用hashmap实现自己的缓存

@SuppressWarnings({"unchecked", "rawtypes"})
public class DefaultCache implements Cache {
private Map cache = new HashMap();

private DefaultCache() {
}

public static DefaultCache getInstance() {
return DefaultCacheFactory.getInstance();
}

private static class DefaultCacheFactory{
private static DefaultCache instance = new DefaultCache();

private static DefaultCache getInstance(){
return instance;
}
}

public void init() {
cache = new HashMap();
}

public void stop() {
}

public void add(String key, Object value) {
cache.put(key, value);
}

public void add(String fqn, String key, Object value) {
Map map = (Map) cache.get(fqn);
if (map == null) {
synchronized (this) {
map = (Map) cache.get(fqn);
if(map == null){
map = new HashMap();
map.put(key, value); // 防止指令重排序
cache.put(fqn, map);
}
}
}
map.put(key, value);
}

public Object get(String fqn, String key) {
Map map = (Map) cache.get(fqn);
if (map == null) {
return null;
}
return map.get(key);
}

public Object get(String key) {
return cache.get(key);
}

public Collection getValues(String key) {
Map map = (Map) cache.get(key);
if (map == null) {
return new ArrayList();
}
return map.values();
}

public void remove(String fqn, String key) {
Map map = (Map) cache.get(fqn);
if (map != null) {
map.remove(key);
}
}

public void remove(String key) {
cache.remove(key);
}
}

原文：http://www.cnblogs.com/panxuejun/p/7834619.html