Java - 一个 Reader 类，能够交错来自多个 Reader 的行

Question

我想要的是最终得到类似的东西:

public class InterleavedBufferedReader extends BufferedReader {
...
}

并将其用作:

Reader[3] readers = ...; // three readers
InterleavedBufferedReader ibr = new InterleavedBufferedReader(readers);

ibr.readLine();  // this returns the first line of Reader 1
ibr.readLine();  // this returns the first line of Reader 2
ibr.readLine();  // this returns the first line of Reader 3

ibr.readLine();  // this returns the second line of Reader 1
ibr.readLine();  // this returns the second line of Reader 2
ibr.readLine();  // hey, Reader 3 had no more lines, return the third line of Reader 1

我尝试过的(不好，我知道，这就是我在这里的原因):

public class InterleavedBufferedReader extends BufferedReader {

    static private int current = 0;
    private BufferedReader[] buffers;


    public InterleavedBufferedReader(BufferedReader[] in) {
        super(new StringReader("dummy"));
        buffers = in;
    }

    public InterleavedBufferedReader(Reader[] in) {
        super(new StringReader("dummy"));
        buffers = new BufferedReader[in.length];
        for (int i=0 ; i < in.length ; i++)
            buffers[i] = new BufferedReader(in[i]);
    }

    @Override
    public String readLine() throws IOException {
        int start = current;
        String line = null;
        while ((line = buffers[current].readLine()) == null) {
            current = (current+1) % buffers.length;
            if (current == start)
                return null;
        }       
        current = (current+1) % buffers.length;
        return line;

    }

    @Override 
    public void close() throws IOException {
        for (int i=0;  i < buffers.length; i++)
            buffers[i].close();
    }
}

评论:

交错readLine()实际上有效!

也许我不应该扩展 BufferedReader .我被迫给它一个虚拟的 Reader 来管理，否则它甚至不会编译。同时，我覆盖了 readLine()方法在 child 读者上调用它。但至少实现是不完整的，因为其他方法，如read() ，实际上是指我的虚拟读者。

我可以以更清洁的方式做到这一点吗？

Answer 1

Perhaps I shouldn't be extending BufferedReader. I'm forced to give it a dummy Reader to manage, or it won't even compile. [...] the implementation is at least incomplete, because other methods, as read(), will actually refer to my dummy reader

您可以而且应该覆盖 read() (和 ready() )也是如此。 readLine() 的实现必须保留，但至少您确定所有阅读方法都符合您希望实现的交错。虚拟阅读器无法避免，但您的实现可以。您甚至可能希望将 BufferedReader 的缓冲区设置为您可以使用的最低值 (1)，以减少内存浪费。

除此之外，您不能忘记流的标记支持:您必须通过覆盖 mark() 重新实现它。和 reset() ，或者只是覆盖 markSupported()所以它总是返回false。