Generate 'org.eclipse.core.resources.prefs' for UTF-8 encoding

Update `EclipseConventions` to generate a prefs file to force
the project to use UTF-8 encoding.

Closes gh-48974

buildSrc/src/main/java/org/springframework/boot/build/EclipseConventions.java

@@ -18,6 +18,7 @@ package org.springframework.boot.build;
 
 import org.gradle.api.Project;
 import org.gradle.api.plugins.JavaBasePlugin;
+import org.gradle.api.tasks.TaskProvider;
 import org.gradle.plugins.ide.api.XmlFileContentMerger;
 import org.gradle.plugins.ide.eclipse.EclipsePlugin;
 import org.gradle.plugins.ide.eclipse.model.Classpath;
@@ -35,12 +36,27 @@ import org.gradle.plugins.ide.eclipse.model.Library;
 class EclipseConventions {
 
 	void apply(Project project) {
-		project.getPlugins()
-			.withType(EclipsePlugin.class,
-					(eclipse) -> project.getPlugins().withType(JavaBasePlugin.class, (javaBase) -> {
-						EclipseModel eclipseModel = project.getExtensions().getByType(EclipseModel.class);
-						eclipseModel.classpath(this::configureClasspath);
-					}));
+		project.getPlugins().withType(EclipsePlugin.class, (eclipse) -> configure(project, eclipse));
+	}
+
+	private void configure(Project project, EclipsePlugin eclipse) {
+		TaskProvider<?> synchronizeResourceSettings = registerEclipseSynchronizeResourceSettings(project);
+		project.getPlugins().withType(JavaBasePlugin.class, (javaBase) -> {
+			EclipseModel model = project.getExtensions().getByType(EclipseModel.class);
+			model.synchronizationTasks(synchronizeResourceSettings);
+			model.classpath(this::configureClasspath);
+		});
+	}
+
+	private TaskProvider<?> registerEclipseSynchronizeResourceSettings(Project project) {
+		TaskProvider<EclipseSynchronizeResourceSettings> eclipseSynchronizateResource = project.getTasks()
+			.register("eclipseSynchronizateResourceSettings", EclipseSynchronizeResourceSettings.class);
+		eclipseSynchronizateResource.configure((task) -> {
+			task.setDescription("Synchronizate the Eclipse resource settings file from Buildship.");
+			task.setOutputFile(project.file(".settings/org.eclipse.core.resources.prefs"));
+			task.setInputFile(project.file(".settings/org.eclipse.core.resources.prefs"));
+		});
+		return eclipseSynchronizateResource;
 	}
 
 	private void configureClasspath(EclipseClasspath classpath) {

buildSrc/src/main/java/org/springframework/boot/build/EclipseSynchronizeResourceSettings.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.build;
+
+import java.util.Properties;
+
+import org.gradle.api.Task;
+import org.gradle.api.internal.PropertiesTransformer;
+import org.gradle.plugins.ide.api.PropertiesGeneratorTask;
+
+import org.springframework.boot.build.EclipseSynchronizeResourceSettings.Configuration;
+
+/**
+ * {@link Task} to synchronize Eclipse resource settings.
+ *
+ * @author Phillip Webb
+ */
+public abstract class EclipseSynchronizeResourceSettings extends PropertiesGeneratorTask<Configuration> {
+
+	@Override
+	protected Configuration create() {
+		return new Configuration(getTransformer());
+	}
+
+	@Override
+	protected void configure(Configuration configuration) {
+	}
+
+	public static class Configuration extends EmptyPropertiesPersistableConfigurationObject {
+
+		Configuration(PropertiesTransformer transformer) {
+			super(transformer);
+		}
+
+		@Override
+		protected void store(Properties properties) {
+			properties.put("encoding/<project>", "UTF-8");
+		}
+
+	}
+
+}

buildSrc/src/main/java/org/springframework/boot/build/EmptyPropertiesPersistableConfigurationObject.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.build;
+
+import java.io.ByteArrayInputStream;
+import java.util.Properties;
+
+import org.gradle.api.internal.PropertiesTransformer;
+import org.gradle.internal.UncheckedException;
+import org.gradle.plugins.ide.internal.generator.PropertiesPersistableConfigurationObject;
+
+/**
+ * Base class for {@link PropertiesPersistableConfigurationObject} instances start empty
+ * and have no default resource.
+ *
+ * @author Phillip Webb
+ */
+abstract class EmptyPropertiesPersistableConfigurationObject extends PropertiesPersistableConfigurationObject {
+
+	EmptyPropertiesPersistableConfigurationObject(PropertiesTransformer transformer) {
+		super(transformer);
+	}
+
+	@Override
+	protected String getDefaultResourceName() {
+		return null;
+	}
+
+	@Override
+	public void loadDefaults() {
+		try {
+			load(new ByteArrayInputStream(new byte[0]));
+		}
+		catch (Exception ex) {
+			throw UncheckedException.throwAsUncheckedException(ex);
+		}
+	}
+
+	@Override
+	protected void load(Properties properties) {
+	}
+
+}