#5 Add validation for SettingsHolder classes: final and hidden constr…

…uctor

src/main/java/ch/jalu/configme/utils/SettingsHolderClassValidator.java

@@ -6,6 +6,7 @@
 import ch.jalu.configme.properties.Property;
 
 import javax.annotation.Nullable;
+import java.lang.reflect.Constructor;
 import java.lang.reflect.Field;
 import java.lang.reflect.Modifier;
 import java.util.ArrayList;
@@ -30,26 +31,28 @@ public class SettingsHolderClassValidator {
      * Runs all validations of this class with the given settings holder classes.
      * More details at {@link #validate(Iterable)}.
      *
-     * @param settingsHolderClasses settings holder classes that make up the configuration data of the project
+     * @param settingHolders settings holder classes that make up the configuration data of the project
      */
     @SafeVarargs
-    public final void validate(Class<? extends SettingsHolder>... settingsHolderClasses) {
-        validate(Arrays.asList(settingsHolderClasses));
+    public final void validate(Class<? extends SettingsHolder>... settingHolders) {
+        validate(Arrays.asList(settingHolders));
     }
 
     /**
      * Runs all validations of this class with the given settings holder classes. Some of the validations
      * are not needed from a technical point of view and may be undesired in your project. They can all be
      * run individually and can be customized (method parameters, or overridable methods).
      *
-     * @param settingsHolderClasses settings holder classes that make up the configuration data of the project
+     * @param settingHolders settings holder classes that make up the configuration data of the project
      */
-    public void validate(Iterable<Class<? extends SettingsHolder>> settingsHolderClasses) {
+    public void validate(Iterable<Class<? extends SettingsHolder>> settingHolders) {
+        validateAllPropertiesAreConstants(settingHolders);
+        validateSettingsHolderClassesFinal(settingHolders);
+        validateClassesHaveHiddenNoArgConstructor(settingHolders);
+
         // Note: creating the ConfigurationData with the default builder validates that
         // no properties have overlapping paths
-        ConfigurationData configurationData = createConfigurationData(settingsHolderClasses);
-
-        validateAllPropertiesAreConstants(settingsHolderClasses);
+        ConfigurationData configurationData = createConfigurationData(settingHolders);
         validateHasCommentOnEveryProperty(configurationData, null);
         validateCommentLengthsAreWithinBounds(configurationData, null, 90);
         validateHasAllEnumEntriesInComment(configurationData, null);
@@ -61,12 +64,12 @@ public void validate(Iterable<Class<? extends SettingsHolder>> settingsHolderCla
     /**
      * Throws an exception if any Property field of the given classes is not public, static, or final.
      *
-     * @param settingsHolderClasses the classes to check
+     * @param settingHolders the classes to check
      */
-    public void validateAllPropertiesAreConstants(Iterable<Class<? extends SettingsHolder>> settingsHolderClasses) {
+    public void validateAllPropertiesAreConstants(Iterable<Class<? extends SettingsHolder>> settingHolders) {
         List<String> invalidFields = new ArrayList<>();
 
-        for (Class<? extends SettingsHolder> clazz : settingsHolderClasses) {
+        for (Class<? extends SettingsHolder> clazz : settingHolders) {
             List<String> invalidFieldsForClazz = getAllFields(clazz)
                 .filter(field -> Property.class.isAssignableFrom(field.getType()))
                 .filter(field -> !isValidConstantField(field))
@@ -81,6 +84,47 @@ public void validateAllPropertiesAreConstants(Iterable<Class<? extends SettingsH
         }
     }
 
+    /**
+     * Throws an exception if any of the provided settings holder classes is not final.
+     *
+     * @param settingHolders the classes to check
+     */
+    public void validateSettingsHolderClassesFinal(Iterable<Class<? extends SettingsHolder>> settingHolders) {
+        List<String> invalidClasses = new ArrayList<>();
+
+        for (Class<? extends SettingsHolder> clazz : settingHolders) {
+            if (!Modifier.isFinal(clazz.getModifiers())) {
+                invalidClasses.add(clazz.getCanonicalName());
+            }
+        }
+
+        if (!invalidClasses.isEmpty()) {
+            throw new IllegalStateException("The following classes are not final:\n- "
+                + String.join("\n- ", invalidClasses));
+        }
+    }
+
+    /**
+     * Throws an exception if any of the provided setting holder classes does not have a single private
+     * no-args constructor.
+     *
+     * @param settingHolders the classes to check
+     */
+    public void validateClassesHaveHiddenNoArgConstructor(Iterable<Class<? extends SettingsHolder>> settingHolders) {
+        List<String> invalidClasses = new ArrayList<>();
+
+        for (Class<? extends SettingsHolder> clazz : settingHolders) {
+            if (!hasValidConstructorSetup(clazz)) {
+                invalidClasses.add(clazz.getCanonicalName());
+            }
+        }
+
+        if (!invalidClasses.isEmpty()) {
+            throw new IllegalStateException("The following classes do not have a single no-args private constructor:"
+                + "\n- " + String.join("\n- ", invalidClasses));
+        }
+    }
+
     /**
      * Throws an exception if there isn't a non-empty comment for every property in the configuration data.
      *
@@ -232,6 +276,13 @@ protected List<String> gatherExpectedEnumNames(Class<? extends Enum<?>> enumClas
             .collect(Collectors.toList());
     }
 
+    protected boolean hasValidConstructorSetup(Class<? extends SettingsHolder> clazz) {
+        Constructor<?>[] constructors = clazz.getDeclaredConstructors();
+        return constructors.length == 1
+            && constructors[0].getParameterCount() == 0
+            && Modifier.isPrivate(constructors[0].getModifiers());
+    }
+
     /**
      * Returns all fields of the class, including all fields of parent classes, recursively.
      *

src/test/java/ch/jalu/configme/samples/settingsholders/SettingsHolderWithInvalidConstants.java

@@ -23,6 +23,10 @@ public class SettingsHolderWithInvalidConstants implements SettingsHolder {
     private SettingsHolderWithInvalidConstants() {
     }
 
+    // used for test ensuring classes only have a sole no-args private constructor
+    private SettingsHolderWithInvalidConstants(boolean other) {
+    }
+
     public static class Child extends SettingsHolderWithInvalidConstants {
 
         private final Property<String> strProp = null;

src/test/java/ch/jalu/configme/utils/SettingsHolderClassValidatorTest.java

@@ -46,6 +46,8 @@ void shouldValidateSuccessfully() {
         // then - no exception
         Matcher<Iterable<Class<? extends SettingsHolder>>> matcher = (Matcher) contains(FullyValidSettingsHolder1.class, FullyValidSettingsHolder2.class);
         verify(validatorSpy).validateAllPropertiesAreConstants(argThat(matcher));
+        verify(validatorSpy).validateSettingsHolderClassesFinal(argThat(matcher));
+        verify(validatorSpy).validateClassesHaveHiddenNoArgConstructor(argThat(matcher));
         verify(validatorSpy).validateHasCommentOnEveryProperty(any(ConfigurationData.class), isNull());
         verify(validatorSpy).validateCommentLengthsAreWithinBounds(any(ConfigurationData.class), isNull(), eq(90));
         verify(validatorSpy).validateHasAllEnumEntriesInComment(any(ConfigurationData.class), isNull());
@@ -165,4 +167,36 @@ void shouldVerifyAllEnumEntriesInComment() {
         assertThat(e2.getMessage(), equalTo("The following enum properties do not list all enum values:"
             + "\n- For Property 'sample.gameMode': missing CREATIVE, SURVIVAL"));
     }
+
+    @Test
+    void shouldThrowForNonFinalClasses() {
+        // given
+        List<Class<? extends SettingsHolder>> classes = Arrays.asList(
+            SettingsHolderWithEnumPropertyComments.class, FullyValidSettingsHolder1.class, SettingsHolderWithInvalidConstants.class);
+
+        // when
+        IllegalStateException e = assertThrows(IllegalStateException.class,
+            () -> validator.validateSettingsHolderClassesFinal(classes));
+
+        // then
+        assertThat(e.getMessage(), equalTo("The following classes are not final:"
+            + "\n- ch.jalu.configme.samples.settingsholders.SettingsHolderWithEnumPropertyComments"
+            + "\n- ch.jalu.configme.samples.settingsholders.SettingsHolderWithInvalidConstants"));
+    }
+
+    @Test
+    void shouldThrowForClassWithoutPrivateConstructor() {
+        // given
+        List<Class<? extends SettingsHolder>> classes = Arrays.asList(
+            SettingsHolderWithEnumPropertyComments.class, FullyValidSettingsHolder1.class, SettingsHolderWithInvalidConstants.class);
+
+        // when
+        IllegalStateException e = assertThrows(IllegalStateException.class,
+            () -> validator.validateClassesHaveHiddenNoArgConstructor(classes));
+
+        // then
+        assertThat(e.getMessage(), equalTo("The following classes do not have a single no-args private constructor:"
+            + "\n- ch.jalu.configme.samples.settingsholders.SettingsHolderWithEnumPropertyComments"
+            + "\n- ch.jalu.configme.samples.settingsholders.SettingsHolderWithInvalidConstants"));
+    }
 }