pool(五)——BasicDataSource

1.一次query流程

query真正执行的时候，才会去获取连接
{@link org.springframework.jdbc.core.JdbcTemplate#query}
{@link org.springframework.jdbc.core.JdbcTemplate#execute}
{@link org.springframework.jdbc.datasource.DataSourceUtils#getConnection}
{@link org.springframework.jdbc.datasource.DataSourceUtils#doGetConnection}
{@link org.apache.commons.dbcp2.BasicDataSource#getConnection}
{@link org.apache.commons.dbcp2.BasicDataSource#createDataSource}
{@link org.apache.commons.dbcp2.PoolingDataSource#getConnection}
<p/>
{@link org.springframework.jdbc.core.StatementCallback#doInStatement}
{@link org.apache.commons.dbcp2.DelegatingStatement#executeQuery}

2.核心方法createDataSource

protected DataSource createDataSource()        throws SQLException {        ...        synchronized (this) {            ...            PoolableConnectionFactory poolableConnectionFactory;            try {                poolableConnectionFactory = <span style="color:#ff0000;"><strong>createPoolableConnectionFactory</strong></span>(                        driverConnectionFactory);                ...            } catch (SQLException se) {                throw se;            }             ...            if (success) {                // create a pool for our connections                <span style="color:#ff0000;"><strong>createConnectionPool</strong></span>(poolableConnectionFactory);            }            ...            try {                dataSource = <span style="color:#ff0000;"><strong>createDataSourceInstance</strong></span>();                ...            } catch (SQLException se) {                ...            }            ...            <span style="color:#ff0000;">startPoolMaintenance</span>();            return dataSource;        }    }

用createPoolableConnectionFactory方法构造一个PoolableConnectionFactory，然后createConnectionPool方法用该PoolableConnectionFactory构造饼初始化connectionPool变量。

createDataSourceInstance方法用上面构造好的connectionPool构造PoolingDataSource作为dataSource变量。

connectionPool(GenericObjectPool<PoolableConnection>，构造方法new GenericObjectPool<>)

dataSource(PoolingDataSource<PoolableConnection>，构造方法new PoolingDataSource<>(connectionPool))。

最后startPoolMaintenance开启Evictor任务，如果timeBetweenEvictionRunsMillis有设置的话。

可以把PoolingDataSource看作GenericObjectPool的包装，BasicDataSource的getConnection最终还是从GenericObjectPool中拿对象。

/**     * Create (if necessary) and return a connection to the database.     *     * @throws SQLException if a database access error occurs     * @return a database connection     */    @Override    public Connection getConnection() throws SQLException {        if (Utils.IS_SECURITY_ENABLED) {            PrivilegedExceptionAction<Connection> action = new PaGetConnection();            try {                return AccessController.doPrivileged(action);            } catch (PrivilegedActionException e) {                Throwable cause = e.getCause();                if (cause instanceof SQLException) {                    throw (SQLException) cause;                }                throw new SQLException(e);            }        }        return createDataSource().getConnection();    }

这里的createDataSource返回的就是PoolingDataSource，它的getConnection方法如下：

/**     * Return a {@link java.sql.Connection} from my pool,     * according to the contract specified by {@link ObjectPool#borrowObject}.     */    @Override    public Connection getConnection() throws SQLException {        try {            C conn = _pool.borrowObject();            if (conn == null) {                return null;            }            return new PoolGuardConnectionWrapper<>(conn);        } catch(SQLException e) {            ...        }    }

也是从_pool这个变量中调用borrowObject拿对象，这个_pool对象就是上面说的GenericObjectPool，所以最终还是调用GenericObjectPool的borrowObject方法拿对象。