在Java中通过UDP传输文件

Question

我在使用TCP / IP的Java中实现了以下算法：

-Client request a file
-Server checks if the file exists
  - if do: send contents of the file to the client
  - if not: send "file not found" msg to the client

现在，我在使用UDP数据包实现它时遇到了麻烦。 这是我的代码：

---

客户：

package br.com.redes.client;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;

import br.com.redes.configuration.CommonKeys;

public class TCPClient {
    public static void exibirCabecalho(){
        System.out.println("-------------------------");
        System.out.println("TCP CLIENT");
        System.out.println("-------------------------");
    }

    public static void main(String[] args) throws IOException {

        TCPClient.exibirCabecalho();

        Socket echoSocket = null;
        PrintWriter out = null;
        BufferedReader in = null;

        if (args.length != 1){
            System.out.println("O Programa deve ser chamado pelo nome + nome do servidor");
            System.out.println("Ex: java TCPClient localhost");
            System.exit(1);
        }

        System.out.println("Conectando ao servidor...");
        try {
            echoSocket = new Socket( args[0] , CommonKeys.PORTA_SERVIDOR);
            out = new PrintWriter(echoSocket.getOutputStream(), true);
            in = new BufferedReader(new InputStreamReader(echoSocket
                    .getInputStream()));
        } catch (UnknownHostException e) {
            System.err.println("Host não encontrado (" + args[0] + ")");
            System.exit(1);
        } catch (IOException e) {
            System.err.println("Erro ao inicializar I/O para conexao");
            System.exit(1);
        }

        System.out.println("Conectado, digite 'sair' sem as aspas para finalizar");

        BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
        String userInput;

        while ((userInput = stdIn.readLine()) != null) {
            out.println(userInput);
            String inputLine = in.readLine(); 

            if (inputLine == null){
                System.out.println("Servidor terminou a conexão.");
                System.out.println("Saindo...");
                break;
            }

            System.out.println("Servidor: " + inputLine.replace("\\n", "\n"));
        }

        out.close();
        in.close();
        stdIn.close();
        echoSocket.close();
    }

}

---

服务器：

package br.com.redes.server;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

import br.com.redes.configuration.CommonKeys;

public class TCPServer {
    public static void exibirCabecalho(){
        System.out.println("-------------------------");
        System.out.println("TCP SERVER");
        System.out.println("-------------------------");
    }

    public static void main(String[] args) throws IOException {

        TCPServer.exibirCabecalho();
        ServerSocket serverSocket = null;
        try {
            serverSocket = new ServerSocket( CommonKeys.PORTA_SERVIDOR );
        } catch (IOException e) {
            System.err.println("Erro ao iniciar servidor na porta: " + CommonKeys.PORTA_SERVIDOR );
            System.exit(1);
        }

        System.out.println("Iniciando servidor na porta: " + CommonKeys.PORTA_SERVIDOR);
        System.out.println("Aguardando cliente...");
        Socket clientSocket = null;
        try {
            clientSocket = serverSocket.accept();
        } catch (IOException e) {
            System.err.println("Erro ao receber conexoes.");
            System.exit(1);
        }

        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

        String inputLine, outputLine;

        System.out.println("Cliente conectado, aguardando caminhos pra leitura...");
        while ((inputLine = in.readLine()) != null) {

            if (inputLine.equalsIgnoreCase("sair")) {
                System.out.println("Sair detectado, fechando servidor...");
                break;
            }

            outputLine = processar(inputLine);
             out.println(outputLine);
        }
        out.close();
        in.close();
        clientSocket.close();
        serverSocket.close();
    }

    private static String processar(String inputLine) {
        final String ARQUIVO_NAO_ENCONTRADO = "arquivo não encontrado.";
        final String ARQUIVO_IO = "erro ao ler arquivo.";

        System.out.println("Procurando arquivo: " + inputLine);
        File f = new File(inputLine);
        try {
            BufferedReader input =  new BufferedReader(new FileReader(f));
            String linha = null;
            StringBuffer retorno = new StringBuffer();

            retorno.append("\\n");
            retorno.append("Arquivo encontrado, lendo conteudo: " + inputLine + "\\n");
            while (( linha = input.readLine()) != null){
                  retorno.append(linha  + "\\n");
            }
            retorno.append("fim da leitura do arquivo\\n");
            return retorno.toString();
        } catch (FileNotFoundException e) {
            return ARQUIVO_NAO_ENCONTRADO;
        } catch (IOException e) {
            return ARQUIVO_IO;
        }
    }
}

Answer 1

当然，这可以使用UDP数据报来完成。 但是，由于UDP本身不提供可靠性或有序的数据包传送，因此将更加困难。 您的应用程序需要这些功能才能将文件传送到客户端。 如果选择使用UDP，则需要编写额外的代码来完成此操作。 您确定您真的要使用UDP吗？

如果您像上面的示例一样选择TCP，则无需担心字节以正确的顺序到达那里。

首先，我将研究Sun Datagram教程中的一些示例

Answer 2

我建议检查UDP协议（ RFC 768 ），然后使用一些基本示例。 UDP和Java有很多示例（例如Java教程->网络 ）

Answer 3

我同意Daniel H的观点。您还应该专门查看java.net.DatagramSocket 。

Answer 4

我想知道您是否对TCP和UDP感到困惑？ 您的代码在类名中引用了TCP等，但是您在谈论UDP？ 这些都是使用IP的不同协议，但是具有不同的特征。 可靠性/碎片化/复制等

看到这里的差异。