使用 Java 套接字发送文件，丢失数据 [英] Sending a file with Java Sockets, losing data
问题描述
我正在尝试使用 Java 套接字将文件从客户端发送到服务器.当我在同一台机器上测试时它工作正常，但是当我在不同的机器上测试时，我丢失了大量数据，导致文件损坏.如果我尝试发送一个非常小的文件(<20 字节)，它甚至不会到达服务器的 while 循环内的 println.
I'm trying to send a file from a client to a server with Sockets in Java. It works fine when I am testing on the same machine, but when I test across different machines, I lose large chunks of data, resulting in a corrupted file. If I try to send a very small file (<20 bytes), it doesn't even reach the println inside the server's while loop.
这是我的代码:
Server.java
package edu.mst.cs.sensorreceiver;
import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
public class Server {
private static final int PORT = 51111;
private static final int CHUNK_SIZE = 1024;
private static final File _downloadDir = new File("downloads/");
public static void main(String[] args) {
if (!_downloadDir.exists()) {
if (!_downloadDir.mkdirs()) {
System.err.println("Error: Could not create download directory");
}
}
Socket socket = null;
try {
ServerSocket server = new ServerSocket(PORT);
while (true) {
System.out.println("Waiting for connection...");
socket = server.accept();
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
String name = in.readLine();
File file = new File(_downloadDir, name);
String size = in.readLine();
int fileSize;
try {
fileSize = Integer.parseInt(size);
} catch (NumberFormatException e) {
System.err.println("Error: Malformed file size:" + size);
e.printStackTrace();
return;
}
System.out.println("Saving " + file + " from user... (" + fileSize + " bytes)");
saveFile(file, socket.getInputStream());
System.out.println("Finished downloading " + file + " from user.");
if (file.length() != fileSize) {
System.err.println("Error: file incomplete");
}
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (socket != null) {
try {
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
private static void saveFile(File file, InputStream inStream) {
FileOutputStream fileOut = null;
try {
fileOut = new FileOutputStream(file);
byte[] buffer = new byte[CHUNK_SIZE];
int bytesRead;
int pos = 0;
while ((bytesRead = inStream.read(buffer, 0, CHUNK_SIZE)) >= 0) {
pos += bytesRead;
System.out.println(pos + " bytes (" + bytesRead + " bytes read)");
fileOut.write(buffer, 0, bytesRead);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (fileOut != null) {
try {
fileOut.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
System.out.println("Finished, filesize = " + file.length());
}
}
Client.java
package edu.mst.cs.sensorreceiver;
import java.io.*;
import java.net.Socket;
public class Client {
private static final String HOSTNAME = "131.151.163.153";
private static final int PORT = 51111;
private static final int CHUNK_SIZE = 1024;
public static void main(String[] args) {
sendFile(args[0]);
}
private static void sendFile(String path) {
if (path == null) {
throw new NullPointerException("Path is null");
}
File file = new File(path);
Socket socket = null;
try {
System.out.println("Connecting to server...");
socket = new Socket(HOSTNAME, PORT);
System.out.println("Connected to server at " + socket.getInetAddress());
PrintStream out = new PrintStream(socket.getOutputStream(), true);
out.println(file.getName());
out.println(file.length());
System.out.println("Sending " + file.getName() + " (" + file.length() + " bytes) to server...");
writeFile(file, socket.getOutputStream());
System.out.println("Finished sending " + file.getName() + " to server");
} catch (IOException e) {
e.printStackTrace();
} finally {
if (socket != null) {
try {
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
private static void writeFile(File file, OutputStream outStream) {
FileInputStream reader = null;
try {
reader = new FileInputStream(file);
byte[] buffer = new byte[CHUNK_SIZE];
int pos = 0;
int bytesRead;
while ((bytesRead = reader.read(buffer, 0, CHUNK_SIZE)) >= 0) {
outStream.write(buffer, 0, bytesRead);
outStream.flush();
pos += bytesRead;
System.out.println(pos + " bytes (" + bytesRead + " bytes read)");
}
} catch (IndexOutOfBoundsException e) {
System.err.println("Error while reading file");
e.printStackTrace();
} catch (IOException e) {
System.err.println("Error while writing " + file.toString() + " to output stream");
e.printStackTrace();
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
我已经为此工作了几个小时，但几乎没有取得任何进展.我以为我对从流中读取/写入的工作方式有很好的理解，但显然我在这里遗漏了一些东西.
I've been working on this for hours and I have made almost no progress. I thought I had a pretty good understanding of how reading/writing from streams works, but clearly I'm missing something here.
同样，当我从同一台机器发送和接收时，一切正常.但是如果我尝试在两台计算机之间发送文件，即使两者在同一个局域网中，我也会丢失很多发送的数据.
Again, everything works perfectly when I am sending and receiving from the same machine. But if I try to send a file between two computers, even if the two are on the same LAN, I lose a lot of the data that was sent.
有人能解决我的问题吗?我已经尝试了所有我能想到的.
Can anybody figure out my problem? I've already tried everything I could think of.
推荐答案
您似乎在混合分块数据和面向行的操作.我建议你使用 DataInputStream 在服务器上，以及 数据输出流.从客户端开始，类似
You appear to be mixing chunked data and line oriented operation. I suggest you use a DataInputStream on the server, and a DataOutputStream. Starting on the client, something like
private static void sendFile(String path) {
if (path == null) {
throw new NullPointerException("Path is null");
}
File file = new File(path);
Socket socket = null;
try {
System.out.println("Connecting to server...");
socket = new Socket(HOSTNAME, PORT);
System.out.println("Connected to server at "
+ socket.getInetAddress());
try (DataOutputStream dos = new DataOutputStream(
new BufferedOutputStream(socket.getOutputStream()));) {
dos.writeUTF(file.getName());
dos.writeLong(file.length());
System.out.println("Sending " + file.getName() + " ("
+ file.length() + " bytes) to server...");
writeFile(file, dos);
System.out.println("Finished sending " + file.getName()
+ " to server");
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (socket != null) {
try {
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
然后在服务器上
socket = server.accept();
DataInputStream dis = new DataInputStream(socket.getInputStream());
String name = dis.readUTF();
File file = new File(_downloadDir, name);
long fileSize = dis.readLong();
System.out.println("Saving " + file + " from user... ("
+ fileSize + " bytes)");
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