GenericObjectPool参数解析

摘要：如果为负值，表示不运行检测线程。默认为策略的类名，默认为这里就用到了上面提到的两个参数对象池原理分析避免泄漏配置参数详解，以及资源回收，从池中获取资源，将资源返还给池逻辑解析

本文主要解析一下apache common pools下的GenericObjectPool的参数设置

commons-pool2-2.4.2-sources.jar!/org/apache/commons/pool2/impl/GenericObjectPool.java

public class GenericObjectPool extends BaseGenericObjectPool
        implements ObjectPool, GenericObjectPoolMXBean, UsageTracking {
   //......
}        

默认配置见
commons-pool2-2.4.2-sources.jar!/org/apache/commons/pool2/impl/GenericObjectPoolConfig.java

public class GenericObjectPoolConfig extends BaseObjectPoolConfig {

    /**
     * The default value for the {@code maxTotal} configuration attribute.
     * @see GenericObjectPool#getMaxTotal()
     */
    public static final int DEFAULT_MAX_TOTAL = 8;

    /**
     * The default value for the {@code maxIdle} configuration attribute.
     * @see GenericObjectPool#getMaxIdle()
     */
    public static final int DEFAULT_MAX_IDLE = 8;

    /**
     * The default value for the {@code minIdle} configuration attribute.
     * @see GenericObjectPool#getMinIdle()
     */
    public static final int DEFAULT_MIN_IDLE = 0;


    private int maxTotal = DEFAULT_MAX_TOTAL;

    private int maxIdle = DEFAULT_MAX_IDLE;

    private int minIdle = DEFAULT_MIN_IDLE;

    //......
}

lifo
GenericObjectPool 提供了后进先出(LIFO)与先进先出(FIFO)两种行为模式的池。默认为true，即当池中有空闲可用的对象时，调用borrowObject方法会返回最近（后进）的实例

fairness
当从池中获取资源或者将资源还回池中时 是否使用java.util.concurrent.locks.ReentrantLock.ReentrantLock 的公平锁机制,默认为false

maxTotal
链接池中最大连接数,默认为8

maxIdle
链接池中最大空闲的连接数,默认也为8

minIdle
连接池中最少空闲的连接数,默认为0

maxWaitMillis
当连接池资源耗尽时，等待时间，超出则抛异常，默认为-1即永不超时

blockWhenExhausted
当这个值为true的时候，maxWaitMillis参数才能生效。为false的时候，当连接池没资源，则立马抛异常。默认为true

testOnCreate
默认false，create的时候检测是有有效，如果无效则从连接池中移除，并尝试获取继续获取

testOnBorrow
默认false，borrow的时候检测是有有效，如果无效则从连接池中移除，并尝试获取继续获取

testOnReturn
默认false，return的时候检测是有有效，如果无效则从连接池中移除，并尝试获取继续获取

testWhileIdle
默认false，在evictor线程里头，当evictionPolicy.evict方法返回false时，而且testWhileIdle为true的时候则检测是否有效，如果无效则移除

timeBetweenEvictionRunsMillis
空闲链接检测线程检测的周期，毫秒数。如果为负值，表示不运行检测线程。默认为-1.

commons-pool2-2.4.2-sources.jar!/org/apache/commons/pool2/impl/GenericObjectPool.java

public GenericObjectPool(PooledObjectFactory factory,
            GenericObjectPoolConfig config) {

        super(config, ONAME_BASE, config.getJmxNamePrefix());

        if (factory == null) {
            jmxUnregister(); // tidy up
            throw new IllegalArgumentException("factory may not be null");
        }
        this.factory = factory;

        idleObjects = new LinkedBlockingDeque>(config.getFairness());

        setConfig(config);

        startEvictor(getTimeBetweenEvictionRunsMillis());
    }

commons-pool2-2.4.2-sources.jar!/org/apache/commons/pool2/impl/BaseGenericObjectPool.java

/**
     * The idle object evictor {@link TimerTask}.
     *
     * @see GenericKeyedObjectPool#setTimeBetweenEvictionRunsMillis
     */
    class Evictor extends TimerTask {
        /**
         * Run pool maintenance.  Evict objects qualifying for eviction and then
         * ensure that the minimum number of idle instances are available.
         * Since the Timer that invokes Evictors is shared for all Pools but
         * pools may exist in different class loaders, the Evictor ensures that
         * any actions taken are under the class loader of the factory
         * associated with the pool.
         */
        @Override
        public void run() {
            ClassLoader savedClassLoader =
                    Thread.currentThread().getContextClassLoader();
            try {
                if (factoryClassLoader != null) {
                    // Set the class loader for the factory
                    ClassLoader cl = factoryClassLoader.get();
                    if (cl == null) {
                        // The pool has been dereferenced and the class loader
                        // GC"d. Cancel this timer so the pool can be GC"d as
                        // well.
                        cancel();
                        return;
                    }
                    Thread.currentThread().setContextClassLoader(cl);
                }

                // Evict from the pool
                try {
                    evict();
                } catch(Exception e) {
                    swallowException(e);
                } catch(OutOfMemoryError oome) {
                    // Log problem but give evictor thread a chance to continue
                    // in case error is recoverable
                    oome.printStackTrace(System.err);
                }
                // Re-create idle instances.
                try {
                    ensureMinIdle();
                } catch (Exception e) {
                    swallowException(e);
                }
            } finally {
                // Restore the previous CCL
                Thread.currentThread().setContextClassLoader(savedClassLoader);
            }
        }
    }

numTestsPerEvictionRun
在每次空闲连接回收器线程(如果有)运行时检查的连接数量，默认为3

private int getNumTests() {
        int numTestsPerEvictionRun = getNumTestsPerEvictionRun();
        if (numTestsPerEvictionRun >= 0) {
            return Math.min(numTestsPerEvictionRun, idleObjects.size());
        } else {
            return (int) (Math.ceil(idleObjects.size() /
                    Math.abs((double) numTestsPerEvictionRun)));
        }
    }

minEvictableIdleTimeMillis
连接空闲的最小时间，达到此值后空闲连接将可能会被移除。默认为1000L 60L 30L

softMinEvictableIdleTimeMillis
连接空闲的最小时间，达到此值后空闲链接将会被移除，且保留minIdle个空闲连接数。默认为-1.

evictionPolicyClassName
evict策略的类名，默认为org.apache.commons.pool2.impl.DefaultEvictionPolicy

public class DefaultEvictionPolicy implements EvictionPolicy {

    @Override
    public boolean evict(EvictionConfig config, PooledObject underTest,
            int idleCount) {

        if ((config.getIdleSoftEvictTime() < underTest.getIdleTimeMillis() &&
                config.getMinIdle() < idleCount) ||
                config.getIdleEvictTime() < underTest.getIdleTimeMillis()) {
            return true;
        }
        return false;
    }
}

这里就用到了上面提到的两个参数

Apache commons-pool对象池原理分析

GenericObjectPool 避免泄漏

apache-common-pool2（配置参数详解，以及资源回收，从池中获取资源，将资源返还给池 逻辑解析）