среда, 5 ноября 2008 г.

Reading from InputStream

Lately I've faced a simple problem: I needed to read all bytes from the InputStream. I didn't know type of the InputStream, so, I've spent more then two hours solving this problem without any success. I didn't want to read each byte from the stream. All evening I could think only about this problem. Solution turned to be very simple! I found a sample in the JDK installation directory($JAVA_HOME/sample/nio/). JDK 1.5(and higher) is a good API to work with streams over channels. The source code to read all bytes from the InputStream is rather simple:

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.Reader;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.ReadableByteChannel;

/**
 * @author Pokidov.Dmitry
 *         Date: 13.04.2009
 */
public class IOHelper {
 /*Block size that we want to read in one time.*/
 private static final int READ_BLOCK = 8192; 

 /*
  * Read all from stream, using nio.
  * @param is source stream.
  * @return result byte array that read from source
  * @throws IOException by {@code Channel.read()}
  */
 public static byte[] readToEnd(InputStream is) throws IOException {
  //create channel for input stream
  ReadableByteChannel bc = Channels.newChannel(is);
  ByteBuffer bb = ByteBuffer.allocate(READ_BLOCK);

  while (bc.read(bb) != -1) {
   bb = resizeBuffer(bb); //get new buffer for read
  }
  byte[] result = new byte[bb.position()];
  bb.position(0);
  bb.get(result);

  return result;
 }

 private static ByteBuffer resizeBuffer(ByteBuffer in) {
  ByteBuffer result = in;
  if (in.remaining() < READ_BLOCK) {
   //create new buffer
   result = ByteBuffer.allocate(in.capacity() * 2);
   //set limit to current position in buffer and set position to zero.
   in.flip();
   //put original buffer to new buffer
   result.put(in);
  }

  return result;
 }

Also I found an interesting book in which you can read about the nio package: get it here

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