为什么没有更多的 Java 代码使用 PipedInputStream/PipedOutputStream? [英] Why doesn't more Java code use PipedInputStream / PipedOutputStream?

问题描述

我最近发现了这个成语，我想知道我是否遗漏了什么.我从未见过它被使用过.我在野外使用过的几乎所有 Java 代码都倾向于将数据放入字符串或缓冲区中，而不是像这个例子那样(例如使用 HttpClient 和 XML API):

I've discovered this idiom recently, and I am wondering if there is something I am missing. I've never seen it used. Nearly all Java code I've worked with in the wild favors slurping data into a string or buffer, rather than something like this example (using HttpClient and XML APIs for example):

    final LSOutput output; // XML stuff initialized elsewhere
    final LSSerializer serializer;
    final Document doc;
    // ...
    PostMethod post; // HttpClient post request
    final PipedOutputStream source = new PipedOutputStream();
    PipedInputStream sink = new PipedInputStream(source);
    // ...
    executor.execute(new Runnable() {
            public void run() {
                output.setByteStream(source);
                serializer.write(doc, output);
                try {
                    source.close();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }});

    post.setRequestEntity(new InputStreamRequestEntity(sink));
    int status = httpClient.executeMethod(post);

该代码使用 Unix 管道风格技术来防止将 XML 数据的多个副本保存在内存中.它使用 HTTP Post 输出流和 DOM Load/Save API 将 XML 文档序列化为 HTTP 请求的内容.据我所知，它通过很少的额外代码(只有 Runnable、PipedInputStream 和 PipedOutputStream 的几行代码)最大限度地减少了内存的使用).

That code uses a Unix-piping style technique to prevent multiple copies of the XML data being kept in memory. It uses the HTTP Post output stream and the DOM Load/Save API to serialize an XML Document as the content of the HTTP request. As far as I can tell it minimizes the use of memory with very little extra code (just the few lines for Runnable, PipedInputStream, and PipedOutputStream).

那么，这个习语有什么问题?如果这个成语没毛病，我怎么没看到?

So, what's wrong with this idiom? If there's nothing wrong with this idiom, why haven't I seen it?

澄清一下，PipedInputStream 和 PipedOutputStream 替换了随处可见的样板缓冲区副本，它们还允许您同时处理传入数据写出处理后的数据.他们不使用操作系统管道.

to clarify, PipedInputStream and PipedOutputStream replace the boilerplate buffer-by-buffer copy that shows up everywhere, and they also allow you to process incoming data concurrently with writing out the processed data. They don't use OS pipes.

推荐答案

来自 Javadocs:

通常，数据由一个线程从 PipedInputStream 对象读取，数据由其他线程写入相应的 PipedOutputStream.不建议尝试从单个线程使用两个对象，因为这可能会使线程死锁.

Typically, data is read from a PipedInputStream object by one thread and data is written to the corresponding PipedOutputStream by some other thread. Attempting to use both objects from a single thread is not recommended, as it may deadlock the thread.

这或许可以部分解释为什么它不常用.

This may partially explain why it is not more commonly used.

我认为另一个原因是许多开发人员不了解其目的/好处.

I'd assume another reason is that many developers do not understand its purpose / benefit.

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