Class GenericObjectPool<T>
- Type Parameters:
- T- Type of element pooled in this pool.
- All Implemented Interfaces:
- Closeable,- AutoCloseable,- GenericObjectPoolMXBean,- ObjectPool<T>,- UsageTracking<T>
ObjectPool implementation.
 
 When coupled with the appropriate PooledObjectFactory,
 GenericObjectPool provides robust pooling functionality for
 arbitrary objects.
 
Optionally, one may configure the pool to examine and possibly evict objects as they sit idle in the pool and to ensure that a minimum number of idle objects are available. This is performed by an "idle object eviction" thread, which runs asynchronously. Caution should be used when configuring this optional feature. Eviction runs contend with client threads for access to objects in the pool, so if they run too frequently performance issues may result.
 The pool can also be configured to detect and remove "abandoned" objects,
 i.e. objects that have been checked out of the pool but neither used nor
 returned before the configured
 removeAbandonedTimeout.
 Abandoned object removal can be configured to happen when
 borrowObject is invoked and the pool is close to starvation, or
 it can be executed by the idle object evictor, or both. If pooled objects
 implement the TrackedUse interface, their last use will be queried
 using the getLastUsed method on that interface; otherwise
 abandonment is determined by how long an object has been checked out from
 the pool.
 
Implementation note: To prevent possible deadlocks, care has been taken to ensure that no call to a factory method will occur within a synchronization block. See POOL-125 and DBCP-44 for more information.
This class is intended to be thread-safe.
- Since:
- 2.0
- See Also:
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Field SummaryFields inherited from class org.apache.tomcat.dbcp.pool2.impl.BaseGenericObjectPoolabandonedConfig, MEAN_TIMING_STATS_CACHE_SIZE
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Constructor SummaryConstructorsConstructorDescriptionGenericObjectPool(PooledObjectFactory<T> factory) Creates a newGenericObjectPoolusing defaults fromGenericObjectPoolConfig.GenericObjectPool(PooledObjectFactory<T> factory, GenericObjectPoolConfig<T> config) Creates a newGenericObjectPoolusing a specific configuration.GenericObjectPool(PooledObjectFactory<T> factory, GenericObjectPoolConfig<T> config, AbandonedConfig abandonedConfig) Creates a newGenericObjectPoolthat tracks and destroys objects that are checked out, but never returned to the pool.
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Method SummaryModifier and TypeMethodDescriptionvoidCreates an object, and place it into the pool. addObject() is useful for "pre-loading" a pool with idle objects.Equivalent toborrowObject(BaseGenericObjectPool.getMaxWaitDuration())borrowObject(long borrowMaxWaitMillis) Borrows an object from the pool using the specific waiting time which only applies ifBaseGenericObjectPool.getBlockWhenExhausted()is true.borrowObject(Duration borrowMaxWaitDuration) Borrows an object from the pool using the specific waiting time which only applies ifBaseGenericObjectPool.getBlockWhenExhausted()is true.voidclear()Clears any objects sitting idle in the pool by removing them from the idle instance pool and then invoking the configuredPooledObjectFactory.destroyObject(PooledObject)method on each idle instance.voidclose()Closes the pool.voidevict()PerformnumTestsidle object eviction tests, evicting examined objects that meet the criteria for eviction.Gets a reference to the factory used to create, destroy and validate the objects used by this pool.Gets the type - including the specific type rather than the generic - of the factory.intGets the cap on the number of "idle" instances in the pool.intGets the target for the minimum number of idle objects to maintain in the pool.intGets the number of instances currently borrowed from this pool.intGets the number of instances currently idle in this pool.intGets an estimate of the number of threads currently blocked waiting for an object from the pool.voidinvalidateObject(T obj) Invalidates an object from the pool.voidinvalidateObject(T obj, DestroyMode destroyMode) Invalidates an object from the pool, using the providedDestroyModeProvides information on all the objects in the pool, both idle (waiting to be borrowed) and active (currently borrowed).voidTries to ensure thatgetMinIdle()idle instances are available in the pool.voidreturnObject(T obj) Returns an instance to the pool.voidsetConfig(GenericObjectPoolConfig<T> conf) Sets the base pool configuration.voidsetMaxIdle(int maxIdle) Sets the cap on the number of "idle" instances in the pool.voidsetMinIdle(int minIdle) Sets the target for the minimum number of idle objects to maintain in the pool.protected voidtoStringAppendFields(StringBuilder builder) Used by sub-classes to include the fields defined by the sub-class in theBaseObject.toString()output.voidCalled every time a pooled object is used to enable the pool to better track borrowed objects.Methods inherited from class org.apache.tomcat.dbcp.pool2.impl.BaseGenericObjectPoolgetBlockWhenExhausted, getBorrowedCount, getCreatedCount, getCreationStackTrace, getDestroyedByBorrowValidationCount, getDestroyedByEvictorCount, getDestroyedCount, getDurationBetweenEvictionRuns, getEvictionPolicy, getEvictionPolicyClassName, getEvictorShutdownTimeout, getEvictorShutdownTimeoutDuration, getEvictorShutdownTimeoutMillis, getFairness, getJmxName, getLifo, getLogAbandoned, getMaxBorrowWaitDuration, getMaxBorrowWaitTimeMillis, getMaxTotal, getMaxWaitDuration, getMaxWaitMillis, getMeanActiveDuration, getMeanActiveTimeMillis, getMeanBorrowWaitDuration, getMeanBorrowWaitTimeMillis, getMeanIdleDuration, getMeanIdleTimeMillis, getMessageStatistics, getMinEvictableIdleDuration, getMinEvictableIdleTime, getMinEvictableIdleTimeMillis, getNumTestsPerEvictionRun, getRemoveAbandonedOnBorrow, getRemoveAbandonedOnMaintenance, getRemoveAbandonedTimeout, getRemoveAbandonedTimeoutDuration, getReturnedCount, getSoftMinEvictableIdleDuration, getSoftMinEvictableIdleTime, getSoftMinEvictableIdleTimeMillis, getSwallowedExceptionListener, getTestOnBorrow, getTestOnCreate, getTestOnReturn, getTestWhileIdle, getTimeBetweenEvictionRuns, getTimeBetweenEvictionRunsMillis, isAbandonedConfig, isClosed, markReturningState, setAbandonedConfig, setBlockWhenExhausted, setConfig, setDurationBetweenEvictionRuns, setEvictionPolicy, setEvictionPolicyClassName, setEvictionPolicyClassName, setEvictorShutdownTimeout, setEvictorShutdownTimeoutMillis, setLifo, setMaxTotal, setMaxWait, setMaxWaitMillis, setMessagesStatistics, setMinEvictableIdle, setMinEvictableIdleDuration, setMinEvictableIdleTime, setMinEvictableIdleTimeMillis, setNumTestsPerEvictionRun, setSoftMinEvictableIdle, setSoftMinEvictableIdleDuration, setSoftMinEvictableIdleTime, setSoftMinEvictableIdleTimeMillis, setSwallowedExceptionListener, setTestOnBorrow, setTestOnCreate, setTestOnReturn, setTestWhileIdle, setTimeBetweenEvictionRuns, setTimeBetweenEvictionRunsMillisMethods inherited from class org.apache.tomcat.dbcp.pool2.BaseObjecttoStringMethods inherited from class java.lang.Objectclone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, waitMethods inherited from interface org.apache.tomcat.dbcp.pool2.impl.GenericObjectPoolMXBeangetBlockWhenExhausted, getBorrowedCount, getCreatedCount, getCreationStackTrace, getDestroyedByBorrowValidationCount, getDestroyedByEvictorCount, getDestroyedCount, getFairness, getLifo, getLogAbandoned, getMaxBorrowWaitTimeMillis, getMaxTotal, getMaxWaitMillis, getMeanActiveTimeMillis, getMeanBorrowWaitTimeMillis, getMeanIdleTimeMillis, getMinEvictableIdleTimeMillis, getNumTestsPerEvictionRun, getRemoveAbandonedOnBorrow, getRemoveAbandonedOnMaintenance, getRemoveAbandonedTimeout, getReturnedCount, getTestOnBorrow, getTestOnCreate, getTestOnReturn, getTestWhileIdle, getTimeBetweenEvictionRunsMillis, isAbandonedConfig, isClosedMethods inherited from interface org.apache.tomcat.dbcp.pool2.ObjectPooladdObjects
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Constructor Details- 
GenericObjectPoolCreates a newGenericObjectPoolusing defaults fromGenericObjectPoolConfig.- Parameters:
- factory- The object factory to be used to create object instances used by this pool
 
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GenericObjectPoolCreates a newGenericObjectPoolusing a specific configuration.- Parameters:
- factory- The object factory to be used to create object instances used by this pool
- config- The configuration to use for this pool instance. The configuration is used by value. Subsequent changes to the configuration object will not be reflected in the pool.
 
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GenericObjectPoolpublic GenericObjectPool(PooledObjectFactory<T> factory, GenericObjectPoolConfig<T> config, AbandonedConfig abandonedConfig) Creates a newGenericObjectPoolthat tracks and destroys objects that are checked out, but never returned to the pool.- Parameters:
- factory- The object factory to be used to create object instances used by this pool
- config- The base pool configuration to use for this pool instance. The configuration is used by value. Subsequent changes to the configuration object will not be reflected in the pool.
- abandonedConfig- Configuration for abandoned object identification and removal. The configuration is used by value.
 
 
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Method Details- 
addObjectCreates an object, and place it into the pool. addObject() is useful for "pre-loading" a pool with idle objects.If there is no capacity available to add to the pool, this is a no-op (no exception, no impact to the pool). If the factory returns null when creating an object, a NullPointerExceptionis thrown. If there is no factory set (factory == null), anIllegalStateExceptionis thrown.- Specified by:
- addObjectin interface- ObjectPool<T>
- Throws:
- Exception- when- PooledObjectFactory.makeObject()fails.
- IllegalStateException- after- ObjectPool.close()has been called on this pool.
- UnsupportedOperationException- when this pool cannot add new idle objects.
 
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borrowObjectEquivalent toborrowObject(BaseGenericObjectPool.getMaxWaitDuration())Instances returned from this method will have been either newly created with PooledObjectFactory.makeObject()or will be a previously idle object and have been activated withPooledObjectFactory.activateObject(org.apache.tomcat.dbcp.pool2.PooledObject<T>)and then validated withPooledObjectFactory.validateObject(org.apache.tomcat.dbcp.pool2.PooledObject<T>).By contract, clients must return the borrowed instance using ObjectPool.returnObject(T),ObjectPool.invalidateObject(T), or a related method as defined in an implementation or sub-interface.The behavior of this method when the pool has been exhausted is not strictly specified (although it may be specified by implementations). - Specified by:
- borrowObjectin interface- ObjectPool<T>
- Returns:
- an instance from this pool.
- Throws:
- IllegalStateException- after- closehas been called on this pool.
- Exception- when- PooledObjectFactory.makeObject()throws an exception.
- NoSuchElementException- when the pool is exhausted and cannot or will not return another instance.
 
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borrowObjectBorrows an object from the pool using the specific waiting time which only applies ifBaseGenericObjectPool.getBlockWhenExhausted()is true.If there is one or more idle instance available in the pool, then an idle instance will be selected based on the value of BaseGenericObjectPool.getLifo(), activated and returned. If activation fails, ortestOnBorrowis set totrueand validation fails, the instance is destroyed and the next available instance is examined. This continues until either a valid instance is returned or there are no more idle instances available.If there are no idle instances available in the pool, behavior depends on the maxTotal, (if applicable)BaseGenericObjectPool.getBlockWhenExhausted()and the value passed in to theborrowMaxWaitMillisparameter. If the number of instances checked out from the pool is less thanmaxTotal,a new instance is created, activated and (if applicable) validated and returned to the caller. If validation fails, aNoSuchElementExceptionis thrown. If the factory returns null when creating an instance, aNullPointerExceptionis thrown.If the pool is exhausted (no available idle instances and no capacity to create new ones), this method will either block (if BaseGenericObjectPool.getBlockWhenExhausted()is true) or throw aNoSuchElementException(ifBaseGenericObjectPool.getBlockWhenExhausted()is false). The length of time that this method will block whenBaseGenericObjectPool.getBlockWhenExhausted()is true is determined by the value passed in to theborrowMaxWaitMillisparameter.When the pool is exhausted, multiple calling threads may be simultaneously blocked waiting for instances to become available. A "fairness" algorithm has been implemented to ensure that threads receive available instances in request arrival order. - Parameters:
- borrowMaxWaitDuration- The time to wait for an object to become available
- Returns:
- object instance from the pool
- Throws:
- NoSuchElementException- if an instance cannot be returned
- Exception- if an object instance cannot be returned due to an error
- Since:
- 2.10.0
 
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borrowObjectBorrows an object from the pool using the specific waiting time which only applies ifBaseGenericObjectPool.getBlockWhenExhausted()is true.If there is one or more idle instance available in the pool, then an idle instance will be selected based on the value of BaseGenericObjectPool.getLifo(), activated and returned. If activation fails, ortestOnBorrowis set totrueand validation fails, the instance is destroyed and the next available instance is examined. This continues until either a valid instance is returned or there are no more idle instances available.If there are no idle instances available in the pool, behavior depends on the maxTotal, (if applicable)BaseGenericObjectPool.getBlockWhenExhausted()and the value passed in to theborrowMaxWaitMillisparameter. If the number of instances checked out from the pool is less thanmaxTotal,a new instance is created, activated and (if applicable) validated and returned to the caller. If validation fails, aNoSuchElementExceptionis thrown. If the factory returns null when creating an instance, aNullPointerExceptionis thrown.If the pool is exhausted (no available idle instances and no capacity to create new ones), this method will either block (if BaseGenericObjectPool.getBlockWhenExhausted()is true) or throw aNoSuchElementException(ifBaseGenericObjectPool.getBlockWhenExhausted()is false). The length of time that this method will block whenBaseGenericObjectPool.getBlockWhenExhausted()is true is determined by the value passed in to theborrowMaxWaitMillisparameter.When the pool is exhausted, multiple calling threads may be simultaneously blocked waiting for instances to become available. A "fairness" algorithm has been implemented to ensure that threads receive available instances in request arrival order. - Parameters:
- borrowMaxWaitMillis- The time to wait in milliseconds for an object to become available
- Returns:
- object instance from the pool
- Throws:
- NoSuchElementException- if an instance cannot be returned
- Exception- if an object instance cannot be returned due to an error
 
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clearpublic void clear()Clears any objects sitting idle in the pool by removing them from the idle instance pool and then invoking the configuredPooledObjectFactory.destroyObject(PooledObject)method on each idle instance.Implementation notes: - This method does not destroy or effect in any way instances that are checked out of the pool when it is invoked.
- Invoking this method does not prevent objects being returned to the idle instance pool, even during its execution. Additional instances may be returned while removed items are being destroyed.
- Exceptions encountered destroying idle instances are swallowed
 but notified via a SwallowedExceptionListener.
 - Specified by:
- clearin interface- ObjectPool<T>
 
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closepublic void close()Closes the pool. Once the pool is closed,borrowObject()will fail with IllegalStateException, butreturnObject(Object)andinvalidateObject(Object)will continue to work, with returned objects destroyed on return.Destroys idle instances in the pool by invoking clear().- Specified by:
- closein interface- AutoCloseable
- Specified by:
- closein interface- Closeable
- Specified by:
- closein interface- ObjectPool<T>
- Specified by:
- closein class- BaseGenericObjectPool<T>
 
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evictPerformnumTestsidle object eviction tests, evicting examined objects that meet the criteria for eviction. IftestWhileIdleis true, examined objects are validated when visited (and removed if invalid); otherwise only objects that have been idle for more thanminEvicableIdleTimeMillisare removed.Successive activations of this method examine objects in sequence, cycling through objects in oldest-to-youngest order. - Specified by:
- evictin class- BaseGenericObjectPool<T>
- Throws:
- Exception- when there is a problem evicting idle objects.
 
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getFactoryGets a reference to the factory used to create, destroy and validate the objects used by this pool.- Returns:
- the factory
 
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getFactoryTypeGets the type - including the specific type rather than the generic - of the factory.- Specified by:
- getFactoryTypein interface- GenericObjectPoolMXBean
- Returns:
- A string representation of the factory type
 
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getMaxIdlepublic int getMaxIdle()Gets the cap on the number of "idle" instances in the pool. If maxIdle is set too low on heavily loaded systems it is possible you will see objects being destroyed and almost immediately new objects being created. This is a result of the active threads momentarily returning objects faster than they are requesting them, causing the number of idle objects to rise above maxIdle. The best value for maxIdle for heavily loaded system will vary but the default is a good starting point.- Specified by:
- getMaxIdlein interface- GenericObjectPoolMXBean
- Returns:
- the maximum number of "idle" instances that can be held in the pool or a negative value if there is no limit
- See Also:
 
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getMinIdlepublic int getMinIdle()Gets the target for the minimum number of idle objects to maintain in the pool. This setting only has an effect if it is positive andBaseGenericObjectPool.getDurationBetweenEvictionRuns()is greater than zero. If this is the case, an attempt is made to ensure that the pool has the required minimum number of instances during idle object eviction runs.If the configured value of minIdle is greater than the configured value for maxIdle then the value of maxIdle will be used instead. - Specified by:
- getMinIdlein interface- GenericObjectPoolMXBean
- Returns:
- The minimum number of objects.
- See Also:
 
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getNumActivepublic int getNumActive()Description copied from interface:ObjectPoolGets the number of instances currently borrowed from this pool. Returns a negative value if this information is not available.- Specified by:
- getNumActivein interface- GenericObjectPoolMXBean
- Specified by:
- getNumActivein interface- ObjectPool<T>
- Returns:
- the number of instances currently borrowed from this pool.
 
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getNumIdlepublic int getNumIdle()Description copied from class:BaseGenericObjectPoolGets the number of instances currently idle in this pool.- Specified by:
- getNumIdlein interface- GenericObjectPoolMXBean
- Specified by:
- getNumIdlein interface- ObjectPool<T>
- Specified by:
- getNumIdlein class- BaseGenericObjectPool<T>
- Returns:
- count of instances available for checkout from the pool
 
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getNumWaiterspublic int getNumWaiters()Gets an estimate of the number of threads currently blocked waiting for an object from the pool. This is intended for monitoring only, not for synchronization control.- Specified by:
- getNumWaitersin interface- GenericObjectPoolMXBean
- Returns:
- The estimate of the number of threads currently blocked waiting for an object from the pool
 
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invalidateObjectInvalidates an object from the pool.By contract, objmust have been obtained usingObjectPool.borrowObject()or a related method as defined in an implementation or sub-interface.This method should be used when an object that has been borrowed is determined (due to an exception or other problem) to be invalid. Activation of this method decrements the active count and attempts to destroy the instance, using the default (NORMAL) DestroyMode.- Specified by:
- invalidateObjectin interface- ObjectPool<T>
- Parameters:
- obj- a- borrowedinstance to be disposed.
- Throws:
- Exception- if an exception occurs destroying the
- IllegalStateException- if obj does not belong to this pool
 
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invalidateObjectInvalidates an object from the pool, using the providedDestroyModeBy contract, objmust have been obtained usingObjectPool.borrowObject()or a related method as defined in an implementation or sub-interface.This method should be used when an object that has been borrowed is determined (due to an exception or other problem) to be invalid. Activation of this method decrements the active count and attempts to destroy the instance, using the provided DestroyMode.- Specified by:
- invalidateObjectin interface- ObjectPool<T>
- Parameters:
- obj- a- borrowedinstance to be disposed.
- destroyMode- destroy activation context provided to the factory
- Throws:
- Exception- if an exception occurs destroying the object
- IllegalStateException- if obj does not belong to this pool
- Since:
- 2.9.0
 
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listAllObjectsProvides information on all the objects in the pool, both idle (waiting to be borrowed) and active (currently borrowed).Note: This is named listAllObjects so it is presented as an operation via JMX. That means it won't be invoked unless the explicitly requested whereas all attributes will be automatically requested when viewing the attributes for an object in a tool like JConsole. - Specified by:
- listAllObjectsin interface- GenericObjectPoolMXBean
- Returns:
- Information grouped on all the objects in the pool
 
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preparePoolTries to ensure thatgetMinIdle()idle instances are available in the pool.- Throws:
- Exception- If the associated factory throws an exception
- Since:
- 2.4
 
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returnObjectReturns an instance to the pool. By contract,objmust have been obtained usingObjectPool.borrowObject()or a related method as defined in an implementation or sub-interface.If maxIdleis set to a positive value and the number of idle instances has reached this value, the returning instance is destroyed.If testOnReturn== true, the returning instance is validated before being returned to the idle instance pool. In this case, if validation fails, the instance is destroyed.Exceptions encountered destroying objects for any reason are swallowed but notified via a SwallowedExceptionListener.- Specified by:
- returnObjectin interface- ObjectPool<T>
- Parameters:
- obj- a- borrowedinstance to be returned.
 
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setConfigSets the base pool configuration.- Parameters:
- conf- the new configuration to use. This is used by value.
- See Also:
 
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setMaxIdlepublic void setMaxIdle(int maxIdle) Sets the cap on the number of "idle" instances in the pool. If maxIdle is set too low on heavily loaded systems it is possible you will see objects being destroyed and almost immediately new objects being created. This is a result of the active threads momentarily returning objects faster than they are requesting them, causing the number of idle objects to rise above maxIdle. The best value for maxIdle for heavily loaded system will vary but the default is a good starting point.- Parameters:
- maxIdle- The cap on the number of "idle" instances in the pool. Use a negative value to indicate an unlimited number of idle instances
- See Also:
 
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setMinIdlepublic void setMinIdle(int minIdle) Sets the target for the minimum number of idle objects to maintain in the pool. This setting only has an effect if it is positive andBaseGenericObjectPool.getDurationBetweenEvictionRuns()is greater than zero. If this is the case, an attempt is made to ensure that the pool has the required minimum number of instances during idle object eviction runs.If the configured value of minIdle is greater than the configured value for maxIdle then the value of maxIdle will be used instead. - Parameters:
- minIdle- The minimum number of objects.
- See Also:
 
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toStringAppendFieldsDescription copied from class:BaseObjectUsed by sub-classes to include the fields defined by the sub-class in theBaseObject.toString()output.- Overrides:
- toStringAppendFieldsin class- BaseGenericObjectPool<T>
- Parameters:
- builder- Field names and values are appended to this object
 
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useDescription copied from interface:UsageTrackingCalled every time a pooled object is used to enable the pool to better track borrowed objects.- Specified by:
- usein interface- UsageTracking<T>
- Parameters:
- pooledObject- The object that is being used.
 
 
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