1 public interface Cache<K, V> {
 2     public String getName();
 3     public V get(K key);
 4     public Map<? extends K, ? extends V> getAll(Iterator<? extends K> keys);
 5     public boolean isPresent(K key);
 6     public void put(K key, V value);
 7     public void putAll(Map<? extends K, ? extends V> entries);
 8     public void invalidate(K key);
 9     public void invalidateAll(Iterator<? extends K> keys);
10     public void invalidateAll();
11     public boolean isEmpty();
12     public int size();
13     public void clear();
14     public Map<? extends K, ? extends V> asMap();
15 }

public class CacheImpl<K, V> implements Cache<K, V> {private final String name;private final HashMap<K, V> cache;private final ReadWriteLock lock = new ReentrantReadWriteLock();private final Lock readLock = lock.readLock();private final Lock writeLock = lock.writeLock();public CacheImpl(String name) {this.name = name;cache = new HashMap<K, V>();}public CacheImpl(String name, int initialCapacity) {this.name = name;cache = new HashMap<K, V>(initialCapacity);}public String getName() {return name;}public V get(K key) {readLock.lock();try {return cache.get(key);} finally {readLock.unlock();}}public Map<? extends K, ? extends V> getAll(Iterator<? extends K> keys) {readLock.lock();try {Map<K, V> map = new HashMap<K, V>();List<K> noEntryKeys = new ArrayList<K>();while(keys.hasNext()) {K key = keys.next();if(isPresent(key)) {map.put(key, cache.get(key));} else {noEntryKeys.add(key);}}if(!noEntryKeys.isEmpty()) {throw new CacheEntriesNotExistException(this, noEntryKeys);}return map;} finally {readLock.unlock();}}public boolean isPresent(K key) {readLock.lock();try {return cache.containsKey(key);} finally {readLock.unlock();}}public void put(K key, V value) {writeLock.lock();try {cache.put(key, value);} finally {writeLock.unlock();}}public void putAll(Map<? extends K, ? extends V> entries) {writeLock.lock();try {cache.putAll(entries);} finally {writeLock.unlock();}}public void invalidate(K key) {writeLock.lock();try {if(!isPresent(key)) {throw new CacheEntryNotExistsException(this, key);}cache.remove(key);} finally {writeLock.unlock();}}public void invalidateAll(Iterator<? extends K> keys) {writeLock.lock();try {List<K> noEntryKeys = new ArrayList<K>();while(keys.hasNext()) {K key = keys.next();if(!isPresent(key)) {noEntryKeys.add(key);}}if(!noEntryKeys.isEmpty()) {throw new CacheEntriesNotExistException(this, noEntryKeys);}while(keys.hasNext()) {K key = keys.next();invalidate(key);}} finally {writeLock.unlock();}}public void invalidateAll() {writeLock.lock();try {cache.clear();} finally {writeLock.unlock();}}public int size() {readLock.lock();try {return cache.size();} finally {readLock.unlock();}}public void clear() {writeLock.lock();try {cache.clear();} finally {writeLock.unlock();}}public Map<? extends K, ? extends V> asMap() {readLock.lock();try {return new ConcurrentHashMap<K, V>(cache);} finally {readLock.unlock();}}public boolean isEmpty() {readLock.lock();try {return cache.isEmpty();} finally {readLock.unlock();}}}

 1     @Test
 2     public void testCacheSimpleUsage() {
 3         Book uml = bookFactory.createUMLDistilled();
 4         Book derivatives = bookFactory.createDerivatives();
 5
 6         String umlBookISBN = uml.getIsbn();
 7         String derivativesBookISBN = derivatives.getIsbn();
 8
 9         Cache<String, Book> cache = cacheFactory.create("book-cache");
10         cache.put(umlBookISBN, uml);
11         cache.put(derivativesBookISBN, derivatives);
12
13         Book fetchedBackUml = cache.get(umlBookISBN);
14         System.out.println(fetchedBackUml);
15
16         Book fetchedBackDerivatives = cache.get(derivativesBookISBN);
17         System.out.println(fetchedBackDerivatives);
18     }