メモリが低下しているときにJavaアプリケーションに自動的に警告するにはどうすればよいでしょうか？

Question

空きメモリが一定のしきい値に達すると自動的にJavaアプリケーションにメモリ警告を発するための洗練された方法はありますか？

これはJeopardyスタイルの質問ですが、私は既に回答があります。ソリューションが私を束にしてくれたので、世界中に発見してほしいと思っています。

Answer 1

Heinz Kabutzによって書かれたすばらしいクラスで、完璧に私のために「すぐに」使えます。 http://www.javaspecialists.eu/archive/Issue092.html

import java.lang.management.ManagementFactory; 
import java.lang.management.MemoryMXBean; 
import java.lang.management.MemoryNotificationInfo; 
import java.lang.management.MemoryPoolMXBean; 
import java.lang.management.MemoryType; 
import java.util.ArrayList; 
import java.util.Collection; 

import javax.management.Notification; 
import javax.management.NotificationEmitter; 
import javax.management.NotificationListener; 

/** 
* This memory warning system will call the listener when we exceed the 
* percentage of available memory specified. There should only be one instance 
* of this object created, since the usage threshold can only be set to one 
* number. 
* 
* (adapted from http://www.javaspecialists.eu/archive/Issue092.html) 
*/ 

public class MemoryWarningSystem { 

    public interface Listener { 

     void memoryUsageLow(long usedMemory, long maxMemory); 
    } 

    private final Collection<Listener> listeners = new ArrayList<Listener>(); 

    private static final MemoryPoolMXBean tenuredGenPool = findTenuredGenPool(); 

    public MemoryWarningSystem() { 
     MemoryMXBean mbean = ManagementFactory.getMemoryMXBean(); 
     NotificationEmitter emitter = (NotificationEmitter) mbean; 
     emitter.addNotificationListener(new NotificationListener() { 
      @Override 
      public void handleNotification(Notification n, Object hb) { 
       if (n.getType().equals(
         MemoryNotificationInfo.MEMORY_THRESHOLD_EXCEEDED)) { 
        long maxMemory = tenuredGenPool.getUsage().getMax(); 
        long usedMemory = tenuredGenPool.getUsage().getUsed(); 
        for (Listener listener : listeners) { 
         listener.memoryUsageLow(usedMemory, maxMemory); 
        } 
       } 
      } 
     }, null, null); 
    } 

    public boolean addListener(Listener listener) { 
     return listeners.add(listener); 
    } 

    public boolean removeListener(Listener listener) { 
     return listeners.remove(listener); 
    } 

    public void setPercentageUsageThreshold(double percentage) { 
     if (percentage <= 0.0 || percentage > 1.0) { 
      throw new IllegalArgumentException("Percentage not in range"); 
     } 
     long maxMemory = tenuredGenPool.getUsage().getMax(); 
     long warningThreshold = (long) (maxMemory * percentage); 
     tenuredGenPool.setUsageThreshold(warningThreshold); 
    } 

    /** 
    * Tenured Space Pool can be determined by it being of type HEAP and by it 
    * being possible to set the usage threshold. 
    */ 
    private static MemoryPoolMXBean findTenuredGenPool() { 
     for (MemoryPoolMXBean pool : ManagementFactory.getMemoryPoolMXBeans()) { 
      // I don't know whether this approach is better, or whether 
      // we should rather check for the pool name "Tenured Gen"? 
      if (pool.getType() == MemoryType.HEAP 
        && pool.isUsageThresholdSupported()) { 
       return pool; 
      } 
     } 
     throw new IllegalStateException("Could not find tenured space"); 
    } 
} 

使用法：等http://stackoverflow.com/として `MemoryMXBean`に言及

MemoryWarningSystem system = new MemoryWarningSystem(); 
    system.setPercentageUsageThreshold(0.8d); 
    system.addListener(new Listener() { 
     @Override 
     public void memoryUsageLow(long usedMemory, long maxMemory) { 
      System.out.println("low: "+usedMemory+"/"+maxMemory); 
     } 
    });