMAN, secondFL);
+
+            assertEquals("Dies ist eine erste Zeile", bundle.getString("First"));
+            // Must contain 'Second' and not throw MissingResourceException if cached properly (no
+            // clash between first and second)
+            assertEquals("Dies ist eine zweite Zeile", bundle.getString("Second"));
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+}

icu4j/main/core/src/test/resources/com/ibm/icu/dev/test/locale/first/localization.properties

@@ -0,0 +1,5 @@
+# Copyright (C) 2026 and later: Unicode, Inc. and others.
+# License & terms of use: http://www.unicode.org/copyright.html#License
+
+First=This is a first line
+# No second one yet, see second/localization.properties

icu4j/main/core/src/test/resources/com/ibm/icu/dev/test/locale/first/localization_de.properties

@@ -0,0 +1,5 @@
+# Copyright (C) 2026 and later: Unicode, Inc. and others.
+# License & terms of use: http://www.unicode.org/copyright.html#License
+
+First=Dies ist eine erste Zeile
+# No second one yet, see second/localization.properties

icu4j/main/core/src/test/resources/com/ibm/icu/dev/test/locale/second/localization.properties

@@ -0,0 +1,5 @@
+# Copyright (C) 2026 and later: Unicode, Inc. and others.
+# License & terms of use: http://www.unicode.org/copyright.html#License
+
+First=This is a first line
+Second=This is a second line

icu4j/main/core/src/test/resources/com/ibm/icu/dev/test/locale/second/localization_de.properties

@@ -0,0 +1,5 @@
+# Copyright (C) 2026 and later: Unicode, Inc. and others.
+# License & terms of use: http://www.unicode.org/copyright.html#License
+
+First=Dies ist eine erste Zeile
+Second=Dies ist eine zweite Zeile