ConnectionPool (Apache Tomcat 9.0.117 API Documentation)
Description: declaration: package: org.apache.tomcat.jdbc.pool, class: ConnectionPool

# Class ConnectionPool

java.lang.Object
org.apache.tomcat.jdbc.pool.ConnectionPool

public class ConnectionPool extends Object
Implementation of simple connection pool. The ConnectionPool uses a `PoolProperties` object for storing all the meta information about the connection pool. As the underlying implementation, the connection pool uses `BlockingQueue` to store active and idle connections. A custom implementation of a fair `FairBlockingQueue` blocking queue is provided with the connection pool itself.

- ## Nested Class Summary

  Nested Classes
  Modifier and Type
  Class
  Description
  `protected class`
  `ConnectionPool.ConnectionFuture`
  Thread safe wrapper around a future for the regular queue This one retrieves the pooled connection object and performs the initialization according to interceptors and validation rules.
  `protected static class`
  `ConnectionPool.PoolCleaner`

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `protected ConnectionPool`
  `jmxPool`
  reference to the JMX mbean
  `static final String`
  `POOL_JMX_DOMAIN`
  Default domain for objects registering with an mbean server
  `static final String`
  `POOL_JMX_TYPE_PREFIX`
  Prefix type for JMX registration

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `ConnectionPool(PoolConfiguration prop)`
  Instantiate a connection pool.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `protected void`
  `abandon(PooledConnection con)`
  thread safe way to abandon a connection signals a connection to be abandoned. this will disconnect the connection, and log the stack trace if logAbandoned=true
  `protected PooledConnection`
  `borrowConnection(long now, PooledConnection con, String username, String password)`
  Validates and configures a previously idle connection
  `void`
  `checkAbandoned()`
  Iterates through all the busy connections and checks for connections that have timed out
  `void`
  `checkIdle()`
  Iterates through the idle connections and resizes the idle pool based on parameters `PoolProperties.maxIdle`, `PoolProperties.minIdle`, `PoolProperties.minEvictableIdleTimeMillis`
  `void`
  `checkIdle(boolean ignoreMinSize)`
  `void`
  `checkPoolConfiguration(PoolConfiguration properties)`
  `protected void`
  `close(boolean force)`
  Closes the pool and all disconnects all idle connections Active connections will be closed upon the `close` method is called on the underlying connection instead of being returned to the pool
  `protected PooledConnection`
  `create(boolean incrementCounter)`
  Create a new pooled connection object.
  `protected PooledConnection`
  `createConnection(long now, PooledConnection notUsed, String username, String password)`
  Creates a JDBC connection and tries to connect to the database.
  `protected void`
  `createMBean()`
  Create MBean object that can be registered.
  `protected void`
  `disconnectEvent(PooledConnection con, boolean finalizing)`
  Hook to perform final actions on a pooled connection object once it has been disconnected and will be discarded
  `protected void`
  `finalize(PooledConnection con)`
  Hook to perform final actions on a pooled connection object once it has been disconnected and will be discarded
  `int`
  `getActive()`
  Returns the number of connections that are in use
  `long`
  `getBorrowedCount()`
  The total number of connections borrowed from this pool.
  `Connection`
  `getConnection()`
  Borrows a connection from the pool.
  `Connection`
  `getConnection(String username, String password)`
  Borrows a connection from the pool.
  `Future<Connection>`
  `getConnectionAsync()`
  Retrieves a Connection future.
  `long`
  `getCreatedCount()`
  The total number of connections created by this pool.
  `int`
  `getIdle()`
  Returns the number of idle connections
  `ConnectionPool`
  `getJmxPool()`
  Return the object that is potentially registered in JMX for notifications
  `String`
  `getName()`
  Returns the name of this pool
  `static Set<TimerTask>`
  `getPoolCleaners()`
  `PoolConfiguration`
  `getPoolProperties()`
  Returns the pool properties associated with this connection pool
  `static Timer`
  `getPoolTimer()`
  `long`
  `getPoolVersion()`
  `Constructor<?>`
  `getProxyConstructor(boolean xa)`
  Creates and caches a `Constructor` used to instantiate the proxy object.
  `long`
  `getReconnectedCount()`
  The total number of connections reconnected by this pool.
  `long`
  `getReleasedCount()`
  The total number of connections released from this pool.
  `long`
  `getReleasedIdleCount()`
  The total number of connections released by eviction.
  `long`
  `getRemoveAbandonedCount()`
  The total number of connections released by remove abandoned.
  `long`
  `getReturnedCount()`
  The total number of connections returned to this pool.
  `int`
  `getSize()`
  Returns the total size of this pool, this includes both busy and idle connections
  `static String`
  `getStackTrace(Throwable x)`
  Convert an exception into a String
  `protected static String`
  `getThreadDump()`
  Creates a stack trace representing the existing thread's current state.
  `int`
  `getWaitCount()`
  Return the number of threads waiting for a connection
  `protected void`
  `init(PoolConfiguration properties)`
  Initialize the connection pool - called from the constructor
  `void`
  `initializePoolCleaner(PoolConfiguration properties)`
  `boolean`
  `isClosed()`
  Returns true if `close` has been called, and the connection pool is unusable
  `void`
  `purge()`
  Purges all connections in the pool.
  `void`
  `purgeOnReturn()`
  Purges connections when they are returned from the pool.
  `protected boolean`
  `reconnectIfExpired(PooledConnection con)`
  Checks whether this connection has `expired` and tries to reconnect if it has.
  `protected void`
  `release(PooledConnection con)`
  thread safe way to release a connection
  `void`
  `resetStats()`
  reset the statistics of this pool.
  `protected void`
  `returnConnection(PooledConnection con)`
  Returns a connection to the pool If the pool is closed, the connection will be released If the connection is not part of the busy queue, it will be released.
  `protected Connection`
  `setupConnection(PooledConnection con)`
  configures a pooled connection as a proxy.
  `protected boolean`
  `shouldAbandon()`
  Determines if a connection should be abandoned based on `PoolProperties.abandonWhenPercentageFull` setting.
  `protected boolean`
  `shouldClose(PooledConnection con, int action)`
  Determines if a connection should be closed upon return to the pool.
  `protected boolean`
  `shouldReleaseIdle(long now, PooledConnection con, long time)`
  `protected void`
  `suspect(PooledConnection con)`
  Thread safe way to suspect a connection.
  `void`
  `terminatePoolCleaner()`
  `protected boolean`
  `terminateTransaction(PooledConnection con)`
  Terminate the current transaction for the given connection.
  `void`
  `testAllIdle()`
  Forces a validation of all idle connections if `PoolProperties.testWhileIdle` is set.
  `void`
  `testAllIdle(boolean checkMaxAgeOnly)`
  Forces a validation of all idle connections if `PoolProperties.testWhileIdle` is set.

  ### Methods inherited from class Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Field Details

  - ### POOL_JMX_DOMAIN

    public static final String POOL_JMX_DOMAIN
    Default domain for objects registering with an mbean server
    See Also:
      - Constant Field Values

  - ### POOL_JMX_TYPE_PREFIX

    public static final String POOL_JMX_TYPE_PREFIX
    Prefix type for JMX registration
    See Also:
      - Constant Field Values

  - ### jmxPool

    protected ConnectionPool jmxPool
    reference to the JMX mbean

- ## Constructor Details

  - ### ConnectionPool

    public ConnectionPool(PoolConfiguration prop) throws SQLException
    Instantiate a connection pool. This will create connections if initialSize is larger than 0. The `PoolProperties` should not be reused for another connection pool.
    Parameters:
      `prop` - PoolProperties - all the properties for this connection pool
    Throws:
      `SQLException` - Pool initialization error

- ## Method Details

  - ### getConnectionAsync

    public Future<Connection> getConnectionAsync() throws SQLException
    Retrieves a Connection future. If a connection is not available, one can block using future.get() until a connection has become available. If a connection is not retrieved, the Future must be cancelled in order for the connection to be returned to the pool.
    Returns:
      a Future containing a reference to the connection or the future connection
    Throws:
      `SQLException` - Cannot use asynchronous connect

  - ### getConnection

    public Connection getConnection() throws SQLException
    Borrows a connection from the pool. If a connection is available (in the idle queue) or the pool has not reached `maxActive` connections a connection is returned immediately. If no connection is available, the pool will attempt to fetch a connection for `maxWait` milliseconds.
    Returns:
      Connection - a java.sql.Connection/javax.sql.PooledConnection reflection proxy, wrapping the underlying object.
    Throws:
      `SQLException` - - if the wait times out or a failure occurs creating a connection

  - ### getConnection

    public Connection getConnection(String username, String password) throws SQLException
    Borrows a connection from the pool. If a connection is available (in the idle queue) or the pool has not reached `maxActive` connections a connection is returned immediately. If no connection is available, the pool will attempt to fetch a connection for `maxWait` milliseconds.
    Parameters:
      `username` - The user name to use for the connection
      `password` - The password for the connection
    Returns:
      Connection - a java.sql.Connection/javax.sql.PooledConnection reflection proxy, wrapping the underlying object.
    Throws:
      `SQLException` - - if the wait times out or a failure occurs creating a connection

  - ### getName

    public String getName()
    Returns the name of this pool
    Returns:
      String - the name of the pool

  - ### getWaitCount

    public int getWaitCount()
    Return the number of threads waiting for a connection
    Returns:
      number of threads waiting for a connection

  - ### getPoolProperties

    public PoolConfiguration getPoolProperties()
    Returns the pool properties associated with this connection pool
    Returns:
      PoolProperties

  - ### getSize

    public int getSize()
    Returns the total size of this pool, this includes both busy and idle connections
    Returns:
      int - number of established connections to the database

  - ### getActive

    public int getActive()
    Returns the number of connections that are in use
    Returns:
      int - number of established connections that are being used by the application

  - ### getIdle

    public int getIdle()
    Returns the number of idle connections
    Returns:
      int - number of established connections not being used

  - ### isClosed

    public boolean isClosed()
    Returns true if `close` has been called, and the connection pool is unusable
    Returns:
      boolean

  - ### setupConnection

    protected Connection setupConnection(PooledConnection con) throws SQLException
    configures a pooled connection as a proxy. This Proxy implements `Connection` and `PooledConnection` interfaces. All calls on `Connection` methods will be propagated down to the actual JDBC connection except for the `Connection.close()` method.
    Parameters:
      `con` - a `PooledConnection` to wrap in a Proxy
    Returns:
      a `Connection` object wrapping a pooled connection.
    Throws:
      `SQLException` - if an interceptor can't be configured, if the proxy can't be instantiated

  - ### getProxyConstructor

    public Constructor<?> getProxyConstructor(boolean xa) throws NoSuchMethodException
    Creates and caches a `Constructor` used to instantiate the proxy object. We cache this, since the creation of a constructor is fairly slow.
    Parameters:
      `xa` - Use a XA connection
    Returns:
      constructor used to instantiate the wrapper object
    Throws:
      `NoSuchMethodException` - Failed to get a constructor

  - ### close

    protected void close(boolean force)
    Closes the pool and all disconnects all idle connections Active connections will be closed upon the `close` method is called on the underlying connection instead of being returned to the pool
    Parameters:
      `force` - - true to even close the active connections

  - ### init

    protected void init(PoolConfiguration properties) throws SQLException
    Initialize the connection pool - called from the constructor
    Parameters:
      `properties` - PoolProperties - properties used to initialize the pool with
    Throws:
      `SQLException` - if initialization fails

  - ### checkPoolConfiguration

    public void checkPoolConfiguration(PoolConfiguration properties)

  - ### initializePoolCleaner

    public void initializePoolCleaner(PoolConfiguration properties)

  - ### terminatePoolCleaner

    public void terminatePoolCleaner()

  - ### abandon

    protected void abandon(PooledConnection con)
    thread safe way to abandon a connection signals a connection to be abandoned. this will disconnect the connection, and log the stack trace if logAbandoned=true
    Parameters:
      `con` - PooledConnection

  - ### suspect

    protected void suspect(PooledConnection con)
    Thread safe way to suspect a connection. Similar to `abandon(PooledConnection)`, but instead of actually abandoning the connection, this will log a warning and set the suspect flag on the `PooledConnection` if logAbandoned=true
    Parameters:
      `con` - PooledConnection

  - ### release

    protected void release(PooledConnection con)
    thread safe way to release a connection
    Parameters:
      `con` - PooledConnection

  - ### createConnection

    protected PooledConnection createConnection(long now, PooledConnection notUsed, String username, String password) throws SQLException
    Creates a JDBC connection and tries to connect to the database.
    Parameters:
      `now` - timestamp of when this was called
      `notUsed` - Argument not used
      `username` - The user name to use for the connection
      `password` - The password for the connection
    Returns:
      a PooledConnection that has been connected
    Throws:
      `SQLException` - Failed to get a connection

  - ### borrowConnection

    protected PooledConnection borrowConnection(long now, PooledConnection con, String username, String password) throws SQLException
    Validates and configures a previously idle connection
    Parameters:
      `now` - - timestamp
      `con` - - the connection to validate and configure
      `username` - The user name to use for the connection
      `password` - The password for the connection
    Returns:
      a connection
    Throws:
      `SQLException` - if a validation error happens

  - ### terminateTransaction

    protected boolean terminateTransaction(PooledConnection con)
    Terminate the current transaction for the given connection.
    Parameters:
      `con` - The connection
    Returns:
      `true` if the connection TX termination succeeded otherwise `false`

  - ### shouldClose

    protected boolean shouldClose(PooledConnection con, int action)
    Determines if a connection should be closed upon return to the pool.
    Parameters:
      `con` - - the connection
      `action` - - the validation action that should be performed
    Returns:
      `true` if the connection should be closed

  - ### reconnectIfExpired

    protected boolean reconnectIfExpired(PooledConnection con)
    Checks whether this connection has `expired` and tries to reconnect if it has.
    Parameters:
      `con` - PooledConnection
    Returns:
      true if the connection was either not expired or expired but reconnecting succeeded, false if reconnecting failed (either because a new connection could not be established or validating the newly created connection failed)
    See Also:
      - `PooledConnection.isMaxAgeExpired()`

  - ### returnConnection

    protected void returnConnection(PooledConnection con)
    Returns a connection to the pool If the pool is closed, the connection will be released If the connection is not part of the busy queue, it will be released. If `PoolProperties.testOnReturn` is set to true it will be validated
    Parameters:
      `con` - PooledConnection to be returned to the pool

  - ### shouldAbandon

    protected boolean shouldAbandon()
    Determines if a connection should be abandoned based on `PoolProperties.abandonWhenPercentageFull` setting.
    Returns:
      `true` if the connection should be abandoned

  - ### checkAbandoned

    public void checkAbandoned()
    Iterates through all the busy connections and checks for connections that have timed out

  - ### checkIdle

    public void checkIdle()
    Iterates through the idle connections and resizes the idle pool based on parameters `PoolProperties.maxIdle`, `PoolProperties.minIdle`, `PoolProperties.minEvictableIdleTimeMillis`

  - ### checkIdle

    public void checkIdle(boolean ignoreMinSize)

  - ### shouldReleaseIdle

    protected boolean shouldReleaseIdle(long now, PooledConnection con, long time)

  - ### testAllIdle

    public void testAllIdle()
    Forces a validation of all idle connections if `PoolProperties.testWhileIdle` is set.

  - ### testAllIdle

    public void testAllIdle(boolean checkMaxAgeOnly)
    Forces a validation of all idle connections if `PoolProperties.testWhileIdle` is set.
    Parameters:
      `checkMaxAgeOnly` - whether to only check `PooledConnection.isMaxAgeExpired()` but not invoke `PooledConnection.validate(int)`

  - ### getThreadDump

    protected static String getThreadDump()
    Creates a stack trace representing the existing thread's current state.
    Returns:
      a string object representing the current state. TODO investigate if we simply should store `Thread.getStackTrace()` elements

  - ### getStackTrace

    public static String getStackTrace(Throwable x)
    Convert an exception into a String
    Parameters:
      `x` - - the throwable
    Returns:
      a string representing the stack trace

  - ### create

    protected PooledConnection create(boolean incrementCounter)
    Create a new pooled connection object. Not connected nor validated.
    Parameters:
      `incrementCounter` - `true` to increment the connection count
    Returns:
      a pooled connection object

  - ### purge

    public void purge()
    Purges all connections in the pool. For connections currently in use, these connections will be purged when returned on the pool. This call also purges connections that are idle and in the pool To only purge used/active connections see `purgeOnReturn()`

  - ### purgeOnReturn

    public void purgeOnReturn()
    Purges connections when they are returned from the pool. This call does not purge idle connections until they are used. To purge idle connections see `purge()`

  - ### finalize

    protected void finalize(PooledConnection con)
    Hook to perform final actions on a pooled connection object once it has been disconnected and will be discarded
    Parameters:
      `con` - The connection

  - ### disconnectEvent

    protected void disconnectEvent(PooledConnection con, boolean finalizing)
    Hook to perform final actions on a pooled connection object once it has been disconnected and will be discarded
    Parameters:
      `con` - The connection
      `finalizing` - `true` if finalizing the connection

  - ### getJmxPool

    public ConnectionPool getJmxPool()
    Return the object that is potentially registered in JMX for notifications
    Returns:
      the object implementing the `ConnectionPoolMBean` interface

  - ### createMBean

    protected void createMBean()
    Create MBean object that can be registered.

  - ### getBorrowedCount

    public long getBorrowedCount()
    The total number of connections borrowed from this pool.
    Returns:
      the borrowed connection count

  - ### getReturnedCount

    public long getReturnedCount()
    The total number of connections returned to this pool.
    Returns:
      the returned connection count

  - ### getCreatedCount

    public long getCreatedCount()
    The total number of connections created by this pool.
    Returns:
      the created connection count

  - ### getReleasedCount

    public long getReleasedCount()
    The total number of connections released from this pool.
    Returns:
      the released connection count

  - ### getReconnectedCount

    public long getReconnectedCount()
    The total number of connections reconnected by this pool.
    Returns:
      the reconnected connection count

  - ### getRemoveAbandonedCount

    public long getRemoveAbandonedCount()
    The total number of connections released by remove abandoned.
    Returns:
      the PoolCleaner removed abandoned connection count

  - ### getReleasedIdleCount

    public long getReleasedIdleCount()
    The total number of connections released by eviction.
    Returns:
      the PoolCleaner evicted idle connection count

  - ### resetStats

    public void resetStats()
    reset the statistics of this pool.

  - ### getPoolCleaners

    public static Set<TimerTask> getPoolCleaners()

  - ### getPoolVersion

    public long getPoolVersion()

  - ### getPoolTimer

    public static Timer getPoolTimer()