JAVA 简单缓存实现-nacos

定义缓存接口:

public interface Cache {
 
    /**
     * Cache a pair of key value. If the key value already exists, the value will be overwritten.
     * @param key cache key
     * @param val cache value
     */
    void put(K key, V val);
    
    /**
     * Take the corresponding value from the cache according to the cache key.
     * @param key cache key
     * @return cache value
     */
    V get(K key);
    
    /**
     * Get the value in the cache according to the primary key, and put it into the cache after processing by the function.
     * @param key cache key
     * @param call a function, the return value of the function will be updated to the cache
     * @return cache value
     * @throws Exception callable function interface throw exception
     */
    V get(K key, Callable call) throws Exception;
    
    /**
     * Take the corresponding value from the cache according to the cache key, and remove this record from the cache.
     * @param key cache key
     * @return cache value
     */
    V remove(K key);
    
    /**
     * Clear the entire cache.
     */
    void clear();
    
    /**
     * Returns the number of key-value pairs in the cache.
     * @return  number of key-value pairs
     */
    int getSize();
}

基于Java-Map的本地缓存实现:

public class SimpleCache implements Cache {
    
    private Map cache;
    
    public SimpleCache(int size) {
        cache = new HashMap<>(size);
    }
    
    @Override
    public void put(K key, V val) {
        cache.put(key, val);
    }
    
    @Override
    public V get(K key) {
        return cache.get(key);
    }
    
    @Override
    public V get(K key, Callable call) throws Exception {
        if (cache.containsKey(key)) {
            return cache.get(key);
        } else {
            V v2 = call.call();
            cache.put(key, v2);
            return v2;
        }
    }
    
    @Override
    public V remove(K key) {
        return cache.remove(key);
    }
    
    @Override
    public void clear() {
        cache.clear();
    }
    
    @Override
    public int getSize() {
        return cache.size();
    }
}

基于LinkedHashMap的LruCache实现:

public class LruCache implements Cache {
    
    private final Cache delegate;
    
    private Map keyMap;
    
    private K eldestKey;
    
    public LruCache(Cache delegate, int size) {
        this.delegate = delegate;
        setSize(size);
    }
    
    @Override
    public int getSize() {
        return delegate.getSize();
    }
    
    public void setSize(final int size) {
        keyMap = new LinkedHashMap(size, .75F, true) {
            private static final long serialVersionUID = 4267176411845948333L;
            
            @Override
            protected boolean removeEldestEntry(Map.Entry eldest) {
                boolean tooBig = size() > size;
                if (tooBig) {
                    eldestKey = eldest.getKey();
                }
                return tooBig;
            }
          
        };
    }
    
    @Override
    public void put(K key, V val) {
        delegate.put(key, val);
        cycleKeyList(key);
    }
    
    @Override
    public V get(K key) {
        keyMap.get(key);
        return delegate.get(key);
    }
    
    @Override
    public V get(K key, Callable call) throws Exception {
        return this.delegate.get(key, call);
    }
    
    @Override
    public V remove(K key) {
        return delegate.remove(key);
    }
    
    @Override
    public void clear() {
        delegate.clear();
        keyMap.clear();
    }
    
    private void cycleKeyList(K key) {
        keyMap.put(key, null);
        if (eldestKey != null) {
            delegate.remove(eldestKey);
            eldestKey = null;
        }
    }
    
}

自动过期缓存实现:

public class AutoExpireCache implements Cache {
    
    private long expireNanos;
    
    private Cache delegate;
    
    private HashMap keyProp = new HashMap<>();
    
    public AutoExpireCache(Cache delegate, long expireNanos) {
        this.expireNanos = expireNanos;
        this.delegate = delegate;
    }
    
    @Override
    public void put(K key, V val) {
        keyProp.put(key, cacheItemProperties());
        this.delegate.put(key, val);
    }
    
    @Override
    public V get(K key) {
        if (keyProp.get(key) != null && isExpire(keyProp.get(key))) {
            this.keyProp.remove(key);
            this.delegate.remove(key);
            return null;
        }
        return this.delegate.get(key);
    }
 
    @Override
    public V get(K key, Callable call) throws Exception {
        V cachedValue = this.get(key);
        if (null == cachedValue) {
            V v2 = call.call();
            this.put(key, v2);
            return v2;
 
        }
        return cachedValue;
 
    }
    
    @Override
    public V remove(K key) {
        keyProp.remove(key);
        return this.delegate.remove(key);
    }
    
    @Override
    public void clear() {
        keyProp.clear();
        this.delegate.clear();
    }
    
    @Override
    public int getSize() {
        return this.delegate.getSize();
    }
    
    private boolean isExpire(CacheItemProperties itemProperties) {
        if (itemProperties == null) {
            return true;
        }
        return expireNanos != -1 && (System.nanoTime() - itemProperties.getExpireNanos() > expireNanos);
    }
    
    private CacheItemProperties cacheItemProperties() {
        CacheItemProperties cacheItemProperties = new CacheItemProperties();
        cacheItemProperties.setExpireNanos(System.nanoTime());
        return cacheItemProperties;
    }
}