用java实现数据库连接池的一个简单示例
转载：http://hi.baidu.com/triceratops/blogimport java.util.Stack;import java.sql.Connection;import java.sql.DriverManager;import java.sql.SQLException;import org.apache.log4j.*;public final class DBConnectionPool {private static DBConnectionPool dbConnectionPool = null;private static int accumulator = 0;private static Logger log = Logger.getLogger(DBConnectionPool.class);private static final int POOL_INIT_SIZE = 128;private static final int POOL_MAX_SIZE = 512;private Stack pool;private String driverName = "com.ibm.db2.jcc.DB2Driver";private String url = "jdbc:db2://192.168.1.100:60000/flamingo";private String user = "daniel";private String password = "850306";public static DBConnectionPool getInstance() throws Exception{ if(dbConnectionPool == null){ synchronized(DBConnectionPool.class){ if(dbConnectionPool == null) dbConnectionPool = new DBConnectionPool(); } } return dbConnectionPool;}private DBConnectionPool() throws ClassNotFoundException, SQLException{ log.setLevel(Level.DEBUG); pool = new Stack(); initializePool();}private void initializePool() throws ClassNotFoundException, SQLException{ log.info("Database connection pool initializing..."); Connection conn = null; try{ Class.forName(driverName); for(int i = 0;i < POOL_INIT_SIZE;i++){ conn = new DBConnection(DriverManager.getConnection (url,user,password),this).getConnection(); pool.push(conn); accumulator++; } } catch(ClassNotFoundException e){ log.error("Failure: Cannot find the db2 driver!"); throw e; } catch(SQLException e){ log.error("Failure: Cannot connect to the database!"); throw e; } log.info("Database connection pool initialized successfully!"); log.info("pool size is: "+pool.size());}public synchronized Connection getConnection() throws ClassNotFoundException, SQLException{ Connection conn; while(true){ if(!pool.isEmpty()){ conn = (Connection)pool.pop(); if(conn == null || conn.isClosed()){ accumulator--; continue; } return conn; } else{ if(accumulator == POOL_MAX_SIZE){ try{ wait(5000); } catch(InterruptedException e){ e.printStackTrace(); } } else{ //create a new database connection try{ Class.forName(driverName); conn = new DBConnection(DriverManager.getConnection (url,"db2inst2","db2inst2"),this).getConnection(); accumulator++; return conn; } catch(ClassNotFoundException e){ log.error("Failure: Cannot find the db2 driver!"); throw e; } catch(SQLException e){ log.error("Failure: Cannot connect to the database!"); throw e; } } } }}public synchronized boolean returnConnection(Connection conn){ if(pool.size() < POOL_MAX_SIZE){ pool.push(conn); log.info(conn +" has been returned!"); notify(); return true; } return false; // The connection pool is full filled.}public static void main(String[] args) throws Exception{ Connection conn = getInstance().getConnection(); System.out.println(conn); conn.close();}}===============================================================================import java.sql.Connection;import java.sql.SQLException;import java.lang.reflect.Proxy;import java.lang.reflect.InvocationHandler;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import org.apache.log4j.Logger;import org.apache.log4j.Level;public class DBConnection implements InvocationHandler{private Connection conn;private DBConnectionPool dbConnectionPool;private static Logger log = Logger.getLogger(DBConnectionPool.class);DBConnection(Connection conn,DBConnectionPool dbConnectionPool){ this.conn = conn; this.dbConnectionPool = dbConnectionPool; log.setLevel(Level.DEBUG);}//return the proxy of an inner hold connectionConnection getConnection(){ return (Connection)Proxy.newProxyInstance( conn.getClass().getClassLoader(),new Class[]{Connection.class},this);}public Object invoke(Object proxy,Method method, Object[] args) throws SQLException, IllegalAccessException,InvocationTargetException{ Object result = null; try{ log.debug("Method: "+method.getName()+" starts......"); if(method.getName().equals("close")){ close(); } else{ result = method.invoke(conn,args); } log.debug("Method: "+method.getName()+" ends......"); } catch(SQLException e){ log.error("Database operation failed, please try later..."); throw e; } catch(IllegalAccessException e){ log.error(method.getName()+" operation forbidden!"); throw e; } catch(InvocationTargetException e){ log.error(method.getName()+" operation forbidden!"); throw e; } return result;}private void close() throws SQLException{ if(!dbConnectionPool.returnConnection(getConnection())){ conn.close(); log.info(conn + " is closed!"); conn = null; }}}
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