Java中如何将OutputStream转换为InputStream？

如何将 OutputStream 转换为 InputStream

在软件开发中，经常会遇到需要将数据从一个流转换为一个流的情况。流类型到另一个。其中一种场景是将 OutputStream 转换为 InputStream。

管道流简介

这个问题的解决方案在于使用 Java 的 PipedInputStream 和 PipedOutputStream 类。这些类通过创建双向管道来实现流之间的通信。

PipedInputStream 到 OutputStream（反之亦然）

Lambda 表达式：

PipedInputStream in = new PipedInputStream();
final PipedOutputStream out = new PipedOutputStream(in);
// in a background thread, write the given output stream to the PipedOutputStream for consumption
new Thread(() -> {
    originalOutputStream.writeTo(out);
}).start();

注意： 必须处理 OutputStream 可能过早关闭的情况，从而导致 ClosedPipeException。为了避免这种情况，您可以反转构造函数：

PipedInputStream in = new PipedInputStream(out);
new Thread(() -> {
    originalOutputStream.writeTo(out);
}).start();

Try-With-Resources:

// take the copy of the stream and re-write it to an InputStream
PipedInputStream in = new PipedInputStream();
new Thread(new Runnable() {
    public void run() {
        // try-with-resources here
        // putting the try block outside the Thread will cause the PipedOutputStream resource to close before the Runnable finishes
        try (final PipedOutputStream out = new PipedOutputStream(in)) {
            // write the original OutputStream to the PipedOutputStream
            // note that in order for the below method to work, you need to ensure that the data has finished writing to the ByteArrayOutputStream
            originalByteArrayOutputStream.writeTo(out);
        } catch (IOException e) {
            // logging and exception handling should go here
        }
    }
}).start();

PipedOutputStream 到 InputStream

如果您没有 ByteArrayOutputStream，可以使用以下代码：

PipedInputStream in = new PipedInputStream();
final PipedOutputStream out = new PipedOutputStream(in);
new Thread(new Runnable() {
    public void run() {
        try {
            // write the original OutputStream to the PipedOutputStream
            // note that in order for the below method to work, you need to ensure that the data has finished writing to the OutputStream
            originalOutputStream.writeTo(out);
        } catch (IOException e) {
            // logging and exception handling should go here
        } finally {
            // close the PipedOutputStream here because we're done writing data
            // once this thread has completed its run
            if (out != null) {
                // close the PipedOutputStream cleanly
                out.close();
            }
        }
    }
}).start();

使用管道流有几个好处，包括：

• 并发性：数据传输发生在单独的线程中，从而实现并行处理。
• 内存效率：管道流避免创建额外的缓冲区副本，从而减少内存消耗。

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