Repository: focus-shift/jollyday (java)

Issue:
Configuration to Specify XML Configuration Service Implementation When Multiple Are on the Classpath
### More information

Currently, if the dependencies `de.focus-shift:jollyday-jackson` and `de.focus-shift:jollyday-jaxb` are present on the classpath, Jollyday will fail to work and throw an `IllegalStateException` at runtime.

This behaviour is problematic and should be avoided. To address this, we aim to introduce a configurable option, `configuration.service.impl`, which can be overridden in the `jollyday.properties` file. The specified `ConfigurationService` will then be used as the default.
By default, this should be set to `de.focus_shift.jollyday.jackson.JacksonConfigurationService`.


Pull request description:
Add 'configuration.service.imp' to define which 'ConfigurationService…
…s' implementation should be used if multiple on classpath...

... the default if both are on the classpath is the one from jackson

closes #694 

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Patch:
diff --git a/README.md b/README.md
index 7eb6e4c8..5c63611d 100644
--- a/README.md
+++ b/README.md
@@ -157,6 +157,21 @@ If you already use one of these libraries in your project than just use the spec
   The configuration property name starts with `parser.impl` and finishes with the XML class name.
   The value is the parser implementation class name which implements the `HolidayParser` interface. 
 
+
+  **Configuration Service implementation**  
+  A configuration service implementation is used to define which xml unmarshalling implementation should be used
+
+  ```properties
+  configuration.service.impl = de.focus_shift.jollyday.jackson.JacksonConfigurationService
+  ```
+
+  The configuration property `configuration.service.impl` contains the class name as string.
+  The value is the configuration service implementation class name which implements the `ConfigurationService` interface.
+
+  Values are:
+  * `de.focus_shift.jollyday.jackson.JacksonConfigurationService` (default)
+  * `de.focus_shift.jollyday.jaxb.JaxbConfigurationService`
+
 </details>
 
 ### Examples
diff --git a/jollyday-core/src/main/java/de/focus_shift/jollyday/core/HolidayManager.java b/jollyday-core/src/main/java/de/focus_shift/jollyday/core/HolidayManager.java
index 73b7ffb7..58f8ced7 100644
--- a/jollyday-core/src/main/java/de/focus_shift/jollyday/core/HolidayManager.java
+++ b/jollyday-core/src/main/java/de/focus_shift/jollyday/core/HolidayManager.java
@@ -114,7 +114,8 @@ public abstract class HolidayManager {
     CONFIGURATION_MANAGER_PROVIDER.mergeConfigurationProperties(parameter);
 
     final String managerImplClassName = readManagerImplClassName(parameter);
-    final HolidayManagerValueHandler holidayManagerValueHandler = new HolidayManagerValueHandler(parameter, managerImplClassName, configurationServiceManager);
+    final String configurationServiceImplClassName = readConfigurationServiceImplClassName(parameter);
+    final HolidayManagerValueHandler holidayManagerValueHandler = new HolidayManagerValueHandler(parameter, managerImplClassName, configurationServiceImplClassName, configurationServiceManager);
     if (isManagerCachingEnabled()) {
       return HOLIDAY_MANAGER_CACHE.get(holidayManagerValueHandler);
     } else {
@@ -136,6 +137,20 @@ public abstract class HolidayManager {
     return className;
   }
 
+  /**
+   * Reads the managers implementation class from the properties config file.
+   *
+   * @param parameter the parameter to read the manager implementation class from
+   * @return the manager implementation class name
+   */
+  private static String readConfigurationServiceImplClassName(final ManagerParameter parameter) {
+    final String className = parameter.getConfigurationServiceImplClassName();
+    if (className == null) {
+      throw new IllegalStateException("Missing configuration '" + ManagerParameter.CONFIGURATION_SERVICE_IMPL + "'. Cannot create configuration service.");
+    }
+    return className;
+  }
+
   /**
    * If true, instantiated managers will be cached. If false every call to
    * getInstance will create new manager. True by default.
diff --git a/jollyday-core/src/main/java/de/focus_shift/jollyday/core/HolidayManagerValueHandler.java b/jollyday-core/src/main/java/de/focus_shift/jollyday/core/HolidayManagerValueHandler.java
index f12237ab..07fcea30 100644
--- a/jollyday-core/src/main/java/de/focus_shift/jollyday/core/HolidayManagerValueHandler.java
+++ b/jollyday-core/src/main/java/de/focus_shift/jollyday/core/HolidayManagerValueHandler.java
@@ -12,11 +12,16 @@ class HolidayManagerValueHandler implements Cache.ValueHandler<HolidayManager> {
 
   private final ManagerParameter parameter;
   private final String managerImplClassName;
+  private final String configurationServiceImplClassName;
   private final ConfigurationServiceManager configurationServiceManager;
 
-  HolidayManagerValueHandler(final ManagerParameter parameter, final String managerImplClassName, final ConfigurationServiceManager configurationServiceManager) {
+  HolidayManagerValueHandler(final ManagerParameter parameter,
+                             final String managerImplClassName,
+                             final String configurationServiceImplClassName,
+                             final ConfigurationServiceManager configurationServiceManager) {
     this.parameter = parameter;
     this.managerImplClassName = managerImplClassName;
+    this.configurationServiceImplClassName = configurationServiceImplClassName;
     this.configurationServiceManager = configurationServiceManager;
   }
 
@@ -29,7 +34,7 @@ class HolidayManagerValueHandler implements Cache.ValueHandler<HolidayManager> {
   public HolidayManager createValue() {
     final HolidayManager manager = instantiateManagerImpl(managerImplClassName);
 
-    final ConfigurationService configurationService = configurationServiceManager.getConfigurationService();
+    final ConfigurationService configurationService = configurationServiceManager.getConfigurationService(configurationServiceImplClassName);
     manager.setConfigurationService(configurationService);
 
     manager.init(parameter);
diff --git a/jollyday-core/src/main/java/de/focus_shift/jollyday/core/ManagerParameter.java b/jollyday-core/src/main/java/de/focus_shift/jollyday/core/ManagerParameter.java
index a5dc3274..43de1a37 100644
--- a/jollyday-core/src/main/java/de/focus_shift/jollyday/core/ManagerParameter.java
+++ b/jollyday-core/src/main/java/de/focus_shift/jollyday/core/ManagerParameter.java
@@ -7,6 +7,8 @@ public interface ManagerParameter {
 
   String MANAGER_IMPL_CLASS_PREFIX = "manager.impl";
 
+  String CONFIGURATION_SERVICE_IMPL = "configuration.service.impl";
+
   void mergeProperties(final Properties properties);
 
   String getProperty(final String key);
@@ -15,6 +17,8 @@ public interface ManagerParameter {
 
   String getManagerImplClassName();
 
+  String getConfigurationServiceImplClassName();
+
   String createCacheKey();
 
   String getDisplayName();
diff --git a/jollyday-core/src/main/java/de/focus_shift/jollyday/core/datasource/ConfigurationServiceManager.java b/jollyday-core/src/main/java/de/focus_shift/jollyday/core/datasource/ConfigurationServiceManager.java
index 9b233e68..60af2e09 100644
--- a/jollyday-core/src/main/java/de/focus_shift/jollyday/core/datasource/ConfigurationServiceManager.java
+++ b/jollyday-core/src/main/java/de/focus_shift/jollyday/core/datasource/ConfigurationServiceManager.java
@@ -18,21 +18,25 @@ public class ConfigurationServiceManager {
     this.configurationServiceCache = configurationServiceCache;
   }
 
-  public ConfigurationService getConfigurationService() {
-    return instantiateDataSource();
+  public ConfigurationService getConfigurationService(final String configurationServiceImplClassName) {
+    return instantiateDataSource(configurationServiceImplClassName);
   }
 
-  private ConfigurationService instantiateDataSource() {
+  private ConfigurationService instantiateDataSource(final String configurationServiceImplClassName) {
 
     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.size() == 1) {
+      return services.get(0);
     }
-    if (services.isEmpty()) {
-      throw new IllegalStateException("Cannot instantiate datasource instance because there is no implementations");
+
+    if (services.size() > 1) {
+      return services.stream()
+        .filter(configurationService -> configurationServiceImplClassName.equals(configurationService.getClass().getName()))
+        .findFirst()
+        .orElseThrow(() -> new IllegalStateException("Cannot instantiate datasource instance because there are two or more implementations available " + configurationServiceImplClassName));
     }
 
-    return services.get(0);
+    throw new IllegalStateException("Cannot instantiate datasource instance because there is no implementations");
   }
 }
diff --git a/jollyday-core/src/main/java/de/focus_shift/jollyday/core/parameter/BaseManagerParameter.java b/jollyday-core/src/main/java/de/focus_shift/jollyday/core/parameter/BaseManagerParameter.java
index 0b187320..32c7c89b 100644
--- a/jollyday-core/src/main/java/de/focus_shift/jollyday/core/parameter/BaseManagerParameter.java
+++ b/jollyday-core/src/main/java/de/focus_shift/jollyday/core/parameter/BaseManagerParameter.java
@@ -38,4 +38,9 @@ public abstract class BaseManagerParameter implements ManagerParameter {
   public String getManagerImplClassName() {
     return getProperty(MANAGER_IMPL_CLASS_PREFIX);
   }
+
+  @Override
+  public String getConfigurationServiceImplClassName() {
+    return getProperty(CONFIGURATION_SERVICE_IMPL);
+  }
 }
diff --git a/jollyday-core/src/main/java/de/focus_shift/jollyday/core/spi/ConfigurationService.java b/jollyday-core/src/main/java/de/focus_shift/jollyday/core/spi/ConfigurationService.java
index bc3b6028..cb43f482 100644
--- a/jollyday-core/src/main/java/de/focus_shift/jollyday/core/spi/ConfigurationService.java
+++ b/jollyday-core/src/main/java/de/focus_shift/jollyday/core/spi/ConfigurationService.java
@@ -6,5 +6,6 @@ import de.focus_shift.jollyday.core.ManagerParameter;
  * Service to provide the serialised configuration from XML files.
  */
 public interface ConfigurationService {
+
   Configuration getConfiguration(ManagerParameter parameter);
 }
diff --git a/jollyday-core/src/main/resources/jollyday.properties b/jollyday-core/src/main/resources/jollyday.properties
index 86623dd2..01a9758e 100644
--- a/jollyday-core/src/main/resources/jollyday.properties
+++ b/jollyday-core/src/main/resources/jollyday.properties
@@ -16,3 +16,5 @@ parser.impl.de.focus_shift.jollyday.core.spi.FixedWeekdayBetweenFixed    = de.fo
 parser.impl.de.focus_shift.jollyday.core.spi.FixedWeekdayRelativeToFixed = de.focus_shift.jollyday.core.parser.impl.FixedWeekdayRelativeToFixedParser
 parser.impl.de.focus_shift.jollyday.core.spi.EthiopianOrthodoxHoliday    = de.focus_shift.jollyday.core.parser.impl.EthiopianOrthodoxHolidayParser
 parser.impl.de.focus_shift.jollyday.core.spi.RelativeToEasterSunday      = de.focus_shift.jollyday.core.parser.impl.RelativeToEasterSundayParser
+
+configuration.service.impl                                               = de.focus_shift.jollyday.jackson.JacksonConfigurationService


Test patch:
diff --git a/jollyday-core/src/test/java/de/focus_shift/jollyday/core/HolidayManagerValueHandlerTest.java b/jollyday-core/src/test/java/de/focus_shift/jollyday/core/HolidayManagerValueHandlerTest.java
index 0030650c..787959c7 100644
--- a/jollyday-core/src/test/java/de/focus_shift/jollyday/core/HolidayManagerValueHandlerTest.java
+++ b/jollyday-core/src/test/java/de/focus_shift/jollyday/core/HolidayManagerValueHandlerTest.java
@@ -27,8 +27,9 @@ class HolidayManagerValueHandlerTest {
   @Test
   void ensureToGetCorrectKey() {
     final String managerImplClassName = "de.focus_shift.jollyday.core.impl.DefaultHolidayManager";
+    final String configurationServiceImplClassName = "de.focus_shift.jollyday.jackson.JacksonConfigurationService";
     final ConfigurationServiceManager configurationServiceManager = mock(ConfigurationServiceManager.class);
-    final HolidayManagerValueHandler sut = new HolidayManagerValueHandler(create("de"), managerImplClassName, configurationServiceManager);
+    final HolidayManagerValueHandler sut = new HolidayManagerValueHandler(create("de"), managerImplClassName, configurationServiceImplClassName, configurationServiceManager);
 
     final String key = sut.getKey();
     assertThat(key).isEqualTo("de");
@@ -49,10 +50,10 @@ class HolidayManagerValueHandlerTest {
     final ConfigurationService configurationService = mock(ConfigurationService.class);
     final Configuration configuration = mock(Configuration.class);
 
-    when(configurationServiceManager.getConfigurationService()).thenReturn(configurationService);
+    when(configurationServiceManager.getConfigurationService(any(String.class))).thenReturn(configurationService);
     when(configurationService.getConfiguration(any(ManagerParameter.class))).thenReturn(configuration);
 
-    final HolidayManagerValueHandler sut = new HolidayManagerValueHandler(create("de"), managerImplClass, configurationServiceManager);
+    final HolidayManagerValueHandler sut = new HolidayManagerValueHandler(create("de"), managerImplClass, "configurationServiceImplClassName", configurationServiceManager);
 
     final HolidayManager holidayManager = sut.createValue();
     assertThat(holidayManager).isInstanceOf(clazz);
@@ -62,7 +63,7 @@ class HolidayManagerValueHandlerTest {
   void ensureToThrowIllegalStateExceptionIfHolidayManagerIsWrong() {
 
     final String wrongManagerImplClassName = "de.focus_shift.jollyday.core.impl.WrongHolidayManager";
-    final HolidayManagerValueHandler sut = new HolidayManagerValueHandler(create("de"), wrongManagerImplClassName, mock(ConfigurationServiceManager.class));
+    final HolidayManagerValueHandler sut = new HolidayManagerValueHandler(create("de"), wrongManagerImplClassName, "configurationServiceImplClassName", mock(ConfigurationServiceManager.class));
 
     assertThatThrownBy(sut::createValue)
       .isInstanceOf(IllegalStateException.class)
diff --git a/jollyday-core/src/test/java/de/focus_shift/jollyday/core/datasource/ConfigurationServiceManagerTest.java b/jollyday-core/src/test/java/de/focus_shift/jollyday/core/datasource/ConfigurationServiceManagerTest.java
index 46d96224..9ae48602 100644
--- a/jollyday-core/src/test/java/de/focus_shift/jollyday/core/datasource/ConfigurationServiceManagerTest.java
+++ b/jollyday-core/src/test/java/de/focus_shift/jollyday/core/datasource/ConfigurationServiceManagerTest.java
@@ -36,7 +36,7 @@ class ConfigurationServiceManagerTest {
 
     when(configurationServiceCache.getServices()).thenReturn(List.of());
 
-    final IllegalStateException exception = assertThrows(IllegalStateException.class, () -> sut.getConfigurationService());
+    final IllegalStateException exception = assertThrows(IllegalStateException.class, () -> sut.getConfigurationService("configurationServiceImplClassName"));
     assertThat(exception.getMessage()).contains("Cannot instantiate datasource instance because there is no implementations");
   }
 
@@ -44,19 +44,29 @@ class ConfigurationServiceManagerTest {
   void ensuresToProvideConfigurationServiceIfExactlyOneIsAvailable() {
     when(configurationServiceCache.getServices()).thenReturn(List.of(new MockConfigurationService()));
 
-    final ConfigurationService configurationService = sut.getConfigurationService();
+    final ConfigurationService configurationService = sut.getConfigurationService("configurationServiceImplClassName");
     assertThat(configurationService).isInstanceOf(MockConfigurationService.class);
   }
 
   @Test
-  void ensuresToThrowExceptionIfMultipleImplementationsAreAvailable() {
+  void ensuresToThrowExceptionIfMultipleImplementationsAreAvailableButNoneOfThatAreConfigured() {
 
     when(configurationServiceCache.getServices()).thenReturn(List.of(new MockConfigurationService(), new MockConfigurationService()));
 
-    final IllegalStateException exception = assertThrows(IllegalStateException.class, () -> sut.getConfigurationService());
+    final IllegalStateException exception = assertThrows(IllegalStateException.class, () -> sut.getConfigurationService("configurationServiceImplClassName"));
     assertThat(exception.getMessage()).contains("Cannot instantiate datasource instance because there are two or more implementations available");
   }
 
+  @Test
+  void ensuresToUseTheConfiguredConfigurationServiceIfMultipleAreOnTheClasspath() {
+
+    final MockConfigurationServiceOther mockConfigurationServiceOther = new MockConfigurationServiceOther();
+    when(configurationServiceCache.getServices()).thenReturn(List.of(new MockConfigurationService(), mockConfigurationServiceOther));
+
+    final ConfigurationService configurationService = sut.getConfigurationService(mockConfigurationServiceOther.getClass().getName());
+    assertThat(configurationService).isInstanceOf(MockConfigurationServiceOther.class);
+  }
+
   private static class MockConfigurationService implements ConfigurationService {
 
     @Override
@@ -84,4 +94,32 @@ class ConfigurationServiceManagerTest {
       };
     }
   }
+
+  private static class MockConfigurationServiceOther 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;
+        }
+      };
+    }
+  }
 }