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[utils] / support / general / src / main / java / org / wamblee / persistence / AbstractDetachable.java

diff --git a/support/general/src/main/java/org/wamblee/persistence/AbstractDetachable.java b/support/general/src/main/java/org/wamblee/persistence/AbstractDetachable.java
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+/*
+ * Copyright 2005-2010 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
+ * 
+ *      http://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.wamblee.persistence;
+
+/**
+ * Detachable implementation that takes care of the basic logic for detachable
+ * objects. All that needs to be done is to implement {@link #load()}.
+ * 
+ * @param <T>
+ *            The type of the object to be attached/detached
+ * @param <Ref>
+ *            The type of the reference to store when the object is detached.
+ */
+public abstract class AbstractDetachable<T, Ref> implements Detachable<T> {
+
+    private T object;
+    private Ref reference;
+
+    /**
+     * Constructs the detachable.
+     * 
+     * @param aObject
+     *            Object.
+     * @throws IllegalArgumentException
+     *             When the object passed in is null.
+     */
+    protected AbstractDetachable(T aObject) {
+        if (aObject == null) {
+            throw new IllegalArgumentException("Object '" + aObject +
+                "' is null");
+        }
+        object = aObject;
+        reference = null;
+    }
+
+    /*
+     * (non-Javadoc)
+     * 
+     * @see org.wamblee.persistence.Detachable#detach()
+     */
+    public void detach() {
+        if (object == null) {
+            return; // Nothing to do.
+        }
+        reference = getReference(object);
+        if (reference == null) {
+            throw new IllegalStateException("Object '" + object +
+                "' not persisted yet'");
+        }
+        object = null;
+    }
+
+    /*
+     * (non-Javadoc)
+     * 
+     * @see org.wamblee.persistence.Detachable#get()
+     */
+    public T get() {
+        if (object == null) {
+            object = load(reference);
+            reference = null;
+        }
+        return object;
+    }
+
+    /**
+     * For testing.
+     * 
+     * @return current object.
+     */
+    T getObject() {
+        return object;
+    }
+
+    /**
+     * For testing.
+     * 
+     * @return The reference.
+     */
+    Ref getReference() {
+        return reference;
+    }
+
+    /**
+     * Loads the object based on a reference.
+     * 
+     * @param aReference
+     *            Reference.
+     * @return Object (may be null ).
+     */
+    protected abstract T load(Ref aReference);
+
+    /**
+     * Obtains the reference for a given object.
+     * 
+     * @param aObject
+     *            Object.
+     * @return Reference.
+     */
+    protected abstract Ref getReference(T aObject);
+
+}