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我们。