Merge pull request #311 from focus-shift/310-service-loader

Introduce service loader to retrieve different configuration services

jollyday-core/src/main/java/de/focus_shift/jollyday/core/ManagerParameter.java

@@ -5,7 +5,6 @@
 
 public interface ManagerParameter {
 
-  String CONFIGURATION_DATASOURCE_IMPL_CLASS = "configuration.datasource.impl";
   String MANAGER_IMPL_CLASS_PREFIX = "manager.impl";
 
   void mergeProperties(Properties properties);

jollyday-core/src/main/java/de/focus_shift/jollyday/core/caching/HolidayManagerValueHandler.java

@@ -4,6 +4,7 @@
 import de.focus_shift.jollyday.core.ManagerParameter;
 import de.focus_shift.jollyday.core.datasource.ConfigurationServiceManager;
 import de.focus_shift.jollyday.core.spi.ConfigurationService;
+import de.focus_shift.jollyday.core.support.LazyServiceLoaderCache;
 import de.focus_shift.jollyday.core.util.ClassLoadingUtil;
 
 /**
@@ -18,7 +19,8 @@ public class HolidayManagerValueHandler implements Cache.ValueHandler<HolidayMan
    * Manager for providing configuration data sources which return the holiday
    * data.
    */
-  private final ConfigurationServiceManager configurationServiceManager = new ConfigurationServiceManager();
+  private final ConfigurationServiceManager configurationServiceManager =
+    new ConfigurationServiceManager(new LazyServiceLoaderCache<>(ConfigurationService.class));
 
   /**
    * Utility to load classes.
@@ -38,7 +40,7 @@ public String getKey() {
   @Override
   public HolidayManager createValue() {
     final HolidayManager manager = instantiateManagerImpl(managerImplClassName);
-    final ConfigurationService configurationService = configurationServiceManager.getConfigurationService(parameter);
+    final ConfigurationService configurationService = configurationServiceManager.getConfigurationService();
     manager.setConfigurationService(configurationService);
     manager.init(parameter);
     return manager;

jollyday-core/src/main/java/de/focus_shift/jollyday/core/datasource/ConfigurationServiceManager.java

@@ -1,35 +1,38 @@
 package de.focus_shift.jollyday.core.datasource;
 
-import de.focus_shift.jollyday.core.ManagerParameter;
 import de.focus_shift.jollyday.core.spi.ConfigurationService;
-import de.focus_shift.jollyday.core.util.ClassLoadingUtil;
+import de.focus_shift.jollyday.core.support.LazyServiceLoaderCache;
+
+import java.util.List;
 
 /**
- * This manager is responsible for instantiating the configured configuration datasource
+ * This manager is responsible for instantiating
+ * the provided implementation of the {@link ConfigurationService}
  * which is used to access the holiday data.
  */
 public class ConfigurationServiceManager {
 
-  private final ClassLoadingUtil classLoadingUtil = new ClassLoadingUtil();
+  private final LazyServiceLoaderCache<ConfigurationService> configurationServiceCache;
 
-  public ConfigurationService getConfigurationService(ManagerParameter parameter) {
-    validateConfiguration(parameter);
-    final String dataSourceClassName = parameter.getProperty(ManagerParameter.CONFIGURATION_DATASOURCE_IMPL_CLASS);
-    return instantiateDataSource(dataSourceClassName);
+  public ConfigurationServiceManager(LazyServiceLoaderCache<ConfigurationService> configurationServiceCache) {
+    this.configurationServiceCache = configurationServiceCache;
   }
 
-  private ConfigurationService instantiateDataSource(String dataSourceClassName) {
-    try {
-      final Class<?> dataSourceClass = classLoadingUtil.loadClass(dataSourceClassName);
-      return (ConfigurationService) dataSourceClass.getDeclaredConstructor().newInstance();
-    } catch (Exception e) {
-      throw new IllegalStateException("Cannot instantiate datasource instance of " + dataSourceClassName, e);
-    }
+  public ConfigurationService getConfigurationService() {
+    return instantiateDataSource();
   }
 
-  private void validateConfiguration(ManagerParameter parameter) {
-    if (parameter.getProperty(ManagerParameter.CONFIGURATION_DATASOURCE_IMPL_CLASS) == null) {
-      throw new IllegalStateException("Missing holiday configuration datasource implementation class under config key " + ManagerParameter.CONFIGURATION_DATASOURCE_IMPL_CLASS);
+  private ConfigurationService instantiateDataSource() {
+
+    final List<ConfigurationService> services = configurationServiceCache.getServices();
+
+    if (services.size() > 1) {
+      throw new IllegalStateException("Cannot instantiate datasource instance because there are two or more implementations available " + services);
+    }
+    if (services.isEmpty()) {
+      throw new IllegalStateException("Cannot instantiate datasource instance because there is no implementations");
     }
+
+    return services.get(0);
   }
 }

jollyday-core/src/main/java/de/focus_shift/jollyday/core/support/LazyServiceLoaderCache.java

@@ -0,0 +1,44 @@
+package de.focus_shift.jollyday.core.support;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.List;
+import java.util.ServiceConfigurationError;
+import java.util.ServiceLoader;
+import java.util.concurrent.CopyOnWriteArrayList;
+
+import static java.lang.String.format;
+
+public class LazyServiceLoaderCache<S> {
+  private static final Logger LOG = LoggerFactory.getLogger(LazyServiceLoaderCache.class.getName());
+
+  private final Class<S> clz;
+  private List<S> services;
+
+  public LazyServiceLoaderCache(Class<S> clz) {
+    this.clz = clz;
+  }
+
+  public List<S> getServices() {
+    if (services == null) {
+      loadServices();
+    }
+    return services;
+  }
+
+  private synchronized void loadServices() {
+    services = new CopyOnWriteArrayList<>();
+    try {
+      for (S s : ServiceLoader.load(clz)) {
+        services.add(s);
+      }
+    } catch (ServiceConfigurationError serviceConfigurationError) {
+      final String message = format("Cannot load services of type [%s].%n    %s",
+        clz.getName(),
+        serviceConfigurationError.getMessage()
+      );
+      LOG.warn(message);
+    }
+  }
+}

jollyday-core/src/main/java/module-info.java

@@ -1,6 +1,7 @@
 module de.focus_shift.jollyday.core {
 
-  opens de.focus_shift.jollyday.core.datasource;
+  uses de.focus_shift.jollyday.core.spi.ConfigurationService;
+
   opens de.focus_shift.jollyday.core.util;
   opens holidays;
   opens descriptions;

jollyday-core/src/main/resources/jollyday.properties

@@ -5,9 +5,6 @@ manager.impl=de.focus_shift.jollyday.core.impl.DefaultHolidayManager
 # Holiday manager for Japan implements some specific Japanese holiday rule.
 manager.impl.jp=de.focus_shift.jollyday.core.impl.JapaneseHolidayManager
 
-# Implementation class for holiday configurations
-configuration.datasource.impl=de.focus_shift.jollyday.jaxb.JaxbConfigurationService
-
 # Configure the parsers to be used for each individual configuration type
 parser.impl.de.focus_shift.jollyday.core.spi.Fixed=de.focus_shift.jollyday.core.parser.impl.FixedParser
 parser.impl.de.focus_shift.jollyday.core.spi.FixedWeekdayInMonth=de.focus_shift.jollyday.core.parser.impl.FixedWeekdayInMonthParser

jollyday-core/src/test/java/de/focus_shift/jollyday/core/configuration/impl/DefaultConfigurationProviderContentTest.java

@@ -12,7 +12,6 @@ class DefaultConfigurationProviderContentTest {
   private static final Set<String> KEYS_DEFAULT_CONFIG = Set.of(
     "manager.impl",
     "manager.impl.jp",
-    "configuration.datasource.impl",
     "parser.impl.de.focus_shift.jollyday.core.spi.Fixed",
     "parser.impl.de.focus_shift.jollyday.core.spi.FixedWeekdayInMonth",
     "parser.impl.de.focus_shift.jollyday.core.spi.IslamicHoliday",

jollyday-core/src/test/java/de/focus_shift/jollyday/core/datasource/ConfigurationServiceManagerTest.java

@@ -0,0 +1,87 @@
+package de.focus_shift.jollyday.core.datasource;
+
+import de.focus_shift.jollyday.core.ManagerParameter;
+import de.focus_shift.jollyday.core.spi.Configuration;
+import de.focus_shift.jollyday.core.spi.ConfigurationService;
+import de.focus_shift.jollyday.core.spi.Holidays;
+import de.focus_shift.jollyday.core.support.LazyServiceLoaderCache;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import java.util.List;
+import java.util.stream.Stream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.mockito.Mockito.when;
+
+@ExtendWith(MockitoExtension.class)
+class ConfigurationServiceManagerTest {
+
+  @Mock
+  private LazyServiceLoaderCache<ConfigurationService> configurationServiceCache;
+
+  private ConfigurationServiceManager sut;
+
+  @BeforeEach
+  void setUp() {
+    sut = new ConfigurationServiceManager(configurationServiceCache);
+  }
+
+  @Test
+  void ensuresToThrowExceptionIfNoImplementationIsAvailable() {
+
+    when(configurationServiceCache.getServices()).thenReturn(List.of());
+
+    final IllegalStateException exception = assertThrows(IllegalStateException.class, () -> sut.getConfigurationService());
+    assertThat(exception.getMessage()).contains("Cannot instantiate datasource instance because there is no implementations");
+  }
+
+  @Test
+  void ensuresToProvideConfigurationServiceIfExactlyOneIsAvailable() {
+    when(configurationServiceCache.getServices()).thenReturn(List.of(new MockConfigurationService()));
+
+    final ConfigurationService configurationService = sut.getConfigurationService();
+    assertThat(configurationService).isInstanceOf(MockConfigurationService.class);
+  }
+
+  @Test
+  void ensuresToThrowExceptionIfMultipleImplementationsAreAvailable() {
+
+    when(configurationServiceCache.getServices()).thenReturn(List.of(new MockConfigurationService(), new MockConfigurationService()));
+
+    final IllegalStateException exception = assertThrows(IllegalStateException.class, () -> sut.getConfigurationService());
+    assertThat(exception.getMessage()).contains("Cannot instantiate datasource instance because there are two or more implementations available");
+  }
+
+  private static class MockConfigurationService implements ConfigurationService {
+
+    @Override
+    public Configuration getConfiguration(ManagerParameter parameter) {
+      return new Configuration() {
+        @Override
+        public Holidays holidays() {
+          return null;
+        }
+
+        @Override
+        public Stream<Configuration> subConfigurations() {
+          return null;
+        }
+
+        @Override
+        public String hierarchy() {
+          return null;
+        }
+
+        @Override
+        public String description() {
+          return null;
+        }
+      };
+    }
+  }
+}

jollyday-jaxb/src/main/java/module-info.java

@@ -1,8 +1,17 @@
+import de.focus_shift.jollyday.core.spi.ConfigurationService;
+import de.focus_shift.jollyday.jaxb.JaxbConfigurationService;
+
 module de.focus_shift.jollyday.jaxb {
+
+  opens de.focus_shift.jollyday.jaxb.mapping to jakarta.xml.bind;
+
   requires java.xml;
   requires jakarta.xml.bind;
   requires org.slf4j;
   requires org.threeten.extra;
-
   requires de.focus_shift.jollyday.core;
+
+  exports de.focus_shift.jollyday.jaxb to de.focus_shift.jollyday.core;
+  provides ConfigurationService
+    with JaxbConfigurationService;
 }

jollyday-jaxb/src/main/resources/META-INF/services/de.focus_shift.jollyday.core.spi.ConfigurationService

@@ -0,0 +1 @@
+de.focus_shift.jollyday.jaxb.JaxbConfigurationService