Java FTPClient连接池的实现

最近在写一个ftp上传工具，用到了apache的ftpclient，为了提高上传效率，我采用了多线程的方式，但是每个线程频繁的创建和销毁ftpclient对象势必会造成不必要的开销，因此，此处最好使用一个ftpclient连接池。仔细翻了一下apache的api，发现它并没有一个ftpclientpool的实现，所以，不得不自己写一个ftpclientpool。下面就大体介绍一下开发连接池的整个过程，供大家参考。

关于对象池

有些对象的创建开销是比较大的，比如数据库连接等。为了减少频繁创建、销毁对象带来的性能消耗，我们可以利用对象池的技术来实现对象的复用。对象池提供了一种机制，它可以管理对象池中对象的生命周期，提供了获取和释放对象的方法，可以让客户端很方便的使用对象池中的对象。

如果我们要自己实现一个对象池，一般需要完成如下功能：

1. 如果池中有可用的对象，对象池应当能返回给客户端
2. 客户端把对象放回池里后，可以对这些对象进行重用
3. 对象池能够创建新的对象来满足客户端不断增长的需求
4. 需要有一个正确关闭池的机制来结束对象的生命周期

apache的对象池工具包

为了方便我们开发自己的对象池，apache 提供的common-pool工具包，里面包含了开发通用对象池的一些接口和实现类。其中最基本的两个接口是objectpool 和poolableobjectfactory。

objectpool接口中有几个最基本的方法：

1. addobject() : 添加对象到池
2. borrowobject()：客户端从池中借出一个对象
3. returnobject()：客户端归还一个对象到池中
4. close()：关闭对象池，清理内存释放资源等
5. setfactory(objectfactory factory)：需要一个工厂来制造池中的对象

poolableobjectfactory接口中几个最基本的方法：

1. makeobject()：制造一个对象
2. destoryobject()：销毁一个对象
3. validateobject()：验证一个对象是否还可用

通过以上两个接口我们就可以自己实现一个对象池了。

实例：开发一个ftpclient对象池

最近在开发一个项目，需要把hdfs中的文件上传到一组ftp服务器，为了提高上传效率，自然考虑到使用多线程的方式进行上传。我上传ftp用的工具是apache common-net包中的ftpclient，但apache并没有提供ftpclientpool，于是为了减少ftpclient的创建销毁次数，我们就自己开发一个ftpclientpool来复用ftpclient连接。

通过上面的介绍，我们可以利用apache提供的common-pool包来协助我们开发连接池。而开发一个简单的对象池，仅需要实现common-pool 包中的objectpool和poolableobjectfactory两个接口即可。下面就看一下我写的实现：

写一个objectpool接口的实现ftpclientpool

import java.io.ioexception;
import java.util.nosuchelementexception;
import java.util.concurrent.arrayblockingqueue;
import java.util.concurrent.blockingqueue;
import java.util.concurrent.timeunit;

import org.apache.commons.net.ftp.ftpclient;
import org.apache.commons.pool.objectpool;
import org.apache.commons.pool.poolableobjectfactory;

/**
* 实现了一个ftpclient连接池
* @author heaven
*/
public class ftpclientpool implements objectpool<ftpclient>{
 private static final int default_pool_size = 10;
 private final blockingqueue<ftpclient> pool;
 private final ftpclientfactory factory;

 /**
 * 初始化连接池，需要注入一个工厂来提供ftpclient实例
 * @param factory
 * @throws exception
 */
 public ftpclientpool(ftpclientfactory factory) throws exception{
   this(default_pool_size, factory);
 }
 /**
 *
 * @param maxpoolsize
 * @param factory
 * @throws exception
 */
 public ftpclientpool(int poolsize, ftpclientfactory factory) throws exception {
   this.factory = factory;
   pool = new arrayblockingqueue<ftpclient>(poolsize*2);
   initpool(poolsize);
 }
 /**
 * 初始化连接池，需要注入一个工厂来提供ftpclient实例
 * @param maxpoolsize
 * @throws exception
 */
 private void initpool(int maxpoolsize) throws exception {
   for(int i=0;i<maxpoolsize;i++){
      //往池中添加对象
      addobject();
   }

 }
 /* (non-javadoc)
 * @see org.apache.commons.pool.objectpool#borrowobject()
 */
 public ftpclient borrowobject() throws exception, nosuchelementexception, illegalstateexception {
   ftpclient client = pool.take();
   if (client == null) {
      client = factory.makeobject();
      addobject();
   }else if(!factory.validateobject(client)){//验证不通过
      //使对象在池中失效
      invalidateobject(client);
      //制造并添加新对象到池中
      client = factory.makeobject();
      addobject();
   }
   return client;

 }

 /* (non-javadoc)
 * @see org.apache.commons.pool.objectpool#returnobject(java.lang.object)
 */
 public void returnobject(ftpclient client) throws exception {
   if ((client != null) && !pool.offer(client,3,timeunit.seconds)) {
      try {
        factory.destroyobject(client);
      } catch (ioexception e) {
        e.printstacktrace();
      }
   }
 }

 public void invalidateobject(ftpclient client) throws exception {
   //移除无效的客户端
   pool.remove(client);
 }

 /* (non-javadoc)
 * @see org.apache.commons.pool.objectpool#addobject()
 */
 public void addobject() throws exception, illegalstateexception, unsupportedoperationexception {
   //插入对象到队列
   pool.offer(factory.makeobject(),3,timeunit.seconds);
 }

 public int getnumidle() throws unsupportedoperationexception {
   return 0;
 }

 public int getnumactive() throws unsupportedoperationexception {
   return 0;
 }

 public void clear() throws exception, unsupportedoperationexception {

 }

 /* (non-javadoc)
 * @see org.apache.commons.pool.objectpool#close()
 */
 public void close() throws exception {
   while(pool.iterator().hasnext()){
      ftpclient client = pool.take();
      factory.destroyobject(client);
   }
 }

 public void setfactory(poolableobjectfactory<ftpclient> factory) throws illegalstateexception, unsupportedoperationexception {

 }
}

再写一个poolableobjectfactory接口的实现ftpclientfactory

import java.io.ioexception;
import org.apache.commons.net.ftp.ftpclient;
import org.apache.commons.net.ftp.ftpreply;
import org.apache.commons.pool.poolableobjectfactory;
import org.slf4j.logger;
import org.slf4j.loggerfactory;

import com.hdfstoftp.util.ftpclientexception;

/**
* ftpclient工厂类，通过ftpclient工厂提供ftpclient实例的创建和销毁
* @author heaven
*/
public class ftpclientfactory implements poolableobjectfactory<ftpclient> {
private static logger logger = loggerfactory.getlogger("file");
 private ftpclientconfigure config;
 //给工厂传入一个参数对象，方便配置ftpclient的相关参数
 public ftpclientfactory(ftpclientconfigure config){
   this.config=config;
 }

 /* (non-javadoc)
 * @see org.apache.commons.pool.poolableobjectfactory#makeobject()
 */
 public ftpclient makeobject() throws exception {
   ftpclient ftpclient = new ftpclient();
   ftpclient.setconnecttimeout(config.getclienttimeout());
   try {
      ftpclient.connect(config.gethost(), config.getport());
      int reply = ftpclient.getreplycode();
      if (!ftpreply.ispositivecompletion(reply)) {
        ftpclient.disconnect();
        logger.warn("ftpserver refused connection");
        return null;
      }
      boolean result = ftpclient.login(config.getusername(), config.getpassword());
      if (!result) {
        throw new ftpclientexception("ftpclient登陆失败! username:" + config.getusername() + " ; password:" + config.getpassword());
      }
      ftpclient.setfiletype(config.gettransferfiletype());
      ftpclient.setbuffersize(1024);
      ftpclient.setcontrolencoding(config.getencoding());
      if (config.getpassivemode().equals("true")) {
        ftpclient.enterlocalpassivemode();
      }
   } catch (ioexception e) {
      e.printstacktrace();
   } catch (ftpclientexception e) {
      e.printstacktrace();
   }
   return ftpclient;
 }

 /* (non-javadoc)
 * @see org.apache.commons.pool.poolableobjectfactory#destroyobject(java.lang.object)
 */
 public void destroyobject(ftpclient ftpclient) throws exception {
   try {
      if (ftpclient != null && ftpclient.isconnected()) {
        ftpclient.logout();
      }
   } catch (ioexception io) {
      io.printstacktrace();
   } finally {
      // 注意,一定要在finally代码中断开连接，否则会导致占用ftp连接情况
      try {
        ftpclient.disconnect();
      } catch (ioexception io) {
        io.printstacktrace();
      }
   }
 }

 /* (non-javadoc)
 * @see org.apache.commons.pool.poolableobjectfactory#validateobject(java.lang.object)
 */
 public boolean validateobject(ftpclient ftpclient) {
   try {
      return ftpclient.sendnoop();
   } catch (ioexception e) {
      throw new runtimeexception("failed to validate client: " + e, e);
   }
 }

 public void activateobject(ftpclient ftpclient) throws exception {
 }

 public void passivateobject(ftpclient ftpclient) throws exception {

 }
}

最后，我们最好给工厂传递一个参数对象，方便我们设置ftpclient的一些参数

package org.apache.commons.pool.impl.contrib;

/**
 * ftpclient配置类，封装了ftpclient的相关配置
 *
 * @author heaven
 */
public class ftpclientconfigure {
 private string host;
 private int port;
 private string username;
 private string password;
 private string passivemode;
 private string encoding;
 private int clienttimeout;
 private int threadnum;
 private int transferfiletype;
 private boolean renameuploaded;
 private int retrytimes;

 public string gethost() {
     return host;
 }

 public void sethost(string host) {
     this. host = host;
 }

 public int getport() {
     return port;
 }

 public void setport(int port) {
     this. port = port;
 }

 public string getusername() {
     return username;
 }

 public void setusername(string username) {
     this. username = username;
 }

 public string getpassword() {
     return password;
 }

 public void setpassword(string password) {
     this. password = password;
 }


 public string getpassivemode() {
     return passivemode;
 }

 public void setpassivemode(string passivemode) {
     this. passivemode = passivemode;
 }

 public string getencoding() {
     return encoding;
 }

 public void setencoding(string encoding) {
     this. encoding = encoding;
 }

 public int getclienttimeout() {
     return clienttimeout;
 }

 public void setclienttimeout( int clienttimeout) {
     this. clienttimeout = clienttimeout;
 }

 public int getthreadnum() {
     return threadnum;
 }

 public void setthreadnum( int threadnum) {
     this. threadnum = threadnum;
 }

 public int gettransferfiletype() {
     return transferfiletype;
 }

 public void settransferfiletype( int transferfiletype) {
     this. transferfiletype = transferfiletype;
 }

 public boolean isrenameuploaded() {
     return renameuploaded;
 }

 public void setrenameuploaded( boolean renameuploaded) {
     this. renameuploaded = renameuploaded;
 }

 public int getretrytimes() {
     return retrytimes;
 }

 public void setretrytimes( int retrytimes) {
     this. retrytimes = retrytimes;
 }

 @override
 public string tostring() {
     return "ftpclientconfig [host=" + host + "\n port=" + port + "\n username=" + username + "\n password=" + password  + "\n passivemode=" + passivemode
          + "\n encoding=" + encoding + "\n clienttimeout=" + clienttimeout + "\n threadnum=" + threadnum + "\n transferfiletype="
          + transferfiletype + "\n renameuploaded=" + renameuploaded + "\n retrytimes=" + retrytimes + "]" ;
 }

}

 ftpclientpool连接池类管理ftpclient对象的生命周期，负责对象的借出、规划、池的销毁等；ftpclientpool类依赖于ftpclientfactory类，由这个工程类来制造和销毁对象；ftpclientfactory又依赖ftpclientconfigure类，ftpclientconfigure负责封装ftpclient的配置参数。至此，我们的ftpclient连接池就开发完成了。

需要注意的是，ftpclientpool中用到了一个阻塞队列arrayblockingqueue来管理存放ftpclient对象，关于阻塞队列，请参考我的这篇文章： 【java并发之】blockingqueue

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。