Interface ObjectPool<T>

Type Parameters:
T - Type of element pooled in this pool.
All Superinterfaces:
AutoCloseable, Closeable
All Known Implementing Classes:
BaseObjectPool, GenericObjectPool, SoftReferenceObjectPool
public interface ObjectPool<T> extends Closeable
A pooling simple interface.

Example of use: 

 Object obj = null;

 try {
     obj = pool.borrowObject();
     try {
         //...use the object...
     } catch (Exception e) {
         // invalidate the object
         pool.invalidateObject(obj);
         // do not return the object to the pool twice
         obj = null;
     } finally {
         // make sure the object is returned to the pool
         if (null != obj) {
             pool.returnObject(obj);
        }
     }
 } catch(Exception e) {
       // failed to borrow an object
 }

See BaseObjectPool for a simple base implementation.

Since:
2.0
See Also:

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    addObject()
    Creates an object using the factory or other implementation dependent mechanism, passivate it, and then place it in the idle object pool.
    default void
    addObjects(int count)
    Calls addObject() count number of times.
    T
    borrowObject()
    Borrows an instance from this pool.
    void
    clear()
    Clears any objects sitting idle in the pool, releasing any associated resources (optional operation).
    void
    close()
    Closes this pool, and free any resources associated with it.
    int
    getNumActive()
    Gets the number of instances currently borrowed from this pool.
    int
    getNumIdle()
    Gets the number of instances currently idle in this pool.
    void
    invalidateObject(T obj)
    Invalidates an object from the pool.
    default void
    invalidateObject(T obj, DestroyMode destroyMode)
    Invalidates an object from the pool, using the provided DestroyMode
    void
    returnObject(T obj)
    Returns an instance to the pool.

  • Method Details

    • addObject

      void addObject() throws Exception
      Creates an object using the factory or other implementation dependent mechanism, passivate it, and then place it in the idle object pool. addObject is useful for "pre-loading" a pool with idle objects. (Optional operation).
      Throws:
      Exception - when PooledObjectFactory.makeObject() fails.
      IllegalStateException - after close() has been called on this pool.
      UnsupportedOperationException - when this pool cannot add new idle objects.

    • addObjects

      default void addObjects(int count) throws Exception
      Calls addObject() count number of times.
      Parameters:
      count - the number of idle objects to add.
      Throws:
      Exception - See addObject().
      Since:
      2.8.0

    • borrowObject

      T borrowObject() throws Exception
      Borrows an instance from this pool.

      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 with PooledObjectFactory.activateObject(org.apache.tomcat.dbcp.pool2.PooledObject<T>) and then validated with PooledObjectFactory.validateObject(org.apache.tomcat.dbcp.pool2.PooledObject<T>).

      By contract, clients must return the borrowed instance using returnObject(T), 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).

      Returns:
      an instance from this pool.
      Throws:
      IllegalStateException - after close has 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.

    • clear

      void clear() throws Exception
      Clears any objects sitting idle in the pool, releasing any associated resources (optional operation). Idle objects cleared must be PooledObjectFactory.destroyObject(PooledObject).
      Throws:
      UnsupportedOperationException - if this implementation does not support the operation
      Exception - if the pool cannot be cleared

    • close

      void close()
      Closes this pool, and free any resources associated with it.

      Calling addObject() or borrowObject() after invoking this method on a pool will cause them to throw an IllegalStateException.

      Implementations should silently fail if not all resources can be freed.

      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable

    • getNumActive

      int getNumActive()
      Gets the number of instances currently borrowed from this pool. Returns a negative value if this information is not available.
      Returns:
      the number of instances currently borrowed from this pool.

    • getNumIdle

      int getNumIdle()
      Gets the number of instances currently idle in this pool. This may be considered an approximation of the number of objects that can be borrowed without creating any new instances. Returns a negative value if this information is not available.
      Returns:
      the number of instances currently idle in this pool.

    • invalidateObject

      void invalidateObject(T obj) throws Exception
      Invalidates an object from the pool.

      By contract, obj must have been obtained using 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.

      Parameters:
      obj - a borrowed instance to be disposed.
      Throws:
      Exception - if the instance cannot be invalidated

    • invalidateObject

      default void invalidateObject(T obj, DestroyMode destroyMode) throws Exception
      Invalidates an object from the pool, using the provided DestroyMode

      By contract, obj must have been obtained using 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.

      Parameters:
      obj - a borrowed instance to be disposed.
      destroyMode - destroy activation context provided to the factory
      Throws:
      Exception - if the instance cannot be invalidated
      Since:
      2.9.0

    • returnObject

      void returnObject(T obj) throws Exception
      Returns an instance to the pool. By contract, obj must have been obtained using borrowObject() or a related method as defined in an implementation or sub-interface.
      Parameters:
      obj - a borrowed instance to be returned.
      Throws:
      IllegalStateException - if an attempt is made to return an object to the pool that is in any state other than allocated (i.e. borrowed). Attempting to return an object more than once or attempting to return an object that was never borrowed from the pool will trigger this exception.
      Exception - if an instance cannot be returned to the pool