NIO Socket實現文件服務器

一、背景

       很多時候我們都會用FTP工具來實現文件的上傳下載功能，於是琢磨着也用Java的相關知識來自己實現一個簡單的文件服務器

二、NIO Socket

       考慮到文件的上傳下載其實就是客戶端和服務器進行通訊，然後進行數據交換。此時就可以採用Socket來實現。從JDK1.4版本以來java提供了更加高效的非阻塞形式的Socket，也就是NIO方式的Socket，通過通道Channel和緩衝器Buffer的方式來進行數據的讀寫。關於NIO的介紹，這裏找了網上的一篇文章，可以參考一下 JAVA NIO簡介

三、實施步驟

       1、實現文件的上傳下載等，需要服務器和客戶端兩部分。服務端我們取名爲FileCenter，客戶端我們取名爲FileClient

       2、首先實現FileCenter，具體代碼如下，理解可參照註釋

package org.filecenter;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CharsetEncoder;
import java.util.Iterator;

/**
 * 文件下中心，命令模式如下
 * 顯示文件：list
 *      列出所有可下載的文件
 * 下載文件：get server_file [local_file]
 *      server_file服務器中的文件名，local_file本地存儲路徑
 * 上傳文件：put local_file [server_file]
 *      local_file本地文件路徑，server_file服務器存儲文件名
 *
 * @author cyxl
 *
 */
public class FileCenter {
    private static Selector selector; // 選擇器
    private static final int server_port = 12345; // 服務器端口
    private static CharsetDecoder decoder = Charset.forName("GB2312")
            .newDecoder(); // 字節轉字符
    private static CharsetEncoder encoder = Charset.forName("GB2312")
            .newEncoder(); // 字符轉字節
    private static ByteBuffer buffer = ByteBuffer.allocate(1024);
    private static final String server_path = "C:\\file_center\\"; // 服務器文件路徑

    public static void main(String[] args) {
        try {
            selector = Selector.open();// 打開選擇器
            ServerSocketChannel serverChannel = ServerSocketChannel.open();
            ServerSocket server = serverChannel.socket();
            server.bind(new InetSocketAddress(server_port));
            serverChannel.configureBlocking(false);
            serverChannel.register(selector, SelectionKey.OP_ACCEPT);
            System.out.println("等待客戶端連接……");
            while (true) {
                selector.select();
                Iterator<SelectionKey> itr = selector.selectedKeys().iterator();
                while (itr.hasNext()) {
                    SelectionKey key = itr.next();
                    itr.remove();
                    process(key);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void process(SelectionKey key) throws IOException {
        if (key.isAcceptable()) {
            // 連接
            ServerSocketChannel serverChannel = (ServerSocketChannel) key
                    .channel();
            SocketChannel client = serverChannel.accept();
            client.configureBlocking(false);
            SelectionKey sKey = client.register(selector, SelectionKey.OP_READ);
            sKey.attach("[r_cmd]"); // 連接好後讀取客戶端發來的命令
        } else if (key.isReadable()) {
            // 讀取
            SocketChannel channel = (SocketChannel) key.channel();

            String attach = key.attachment().toString();
            if (attach.equals("[r_cmd]")) {
                // 獲取命令
                int len = channel.read(buffer);

                if (len > 0) {
                    buffer.flip();
                    String cmd = "";
                    CharBuffer charBuffer = decoder.decode(buffer);
                    cmd = charBuffer.toString();

                    SelectionKey sKey = channel.register(selector,
                            SelectionKey.OP_WRITE);
                    System.out.println("cmd:" + cmd);
                    if (cmd.trim().equals("list")) {
                        sKey.attach("[list_file]");
                    } else {
                        String[] temp = cmd.split(" ");
                        if (temp.length >= 2) {
                            cmd = temp[0];
                            String filename = temp[1];

                            if (cmd.equals("get")) {
                                // 下載
                                File file = new File(server_path, filename);
                                if (file.exists()) {
                                    sKey.attach("[get]:" + filename);
                                } else {
                                    sKey.attach("[no_file]");
                                }
                            } else if (cmd.equals("put")) {
                                // 上傳
                                sKey.attach("[put]:" + filename);
                            } else {
                                // 錯誤命令格式
                                sKey.attach("[error_command]");
                            }
                        }

                    }
                } else {
                    channel.close();
                }
            }
            buffer.clear();
        } else if (key.isWritable()) {
            // 寫入
            SocketChannel channel = (SocketChannel) key.channel();
            String attach = key.attachment().toString();
            if (attach.startsWith("[list_file]")) {
                channel.write(encoder.encode(CharBuffer.wrap("list files")));
                File file = new File(server_path);
                String[] filenames = file.list();
                String temp = "";
                for (String filename : filenames) {
                    temp += filename + ";";
                }
                temp = temp.substring(0, temp.length() - 1);
                // 寫入所有可下載的文件
                channel.write(ByteBuffer.wrap(temp.getBytes()));

                channel.close();
            } else if (attach.equals("[no_file]")) {
                channel.write(ByteBuffer.wrap("no such file".getBytes()));

                channel.close();
            } else if (attach.equals("[error_command]")) {
                channel.write(ByteBuffer.wrap("error command".getBytes()));

                channel.close();
            } else if (attach.startsWith("[get]")) {
                channel.write(encoder.encode(CharBuffer.wrap("開始下載")));
                File file = new File(server_path, attach.split(":")[1]);
                DataInputStream dis = new DataInputStream(
                        new BufferedInputStream(new FileInputStream(file)));

                int len = 0;
                byte[] buf = new byte[1024];
                while ((len = dis.read(buf)) != -1) {
                    channel.write(ByteBuffer.wrap(buf, 0, len));
                }
                dis.close();
                System.out.println("下載完成");
                channel.close();
            } else if (attach.startsWith("[put]")) {
                channel.write(encoder.encode(CharBuffer.wrap("開始上傳")));
                DataOutputStream dos = new DataOutputStream(
                        new BufferedOutputStream(new FileOutputStream(new File(
                                server_path, attach.split(":")[1]))));
                int len = channel.read(buffer);
                while (len >= 0) {
                    if (len != 0) {
                        buffer.flip();
                    }
                    dos.write(buffer.array(), 0, len);
                    len = channel.read(buffer);
                }
                dos.close();
                channel.close();
                System.out.println("上傳完畢");
            }
        }
    }

}

作爲服務器，我們首先在C盤根目錄下新建一個file_center的目錄，該目錄下的的所有文件可提供下載，上傳的文件也是保存在這個目錄下

       3、客戶端FileClient的實現代碼如下

package org.filecenter;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.net.InetAddress;
import java.net.Socket;
import java.util.Scanner;

public class FileClient {

    private int ServerPort = 12345;
    private String ServerAddress = "127.0.0.1";
    private String CMD = "list";
    private String local_file = "";
    private String server_file = "";

    class SocketThread extends Thread {

        @Override
        public void run() {
            try {
                File file = new File(local_file);
                if (!file.exists() && CMD.equals("put")) {
                    System.out.println("本地沒有這個文件，無法上傳！");
                    return;
                }

                InetAddress loalhost = InetAddress.getLocalHost();
                Socket socket = new Socket(ServerAddress, ServerPort, loalhost,
                        44);
                // 服務器IP地址 端口號 本機IP 本機端口號
                DataInputStream dis = new DataInputStream(socket
                        .getInputStream());
                DataOutputStream dos = new DataOutputStream(socket
                        .getOutputStream());

                // dos.writeUTF(GetOrPut+" "+server_file);//服務器端如果是do的socket，writeUTF和writeUTF對接
                dos.write((CMD + " " + server_file).getBytes());
                dos.flush();

                // String tempString = dis.writeUTF();
                byte[] buf = new byte[1024];
                int len = dis.read(buf);
                String tempString = new String(buf, 0, len);// 服務器反饋的信息

                // System.out.println(tempString);
                if (tempString.equals("no such file")) {
                    System.out.println("服務器沒有這個文件，無法下載！");
                    dos.close();
                    dis.close();
                    socket.close();
                    return;
                }

                if (tempString.startsWith("開始下載")) {
                    DataOutputStream fileOut = new DataOutputStream(
                            new BufferedOutputStream(new FileOutputStream(file)));

                    while ((len = dis.read(buf)) != -1) {
                        fileOut.write(buf, 0, len);
                    }
                    System.out.println("下載完畢！");
                    fileOut.close();
                    dos.close();
                    dis.close();
                    socket.close();
                } else if (tempString.equals("開始上傳")) {
                    System.out.println("正在上傳文件.......");
                    DataInputStream fis = new DataInputStream(
                            new BufferedInputStream(new FileInputStream(file)));

                    while ((len = fis.read(buf)) != -1) {
                        dos.write(buf, 0, len);
                    }
                    dos.flush();
                    System.out.println("上傳完畢！");
                    fis.close();
                    dis.close();
                    dos.close();
                    socket.close();
                }
                else if(tempString.equals("list files"))
                {
                    len=dis.read(buf);
                    String temp=new String(buf,0,len);
                    String[] strs=temp.split(";");
                    System.out.println("文件列表");
                    for(String str:strs)
                    {
                        System.out.println(str);
                    }
                    dis.close();
                    dos.close();
                    socket.close();
                }

            } catch (Exception e) {
                e.printStackTrace();
            }
        }

    }

    public boolean checkCommand(String command) {
        if (!command.startsWith("put") && !command.startsWith("get") && !command.equals("list")) {
            System.out.println("輸入命令錯誤");
            return false;
        }

        int index = -1;
        String temp = "";
        String[] tempStrings = null;

        if ((index = command.indexOf("-h")) > 0) {
            temp = command.substring(index + 3);
            temp = temp.substring(0, temp.indexOf(' '));
            ServerAddress = temp;
        }
        if ((index = command.indexOf("-p")) > 0) {
            temp = command.substring(index + 3);
            temp = temp.substring(0, temp.indexOf(' '));
            ServerPort = Integer.valueOf(temp);
        }

        tempStrings = command.split(" ");
        if (command.startsWith("put")) {
            CMD = "put";
            local_file = tempStrings[tempStrings.length - 2];
            server_file = tempStrings[tempStrings.length - 1];
        } else if (command.startsWith("get")) {
            CMD = "get";
            local_file = tempStrings[tempStrings.length - 1];
            server_file = tempStrings[tempStrings.length - 2];
        }
        else
        {
            CMD = "list";
        }

        return true;
    }

    public static void main(String[] args) {
        FileClient client = new FileClient();
        Scanner sc = new Scanner(System.in);
        String commandString = "";
        do {
            System.out.println("請輸入命令：");
            commandString = sc.nextLine();
        } while (!client.checkCommand(commandString));

        FileClient.SocketThread a = client.new SocketThread();
        a.start();

    }
}