package sterning;

import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class ServerTest {
int port = 8821;

void start() {
Socket s = null;
try {
ServerSocket ss = new ServerSocket(port);
while (true) {
// 选择进行传输的文件
String filePath = "D:\lib.rar";
File fi = new File(filePath);

System.out.println("文件长度:" + (int) fi.length());

// public Socket accept() throws
// IOException侦听并接受到此套接字的连接。此方法在进行连接之前一直阻塞。

s = ss.accept();
System.out.println("建立socket链接");
DataInputStream dis = new DataInputStream(new BufferedInputStream(
s.getInputStream()));
dis.readByte();

DataInputStream fis = new DataInputStream(new BufferedInputStream(
new FileInputStream(filePath)));
DataOutputStream ps = new DataOutputStream(s.getOutputStream());
//将文件名及长度传给客户端。这里要真正适用所有平台，例如中文名的处理，
//还需要加工，具体可以参见Think In Java 4th里有现成的代码。
ps.writeUTF(fi.getName());
ps.flush();
ps.writeLong((long) fi.length());
ps.flush();

int bufferSize = 8192;
byte[] buf = new byte[bufferSize];

while (true) {
int read = 0;
if (fis != null) {
read = fis.read(buf);
}

if (read == -1) {
break;
}
ps.write(buf, 0, read);
}
ps.flush();
// 注意关闭socket链接哦，不然客户端会等待server的数据过来，
// 直到socket超时，导致数据不完整。
fis.close();
s.close();
System.out.println("文件传输完成");
}

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

public static void main(String arg[]) {
new ServerTest().start();
}
}



2.socket的Util辅助类



package sterning;

import java.net.*;
import java.io.*;

public class ClientSocket {
private String ip;

private int port;

private Socket socket = null;

DataOutputStream out = null;

DataInputStream getMessageStream = null;

public ClientSocket(String ip, int port) {
this.ip = ip;
this.port = port;
}

/** *//**
* 创建socket连接
*
* @throws Exception
* exception
*/
public void CreateConnection() throws Exception {
try {
socket = new Socket(ip, port);
} catch (Exception e) {
e.printStackTrace();
if (socket != null)
socket.close();
throw e;
} finally {
}
}

public void sendMessage(String sendMessage) throws Exception {
try {
out = new DataOutputStream(socket.getOutputStream());
if (sendMessage.equals("Windows")) {
out.writeByte(0x1);
out.flush();
return;
}
if (sendMessage.equals("Unix")) {
out.writeByte(0x2);
out.flush();
return;
}
if (sendMessage.equals("Linux")) {
out.writeByte(0x3);
out.flush();
} else {
out.writeUTF(sendMessage);
out.flush();
}
} catch (Exception e) {
e.printStackTrace();
if (out != null)
out.close();
throw e;
} finally {
}
}

public DataInputStream getMessageStream() throws Exception {
try {
getMessageStream = new DataInputStream(new BufferedInputStream(
socket.getInputStream()));
return getMessageStream;
} catch (Exception e) {
e.printStackTrace();
if (getMessageStream != null)
getMessageStream.close();
throw e;
} finally {
}
}

public void shutDownConnection() {
try {
if (out != null)
out.close();
if (getMessageStream != null)
getMessageStream.close();
if (socket != null)
socket.close();
} catch (Exception e) {

}
}
}



3.客户端



package sterning;

import java.io.BufferedOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileOutputStream;

public class ClientTest {
private ClientSocket cs = null;

private String ip = "localhost"; // 设置成服务器IP

private int port = 8821;

private String sendMessage = "Windwos";

public ClientTest() {
try {
if (createConnection()) {
sendMessage();
getMessage();
}

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

private boolean createConnection() {
cs = new ClientSocket(ip, port);
try {
cs.CreateConnection();
System.out.print("连接服务器成功!" + "
");
return true;
} catch (Exception e) {
System.out.print("连接服务器失败!" + "
");
return false;
}

}

private void sendMessage() {
if (cs == null)
return;
try {
cs.sendMessage(sendMessage);
} catch (Exception e) {
System.out.print("发送消息失败!" + "
");
}
}

private void getMessage() {
if (cs == null)
return;
DataInputStream inputStream = null;
try {
inputStream = cs.getMessageStream();
} catch (Exception e) {
System.out.print("接收消息缓存错误
");
return;
}

try {
//本地保存路径，文件名会自动从服务器端继承而来。
String savePath = "E:\";
int bufferSize = 8192;
byte[] buf = new byte[bufferSize];
int passedlen = 0;
long len=0;

savePath += inputStream.readUTF();
DataOutputStream fileOut = new DataOutputStream(new BufferedOutputStream(
new BufferedOutputStream(new FileOutputStream(savePath))));
len = inputStream.readLong();

System.out.println("文件的长度为:" + len + "
");
System.out.println("开始接收文件!" + "
");

while (true) {
int read = 0;
if (inputStream != null) {
read = inputStream.read(buf);
}
passedlen += read;
if (read == -1) {
break;
}
//下面进度条本为图形界面的prograssBar做的，这里如果是打文件，
//可能会重复打印出一些相同的百分比
System.out.println("文件接收了" + (passedlen * 100/ len) + "%
");
fileOut.write(buf, 0, read);
}
System.out.println("接收完成，文件存为" + savePath + "
");

fileOut.close();
} catch (Exception e) {
System.out.println("接收消息错误" + "
");
return;
}
}

public static void main(String arg[]) {
new ClientTest();
}
}


这就实现了从服务器端向客户端发送文件的过程,当然,反过来,也一样.稍有不同.代码中对跨平台的细节没有实现,有时间或兴趣的朋友可以提供一下