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  • HashMap에서 만료된 요소를 제거하고 동시에 더 많은 요소를 추가하는 방법 – Java Timer, TimerTask 및 futures() – 전체 예제

HashMap에서 만료된 요소를 제거하고 동시에 더 많은 요소를 추가하는 방법 – Java Timer, TimerTask 및 futures() – 전체 예제

게시 됨: 2021-04-02
HashMap에서 만료된 요소를 제거하고 동시에 더 많은 요소를 추가하는 방법 - Java Timer, TimerTask 및 futures()

Hashmap, ArrayList, Static Map, Vector 등은 가장 많이 사용되는 Java 컬렉션 프레임워크 요소입니다. 필요에 따라 이것을 사용할 수 있는 시나리오가 무한합니다.

이 예제는 매우 흥미로운 Java 예제입니다. 하나의 HashMap()에 대해 아래의 연산을 수행할 것이다.

  • crunchifyMap 객체 생성
  • 만료 시간이 5 seconds 설정된 매초 맵에 요소를 계속 추가합니다.
  • 매초 캐시와 같은 만료된 요소를 Check 하고 만료된 delete from map if expired
  • 5초 후에는 1초마다 만료된 요소를 추가 및 삭제하는 always same size 와 always 5 elements 를 얻게 됩니다.

또한 below questions 이 있는 경우 올바른 위치에 있습니다.

  • 수동 만료 맵이란 무엇입니까?
  • 시간 초과 요소가 있는 동시 맵
  • 자바 캐시 맵 예
  • 자바 TimerTask 예제
  • Evictor – Java 동시 맵 예제

시작하자:

포인트-1

  • 타이머 요소 만들기 crunchifyTimer
  • 1초인 반복되는 고정 지연 실행을 위해 지정된 작업 CrunchifyReminder() 를 예약합니다.
  • 예약된 작업에서
    • crunchifyMap에 요소 add
    • crunchifyMap에서 만료된 요소를 확인하고 삭제

포인트-2

  • addElement() 작업 중
    • 각 요소에 current time 을 연결하고 있습니다.
  • crunchifyClearExipredElementsFromMap() 작업 중
    • 요소의 시간으로 현재 시간을 확인하고 있습니다.
    • 시차가 5초 이상이면 crunchifyMap에서 요소를 삭제하십시오.

포인트-3

  • Eclipse 콘솔에서 추가 및 제거 작업 인쇄 요소 중
  • 첫 번째로 추가된 요소가 첫 번째로 제거되는 식입니다.
  • 결과는 Eclipse 콘솔 출력을 확인하십시오.

다음은 자바 프로그램입니다.

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package crunchify . com . tutorials ;
 
import java . util . ArrayList ;
import java . util . Date ;
import java . util . HashMap ;
import java . util . Iterator ;
import java . util . Map ;
import java . util . Map . Entry ;
import java . util . Timer ;
import java . util . TimerTask ;
 
/**
* @author Crunchify.com
* <p>
* - Keep adding element to Map every second which has expire time set to 5 seconds
* - Check for expired element every second and delete from map if expired
* - After 5 seconds you will get always same size as you are adding and deleting expired elements every second
*/
 
public class CrunchifyCleanExipredMapElements {
Timer crunchifyTimer ;
private static final long EXPIRED_TIME_IN_SEC = 5L ;
private static final Map < Double , ArrayList < Date > > crunchifyMap = new HashMap < > ( ) ;
public static void main ( String [ ] args ) {
new CrunchifyCleanExipredMapElements ( 1 ) ;
crunchifyLog ( "Start Adding element every second\n\n" ) ;
}
public CrunchifyCleanExipredMapElements ( int seconds ) {
// Timer() - Creates a new timer. The associated thread does not run as a daemon.
crunchifyTimer = new Timer ( ) ;
// Schedules the specified task for repeated fixed-delay execution
// schedule(): Schedules the specified task for repeated fixed-delay execution, beginning after the specified delay.
// Subsequent executions take place at approximately regular intervals separated by the specified period.
// In fixed-delay execution, each execution is scheduled relative to the actual execution time of the previous execution.
// If an execution is delayed for any reason (such as garbage collection or other background activity), subsequent executions will be delayed as well.
// In the long run, the frequency of execution will generally be slightly lower than the reciprocal of the specified period (assuming the system clock underlying Object.wait(long) is accurate).
crunchifyTimer . schedule ( new CrunchifyReminder ( ) , 0 , seconds * 1000L ) ;
}
// TimeTask: A task that can be scheduled for one-time or repeated execution by a Timer.
// A timer task is not reusable. Once a task has been scheduled for execution on a Timer or cancelled,
// subsequent attempts to schedule it for execution will throw IllegalStateException.
class CrunchifyReminder extends TimerTask {
public void run ( ) {
// We are checking for expired element from map every second
crunchifyClearExpiredElementsFromMap ( ) ;
// We are adding element every second
addElement ( ) ;
}
}
public void addElement ( ) {
crunchifyAddElementToMap ( Math . random ( ) ) ;
}
// Check for element's expired time. If element is > 5 seconds old then remove it
private static void crunchifyClearExpiredElementsFromMap ( ) {
// Date() - Allocates a Date object and initializes it so that it represents the time at which it was allocated, measured to the nearest millisecond.
Date currentTime = new Date ( ) ;
Date actualExpiredTime = new Date ( ) ;
// if element time stamp and current time stamp difference is 5 second then delete element
actualExpiredTime . setTime ( currentTime . getTime ( ) - EXPIRED_TIME_IN_SEC * 1000L ) ;
// size() - Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
System . out . println ( "crunchifyMap size:" + CrunchifyCleanExipredMapElements . crunchifyMap . size ( ) ) ;
Iterator < Entry < Double , ArrayList < Date > > > crunchifyIterator = CrunchifyCleanExipredMapElements . crunchifyMap . entrySet ( ) . iterator ( ) ;
// hasNext() - Returns true if the iteration has more elements. (In other words, returns true if next would return an element rather than throwing an exception.)
while ( crunchifyIterator . hasNext ( ) ) {
// next() - Returns the next element in the iteration.
Entry < Double , ArrayList < Date > > entry = crunchifyIterator . next ( ) ;
// getValue() - Returns the value corresponding to this entry.
// If the mapping has been removed from the backing map (by the iterator's remove operation), the results of this call are undefined.
ArrayList < Date > crunchifyElement = entry . getValue ( ) ;
while ( crunchifyElement . size ( ) > 0
&& crunchifyElement.get(0).compareTo(actualExpiredTime) < 0) {
crunchifyLog("----------- Expired Element Deleted: " + entry.getKey());
crunchifyElement . remove ( 0 ) ;
}
if ( crunchifyElement . size ( ) == 0 ) {
// remove() - Removes from the underlying collection the last element returned by this iterator (optional operation).
// This method can be called only once per call to next.
crunchifyIterator . remove ( ) ;
}
}
}
// Adding new element to map with current timestamp
private static void crunchifyAddElementToMap ( Double digit ) {
ArrayList < Date > crunchifyList = new ArrayList < > ( ) ;
CrunchifyCleanExipredMapElements . crunchifyMap . put ( digit , crunchifyList ) ;
// add() - Appends the specified element to the end of this list.
crunchifyList . add ( new Date ( ) ) ;
crunchifyLog ( "+++++++++++ Add Element:" + digit + "\n" ) ;
}
private static void crunchifyLog ( String string ) {
System . out . println ( string ) ;
}
}
 

Eclipse 콘솔 출력:

위의 프로그램을 실행하면 아래와 같은 결과를 볼 수 있습니다.

HashMap에서 만료된 요소를 제거하고 동시에 더 많은 요소를 추가하는 방법 - Java Timer, TimerTask 및 futures() - 콘솔 결과
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Start Adding element every second
crunchifyMap size : 0
+++++++++++ Add Element : 0.6970683199424504
crunchifyMap size : 1
+++++++++++ Add Element : 0.8103548990859972
crunchifyMap size : 2
+++++++++++ Add Element : 0.849973176897403
crunchifyMap size : 3
+++++++++++ Add Element : 0.2770459184269851
crunchifyMap size : 4
+++++++++++ Add Element : 0.9136028332849369
crunchifyMap size : 5
----------- Expired Element Deleted : 0.6970683199424504
+++++++++++ Add Element : 0.6630362698520832
crunchifyMap size : 5
----------- Expired Element Deleted : 0.8103548990859972
+++++++++++ Add Element : 0.38906826918659854
crunchifyMap size : 5
----------- Expired Element Deleted : 0.849973176897403
+++++++++++ Add Element : 0.3997935729434138
crunchifyMap size : 5
----------- Expired Element Deleted : 0.2770459184269851
+++++++++++ Add Element : 0.20373441843273887
 
Process finished with exit code 130 ( interrupted by signal 2 : SIGINT )

Java 프로그램을 실행하는 데 문제가 있으면 알려주십시오.