用Java写一个S3ObjectInputStream转换为OutputStream的接口返回值为OutputStream

可以使用Java标准库中的PipedInputStream和PipedOutputStream来实现S3ObjectInputStream转换为OutputStream。具体实现代码如下：

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;

import com.amazonaws.services.s3.model.S3ObjectInputStream;

public class S3ObjectInputStreamConverter {
    public static OutputStream convert(S3ObjectInputStream s3is) throws IOException {
        PipedInputStream pis = new PipedInputStream();
        PipedOutputStream pos = new PipedOutputStream(pis);

        // 将S3ObjectInputStream的数据写入PipedOutputStream
        new Thread(() -> {
            try {
                byte[] buffer = new byte[1024];
                int len;
                while ((len = s3is.read(buffer)) != -1) {
                    pos.write(buffer, 0, len);
                }
                s3is.close();
                pos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }).start();

        return pos;
    }
}

使用时，只需要调用`S3ObjectInputStreamConverter.convert()`方法，将S3ObjectInputStream作为参数传入即可。

S3ObjectInputStream s3is = ...;
OutputStream os = S3ObjectInputStreamConverter.convert(s3is);