filetrasmission.java

用Java写的收发文件的简单实例

package jave_default;

import java.io.*; 
import java.net.ServerSocket; 
import java.net.Socket; 

/** 
* 简单的文件发送与接收示例 
*/ 
public class FileTrasmission { 

//程序入口 
public static void main(String[] args) throws Exception { 
int port = 7788; 
new Server(port, "c:\\save\\").start(); 
new Client().sendFile("127.0.0.1", port, "c:\\123.txt"); 
} 
} 

/** 
* 接收端。可同时接收多个发送端发来的文件。但如果发来的文件是同名的话那就乱了。 
*/ 
class Server { 

private int listenPort; 

private String savePath; 

/** 
* 构造方法 
* 
* @param listenPort 侦听端口 
* @param savePath 接收的文件要保存的路径 
* 
* @throws IOException 如果创建保存路径失败 
*/ 
Server(int listenPort, String savePath) throws IOException { 
this.listenPort = listenPort; 
this.savePath = savePath; 

File file = new File(savePath); 
if (!file.exists() && !file.mkdirs()) { 
throw new IOException("无法创建文件夹 " + savePath); 
} 
} 

// 开始侦听 
public void start() { 
new ListenThread().start(); 
} 

// 网上抄来的，将字节转成 int。b 长度不得小于 4，且只会取前 4 位。 
public static int b2i(byte[] b) { 
int value = 0; 
for (int i = 0; i < 4; i++) { 
int shift = (4 - 1 - i) * 8; 
value += (b[i] & 0x000000FF) << shift; 
} 
return value; 
} 


/** 
* 侦听线程 
*/ 
private class ListenThread extends Thread { 

@Override 
public void run() { 
try { 
ServerSocket server = new ServerSocket(listenPort); 

// 开始循环 
while (true) { 
Socket socket = server.accept(); 
new HandleThread(socket).start(); 
} 
} catch (IOException e) { 
e.printStackTrace(); 
} 
} 
} 

/** 
* 读取流并保存文件的线程 
*/ 
private class HandleThread extends Thread { 

private Socket socket; 

private HandleThread(Socket socket) { 
this.socket = socket; 
} 

@Override 
public void run() { 
try { 
InputStream is = socket.getInputStream(); 
readAndSave(is); 
} catch (IOException e) { 
e.printStackTrace(); 
} finally { 
try { 
socket.close(); 
} catch (IOException e) { 
// nothing to do 
} 
} 
} 

// 从流中读取内容并保存 
private void readAndSave(InputStream is) throws IOException { 
String filename = getFileName(is); 
int file_len = readInteger(is); 
System.out.println("接收文件：" + filename + "，长度：" + file_len); 

readAndSave0(is, savePath + filename, file_len); 

System.out.println("文件保存成功（" + file_len + "字节）。"); 
} 

private void readAndSave0(InputStream is, String path, int file_len) throws IOException { 
FileOutputStream os = getFileOS(path); 
readAndWrite(is, os, file_len); 
os.close(); 
} 

// 边读边写，直到读取 size 个字节 
private void readAndWrite(InputStream is, FileOutputStream os, int size) throws IOException { 
byte[] buffer = new byte[4096]; 
int count = 0; 
while (count < size) { 
int n = is.read(buffer); 
// 这里没有考虑 n = -1 的情况 
os.write(buffer, 0, n); 
count += n; 
} 
} 

// 读取文件名 
private String getFileName(InputStream is) throws IOException { 
int name_len = readInteger(is); 
byte[] result = new byte[name_len]; 
is.read(result); 
return new String(result); 
} 

// 读取一个数字 
private int readInteger(InputStream is) throws IOException { 
byte[] bytes = new byte[4]; 
is.read(bytes); 
return b2i(bytes); 
} 

// 创建文件并返回输出流 
private FileOutputStream getFileOS(String path) throws IOException { 
File file = new File(path); 
if (!file.exists()) { 
file.createNewFile(); 
} 

return new FileOutputStream(file); 
} 
} 
} 

/** 
* 发送端 
*/ 
class Client { 

// 网上抄来的，将 int 转成字节 
public static byte[] i2b(int i) { 
return new byte[]{ 
(byte) ((i >> 24) & 0xFF), 
(byte) ((i >> 16) & 0xFF), 
(byte) ((i >> 8) & 0xFF), 
(byte) (i & 0xFF) 
}; 
} 

/** 
* 发送文件。文件大小不能大于 {@link Integer#MAX_VALUE} 
* 
* @param hostname 接收端主机名或 IP 地址 
* @param port 接收端端口号 
* @param filepath 文件路径 
* 
* @throws IOException 如果读取文件或发送失败 
*/ 
public void sendFile(String hostname, int port, String filepath) throws IOException { 
File file = new File(filepath); 
FileInputStream is = new FileInputStream(filepath); 

Socket socket = new Socket(hostname, port); 
OutputStream os = socket.getOutputStream(); 

try { 
int length = (int) file.length(); 
System.out.println("发送文件：" + file.getName() + "，长度：" + length); 

// 发送文件名和文件内容 
writeFileName(file, os); 
writeFileContent(is, os, length); 
} finally { 
os.close(); 
is.close(); 
} 
} 

// 输出文件内容 
private void writeFileContent(InputStream is, OutputStream os, int length) throws IOException { 
// 输出文件长度 
os.write(i2b(length)); 

// 输出文件内容 
byte[] buffer = new byte[4096]; 
int size; 
while ((size = is.read(buffer)) != -1) { 
os.write(buffer, 0, size); 
} 
} 

// 输出文件名 
private void writeFileName(File file, OutputStream os) throws IOException { 
byte[] fn_bytes = file.getName().getBytes(); 

os.write(i2b(fn_bytes.length)); // 输出文件名长度 
os.write(fn_bytes); // 输出文件名 
} 
}