map缓存

     

有时候需要将一批数据缓存，并且按照最近最少使用的规则淘汰。这时候就应该想到LRUMap。

LRUMap是一种尺寸固定的Map，当它的容量达到最大时采用最近最少使用的规则淘汰相应的元素。

    LRUMap cache = newLRUMap(5);    cache.put("01", "news 1");    cache.put("02", "news 2");    cache.put("03", "news 3");    cache.put("04", "news 4");    cache.put("05", "news 5");    String news1 = (String)cache.get("01");    String news2 = (String)cache.get("02");    String news3 = (String)cache.get("04");    String news4 = (String)cache.get("03");    String news5 = (String)cache.get("02");    String news6 = (String)cache.get("05");    cache.put("06", "news 6");    Iterator it = cache.entrySet().iterator();    while(it.hasNext()){       Map.Entry entry = (Map.Entry)it.next();       System.out.println(entry.getValue());    }

 

LazyMap:当你需要获取某个键值但发现该键值不存在时自动填充该键值，那就该考虑使用LazyMap，LazyMap采用了装饰模式装饰一个Map，并采用一个Transformer来决定当键值不存在时填充的规则（或者Factory）。

 

Transformer reverseString = newTransformer(){       publicObject transform(Object object){           String name = (String)object;           String reverse = StringUtils.reverse(name);           returnreverse;       }    };    Map names = newHashMap();    Map lazynames = LazyMap.decorate(names, reverseString);    System.out.println(lazynames.get("hello"));    System.out.println(lazynames.get("thanks"));    System.out.println(lazynames.get("not at all"));    Factory factory = newFactory(){       publicObject create(){           return"NB";       }    };    Map lazyname = LazyMap.decorate(names, factory);    System.out.println(lazyname.get("woshishei"));    System.out.println(lazyname.get("nishishei"));    System.out.println(lazyname.get("not at all"));

 

综合使用LRUMap和LazyMap：

Transformer reverseString = newTransformer(){       publicObject transform(Object object){           String name = (String)object;           String reverse = StringUtils.reverse(name);           returnreverse;       }    };    LRUMap lruMap = newLRUMap(5);    Map lazyMap = LazyMap.decorate(lruMap, reverseString);    String name0 = (String)lazyMap.get("test0");    String name1 = (String)lazyMap.get("test0");    String name2 = (String)lazyMap.get("test0");    String name3 = (String)lazyMap.get("test2");    String name4 = (String)lazyMap.get("test4");    String name5 = (String)lazyMap.get("test5");    String name6 = (String)lazyMap.get("test0");    String name7 = (String)lazyMap.get("test6");    String name8 = (String)lazyMap.get("test8");    String name9 = (String)lazyMap.get("test5");    Iterator it = lazyMap.entrySet().iterator();    while(it.hasNext()){       Map.Entry entry = (Map.Entry)it.next();       System.out.println(entry.getValue());    }

 

当然可以在Transformer里可以做任何事，比如从网站爬取数据，并转换成相应的对象等。

如下代码从pchome的ip地址库中查询IP地址，首先定义一个ArticleTransformer对象，每次根据传入的参数从一个URL查询数据并返回。

public class ArticleTransformer implements Transformer {protected final static int BUF_SIZE = 300;protected String queryURL;public String getQueryURL(){return queryURL;}public void setQueryURL(String queryURL){this.queryURL = queryURL;}protected long timeOut;public long getTimeOut(){return timeOut;}/** * @param timeOut 单位:ms */public void setTimeOut(long timeOut){this.timeOut = timeOut;}public Object transform(Object obj){ArticleRetriever retriever = new ArticleRetriever((String)obj);try{Thread thread = new Thread(retriever);thread.start();thread.join(timeOut);//Thread.sleep(3*1000);}catch(InterruptedException e){System.out.println("url request time out.");}return retriever.getResponse();}public class ArticleRetriever implements Runnable{private String name;private String response;public ArticleRetriever(String name){this.name = name;}public String getResponse(){return this.response;}public void run(){HttpURL url = null;try{HttpClient client = new HttpClient();url = new HttpURL(queryURL+name);GetMethod getMethod = new GetMethod(url.toString());getMethod.getParams().setContentCharset("UTF-8");client.executeMethod(getMethod);response = getMethod.getResponseBodyAsString();}catch(Exception e){System.out.println("Error get Article  " + url);}}}} 

 

然后如下代码调用

String queryURL = "http://whois.pconline.com.cn/ip.jsp?ip=";ArticleTransformer transformer = new ArticleTransformer();transformer.setQueryURL(queryURL);transformer.setTimeOut(500);Map lruMap = new LRUMap(3);articleMap = LazyMap.decorate(lruMap, transformer);String ip1 = (String)articleMap.get("127.0.0.1");String ip2 = (String)articleMap.get("121.0.29.241");String ip3 = (String)articleMap.get("10.25.145.123");String ip4 = (String)articleMap.get("10.121.20.35");String ip5 = (String)articleMap.get("121.230.145.60");String ip6 = (String)articleMap.get("27.186.214.221");String ip7 = (String)articleMap.get("127.0.0.1");try {Writer writer = new FileWriter("D://hello.txt");Iterator it = articleMap.entrySet().iterator();while (it.hasNext()) {Map.Entry entry = (Map.Entry) it.next();System.out.println(entry.getValue());if(entry.getValue() == null){writer.write("null\n");}else{writer.write((String)entry.getValue());}}if(writer!=null) writer.close();} catch (IOException e) {System.out.println("Error write file");}