pool(五)——BasicDataSource

最新推荐文章于 2024-08-27 15:30:51 发布

原创最新推荐文章于 2024-08-27 15:30:51 发布 · 538 阅读

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本文深入解析了Spring框架中的JdbcTemplate组件如何与Apache DBCP2连接池进行交互，详细介绍了从创建连接池到获取数据库连接的具体流程，并强调了核心方法createDataSource的作用。

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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。