UDP获取图片列表，下载图片

这是我们的一次java作业中的一道题目，第一次接触javaUDP，如果哪位觉有需要改正的地方，尽管提出，谢谢！
Client:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.net.*;
import java.util.Date;
import java.io.*;
import java.awt.image.*;
import javax.imageio.*;
import javax.imageio.ImageIO;
public class GetRemoteImageClient extends JFrame implements Runnable, ActionListener
{
	JTable table;
	Object a[][] ={ 
	    {"", "", ""}
	};
	Object name[] = { "名称", "类型", "大小"};
	JButton GetImage, GetImageData;
	JTextField inputImgName;
	JPanel pSouth, pNorth;
	Thread thread;
	boolean isImage = false;
	GetRemoteImageClient()
	{
		GetImage = new JButton("下载图片");
		GetImageData = new JButton("获得图片列表");
		GetImage.addActionListener(this);
		GetImageData.addActionListener(this);
		inputImgName = new JTextField(20);
		inputImgName.setEnabled(false);
		table = new JTable(a, name);
		pSouth = new JPanel();
		pNorth = new JPanel();
		pNorth.add(new JLabel("输入要下载的图片的名称"));
		pNorth.add(inputImgName);
		pSouth.add(GetImage);
		pSouth.add(GetImageData);
		add(pSouth, BorderLayout.SOUTH);
		add(pNorth, BorderLayout.NORTH);
		add(new JScrollPane(table), BorderLayout.CENTER);
		setBounds(100, 100, 600, 400);
		setVisible(true);
		validate();
		thread = new Thread(this);
		thread.start();
		setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
	}
	public void actionPerformed(ActionEvent e)
	{
		if (e.getSource() == GetImageData)
		{
			Send("图片列表");
		}
		if (e.getSource() == GetImage)
		{
			if (!inputImgName.getText().equals(""))
			{
				JOptionPane.showMessageDialog(null, inputImgName.getText());
				Send(inputImgName.getText());
				isImage = true;
			}
			else
				JOptionPane.showMessageDialog(null, "请选中要下载的图片！");
		}

	}
	public void Send(String msg)
	{
		byte b[] = msg.getBytes();
		try
		{
			InetAddress address = InetAddress.getByName("127.0.0.1");
			DatagramPacket data = new DatagramPacket(b, b.length, address, 5678);
			DatagramSocket mail = new DatagramSocket();
			mail.send(data);
		}
		catch (Exception ex)
		{ }
	}
	public void run()
	{
		DatagramPacket pack = null;
		DatagramSocket mail = null;
		byte b[] = new byte[8192];
		try
		{
			pack = new DatagramPacket(b, b.length);
			mail = new DatagramSocket(1234);
		}
		catch (Exception e)
		{ }
		while (true)
		{
			int i=0;
			try
			{
				mail.receive(pack);
				if (!isImage)
				{
					String message = new String(pack.getData(), 0, pack.getLength());
					GetTableData(message);
				}
				else
				{
					
					String message = new String(pack.getData(), 0, pack.getLength());
					File output = new File("C:\\a.jpg");
					FileOutputStream fos = new FileOutputStream(output);
					int len = Integer.parseInt(message);
					int length = 0;
					while (length < len)
					{
						try
						{
							mail.receive(pack);
							length += pack.getLength();
							JOptionPane.showMessageDialog(null, length);
							fos.write(pack.getData(), 0, pack.getLength());
						}
						catch (Exception e)
						{
							fos.flush();
							fos.close();
						}
					}
					JOptionPane.showMessageDialog(null, "读取完毕，存储中...");
					isImage = false;
				}
				//FormTable();
			}
			catch (Exception ex)
			{ }
		}
	}
	public void GetTableData(String recvData)
	{
		//JOptionPane.showMessageDialog(null, recvData);
		String[] rows = recvData.split("#");
		Object a[][] = new Object[rows.length][3];
		//JOptionPane.showMessageDialog(null, rows);
		for (int i = 0;i< rows.length; i++)
		{
			String columns[] = rows[i].split(",");
			for (int j = 0; j < columns.length; j++)
			{
				if (j == columns.length - 1)
					a[i][j] = new Date(Long.parseLong(columns[j]));
				else
					a[i][j] = columns[j];
			}
		} 
		
		getContentPane().removeAll();
		table = new JTable(a, name);
		table.setRowHeight(20);//设置每行的高度为20
		//table.setRowHeight(0, 30);//设置第1行的高度为15
		table.addMouseListener(new MouseAdapter()
		{
			public void mouseClicked(MouseEvent e)
			{
				String value = table.getValueAt(table.getSelectedRow(), 0).toString();
				inputImgName.setText(value);
			}
		});
		table.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
		//table.setEnabled(false);
		add(new JScrollPane(table), BorderLayout.CENTER);
		add(pSouth, BorderLayout.SOUTH);
		add(pNorth, BorderLayout.NORTH);
		validate();
	}
	public static void main(String args[])
	{
		new GetRemoteImageClient();
	}
}

Server

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.net.*;
import java.io.*;
import java.util.Date;
public class ImageServer implements Runnable
{
	File dir = new File("C:\\images");
	File fileName[];
	ImageServer()
	{
		Thread thread = new Thread(this);
		thread.start();
	}
	public void Send(byte b[])
	{
		//byte b[] = datas.getBytes();
		try
		{
			InetAddress address = InetAddress.getByName("127.0.0.1");
			DatagramPacket data = new DatagramPacket(b, b.length, address, 1234);
			DatagramSocket mail = new DatagramSocket();
			mail.send(data);
		}
		catch (Exception e)
		{ }
	}
	public void run()
	{
		DatagramPacket pack = null;
		DatagramSocket mail = null;
		byte b[] = new byte[8192];
		try
		{
			pack = new DatagramPacket(b, b.length);
			mail = new DatagramSocket(5678);
		}
		catch (Exception e)
		{ }
		while (true)
		{
			try
			{
				mail.receive(pack);
				String message = new String(pack.getData(), 0, pack.getLength());
				if (message.equals("图片列表"))
				{
					String extendNames = "jpg,jpeg,bmp,png,gif";
					String datas = GetImageInfoFromFile(extendNames);
					Send(datas.getBytes());
				}
				else
				{
					for (int i = 0; i < fileName.length; i++)
					{
						if (message.equals(fileName[i].getName()))
						{
							InputStream is = new FileInputStream(fileName[i]);
							System.out.println(fileName[i].getName());
							//b = new byte[(int)fileName[i].length()];
							String length = ""+fileName[i].length();
							Send(length.getBytes());
							byte[] buffer = new byte[8192];
							int len = 0;
							while ((len = is.read(buffer)) != -1)
							{
								System.out.println(len);
								Send(buffer);
							}
							break;
						}
					}
				}
			}
			catch (Exception ex)
			{ }
		}
	}
	public String GetImageInfoFromFile(String extendNames)
	{
		String data="";
		OnlyExtendName imgFilter = new OnlyExtendName(extendNames);
		dir = new File("C:\\images");
		fileName = dir.listFiles(imgFilter);
		
		for (int i = 0; i < fileName.length; i++)
		{
			System.out.println("文件名称：" + fileName[i].getName() + "，长度：" + fileName[i].length() + "，修改时间：" + new Date(fileName[i].lastModified()));
			data += fileName[i].getName() + "," + fileName[i].length() + "," + fileName[i].lastModified() + "#";
		}
		data = data.substring(0, data.length() - 1);
		return data;
	}
	public static void main(String args[])
	{
		new ImageServer();
	}
}

class OnlyExtendName implements FilenameFilter
{
	/*
	 * 扩展名数组
	 * */
	private String[] extendName;

	public OnlyExtendName(String extendNames)
	{
		this.extendName = extendNames.split(",");
	}

	public boolean accept(File dir, String name)
	{
		if (extendName != null)
		{ 
			boolean isAccept = false;
			for (int i = 0; i < extendName.length; i++)
			{
				isAccept = isAccept || name.endsWith("." + extendName[i]);
			}
			return isAccept;
		}
		return false;
	}
}

小结：之前计算机网络课，制作了一个C#的聊天程序TCP的，因为TCP是面向连接的，所以使用异步，但是UDP不同，无连接的数据报传送，只管网服务端的端口发送，收没收到不清楚。