如何同时向两个java.io.OutputStream对象写入数据？

Question

我正在寻找神奇的 Java 类，它可以让我做这样的事情：

ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
FileOutputStream fileStream = new FileOutputStream(new File("/tmp/somefile"));

MultiOutputStream outStream = new MultiOutputStream(byteStream, fileStream);

outStream.write("Hello world".getBytes());

基本上，我想要

tee

来表示 Java 中的

OutputStream

。有什么想法吗？

谢谢！

Answer 1

尝试 Apache Commons TeeOutputStream。

Answer 2

自己动手。根本没有任何魔法。使用 Apache 的 TeeOutputStream 您基本上可以使用下面的代码。当然，使用 Apache Commons I/O 库，您可以利用其他类，但有时“实际上”为自己编写一些东西是很好的。 :)

public final class TeeOutputStream extends OutputStream {

  private final OutputStream out;
  private final OutputStream tee;

  public TeeOutputStream(OutputStream out, OutputStream tee) {
    if (out == null)
      throw new NullPointerException();
    else if (tee == null)
      throw new NullPointerException();

    this.out = out;
    this.tee = tee;
  }

  @Override
  public void write(int b) throws IOException {
    out.write(b);
    tee.write(b);
  }

  @Override
  public void write(byte[] b) throws IOException {
    out.write(b);
    tee.write(b);
  }

  @Override
  public void write(byte[] b, int off, int len) throws IOException {
    out.write(b, off, len);
    tee.write(b, off, len);
  }

  @Override
  public void flush() throws IOException {
    out.flush();
    tee.flush();
  }

  @Override
  public void close() throws IOException {
    try {
      out.close();
    } finally {
      tee.close();
    }
  }
}

使用上面的类进行测试，如下

public static void main(String[] args) throws IOException {
  TeeOutputStream out = new TeeOutputStream(System.out, System.out);
  out.write("Hello world!".getBytes());
  out.flush();
  out.close();
}

会打印 

Hello World!Hello World!

。

（注意：被覆盖的

close()

可能需要一些小心：）

Answer 3

Answer 4

package Core;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;

public class MultiOutputStream extends OutputStream {

private List<OutputStream> out;

public MultiOutputStream(List<OutputStream> outStreams) {

    this.out = new LinkedList<OutputStream>();

    for (Iterator<OutputStream> i = outStreams.iterator(); i.hasNext();) {
        OutputStream outputStream = (OutputStream) i.next();

        if(outputStream == null){
            throw new NullPointerException();
        }
        this.out.add(outputStream);
    }
}

@Override
public void write(int arg0) throws IOException {

    for (Iterator<OutputStream> i = out.iterator(); i.hasNext();) {
        OutputStream var = (OutputStream) i.next();

        var.write(arg0);
    }
}

@Override
public void write(byte[] b) throws IOException{

    for (Iterator<OutputStream> i = out.iterator(); i.hasNext();) {
        OutputStream var = (OutputStream) i.next();

        var.write(b);
    }
}

@Override
public void write(byte[] b, int off, int len) throws IOException{

    for (Iterator<OutputStream> i = out.iterator(); i.hasNext();) {
        OutputStream var = (OutputStream) i.next();

        var.write(b, off, len);
    }
}

@Override
public void close() throws IOException{

    for (Iterator<OutputStream> i = out.iterator(); i.hasNext();) {
        OutputStream var = (OutputStream) i.next();

        var.close();
    }
}

@Override
public void flush() throws IOException{

    for (Iterator<OutputStream> i = out.iterator(); i.hasNext();) {
        OutputStream var = (OutputStream) i.next();

        var.flush();
    }
}

}

到目前为止工作正常，只是测试了一些基本操作，例如从 System.out Stream 设置一个 MultiOutputStream 和 2 个 PrintStream，每个 PrintStream 写入一个单独的日志。
我用过

System.setOut(multiOutputStream);

写入我的终端屏幕和两个日志，没有任何问题。

Answer 5

ArrayList<OutputStream>

或当今流行的任何东西来存储您想要的所有流，并编写

write

方法来循环所有流，写入每个流。

Answer 6

public static void main(String[] args) throws IOException {

    System.setOut(new PrintStream(new TeeOutputStream(System.out, new PrintStream("out.log"))));
    System.setErr(new PrintStream(new TeeOutputStream(System.err, new PrintStream("err.log"))));
...