数据库连接池DBCP浅析

import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.Statement;
import java.sql.ResultSet;
import java.sql.SQLException;


import org.apache.commons.dbcp2.BasicDataSource;


public class BasicDataSourceExample {

    public static void main(String[] args) {
        // First we set up the BasicDataSource.
        // Normally this would be handled auto-magically by
        // an external configuration, but in this example we'll
        // do it manually.
        //
        System.out.println("Setting up data source.");
        DataSource dataSource = setupDataSource(args[0]);
        System.out.println("Done.");

        //
        // Now, we can use JDBC DataSource as we normally would.
        //
        Connection conn = null;
        Statement stmt = null;
        ResultSet rset = null;

        try {
            System.out.println("Creating connection.");
            conn = dataSource.getConnection();
            System.out.println("Creating statement.");
            stmt = conn.createStatement();
            System.out.println("Executing statement.");
            rset = stmt.executeQuery(args[1]);
            System.out.println("Results:");
            int numcols = rset.getMetaData().getColumnCount();
            while(rset.next()) {
                for(int i=1;i<=numcols;i++) {
                    System.out.print("\t" + rset.getString(i));
                }
                System.out.println("");
            }
        } catch(SQLException e) {
            e.printStackTrace();
        } finally {
            try { if (rset != null) rset.close(); } catch(Exception e) { }
            try { if (stmt != null) stmt.close(); } catch(Exception e) { }
            try { if (conn != null) conn.close(); } catch(Exception e) { }
        }
    }

    public static DataSource setupDataSource(String connectURI) {
        BasicDataSource ds = new BasicDataSource();
        ds.setDriverClassName("oracle.jdbc.driver.OracleDriver");
        ds.setUsername("scott");
        ds.setPassword("tiger");
        ds.setUrl(connectURI);
        return ds;
    }

    public static void printDataSourceStats(DataSource ds) {
        BasicDataSource bds = (BasicDataSource) ds;
        System.out.println("NumActive: " + bds.getNumActive());
        System.out.println("NumIdle: " + bds.getNumIdle());
    }

    public static void shutdownDataSource(DataSource ds) throws SQLException {
        BasicDataSource bds = (BasicDataSource) ds;
        bds.close();
    }
}

This ad is supporting your extension Smooth GesturesTurn off these ads?

  public Connection getConnection() throws SQLException {
        return createDataSource().getConnection();
    }

   protected synchronized DataSource createDataSource()
        throws SQLException {
        if (closed) {
            throw new SQLException("Data source is closed");
        }

        // Return the pool if we have already created it
        if (dataSource != null) {
            return (dataSource);
        }

        //  用户第一次使用getConnection请求连接时，建立数据库连接池
        ConnectionFactory driverConnectionFactory = createConnectionFactory();

        //建立连接池，使用commons-pool的GenericObjectPool
        createConnectionPool();

        // Set up statement pool, if desired
        GenericKeyedObjectPoolFactory statementPoolFactory = null;
        if (isPoolPreparedStatements()) {
            statementPoolFactory = new GenericKeyedObjectPoolFactory(null,
                        -1, // unlimited maxActive (per key)
                        GenericKeyedObjectPool.WHEN_EXHAUSTED_FAIL,
                        0, // maxWait
                        1, // maxIdle (per key)
                        maxOpenPreparedStatements);
        }

        // 设置连接池工厂
        createPoolableConnectionFactory(driverConnectionFactory, statementPoolFactory, abandonedConfig);

        // 建立数据库连接池实例
        createDataSourceInstance();
        
       // 根据配置，初始化建立一些数据库连接
        try {
            for (int i = 0 ; i < initialSize ; i++) {
                connectionPool.addObject();
            }
        } catch (Exception e) {
            throw new SQLNestedException("Error preloading the connection pool", e);
        }
        
        return dataSource;
    }

    protected void createDataSourceInstance() throws SQLException {
        PoolingDataSource pds = new PoolingDataSource(connectionPool);
        pds.setAccessToUnderlyingConnectionAllowed(isAccessToUnderlyingConnectionAllowed());
        pds.setLogWriter(logWriter);
        dataSource = pds;
    }

  public Connection getConnection() throws SQLException {
        try {
            Connection conn = (Connection)(_pool.borrowObject());
            if (conn != null) {
                conn = new PoolGuardConnectionWrapper(conn);
            } 
            return conn;
        } catch(SQLException e) {
            throw e;
        } catch(NoSuchElementException e) {
            throw new SQLNestedException("Cannot get a connection, pool error " + e.getMessage(), e);
        } catch(RuntimeException e) {
            throw e;
        } catch(Exception e) {
            throw new SQLNestedException("Cannot get a connection, general error", e);
        }
    }

    public Object makeObject() throws Exception {
        Connection conn = _connFactory.createConnection();
        if (conn == null) {
            throw new IllegalStateException("Connection factory returned null from createConnection");
        }
        initializeConnection(conn);
        if(null != _stmtPoolFactory) {
            KeyedObjectPool stmtpool = _stmtPoolFactory.createPool();
            conn = new PoolingConnection(conn,stmtpool);
            stmtpool.setFactory((PoolingConnection)conn);
        }
        return new PoolableConnection(conn,_pool,_config);
    }   

    public synchronized void close() throws SQLException {
        if (_closed) {
            // already closed
            return;
        }
        ......
        if (!isUnderlyingConectionClosed) {
            // Normal close: underlying connection is still open, so we
            // simply need to return this proxy to the pool
            try {
                _pool.returnObject(this); // XXX should be guarded to happen at most once
            } catch(IllegalStateException e) {
         ......
    }