Add Generic way of calling Persistence Adapter when the state of a set changes

3-Domain/src/main/java/abstraction/CustomSet.java

@@ -0,0 +1,17 @@
+package abstraction;
+
+import java.util.Set;
+import java.util.stream.Stream;
+
+public interface CustomSet<T> {
+
+
+
+	Stream<T> stream();
+
+	boolean add(T value);
+
+	boolean remove(T value);
+
+	Set<T> getSet();
+}

3-Domain/src/main/java/abstraction/CustomSetPersistenceDecorator.java

@@ -0,0 +1,43 @@
+package abstraction;
+
+import java.util.Set;
+import java.util.stream.Stream;
+
+/**
+ * A Decorator to intercept all state changes on a set and sync them with the persistence layer of the
+ * application.
+ * @param <T> The data type that should be stored and updated in the persistence layer
+ */
+public class CustomSetPersistenceDecorator<T> implements CustomSet<T> {
+
+	private final CustomSet<T> set;
+	private final PersistenceAdapter<T> persistenceAdapter;
+
+	public CustomSetPersistenceDecorator(PersistenceAdapter<T> persistenceAdapter) {
+		this.persistenceAdapter = persistenceAdapter;
+		this.set = new CustomStrictSet(persistenceAdapter.getAll());
+	}
+
+	@Override
+	public Stream<T> stream(){
+		return set.stream();
+	}
+
+	@Override
+	public boolean add(T value){
+		persistenceAdapter.add(value);
+		return set.add(value);
+	}
+
+	@Override
+	public boolean remove(T value) {
+		persistenceAdapter.remove(value);
+		return this.set.remove(value);
+	}
+
+	@Override
+	public Set<T> getSet() {
+		return this.set.getSet();
+	}
+
+}

3-Domain/src/main/java/abstraction/CustomStrictSet.java

@@ -0,0 +1,47 @@
+package abstraction;
+
+import exeptions.ElementAlreadyInSet;
+import exeptions.ElementNotInSet;
+
+import java.util.Set;
+import java.util.stream.Stream;
+
+public class CustomStrictSet<T> implements CustomSet<T> {
+
+	private final Set<T> set;
+
+	public CustomStrictSet(Set<T> set) {
+		this.set = set;
+	}
+
+	@Override
+	public Stream<T> stream() {
+		return this.set.stream();
+	}
+
+	@Override
+	public Set<T> getSet() {
+		return this.set;
+	}
+
+	@Override
+	public boolean add(T value) {
+
+		if (this.set.contains(value)) {
+			throw new ElementAlreadyInSet("Tried adding " + value + " of class " + value
+					.getClass()
+					.getName() + " but the set already contains it.");
+		}
+		return this.set.add(value);
+	}
+
+	@Override
+	public boolean remove(T value) {
+		if (!this.set.contains(value)) {
+			throw new ElementNotInSet("Tried removing " + value + " of class " + value
+					.getClass()
+					.getName() + " but the set not contains it.");
+		}
+		return this.set.remove(value);
+	}
+}

3-Domain/src/main/java/abstraction/PersistenceAdapter.java

@@ -0,0 +1,11 @@
+package abstraction;
+
+import java.util.Set;
+
+public interface PersistenceAdapter<T> {
+
+	Set<T> getAll();
+	Boolean add(T value);
+	Boolean remove(T value);
+
+}

3-Domain/src/main/java/category/CategoryPersistenceAdapter.java

@@ -1,10 +0,0 @@
-package category;
-
-import java.util.Set;
-
-public interface CategoryPersistenceAdapter {
-
-	Set<Category> getAll();
-	Boolean add(Category category);
-
-}

3-Domain/src/main/java/link/LinkPersistenceAdapter.java

@@ -1,10 +0,0 @@
-package link;
-
-import java.util.Set;
-
-public interface LinkPersistenceAdapter {
-
-	Set<Link> getAll();
-	Boolean add(Link link);
-
-}