opencms7.5

// 系统编码
String systemEncoding = (new OutputStreamWriter(new ByteArrayOutputStream())).getEncoding();

HashMap vs FastHashMap:原文参考http://frenchmay.iteye.com/blog/226784

public class FastHashMap extends HashMap {   
    protected HashMap map = null;   
    protected boolean fast = false;       
    public FastHashMap() {   
            super();   
            this.map = new HashMap();   
        }   
} 
FastHashMap继承于HashMap,存储由HashMap实现的,通过fast来设置是否是以快速模式执行.可以初步认为FashHashMap是HashMap的一个代理.

public Object get(Object key) {   
        if (fast) {  
            // get方法的实现是线程安全的 
            return (map.get(key));   
        } else {   
            // 对整个map对象同步
            synchronized (map) {   
                return (map.get(key));   
            }   
        }   
    }
所以FastHashMap在get速度上比HashMap快！

public Object put(Object key, Object value) {   
        if (fast) {   
            synchronized (this) { 
                // 克隆一个map，再在map上操作，再替换map；在替换map前所有对象都读取map；  
                HashMap temp = (HashMap) map.clone();   
                Object result = temp.put(key, value);   
                map = temp;   
                return (result);   
            }   
        } else {   
            synchronized (map) {   
                return (map.put(key, value));   
            }   
        }   
    } 

做的测试是在slow模式下的FastHashMap和hashmap在单线程访问的情形下,读/取50000
个long类型的测试举例.


结果是

Result:

HashMap put 50000 Object using1.021s

FastHashMap put 50000 Object using1.221s

HashMap get 50000 Object using0.561s

FastHashMap get 50000 Object using0.04s