设计模式
FTPClient与commons-pool2整合过程中涉及到的设计模式有：工厂方法模式、单例模式。
工厂方法模式
工厂方法模式定义了一个创建对象的接口，但由子类决定要实例化的类是哪一个，工厂方法让实例化推迟到子类。当需要增加一个新的产品时，只需要增加一个具体的产品类和与之对应的具体工厂即可，无须修改原有系统。但是由于每新增一个新产品时就需要增加两个类，这样会导致系统的复杂度增加。
详细信息见:
单例模式
单例模式确保一个类只有一个实例，并提供一个全局访问点。
单例模式有五种实现方法：双重校验锁、枚举、静态内部类、恶汉、懒汉。
在这里选择静态内部类。
详细信息见:
代码
主要有FTPClientFactory和FTPClientUtil两个类
使用commons-pool2
import org.apache.commons.net.ftp.FTPClient;import org.apache.commons.pool2.BasePooledObjectFactory;import org.apache.commons.pool2.PooledObject;import org.apache.commons.pool2.impl.DefaultPooledObject;import java.util.Properties;/** * Created by udbwcso on 2016/3/14. */public class FTPClientFactory extends BasePooledObjectFactory{ private final String host; private final int port; private final String username; private final String password; public FTPClientFactory(final String host, final int port, final String username, final String password){ this.host = host; this.port = port; this.username = username; this.password = password; } public FTPClientFactory(Properties properties){ this.host = properties.getProperty("host"); this.port = Integer.parseInt(properties.getProperty("port")); this.username = properties.getProperty("username"); this.password = properties.getProperty("password"); } /** * Creates an object instance, to be wrapped in a {@link PooledObject}. * This method must support concurrent, multi-threaded * activation.
* * @return an instance to be served by the pool * @throws Exception if there is a problem creating a new instance, * this will be propagated to the code requesting an object. */ public FTPClient create() throws Exception { FTPClient client = new FTPClient(); client.connect(host, port); client.login(username, password); return client; } /** * Wrap the provided instance with an implementation of * {@link PooledObject}. * * @param obj the instance to wrap * @return The provided instance, wrapped by a {@link PooledObject} */ public PooledObjectwrap(FTPClient obj) { return new DefaultPooledObject (obj); } /** * destroy object */ @Override public void destroyObject(PooledObject p) throws Exception { FTPClient ftpClient = p.getObject(); ftpClient.logout(); ftpClient.disconnect(); }}
工具类
import org.apache.commons.net.ftp.FTPClient;import org.apache.commons.pool2.ObjectPool;import org.apache.commons.pool2.impl.GenericObjectPool;import java.io.IOException;import java.io.InputStream;import java.util.Properties;/** * Created by udbwcso on 2016/3/15. */public class FTPClientUtil { private static final String FTP_PROPERTIES = "/ftp.properties"; private FTPClientUtil(){ } public static FTPClientUtil getInstance(){ return SingletonHolder.instance; } /** * Returns the pathname of the current working directory. * @return */ public String getWorkingDirectory() throws Exception { FTPClient client = getClientPool().borrowObject(); String workingDir = client.printWorkingDirectory(); getClientPool().returnObject(client); return workingDir; } private ObjectPool getClientPool(){ return SingletonHolder.POOL; } private static class SingletonHolder { private static final ObjectPool POOL; static { InputStream resourceAsStream = FTPClientUtil.class.getResourceAsStream(FTP_PROPERTIES); Properties p = null; if (resourceAsStream != null) { p = new Properties(); try { p.load(resourceAsStream); } catch (IOException e) { } finally { try { resourceAsStream.close(); } catch (IOException e) { // Ignored } } } POOL = new GenericObjectPool (new FTPClientFactory(p)); } private static FTPClientUtil instance = new FTPClientUtil(); }} 目前只有获取工作目录的方法，有待后续开发。