How to convert outputStream to a byte array?

Question

How can I convert an OutputStream to a byte array? I have found that first I need to convert this OutputStream to a ByteArrayOutputStream. There is only write() method in this OutputStream class and I don't know what to do. Is there any idea?

Answer 1

Create a ByteArrayOutputStream .

Grab its content by calling toByteArray()

ByteArrayOutputStream baos = new ByteArrayOutputStream(); 
baos.writeTo(myOutputStream); 
baos.toByteArray();

Reference

Answer 2

If the OutputStream object supplied is not already a ByteArrayOutputStream , one can wrap it inside a delegate class that will "grab" the bytes supplied to the write() methods, eg

public class DrainableOutputStream extends FilterOutputStream {
  private final ByteArrayOutputStream buffer;
  public DrainableOutputStream(OutputStream out) {
    super(out);
    this.buffer = new ByteArrayOutputStream();
  }
  @Override
  public void write(byte b[]) throws IOException {
    this.buffer.write(b);
    super.write(b);
  }
  @Override
  public void write(byte b[], int off, int len) throws IOException {
    this.buffer.write(b, off, len);
    super.write(b, off, len);
  }
  @Override
  public void write(int b) throws IOException {
    this.buffer.write(b);    
    super.write(b);
  }
  public byte[] toByteArray() {
    return this.buffer.toByteArray();
  }
}

To reduce the overhead, the calls to super in the above class can be omitted - eg, if only the "conversion" to a byte array is desired.

A more detailed discussion can be found in another StackOverflow question .

Answer 3

You need to do 2 things

• Using ByteArrayOutputStream write to it
• Using toByteArray(), you will get the contents as byte[]

You could even extend it as mentioned here

Answer 4

您可以简单地将输出流声明为ByteArrayOutputStream然后使用ByteArrayOutputStream#toByteArray() 。

Answer 5

If You try ByteArrayOutputStream bos=(ByteArrayOutputStream)outputStream then throw ClassCastException . I did it when I get OutputStream from HttpServletResponse and it is CoyoteOutputStream .(You can create file so dont create file temp).

You can use Java Reflection to convert OutputStream to byte[] :

 byte[] bytes = this.getBytes(outStream);

/**
 * Get byte from OutputStream
 *
 * @param outStream
 * @return
 */
@SneakyThrows
private byte[] getBytes(OutputStream outStream) {
    OutputBuffer outputBuffer = (OutputBuffer) this.getValueByName("ob", outStream);
    ByteBuffer byteBuffer = (ByteBuffer) this.getValueByName("bb", outputBuffer);
    return (byte[]) this.getValueByName("hb", byteBuffer);
}

/**
 * Get value from property
 *
 * @param name
 * @param value
 * @return
 */
@SneakyThrows
@SuppressWarnings("unchecked")
private Object getValueByName(String name, Object value) {
    List<Field> listFiled = new ArrayList<>();
    if (value.getClass().getSuperclass() != null) {
        listFiled.addAll(Arrays.asList(value.getClass().getSuperclass().getDeclaredFields()));
    }
    listFiled.addAll(Arrays.asList(value.getClass().getDeclaredFields()));
    Optional<Field> fieldOb = listFiled.stream()
        .filter(field -> StringUtils.equalsAnyIgnoreCase(name, field.getName()))
        .findFirst();
    if (fieldOb.isPresent()) {
        Field field = fieldOb.get();
        field.setAccessible(true);
        return field.get(value);
    }
    return StringUtils.EMPTY; // FIXME
}