问题
Is there a more concise/standard idiom (e.g., a JDK method) for "piping" an input to an output in Java than the following?
public void pipe(Reader in, Writer out) {
CharBuffer buf = CharBuffer.allocate(DEFAULT_BUFFER_SIZE);
while (in.read(buf) >= 0 ) {
out.append(buf.flip());
buf.clear();
}
}
[EDIT] Please note the Reader and Writer are given. The correct answer will demonstrate how to take in and out and form a pipe (preferably with no more than 1 or 2 method calls). I will accept answers where in and out are an InputStream and an OutputStream (preferably with a conversion from/to Reader/Writer). I will not accept answers where either in or out is a subclass of Reader/InputStream or Writer/OutputStrem.
回答1:
IOUtils from the Apache Commons project has a number of utilily methods that do exactly what you need.
IOUtils.copy(in, out) will perform a buffered copy of all input to the output. If there is more than one spot in your codebase that requires Stream or Reader/Writer handling, using IOUtils could be a good idea.
回答2:
Take a look at java.io.PipedInputStream and PipedOutputStream, or PipedReader/PipedWriter from the same package.
From the Documentation of PipedInputStream:
A piped input stream should be connected to a piped output stream; the piped input stream then provides whatever data bytes are written to the piped output stream. 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. The piped input stream contains a buffer, decoupling read operations from write operations, within limits. A pipe is said to be broken if a thread that was providing data bytes to the connected piped output stream is no longer alive.
回答3:
The only optimization available is through FileChannels in the NIO API: Reads, Writes. The JVM can optimize this call to move the data from a file to a destination Channel without first having to move the data to kernel space. See this article for details.
来源：https://stackoverflow.com/questions/127753/java-idiom-for-piping