套接字上的 Java 流属性 [英] Java streaming Properties over Socket

问题描述

首先，这是一道作业题.话虽这么说，我被卡住了.在套接字上搜索 java 属性会导致很多不相关的事情.

First of all, this is a homework problem. That being said, I'm stuck. Googling for java Properties over Sockets results in a lot of irrelevant things.

我正在尝试通过套接字传输 Properties 对象.API 说它可以用 Stream 或 Writer/Reader 来完成，但我无法让它工作.我可以手动完成，也就是说，如果我逐行读取文件并通过 PrintWriter 传递它.

I'm trying to transfer a Properties object over a socket. The API says it can be done with a Stream or a Writer/Reader, but I can't get it to work. I can do it manually, that is, if I read the file line by line and pass it through a PrintWriter.

在客户端，我大致了解:

On the client side I've got roughly:

socket = new Socket(host, port);
outStream = socket.getOutputStream();
out = new PrintWriter(outStream, true);
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
reader = new BufferedReader(new FileReader(file));
...
props.load(reader);
props.store(out, null);

在服务器端，接收位看起来像:

On the server side the receiving bits look like:

out = new PrintWriter(sock.getOutputStream(), true);
inStream = sock.getInputStream();
in = new BufferedReader( new InputStreamReader(inStream));
...
props.load(in); // hangs
// doesn't get to code here...

在这种情况下，它挂在 props.load(in) 上.我没有执行 props.load(in)，而是逐行读取它以确保 props.store(out, null) 正常工作，并且数据看起来像是在传输.

In this case it hangs at the props.load(in). Instead of doing props.load(in), I read it in line by line to make sure props.store(out, null) was working, and the data looks like its being transferred.

是否有关于加载/存储的问题我不明白，或者是 Stream/Writer/Reader 的问题?

Is there something about load/store I don't understand, or is it an issue with the Stream/Writer/Reader?

推荐答案

我认为这将回答这个问题以及 如何识别 Java 套接字中的 EOF? 和 我可以向 InputStream 发送什么来表示已达到 EOF?

I think this will answer this question as well as How do I recognize EOF in Java Sockets? and What can I send to an InputStream to signify EOF has been reached?

我遇到了类似的问题；我的困境是我有一个客户端/服务器请求-响应协议，其中一个请求包括使用 clientProps.store() 从客户端发送的流.服务器端相应的 serverProps.load() 永远不会返回，因为它需要查看文件结尾"——这在 Java 中意味着客户端必须关闭它的流；导致套接字连接关闭.不想要的结果是，我不仅不能为无限期的请求-响应交换保持套接字打开，我什至不能保持它打开以便服务器发送其回复.

I had a similar problem; my dilemma was that I had a client/server request-response protocol where one of the requests included a stream sent from the client side using clientProps.store(). The corresponding serverProps.load() on the server side never returns because it needs to see the "end-of-file" - which in Java means the client has to close it's stream; resulting in the socket connection closing. The unwanted result was that, not only could I not keep the socket open for indefinite request-response exchanges, I couldn't even keep it open for the server to send its reply.

我讨厌 Java 让我这样做，更因为 Properties.load() 的文档说:

I hated Java for making me do that, even more because the documentation for Properties.load() says:

此方法返回后，指定的流保持打开状态.

The specified stream remains open after this method returns.

如果它通过看到流关闭来检测文件结尾，那永远不会发生！！无论如何，现在，我仍然喜欢 Java，因为它允许我使用此解决方案(如果您对流式传输的数据有任何特殊编码或本地化，则可能没有用):

That could never happen if it's detecting end-of-file by seeing the stream close!! Anyway, now, I still love Java because it allowed me to use this solution (might not be useful if you have any special encoding or localization of the data you are streaming):

我在客户端使用了这个:

I used this on the client side:

    PrintWriter toServer;
    Properties clientProps = new Properties();

//  ... code to populate the properties and to 
//      construct toServer from the socket ...

    clientProps.store(toServer, null);
    toServer.write('\u001A'); // this is an old-school ASCII end-of-file
    toServer.flush();

在服务器端，我扩展了 Reader 以检测 1A 并返回 -1(以便 serverProps.load() 以正常方式了解文件结尾(通过查看 -1 从对 read()) 的调用返回，但在下面，流和套接字保持打开状态.

On the server side I extended Reader to detect the 1A and return -1 (so that the serverProps.load() learns about the end-of-file in the normal way (by seeing -1 returned from a call to read()), but below that, the stream and the socket stay open.

    BufferedReader fromClient;
    Properties serverProps = new Properties();


// ... code to construct fromClient from the socket ...

    serverProps.load (new PropReader (fromClient));

/////

    private static class PropReader extends Reader {

    BufferedReader src;
    boolean eof=false;

    private PropReader(BufferedReader fromClient) {
        super();
        src=fromClient;
    }


    @Override
    public int read(char[] cbuf, int off, int len) throws IOException {
        int inCount;

        if (!eof) {
            inCount = src.read(cbuf, off, len);

            if (inCount > 0) {
                // we read a buffer... look at the end for the EOF that the client used to mark the end of file
                if (cbuf[off+inCount-1] == '\u001A') {
                    --inCount; // don't send eof with the data
                    eof = true; // next time... we'll return -1
                }
            }
        } else {
            inCount = -1;
        }

        return inCount;
    }

    @Override
    public void close() throws IOException {
        src.close();
    }

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