Creating persistence service.

Change-Id: Ib78b4001a24c71b4096e5a2a446dbd5009aa1090

@@ -19,7 +19,6 @@
         <command>
         <command>
             <action class="org.onosproject.cli.SummaryCommand"/>
             <action class="org.onosproject.cli.SummaryCommand"/>
         </command>
         </command>
-
         <command>
         <command>
             <action class="org.onosproject.cli.security.ReviewCommand"/>
             <action class="org.onosproject.cli.security.ReviewCommand"/>
             <completers>
             <completers>

@@ -63,6 +63,11 @@
             <artifactId>onlab-rest</artifactId>
             <artifactId>onlab-rest</artifactId>
             <version>${project.version}</version>
             <version>${project.version}</version>
         </dependency>
         </dependency>
+        <dependency>
+            <groupId>org.mapdb</groupId>
+            <artifactId>mapdb</artifactId>
+            <version>1.0.8</version>
+        </dependency>
     </dependencies>
     </dependencies>
 
 
 </project>
 </project>

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * 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.onosproject.persistence;
+
+/**
+ * Service that allows for the creation of local disk backed map for instance specific values that persist across
+ * restarts. Empty maps and sets are deleted on shutdown.
+ */
+public interface PersistenceService {
+    /**
+     * A builder for the creation of local persistent maps backed by disk.
+     *
+     * @param <K> the type of keys in this map
+     * @param <V> the type of values in this map
+     * @return a persistent map builder
+     */
+    <K, V> PersistentMapBuilder<K, V> persistentMapBuilder();
+
+    /**
+     * A builder for the creation of local persistent sets backed by disk.
+     *
+     * @param <E> the type of the elements
+     * @return a persistent set builder
+     */
+    <E> PersistentSetBuilder<E> persistentSetBuilder();
+}
\ No newline at end of file

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * 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.onosproject.persistence;
+
+
+import org.onosproject.store.service.Serializer;
+
+import java.util.Map;
+
+/**
+ * The interface for a persistent map builder for use with mapDB.
+ */
+public interface PersistentMapBuilder<K, V> {
+
+    /**
+     * Sets the name of this map.
+     * @param name the string name of this map
+     * @return a persistent map builder with the name option now set
+     */
+    PersistentMapBuilder<K, V> withName(String name);
+
+    /**
+     * Sets the key serializer to be used to serialize this map, this is a required parameter.
+     * @param serializer the serializer to be used for keys
+     * @return a persistent map builder with the key serializer set
+     */
+    PersistentMapBuilder<K, V> withSerializer(Serializer serializer);
+
+    /**
+     * Validates the map settings and then builds this map in the database.  Throws an exception if invalid settings
+     * are found.
+     * @return The map that was created
+     */
+    Map<K, V> build();
+}
\ No newline at end of file

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * 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.onosproject.persistence;
+
+import org.onosproject.store.service.Serializer;
+
+import java.util.Set;
+
+/**
+ * The default interface for the persistent set builder for use with mapDB.
+ */
+public interface PersistentSetBuilder<E> {
+
+    /**
+     * Sets the name of this set.
+     * @param name the string name of this set
+     * @return a persistent set builder with the name option now set
+     */
+    PersistentSetBuilder<E> withName(String name);
+
+    /**
+     * Sets the serializer to be used to serialize this set, this is a required parameter.
+     * @param serializer the serializer to be used
+     * @return a persistent set builder with the serializer set
+     */
+    PersistentSetBuilder<E> withSerializer(Serializer serializer);
+
+    /**
+     * Validates the set settings and then builds this map in the database.  Throws an exception if invalid settings
+     * are found.
+     * @return The set that was created
+     */
+    Set<E> build();
+}
\ No newline at end of file

@@ -71,7 +71,7 @@
         <dependency>
         <dependency>
             <groupId>org.mapdb</groupId>
             <groupId>org.mapdb</groupId>
             <artifactId>mapdb</artifactId>
             <artifactId>mapdb</artifactId>
-            <version>1.0.7</version>
+            <version>1.0.8</version>
         </dependency>
         </dependency>
 
 
         <dependency>
         <dependency>

@@ -100,4 +100,4 @@ class MapDbPersistentStore<K, V> implements PersistentStore<K, V> {
         items.remove(keyBytes);
         items.remove(keyBytes);
         database.commit();
         database.commit();
     }
     }
-}
+}
\ No newline at end of file

+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ Copyright 2015 Open Networking Laboratory
+  ~
+  ~ 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.
+  -->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <repositories>
+        <repository>
+            <id>repository.springsource.com.release</id>
+            <name>SpringSource OBR - Release</name>
+            <url>http://repository.springsource.com/maven/bundles/release</url>
+        </repository>
+        <repository>
+            <id>repository.springsource.com.external</id>
+            <name>SpringSource OBR - External</name>
+            <url>http://repository.springsource.com/maven/bundles/external</url>
+        </repository>
+    </repositories>
+
+    <parent>
+        <groupId>org.onosproject</groupId>
+        <artifactId>onos-core-store</artifactId>
+        <version>1.4.0-SNAPSHOT</version>
+        <relativePath>../pom.xml</relativePath>
+    </parent>
+
+    <artifactId>onos-core-persistence</artifactId>
+    <packaging>bundle</packaging>
+
+    <description>ONOS Core persistent local store subsystem</description>
+
+
+
+    <dependencies>
+        <dependency>
+            <groupId>org.onosproject</groupId>
+            <artifactId>onos-api</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.mapdb</groupId>
+            <artifactId>mapdb</artifactId>
+            <version>1.0.8</version>
+        </dependency>
+        <dependency>
+            <groupId>org.junit</groupId>
+            <artifactId>com.springsource.org.junit</artifactId>
+            <version>4.11.0</version>
+        </dependency>
+    </dependencies>
+
+</project>

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * 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.onosproject.persistence.impl;
+
+import org.mapdb.DB;
+import org.onosproject.persistence.PersistentMapBuilder;
+import org.onosproject.store.service.Serializer;
+
+import java.util.Map;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * Default builder for persistent maps stored in the mapDB local database via the persistence service.
+ */
+public class DefaultPersistentMapBuilder<K, V> implements PersistentMapBuilder<K, V> {
+
+    private final DB localDB;
+
+    private String name = null;
+
+    private Serializer serializer = null;
+
+
+    public DefaultPersistentMapBuilder(DB localDB) {
+        checkNotNull(localDB, "The local database cannot be null.");
+        this.localDB = localDB;
+    }
+
+    public PersistentMapBuilder<K, V> withName(String name) {
+        this.name = PersistenceManager.MAP_PREFIX + checkNotNull(name);
+        return this;
+    }
+
+    public PersistentMapBuilder<K, V> withSerializer(Serializer serializer) {
+        checkArgument(this.serializer == null);
+        checkNotNull(serializer);
+        this.serializer = serializer;
+        return this;
+    }
+
+    public Map<K, V> build() {
+        checkNotNull(name, "The name must be assigned.");
+        checkNotNull(serializer, "The key serializer must be assigned.");
+
+        return new PersistentMap<K, V>(serializer, localDB, name);
+    }
+}
\ No newline at end of file

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * 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.onosproject.persistence.impl;
+
+import org.mapdb.DB;
+import org.onosproject.persistence.PersistentSetBuilder;
+import org.onosproject.store.service.Serializer;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * Default builder for persistent sets stored in the mapDB local database via the persistence service..
+ */
+public class DefaultPersistentSetBuilder<E> implements PersistentSetBuilder<E> {
+
+    private final DB localDB;
+
+    private String name = null;
+
+    private Serializer serializer = null;
+
+    public DefaultPersistentSetBuilder(DB localDB) {
+        this.localDB = checkNotNull(localDB, "The local database cannot be null.");
+    }
+
+    public PersistentSetBuilder<E> withName(String name) {
+        this.name = PersistenceManager.SET_PREFIX + checkNotNull(name);
+        return this;
+    }
+
+    public PersistentSetBuilder<E> withSerializer(Serializer serializer) {
+        checkArgument(this.serializer == null);
+        checkNotNull(serializer);
+        this.serializer = serializer;
+        return this;
+    }
+
+    public PersistentSet<E> build() {
+        checkNotNull(name, "The name must be assigned.");
+        checkNotNull(serializer, "The serializer must be assigned.");
+
+        return new PersistentSet<E>(serializer, localDB, name);
+    }
+}
\ No newline at end of file

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * 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.onosproject.persistence.impl;
+
+/**
+ * An exception defined for failures of the local persistent store system.
+ */
+
+/**
+ * Throws an exception with the specified message.
+ */
+public class PersistenceException extends RuntimeException {
+    public PersistenceException(String s) {
+        super(s);
+    }
+}

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * 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.onosproject.persistence.impl;
+
+import org.apache.felix.scr.annotations.Activate;
+import org.apache.felix.scr.annotations.Component;
+import org.apache.felix.scr.annotations.Deactivate;
+import org.apache.felix.scr.annotations.Service;
+import org.mapdb.DB;
+import org.mapdb.DBMaker;
+import org.onosproject.persistence.PersistenceService;
+import org.onosproject.persistence.PersistentMapBuilder;
+import org.onosproject.persistence.PersistentSetBuilder;
+import org.slf4j.Logger;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.Map;
+import java.util.Set;
+import java.util.Timer;
+import java.util.TimerTask;
+
+import static org.slf4j.LoggerFactory.getLogger;
+
+/**
+ * Service that maintains local disk backed maps and sets.  This implementation automatically deletes empty structures
+ * on shutdown.
+ */
+@Component(immediate = true)
+@Service
+public class PersistenceManager implements PersistenceService {
+
+    private static final String DATABASE_PATH = "../data/localDB";
+
+    private static final String ENCLOSING_FOLDER = "../data";
+
+    static final String MAP_PREFIX = "map:";
+
+    static final String SET_PREFIX = "set:";
+
+    private final Logger log = getLogger(getClass());
+
+    private DB localDB = null;
+
+    private static final int FLUSH_FREQUENCY_MILLIS = 3000;
+
+    private final Timer timer = new Timer();
+
+    private final CommitTask commitTask = new CommitTask();
+
+    @Activate
+    public void activate() {
+        Path dbPath = Paths.get(DATABASE_PATH);
+        Path dbFolderPath = Paths.get(ENCLOSING_FOLDER);
+        //Make sure the directory exists, if it does not, make it.
+        if (!dbFolderPath.toFile().isDirectory()) {
+            log.info("The specified folder location for the database did not exist and will be created.");
+            try {
+                Files.createDirectories(dbFolderPath);
+            } catch (IOException e) {
+                log.error("Could not create the required folder for the database.");
+                throw new PersistenceException("Database folder could not be created.");
+            }
+        }
+        //Notify if the database file does not exist.
+        boolean dbFound = Files.exists(dbPath);
+        if (!dbFound) {
+            log.info("The database file could not be located, a new database will be constructed.");
+
+        } else {
+            log.info("A previous database file has been found.");
+        }
+        localDB = DBMaker.newFileDB(dbPath.toFile())
+                .asyncWriteEnable()
+                .closeOnJvmShutdown()
+                .make();
+        timer.schedule(commitTask, FLUSH_FREQUENCY_MILLIS, FLUSH_FREQUENCY_MILLIS);
+        log.info("Started");
+    }
+
+    @Deactivate
+    public void deactivate() {
+        for (Map.Entry<String, Object> entry : localDB.getAll().entrySet()) {
+            String key = entry.getKey();
+            Object value = entry.getValue();
+                //This is a map implementation to be handled as such
+            if (value instanceof Map) {
+                Map asMap = (Map) value;
+                if (asMap.isEmpty()) {
+                    //the map is empty and may be deleted
+                    localDB.delete(key);
+                }
+                //This is a set implementation and can be handled as such
+            } else if (value instanceof Set) {
+                Set asSet = (Set) value;
+                if (asSet.isEmpty()) {
+                    //the set is empty and may be deleted
+                    localDB.delete(key);
+                }
+            }
+        }
+        localDB.commit();
+        localDB.close();
+        log.info("Stopped");
+    }
+
+    public <K, V> PersistentMapBuilder<K, V> persistentMapBuilder() {
+        return new DefaultPersistentMapBuilder<>(localDB);
+    }
+
+    public <E> PersistentSetBuilder<E> persistentSetBuilder() {
+        return new DefaultPersistentSetBuilder<>(localDB);
+    }
+
+    private class CommitTask extends TimerTask {
+
+        @Override
+        public void run() {
+            localDB.commit();
+        }
+    }
+}
\ No newline at end of file

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * 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.onosproject.persistence.impl;
+
+import com.google.common.collect.Maps;
+import com.google.common.collect.Sets;
+import org.mapdb.DB;
+import org.mapdb.Hasher;
+import org.onosproject.store.service.Serializer;
+
+import java.util.Collection;
+import java.util.Map;
+import java.util.Set;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+
+/**
+ * A map implementation that stores and receives all data from a serialized internal map.
+ */
+public class PersistentMap<K, V> implements Map<K, V> {
+
+    private final Serializer serializer;
+
+    private final org.mapdb.DB database;
+
+    private final Map<byte[], byte[]> items;
+
+    private final String name;
+
+    public PersistentMap(Serializer serializer, DB database, String name) {
+        this.serializer = checkNotNull(serializer);
+        this.database = checkNotNull(database);
+        this.name = checkNotNull(name);
+
+        items = database
+                .createHashMap(name)
+                .keySerializer(org.mapdb.Serializer.BYTE_ARRAY)
+                .valueSerializer(org.mapdb.Serializer.BYTE_ARRAY)
+                .hasher(Hasher.BYTE_ARRAY)
+                .makeOrGet();
+    }
+
+    /**
+     * Reads this set in deserialized form into the provided map.
+     *
+     * @param items the map to be populated
+     */
+    public void readInto(Map<K, V> items) {
+        this.items.forEach((keyBytes, valueBytes) ->
+                                   items.put(serializer.decode(keyBytes),
+                                             serializer.decode(valueBytes)));
+    }
+
+    @Override
+    public V remove(Object key) {
+        checkNotNull(key, "Key can not be null.");
+        V removed = get(key);
+        items.remove(serializer.encode(key));
+        return removed;
+    }
+
+    @Override
+    public int size() {
+        return items.size();
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return items.isEmpty();
+    }
+
+    @Override
+    public boolean containsKey(Object key) {
+        checkNotNull(key, "Key cannot be null.");
+        return items.containsKey(serializer.encode(key));
+    }
+
+    @Override
+    public boolean containsValue(Object value) {
+        checkNotNull(value, "Value cannot be null.");
+        byte[] serialized = serializer.encode(value);
+        for (byte[] compareValue : items.values()) {
+            boolean same = true;
+            if (compareValue == null) {
+                same = false;
+            } else if (compareValue.length != serialized.length) {
+                same = false;
+            } else {
+                for (int i = 0; i < serialized.length; i++) {
+                    if (serialized[i] != compareValue[i]) {
+                        same = false;
+                        break;
+                    }
+                }
+            }
+            if (same) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    @Override
+    public V get(Object key) {
+        checkNotNull(key, "Key cannot be null.");
+        return serializer.decode(items.get(serializer.encode(key)));
+    }
+
+    @Override
+    public V put(K key, V value) {
+        checkNotNull(key, "Key cannot be null.");
+        checkNotNull(value, "Value cannot be null.");
+        byte[] prevVal = items.put(serializer.encode(key), serializer.encode(value));
+        if (prevVal == null) {
+            return null;
+        }
+        return serializer.decode(prevVal);
+    }
+
+    @Override
+    public void putAll(Map<? extends K, ? extends V> m) {
+        checkNotNull(m, "The passed in map cannot be null.");
+        m.forEach((k, v) -> items.put(serializer.encode(k), serializer.encode(v)));
+    }
+
+    @Override
+    public void clear() {
+        items.clear();
+    }
+
+    @Override
+    public Set<K> keySet() {
+        Set<K> keys = Sets.newHashSet();
+        items.keySet().forEach(k -> keys.add(serializer.decode(k)));
+        return keys;
+    }
+
+    @Override
+    public Collection<V> values() {
+        Collection<V> values = Sets.newHashSet();
+        items.values().forEach(v -> values.add(serializer.decode(v)));
+        return values;
+    }
+
+    @Override
+    public Set<Entry<K, V>> entrySet() {
+        Set<Entry<K, V>> entries = Sets.newHashSet();
+        items.entrySet().
+                forEach(e -> entries.add(Maps.immutableEntry(serializer.decode(e.getKey()),
+                                                             serializer.decode(e.getValue()))));
+        return entries;
+    }
+
+    @Override
+    public boolean equals(Object map) {
+        //This is not threadsafe and on larger maps incurs a significant processing cost
+        if (!(map instanceof Map)) {
+            return false;
+        }
+        Map asMap = (Map) map;
+        if (this.size() != asMap.size()) {
+            return false;
+        }
+        for (Entry entry : this.entrySet()) {
+            Object key = entry.getKey();
+            if (!asMap.containsKey(key) || !asMap.get(key).equals(entry.getValue())) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    @Override
+    public int hashCode() {
+        return super.hashCode();
+    }
+}
\ No newline at end of file

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * 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.onosproject.persistence.impl;
+
+import com.google.common.collect.Iterators;
+import org.mapdb.DB;
+import org.mapdb.Hasher;
+import org.mapdb.Serializer;
+
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.Set;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * A set implementation that gets and receives all data from a serialized internal set.
+ */
+//TODO add locking for reads and writes
+public class PersistentSet<E> implements Set<E> {
+
+    private final org.onosproject.store.service.Serializer serializer;
+
+    private final org.mapdb.DB database;
+
+    private final Set<byte[]> items;
+
+    private final String name;
+
+    public PersistentSet(org.onosproject.store.service.Serializer serializer, DB database, String name) {
+        this.serializer = checkNotNull(serializer);
+        this.database = checkNotNull(database);
+        this.name = checkNotNull(name);
+
+        items = database
+                .createHashSet(name)
+                .serializer(Serializer.BYTE_ARRAY)
+                .hasher(Hasher.BYTE_ARRAY)
+                .makeOrGet();
+    }
+
+    public void readInto(Set<E> items) {
+        this.items.forEach(item -> items.add(serializer.decode(item)));
+    }
+
+    @Override
+    public int size() {
+        return items.size();
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return items.isEmpty();
+    }
+
+    @Override
+    public boolean contains(Object o) {
+        checkNotNull(o, "The argument cannot be null");
+        return items.contains(serializer.encode(o));
+    }
+
+    @Override
+    public Iterator<E> iterator() {
+        return Iterators.transform(items.iterator(), serializer::decode);
+    }
+
+    @Override
+    public Object[] toArray() {
+        Object[] retArray = new Object[items.size()];
+        int index = 0;
+        Iterator<byte[]> iterator = items.iterator();
+        while (iterator.hasNext()) {
+            retArray[index] = serializer.decode(iterator.next());
+            index++;
+        }
+        return retArray;
+    }
+
+    @Override
+    public <T> T[] toArray(T[] a) {
+        checkNotNull(a, "The passed in array cannot be null.");
+        int index = 0;
+        Iterator<byte[]> iterator = items.iterator();
+        T[] retArray;
+        if (a.length >= items.size()) {
+            retArray = a;
+        } else {
+            retArray = (T[]) new Object[items.size()];
+        }
+        while (iterator.hasNext()) {
+            retArray[index++] = serializer.decode(iterator.next());
+        }
+        if (retArray.length > items.size()) {
+            retArray[index] = null;
+        }
+        return retArray;
+    }
+
+    @Override
+    public boolean add(E item) {
+        checkNotNull("Item to be added cannot be null.");
+        return items.add(serializer.encode(item));
+    }
+
+    @Override
+    public boolean remove(Object o) {
+        checkNotNull(o, "Item to be removed cannot be null.");
+        return items.remove(serializer.encode(o));
+    }
+
+    @Override
+    public boolean containsAll(Collection<?> c) {
+        checkNotNull(c, "Collection cannot be internal.");
+        for (Object item : c) {
+            if (!items.contains(serializer.encode(item))) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    @Override
+    public boolean addAll(Collection<? extends E> c) {
+        checkNotNull(c, "The collection to be added cannot be null.");
+        boolean changed = false;
+        for (Object item : c) {
+            changed = items.add(serializer.encode(item)) || changed;
+        }
+        return changed;
+    }
+
+    @Override
+    public boolean retainAll(Collection<?> c) {
+        boolean changed = false;
+        for (byte[] item : items) {
+            E deserialized = serializer.decode(item);
+            if (!c.contains(deserialized)) {
+                changed = items.remove(item) || changed;
+            }
+        }
+        return changed;
+    }
+
+    @Override
+    public boolean removeAll(Collection<?> c) {
+        boolean changed = false;
+        for (Object item : c) {
+            changed = items.remove(serializer.encode(item)) || changed;
+        }
+        return changed;
+    }
+
+    @Override
+    public void clear() {
+        items.clear();
+    }
+
+    @Override
+    public boolean equals(Object set) {
+        //This is not threadsafe and on larger sets incurs a significant processing cost
+        if (!(set instanceof Set)) {
+            return false;
+        }
+        Set asSet = (Set) set;
+        if (asSet.size() != this.size()) {
+            return false;
+        }
+        for (Object item : this) {
+            if (!asSet.contains(item)) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    @Override
+    public int hashCode() {
+        return super.hashCode();
+    }
+}
\ No newline at end of file

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * 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.onosproject.persistence.impl.test;
+
+import com.google.common.collect.Maps;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.mapdb.DB;
+import org.mapdb.DBMaker;
+import org.onosproject.persistence.impl.PersistentMap;
+import org.onosproject.store.service.Serializer;
+
+import java.nio.file.Paths;
+import java.util.Map;
+import java.util.Set;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Test suite for Persistent Map.
+ */
+public class PersistentMapTest {
+
+    private Map<Integer, Integer> map = null;
+    private DB fakeDB = null;
+
+
+    /**
+     * Set up the database, create a map and a direct executor to handle it.
+     *
+     * @throws Exception if instantiation fails
+     */
+    @Before
+    public void setUp() throws Exception {
+        //Creates a db, a map within it and a basic integer serializer (async writing is off)
+        fakeDB = DBMaker
+                .newFileDB(Paths.get("../testDb").toFile())
+                .asyncWriteEnable()
+                .closeOnJvmShutdown()
+                .make();
+        map = new PersistentMap<Integer, Integer>(new Serializer() {
+            @Override
+            public <T> byte[] encode(T object) {
+                if (object == null) {
+                    return null;
+                }
+                int num = (Integer) object;
+                byte[] result = new byte[4];
+
+                result[0] = (byte) (num >> 24);
+                result[1] = (byte) (num >> 16);
+                result[2] = (byte) (num >> 8);
+                result[3] = (byte) num;
+                return result;
+            }
+
+            @Override
+            public <T> T decode(byte[] bytes) {
+                if (bytes == null) {
+                    return null;
+                }
+                int num = 0x00000000;
+
+                num = num | bytes[0] << 24;
+                num = num | bytes[1] << 16;
+                num = num | bytes[2] << 8;
+                num = num | bytes[3];
+
+                return (T) new java.lang.Integer(num);
+            }
+        }, fakeDB, "map");
+    }
+
+    /**
+     * Clears and deletes the map, closes the datbase and deletes the file.
+     *
+     * @throws Exception if shutdown fails
+     */
+    @After
+    public void tearDown() throws Exception {
+        map.clear();
+        fakeDB.delete("map:map");
+        fakeDB.commit();
+        fakeDB.close();
+        //This is key to prevent artifacts persisting between tests.
+        Paths.get("../testDB").toFile().delete();
+
+
+    }
+
+    @Test
+    public void testRemove() throws Exception {
+        //Checks removal and return values
+        fillMap(10);
+        assertEquals(10, map.size());
+        for (int i = 0; i < 10; i++) {
+            assertEquals("The previous value was wrong.", new Integer(i), map.remove(i));
+            assertNull("The previous value was wrong.", map.remove(i));
+            //(i+1) compensates for base zero.
+            assertEquals("The size was wrong.", 10 - (i + 1), map.size());
+        }
+    }
+
+    @Test
+    public void testSize() throws Exception {
+        //Checks size values throughout addition and removal
+        for (int i = 0; i < 10; i++) {
+            map.put(i, i);
+            assertEquals("The map size is wrong.", i + 1, map.size());
+        }
+        for (int i = 0; i < 10; i++) {
+            map.remove(i);
+            assertEquals("The map size is wrong.", 9 - i, map.size());
+        }
+    }
+
+    @Test
+    public void testIsEmpty() throws Exception {
+        //Checks empty condition
+        //asserts that the map starts out empty
+        assertTrue("Map should be empty", map.isEmpty());
+        map.put(1, 1);
+        assertFalse("Map shouldn't be empty.", map.isEmpty());
+        map.remove(1);
+        assertTrue("Map should be empty", map.isEmpty());
+    }
+
+    @Test
+    public void testContains() throws Exception {
+        //Checks both containsKey and containsValue be aware the implementations vary widely (value does not use mapDB
+        //due to object '=='being an insufficient check)
+        for (int i = 0; i < 10; i++) {
+            assertFalse("Map should not contain the key", map.containsKey(i));
+            assertFalse("Map should not contain the value", map.containsValue(i));
+            map.put(i, i);
+            assertTrue("Map should contain the key", map.containsKey(i));
+            assertTrue("Map should contain the value", map.containsValue(i));
+        }
+    }
+
+    @Test
+    public void testGet() throws Exception {
+        //Tests value retrieval and nonexistent key return values
+        for (int i = 0; i < 10; i++) {
+            map.put(i, i);
+            for (int j = 0; j <= i; j++) {
+                assertEquals("The value was wrong.", new Integer(j), map.get(j));
+            }
+        }
+        assertNull("Null return value for nonexistent keys.", map.get(10));
+    }
+
+    @Test
+    public void testPutAll() throws Exception {
+        //Tests adding of an outside map
+        Map<Integer, Integer> testMap = Maps.newHashMap();
+        fillMap(10);
+        map.putAll(testMap);
+        for (int i = 0; i < 10; i++) {
+            assertTrue("The map should contain the current 'i' value.", map.containsKey(i));
+            assertTrue("The map should contain the current 'i' value.", map.containsValue(i));
+        }
+    }
+
+    @Test
+    public void testClear() throws Exception {
+        //Tests clearing the map
+        assertTrue("Map was initialized incorrectly, should be empty.", map.isEmpty());
+        fillMap(10);
+        assertFalse("Map should contain entries now.", map.isEmpty());
+        map.clear();
+        assertTrue("Map should have been cleared of entries.", map.isEmpty());
+
+    }
+
+    @Test
+    public void testKeySet() throws Exception {
+        //Tests key set generation
+        fillMap(10);
+        Set<Integer> keys = map.keySet();
+        for (int i = 0; i < 10; i++) {
+            assertTrue("The key set doesn't contain all keys 0-9", keys.contains(i));
+        }
+        assertEquals("The key set has an incorrect number of entries", 10, keys.size());
+    }
+
+    @Test
+    public void testValues() throws Exception {
+        //Tests value set generation
+        fillMap(10);
+        Set<Integer> values = (Set<Integer>) map.values();
+        for (int i = 0; i < 10; i++) {
+            assertTrue("The key set doesn't contain all keys 0-9", values.contains(i));
+        }
+        assertEquals("The key set has an incorrect number of entries", 10, values.size());
+    }
+
+    @Test
+    public void testEntrySet() throws Exception {
+        //Test entry set generation (violates abstraction by knowing the type of the returned entries)
+        fillMap(10);
+        Set<Map.Entry<Integer, Integer>> entries = map.entrySet();
+        for (int i = 0; i < 10; i++) {
+            assertTrue("The key set doesn't contain all keys 0-9", entries.contains(Maps.immutableEntry(i, i)));
+        }
+        assertEquals("The key set has an incorrect number of entries", 10, entries.size());
+    }
+
+    @Test public void testPut() throws Exception {
+        //Tests insertion behavior (particularly the returning of previous value)
+        fillMap(10);
+        for (int i = 0; i < 10; i++) {
+            assertEquals("Put should return the previous value", new Integer(i), map.put(i, i + 1));
+        }
+        assertNull(map.put(11, 11));
+    }
+
+    /**
+     * Populated the map with pairs of integers from (0, 0) up to (numEntries - 1, numEntries -1).
+     * @param numEntries number of entries to add
+     */
+    private void fillMap(int numEntries) {
+        for (int i = 0; i < numEntries; i++) {
+            map.put(i, i);
+        }
+    }
+}
\ No newline at end of file

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * 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.onosproject.persistence.impl.test;
+
+import com.google.common.collect.Sets;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.mapdb.DB;
+import org.mapdb.DBMaker;
+import org.onosproject.persistence.impl.PersistentSet;
+import org.onosproject.store.service.Serializer;
+
+import java.nio.file.Paths;
+import java.util.HashSet;
+import java.util.Set;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Test suite for Persistent Set.
+ */
+public class PersistentSetTest {
+
+    private Set<Integer> set = null;
+    private DB fakeDB = null;
+
+    @Before
+    public void setUp() throws Exception {
+        //Creates a db, a set within it and a basic integer serializer (async writing is off)
+        fakeDB = DBMaker
+                .newFileDB(Paths.get("../testDb").toFile())
+                .asyncWriteEnable()
+                .closeOnJvmShutdown()
+                .make();
+        set = new PersistentSet<Integer>(new Serializer() {
+            @Override
+            public <T> byte[] encode(T object) {
+                if (object == null) {
+                    return null;
+                }
+                int num = (Integer) object;
+                byte[] result = new byte[4];
+
+                result[0] = (byte) (num >> 24);
+                result[1] = (byte) (num >> 16);
+                result[2] = (byte) (num >> 8);
+                result[3] = (byte) num;
+                return result;
+            }
+
+            @Override
+            public <T> T decode(byte[] bytes) {
+                if (bytes == null) {
+                    return null;
+                }
+                int num = 0x00000000;
+
+                num = num | bytes[0] << 24;
+                num = num | bytes[1] << 16;
+                num = num | bytes[2] << 8;
+                num = num | bytes[3];
+
+                return (T) new java.lang.Integer(num);
+            }
+        }, fakeDB, "set");
+
+    }
+
+    @After
+    public void tearDown() throws Exception {
+        set.clear();
+        fakeDB.delete("map:map");
+        fakeDB.commit();
+        fakeDB.close();
+        //This is key to prevent artifacts persisting between tests.
+        Paths.get("../testDB").toFile().delete();
+    }
+
+    @Test
+    public void testSize() throws Exception {
+        //Check correct sizing throughout population
+        for (int i = 0; i < 10; i++) {
+            set.add(i);
+            assertEquals("The set should have i + 1 entries.", i + 1, set.size());
+        }
+    }
+
+    @Test
+    public void testIsEmpty() throws Exception {
+        //test empty condition
+        assertTrue("The set should be initialized empty.", set.isEmpty());
+        fillSet(5, this.set);
+        assertFalse("The set should no longer be empty.", set.isEmpty());
+        set.clear();
+        assertTrue("The set should have been cleared.", set.isEmpty());
+    }
+
+    @Test
+    public void testContains() throws Exception {
+        //Test contains
+        assertFalse("The set should not contain anything", set.contains(1));
+        fillSet(10, this.set);
+        for (int i = 0; i < 10; i++) {
+            assertTrue("The set should contain all values 0-9.", set.contains(i));
+        }
+    }
+
+    @Test
+    public void testIterator() throws Exception {
+        //Test iterator behavior (no order guarantees are made)
+        Set<Integer> validationSet = Sets.newHashSet();
+        fillSet(10, this.set);
+        fillSet(10, validationSet);
+        set.iterator().forEachRemaining(item -> assertTrue("Items were mismatched.", validationSet.remove(item)));
+        //All values should have been seen and removed
+        assertTrue("All entries in the validation set should have been removed.", validationSet.isEmpty());
+    }
+
+    @Test
+    public void testToArray() throws Exception {
+        //Test creation of a new array of the values
+        fillSet(10, set);
+        Object[] arr = set.toArray();
+        assertEquals("The array should be of length 10.", 10, arr.length);
+        for (int i = 0; i < 10; i++) {
+            assertTrue("All elements of the array should be in the set.", set.contains((Integer) arr[i]));
+        }
+    }
+
+    @Test
+    public void testToArray1() throws Exception {
+        //Test creation of a new array with the possibility of populating passed array if space allows
+        Integer[] originalArray = new Integer[9];
+        fillSet(9, set);
+        //Test the case where the array and set match in size
+        Object[] retArray = set.toArray(originalArray);
+        assertEquals("If the set can fit the array should be the one passed in.", originalArray, retArray);
+        //Test the case where the passe array is too small to fit the set
+        set.add(9);
+        assertNotEquals("A new set should be generated if the contents will not fit in the passed set",
+                        set.toArray(originalArray), originalArray);
+        //Now test the case where there should be a null terminator
+        set.clear();
+        fillSet(5, set);
+        assertNull("The character one after last should be null if the array is larger than the set.",
+                   set.toArray(originalArray)[5]);
+    }
+
+    @Test
+    public void testAdd() throws Exception {
+        //Test of add
+        for (int i = 0; i < 10; i++) {
+            assertEquals("The size of the set is wrong.", i, set.size());
+            assertTrue("The first add of an element should be true.", set.add(i));
+            assertFalse("The second add of an element should be false.", set.add(i));
+        }
+    }
+
+    @Test
+    public void testRemove() throws Exception {
+        //Test removal
+        fillSet(10, set);
+        for (int i = 0; i < 10; i++) {
+            assertEquals("The size of the set is wrong.", 10 - i, set.size());
+            assertTrue("The first removal should be true.", set.remove(i));
+            assertFalse("The second removal should be false (item no longer contained).", set.remove(i));
+        }
+        assertTrue("All elements should have been removed.", set.isEmpty());
+    }
+
+    @Test
+    public void testContainsAll() throws Exception {
+        //Test contains with short circuiting
+        Set<Integer> integersToCheck = Sets.newHashSet();
+        fillSet(10, integersToCheck);
+        fillSet(10, set);
+        assertTrue("The sets should be identical so mutual subsets.", set.containsAll(integersToCheck));
+        set.remove(9);
+        assertFalse("The set should contain one fewer value.", set.containsAll(integersToCheck));
+    }
+
+    @Test
+    public void testAddAll() throws Exception {
+        //Test multi-adds with change checking
+        Set<Integer> integersToCheck = Sets.newHashSet();
+        fillSet(10, integersToCheck);
+        assertFalse("Set should be empty and so integers to check should not be a subset.",
+                    set.containsAll(integersToCheck));
+        assertTrue("The set should have changed as a result of add all.", set.addAll(integersToCheck));
+        assertFalse("The set should not have changed as a result of add all a second time.",
+                    set.addAll(integersToCheck));
+        assertTrue("The sets should now be equivalent.", set.containsAll(integersToCheck));
+        assertTrue("The sets should now be equivalent.", integersToCheck.containsAll(set));
+    }
+
+    @Test
+    public void testRetainAll() throws Exception {
+        //Test ability to generate the intersection set
+        Set<Integer> retainSet = Sets.newHashSet();
+        fillSet(10, set);
+        assertTrue("The set should have changed.", set.retainAll(retainSet));
+        assertTrue("The set should have been emptied.", set.isEmpty());
+        fillSet(10, set);
+        fillSet(10, retainSet);
+        Set<Integer> duplicateSet = new HashSet<>(set);
+        assertFalse("The set should not have changed.", set.retainAll(retainSet));
+        assertEquals("The set should be the same as the duplicate.", duplicateSet, set);
+        retainSet.remove(9);
+        assertTrue("The set should have changed.", set.retainAll(retainSet));
+        duplicateSet.remove(9);
+        assertEquals("The set should have had the nine element removed.", duplicateSet, set);
+    }
+
+    @Test
+    public void testRemoveAll() throws Exception {
+        //Test for mass removal and change checking
+        Set<Integer> removeSet = Sets.newHashSet();
+        fillSet(10, set);
+        Set<Integer> duplicateSet = Sets.newHashSet(set);
+        assertFalse("No elements should change.", set.removeAll(removeSet));
+        assertEquals("Set should not have diverged from the duplicate.", duplicateSet, set);
+        fillSet(5, removeSet);
+        assertTrue("Elements should have been removed.", set.removeAll(removeSet));
+        assertNotEquals("Duplicate set should no longer be equivalent.", duplicateSet, set);
+        assertEquals("Five elements should have been removed from set.", 5, set.size());
+        for (Integer item : removeSet) {
+            assertFalse("No element of remove set should remain.", set.contains(item));
+        }
+    }
+
+    @Test
+    public void testClear() throws Exception {
+        //Test set emptying
+        assertTrue("The set should be initialized empty.", set.isEmpty());
+        set.clear();
+        assertTrue("Clear should have no effect on an empty set.", set.isEmpty());
+        fillSet(10, set);
+        assertFalse("The set should no longer be empty.", set.isEmpty());
+        set.clear();
+        assertTrue("The set should be empty after clear.", set.isEmpty());
+    }
+
+    /**
+     * Populated the map with integers from (0) up to (numEntries - 1).
+     *
+     * @param numEntries number of entries to add
+     */
+    private void fillSet(int numEntries, Set<Integer> set) {
+        checkNotNull(set);
+        for (int i = 0; i < numEntries; i++) {
+            set.add(i);
+        }
+    }
+}
\ No newline at end of file

@@ -33,7 +33,8 @@
 
 
     <modules>
     <modules>
         <module>dist</module>
         <module>dist</module>
-        <module>serializers</module>
+        <module>persistence</module>
+	<module>serializers</module>
     </modules>
     </modules>
 
 
     <dependencies>
     <dependencies>

@@ -96,6 +96,7 @@
         <bundle>mvn:org.onosproject/onos-core-net/@ONOS-VERSION</bundle>
         <bundle>mvn:org.onosproject/onos-core-net/@ONOS-VERSION</bundle>
         <bundle>mvn:org.onosproject/onos-core-common/@ONOS-VERSION</bundle>
         <bundle>mvn:org.onosproject/onos-core-common/@ONOS-VERSION</bundle>
         <bundle>mvn:org.onosproject/onos-core-dist/@ONOS-VERSION</bundle>
         <bundle>mvn:org.onosproject/onos-core-dist/@ONOS-VERSION</bundle>
+        <bundle>mvn:org.onosproject/onos-core-persistence/@ONOS-VERSION</bundle>
         <bundle>mvn:org.onosproject/onos-core-serializers/@ONOS-VERSION</bundle>
         <bundle>mvn:org.onosproject/onos-core-serializers/@ONOS-VERSION</bundle>
         <bundle>mvn:org.onosproject/onlab-netty/@ONOS-VERSION</bundle>
         <bundle>mvn:org.onosproject/onlab-netty/@ONOS-VERSION</bundle>
     </feature>
     </feature>