java设计模式之实现对象池模式示例分享

objectpool抽象父类

import java.util.iterator;
import java.util.vector;

public abstract class objectpool<t> {

   private vector<t> locked, unlocked;   // locked是已占用的对象集合，unlocked是可用对象集合

   public objectpool() {
    locked = new vector<t>();
    unlocked = new vector<t>();
   }

   // 创建对象
   protected abstract t create();

   // 验证对象有效性
   public abstract boolean validate(t o);

   // 使对象失效
   public abstract void expire(t o);

   // 检出：从对象池获取对象
   public synchronized t checkout() {
    t t;
    if (unlocked.size() > 0) {
     iterator<t> iter = unlocked.iterator();
     while(iter.hasnext()) {
      t = iter.next();
      if(validate(t)) {   // 对象有效
       unlocked.remove(t);
       locked.add(t);

       return t;
      }
      else {   // 对象已经失效
       unlocked.remove(t);
       expire(t);
      }
     }
    }

    // 对象池塘没有可用对象，创建新对象
    t = create();
    locked.add(t);

    return (t);
   }

   // 检入：释放对象回对象池
   public synchronized void checkin(t t) {
    locked.remove(t);
    if(validate(t)) {   // 如果对象仍有效则放回可用对象集合中
     unlocked.add(t);
    }
    else {   // 否则使对象失效
     expire(t);
    }
   }

}

jdbcconnectionpool子类

import java.sql.connection;
import java.sql.drivermanager;
import java.sql.sqlexception;

public class jdbcconnectionpool extends objectpool<connection> {

 private string url, usr, pwd;

 public jdbcconnectionpool(string driver, string url, string usr, string pwd) {
  super();

  // 加载对应的数据库驱动
  try {
   class.forname(driver).newinstance();
  }
  catch(exception e) {
   e.printstacktrace();
  }

  this.url = url;
  this.usr = usr;
  this.pwd = pwd;
 }

 @override
 protected connection create() {
  try {
   return drivermanager.getconnection(url, usr, pwd);
  }
  catch(sqlexception e) {
   e.printstacktrace();
  }

  return null;
 }

 @override
 public boolean validate(connection o) {
  try {
   return o.isclosed();
  }
  catch(sqlexception e) {
   e.printstacktrace();
  }

  return false;
 }

 @override
 public void expire(connection o) {
  try {
   o.close();
  }
  catch(sqlexception e) {
   e.printstacktrace();
  }
  finally {
   o = null;
  }
 }

 public static void main(string[] args) {
  jdbcconnectionpool dbconnpool = new jdbcconnectionpool("com.mysql.jdbc.driver", "jdbc:mysql://127.0.0.1:3306/test", "root", "123");

  // 获取数据库连接对象
  connection conn = dbconnpool.checkout();

  // 使用数据库连接对象
  // ...

  // 释放数据库连接对象
  dbconnpool.checkin(conn);

 }

}

class pool {
   private static final max_available = 100;
   private final semaphore available = new semaphore(max_available, true);

   public object getitem() throws interruptedexception {
     available.acquire();
     return getnextavailableitem();
   }

   public void putitem(object x) {
     if (markasunused(x))
       available.release();
   }

   // not a particularly efficient data structure; just for demo

   protected object[] items = ... whatever kinds of items being managed
   protected boolean[] used = new boolean[max_available];

   protected synchronized object getnextavailableitem() {
     for (int i = 0; i < max_available; ++i) {
       if (!used[i]) {
          used[i] = true;
          return items[i];
       }
     }
     return null; // not reached
   }

   protected synchronized boolean markasunused(object item) {
     for (int i = 0; i < max_available; ++i) {
       if (item == items[i]) {
          if (used[i]) {
            used[i] = false;
            return true;
          } else
            return false;
       }
     }
     return false;
   }

 }