Java请求文件，发送文件(客户端-服务器) [英] Java request file, send file (Client-server)

问题描述

我正在制作一个客户端-服务器.我已经知道服务器可以发送硬编码文件，但不能发送指定的客户端.我将只需要发送文本文件.据我所知:客户端首先发送文件名，然后服务器发送它，没有什么复杂的，但是我遇到了各种各样的错误，这段代码出现了连接重置/套接字关闭错误.主要问题是，没有太多时间研究网络.

I'm making a Client-Server. I've gotten as far as that the server can send a hardcoded file, but not a client specified. I will have to send only text files. As far as I have understood: the clients firstly sends the file name and then, the server sends it, nothing complicated, but I'm getting all kinds of errors, this code is getting a connection reset/socket closed error. The main problem is, that hadn't got much time to research networking.

非常感谢我能得到的任何帮助.

Ill appreciate any help I can get.

编辑.我找到了一个解决方法，关闭流会导致套接字关闭，这是为什么?这不应该发生，是吗?

EDIT. I found a work around, closing a stream causes the socket to close, why is that? It shouldn't happen, should it?

服务器端:

    InputStream sin=newCon.getInputStream();
    DataInputStream sdata=new DataInputStream(sin);
    location=sdata.readUTF();   
    //sdata.close();
    //sin.close();

File toSend=new File(location);
byte[] array=new byte[(int)toSend.length()];
FileInputStream fromFile=new FileInputStream(toSend);
BufferedInputStream toBuffer=new BufferedInputStream(fromFile);
toBuffer.read(array,0,array.length);

OutputStream out=newCon.getOutputStream(); //Socket-closed...
out.write(array,0,array.length);
out.flush();
toBuffer.close();
newCon.close();

客户端:

int bytesRead;
server=new Socket(host,port);

OutputStream sout=server.getOutputStream();
DataOutputStream sdata=new DataOutputStream(sout);
sdata.writeUTF(interestFile);
//sdata.close();
//sout.close();

InputStream in=server.getInputStream();     //socket closed..
OutputStream out=new FileOutputStream("data.txt");
byte[] buffer=new byte[1024];
while((bytesRead=in.read(buffer))!=-1)
{
    out.write(buffer,0,bytesRead);
}
out.close();
server.close();

推荐答案

尝试在写入客户端输出流的同时从服务器以块的形式读取文件，而不是创建临时字节数组并将整个文件读入内存.如果请求的文件很大怎么办?还要在 finally 块中关闭服务器端的新 Socket，这样即使抛出异常，socket 也会关闭.

Try reading the file in chunks from Server while writing to client output stream rather than creating a temp byte array and reading entire file into memory. What if requested file is large? Also close the new Socket on server-side in a finally block so socket is closed even if an exception is thrown.

服务器端:

    Socket newCon = ss.accept();
    FileInputStream is = null;
    OutputStream out = null;
    try {
        InputStream sin = newCon.getInputStream();
        DataInputStream sdata = new DataInputStream(sin);
        String location = sdata.readUTF();
        System.out.println("location=" + location);
        File toSend = new File(location);
        // TODO: validate file is safe to access here
        if (!toSend.exists()) {
            System.out.println("File does not exist");
            return;
        }
        is = new FileInputStream(toSend);
        out = newCon.getOutputStream();
        int bytesRead;
        byte[] buffer = new byte[4096];
        while ((bytesRead = is.read(buffer)) != -1) {
            out.write(buffer, 0, bytesRead);
        }
        out.flush();
    } finally {
        if (out != null)
            try {
               out.close();
            } catch(IOException e) {
            }
        if (is != null)
            try {
               is.close();
            } catch(IOException e) {
            }
        newCon.close();
    }

如果您使用 Apache Common IOUtils 库，那么您可以减少大部分代码以进行读/写文件到流.这里是 5 行到 1 行.

If you use Apache Common IOUtils library then you can reduce much of the code to read/write files to streams. Here 5-lines down to one line.

org.apache.commons.io.IOUtils.copy(is, out);

请注意，使用通过绝对路径向远程客户端提供文件的服务器具有潜在危险，目标文件应限制为给定目录和/或文件类型集.不想向未经身份验证的客户提供系统级文件.

Note that having a server that serves files by absolute path to remote clients is potentially dangerous and the target file should be restricted to a given directory and/or set of file types. Don't want to serve out system-level files to unauthenticated clients.

这篇关于Java请求文件，发送文件(客户端-服务器)的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！