Java uses Map to cache a simple instance

Sometimes a batch of data needs to be cached and eliminated according to the least recently used rules. At this time, we should think of LRUMap.
LRUMap is a fixed-size Map. When its capacity reaches the maximum value, the corresponding elements are eliminated using the least recently used rules.

The code is as follows:

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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: when you need to obtain a key value but find that the key value does not exist, the key value is automatically filled, so you should consider using LazyMap. LazyMap uses the decoration mode to decorate a Map, A Transformer is used to determine the filling rule (or Factory) when the key value does not exist ).
 

The code is as follows:

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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 "));

 

Combined use of LRUMap and LazyMap:

The code is as follows:

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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 ());     }

 

Of course, you can do anything in Transformer, such as crawling data from a website and converting it into a corresponding object.
The following code queries the IP address from the IP address library of pchome. First, it defines an ArticleTransformer object. Data is queried from a URL and returned each time based on the input parameters.

The code is as follows:

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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 unit: 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.exe cuteMethod (getMethod );   Response = getMethod. getResponseBodyAsString (); } Catch (Exception e ){ System. out. println ("Error get Article" + url );             }           }     }   } <SPAN style = "DISPLAY: none"> </SPAN>

 

Then the following code calls

The code is as follows:

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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 ("nulln "); } Else { Writer. write (String) entry. getValue ());             }         } If (writer! = Null) writer. close (); } Catch (IOException e ){ System. out. println ("Error write file ");     }

Finally, the following results are output:

Taizhou (Taixing) Telecom, Jiangsu province
Baoding Telecom, Hebei province
Internet reserved address