用java实现数据库连接池的一个简单示例

转载：http://hi.baidu.com/triceratops/blog

import 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 connection
Connection 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;
   }
}
}

评论

1 楼 ranguisheng 2013-04-12  

可以加点注释,代码不便于阅读.