尝试将 Apache Common exec 与 bytebuffer 一起使用以将输出从一个命令推送到 java 中的另一个命令

Question

我的计划是使用 ByteBuffer 和 Apache Common Exec 将一个命令的输出作为输入发送到另一个命令。

我可以使用 PipedOutputStream 和 PipedInputStream 来做到这一点，下面是工作正常的代码。

public static void testApacheCommons1() throws ExecuteException, IOException {
        PipedOutputStream ifOutputStream = new PipedOutputStream();
        PipedInputStream ifInputStream = new PipedInputStream();
        ifOutputStream.connect(ifInputStream);

        String readCommand = "sudo dd bs=1 count=30 if=" + "/dev/sdb1" + " skip=50k";
        CommandLine cmdLineForRead = CommandLine.parse(readCommand);
        DefaultExecutor executorRead = new DefaultExecutor();
        ExecuteStreamHandler executeReadStreamHandler = new PumpStreamHandler(ifOutputStream);
        executorRead.setStreamHandler(executeReadStreamHandler);
        executorRead.execute(cmdLineForRead, new DefaultExecuteResultHandler());

        String writeCommand = "sudo dd bs=1 of=" + "/dev/sdb2"+ " seek=50k";
        CommandLine cmdLineForWrite = CommandLine.parse(writeCommand);
        DefaultExecutor executorWrite = new DefaultExecutor();
        ExecuteStreamHandler executeWriteStreamHandler = new PumpStreamHandler(System.out, System.err, ifInputStream);
        executorWrite.setStreamHandler(executeWriteStreamHandler);
        executeWriteStreamHandler.start();
        executorWrite.execute(cmdLineForWrite, new DefaultExecuteResultHandler());
    }

上面的代码工作正常，但我想从第一个命令中获取输出，并将其放入 ByteBuffer 并将其作为下一个命令的输入提供。

下面是我正在尝试执行的代码，但它没有按预期工作（我能够看到缓冲区被填充但它没有写入磁盘，当我在上面的代码中发生这种情况时使用 PipedOutputStream 和 PipedInputStream).

在这种情况下，我使用的是 ByteBufferBackedOutputStream 和 ByteBufferBackedInputStream，它们是自定义的类，我在 SO 处从另一个 post 那里获得了实现。

public static void testApacheCommons() throws ExecuteException, IOException {

        ByteBuffer byteBuffer = ByteBuffer.allocate(30);

        String readCommand = "sudo dd bs=1 count=30 if=" + "/dev/sdb1" + " skip=50k";
        CommandLine cmdLineForRead = CommandLine.parse(readCommand);
        DefaultExecutor executorRead = new DefaultExecutor();
        ExecuteStreamHandler executeReadStreamHandler = new PumpStreamHandler(
                new ByteBufferBackedOutputStream(byteBuffer));
        executorRead.setStreamHandler(executeReadStreamHandler);
        executorRead.execute(cmdLineForRead, new DefaultExecuteResultHandler());

        String writeCommand = "sudo dd bs=1 of=" + "/dev/sdb2" + " seek=50k";
        CommandLine cmdLineForWrite = CommandLine.parse(writeCommand);

        DefaultExecutor executorWrite = new DefaultExecutor();
        ExecuteStreamHandler executeWriteStreamHandler = new PumpStreamHandler(System.out, System.err,
                new ByteBufferBackedInputStream(byteBuffer));
        executorWrite.setStreamHandler(executeWriteStreamHandler);
        executorWrite.execute(cmdLineForWrite, new DefaultExecuteResultHandler());

    }

public class ByteBufferBackedInputStream extends InputStream {

    ByteBuffer buf;

    public ByteBufferBackedInputStream(ByteBuffer buf) {
        this.buf = buf;
    }

    public int read() throws IOException {
        if (!buf.hasRemaining()) {
            return -1;
        }
        return buf.get() & 0xFF;
    }

    public int read(byte[] bytes, int off, int len) throws IOException {
        if (!buf.hasRemaining()) {
            return -1;
        }

        len = Math.min(len, buf.remaining());
        buf.get(bytes, off, len);
        return len;
    }
}



public class ByteBufferBackedOutputStream extends OutputStream {
    ByteBuffer buf;

    public ByteBufferBackedOutputStream(ByteBuffer buf) {
        this.buf = buf;
    }

    public void write(int b) throws IOException {
        buf.put((byte) b);
    }

    public void write(byte[] bytes, int off, int len) throws IOException {
        buf.put(bytes, off, len);
    }

}

Answer 1

好的，所以问题是 bytebuffer 的 position 位于最后一个位置，因此当写入发生时，它没有找到缓冲区中保存的元素。通过反复试验并遍历我开始了解的所有功能 buffer.rewind()

Buffer java.nio.Buffer.rewind() 
Rewinds this buffer. The position is set to zero and the mark is discarded.

所以在从磁盘读取运行 buffer.rewind() 之后，我能够看到写入磁盘的值。

尝试将 Apache Common exec 与 bytebuffer 一起使用以将输出从一个命令推送到 java 中的另一个命令

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