J Kneeland

Well,as you may know, you use Buffers to work with NIO channels. You can get an object into a byte array by using an ObjectOutputStream wrapped around a ByteArrayOutputStream. After you are done writing the object, you can get the array from the ByteArrayOutputStream by calling its toByteArray() method which returns a byte array. Now that you have the object in a byte array, you need to get it into a Buffer. The best choice for this is the ByteBuffer class since it is implemented using a byte array internaly. You can obtain a ByteBUffer object that contains this data by calling the static method wrap(byte[]) and passing the byte array you had. You can now send the data through the channel by calling it's write(Buffer) method and passing the buffer. In order to retrieve the data using NIO, you would do the exact opposite using the input stream complements to the output streams you used.

Done using NIO SocketChannels:
* Note, not accounting for exceptions. Catch them yourself *

if(channel.isWriteable()) { sc = (SocketChannel) channel; ByteArrayOutputStream baos = new ByteArrayOutputStream(); //make a BAOS stream ObjectOutputStream oos = new ObjectOutputStream(baos); // wrap and OOS around the stream oos.write(new Integer(5)); // write an object to the stream byte[] objData = baos.toByteArray(); // get the byte array ByteBuffer buffer = ByteBuffer.wrap(objData); // wrap around the data buffer.flip(); //prep for writing sc.write(buffer); //write }

You need to be using the file scheme to do that. new URL("file://....."); The file is supposed to be on the same machine and it is just another way of giving the location on the system. You probably need to figure out another way instead of using Files.

http://64.233.179.104/search?q=cache:nq74MZJIs30J:forum.java.sun.com/thread.jsp%3Fforum%3D11%26thread%3D543017%26tstart%3D60%26trange%3D15+SocketChannel+close&hl=en

I am trying to make a download manager. I am using a class download that will do most of the work and will allow you to use multiple connections like FlashGet or the like.

Here is a proof of concept class that copies a file using more than one thread at the same time. The only problem I have is that I can't figure out how change the number of threads after download.

Current algorithm:

1) Call to copy()
2) It makes x amount of Threads using Thread(this) and runs them
3) Check if the length of the destination file is set - set it
4) Divide the file length by the number of threads; multiply this by the id of the thread and you get the end position ; id -1 for the start postion
5)Synch on the file and seek to the current position
6)Read
7)Synch on the other file and seek to the current position
8)Write
9)Go to 5 till you have read till stop

Anyone got any ideas on how to allow it to resize the partitions and add/remove threads?

import java.io.*; import java.net.*; public class RAFCopy implements Runnable { private int numberOfThreads; private int threadId = 1; private RandomAccessFile destination = null; private RandomAccessFile source = null; public RAFCopy(File from, File to, int threads) { try { this.destination = new RandomAccessFile(to, "rw"); this.source = new RandomAccessFile(from, "r"); numberOfThreads = threads; this.destination.seek(0); this.source.seek(0); } catch(IOException ioe) { } } public RAFCopy(File from, File to) { this(from,to,2); } public void copy() { for(int i = 0; i < this.numberOfThreads; i++) { Thread t = new Thread(this); t.start(); } } public void run() { //catch all try { int start; int stop; int position; int id; Object synchObjForId = new Object(); //check length if((destination.length() == 0) && (source.length() == 0)) { //is the source empty? if(source.length() == 0) { //return then - nothing to copy return; } //set the length so you can copy byte for byte else { destination.setLength(source.length()); } } //get positions & id - make sure we aren't extra if(threadId > numberOfThreads) { //we are too many, the file has already been divided enough return; } else { //we are id number threadId - increment it after synchronized(synchObjForId) { id = threadId++; } //get positions start = Math.round((source.length() / this.numberOfThreads) * (id -1)); stop = Math.round((source.length() / this.numberOfThreads) * id); position = start; } //copy byte[] buffer = new byte[1024]; while(true) { int bytesRead= 0; //read until the end of the segment or the buffer - whichever is shorter int howFarToRead = 0; //buffer is too much if(position + buffer.length > stop) { howFarToRead = (int) (stop - position); } //buffer length is fine else { howFarToRead = buffer.length; } //anything left? if(howFarToRead == 0) { //nope return; } //read synchronized(source) { source.seek(position); bytesRead = source.read(buffer,0, howFarToRead); } //check for EOF - should never get here; see howFarToRead if(bytesRead == -1) { return; } //write synchronized(destination) { destination.seek(position); destination.write(buffer, 0, bytesRead); } //increment the position by the bytes read position += bytesRead; } } catch(IOException ioe) { } } public static void main(String args[]) { RAFCopy rc = new RAFCopy(new File(args[0]), new File(args[1]) , Integer.parseInt(args[2])); rc.copy(); } }

That was what I was looking for.


Thanks Mike

Originally posted by Jeanne Boyarsky:
You also want to make sure you download and study the case study from the AP test web site.

Yes, I was also going to do that.

Thanks

The only problem with this is it has to go into a ByteBuffer. I guess I could store it into a ShortBuffer though.

Edit: Yeah, I need a ByteBuffer so I need an array of bytes.

Thanks
[ September 25, 2004: Message edited by: J Kneeland ]

Do I see prefix arithmetic?


I noticed that about most Java books. They tended to cover way more than was required like Applets and graphics which they don't even talk about on the test. I was looking for something pretty bareboned, but I will look in to this book

Thanks
[ September 24, 2004: Message edited by: J Kneeland ]

I found some code used as an example of how to get the time since 1900 and unsinged 32 bit number for implenting a time server.

long differenceBetweenEpochs = 2208988800L; long msSince1970 = now.getTime( ); long secondsSince1970 = msSince1970/1000; long secondsSince1900 = secondsSince1970 + differenceBetweenEpochs; byte[] time = new byte[4]; time[0] = (byte) ((secondsSince1900 & 0x00000000FF000000L) >> 24); time[1] = (byte) ((secondsSince1900 & 0x0000000000FF0000L) >> 16); time[2] = (byte) ((secondsSince1900 & 0x000000000000FF00L) >> 8); time[3] = (byte) (secondsSince1900 & 0x00000000000000FFL);

Well it doesn't seem to work and this is the first time I have used bit wise operators before. Anyone spot the problem?

I know Java pretty well if you don't count graphics or applets. I was wondering what you would suggest for studying for the AP CS test. I was going to take the AP class, but they notified me at the last minute that they figured out that I would have to pass a C++ course in two weeks and make a 90. Well, this wasn't working to well for me, so I think I may take the test by myself. What review books and study guides are good?

You have the right idea, but wrong way. Look at the system.exec() method. It returns a Process object on which you can get an input stream and and output stream to talk to it.

I am using telnet to test it out. I telnet in and it works find, but it always says I'm still connected on the other side. I can even call isConnected(); on the channel and it still returns true. You need Java 1.5 to compile this since I am using BlockingQueue and Generics. You can find the precompiled versions at http://files.amdfanboy.com under JChat.

//main chat program import java.net.*; import java.nio.*; import java.nio.channels.*; import java.io.*; public class JChatServer { public static void main(String[] args) { ChatController controller = new ChatController(); try { ServerSocketChannel ssc = ServerSocketChannel.open(); ssc.configureBlocking(true); ssc.socket().bind(new InetSocketAddress(70)); while(true) { ChatThread t = new ChatThread(ssc.accept(), controller); controller.register(t); t.start(); } } catch(IOException ioe) { System.out.println(ioe); } } } //chat controller import java.util.*; public class ChatController { //ArrayList of the ChatThreads that have been registered private ArrayList<ChatThread> registeredThreads; //makes a new chatcontoller public ChatController() { this.registeredThreads = new ArrayList<ChatThread>(); } //adds ct to registeredThreads public boolean register(ChatThread ct) { this.registeredThreads.add(ct); return true; } //removes ct from registeredThreads public boolean unregister(ChatThread ct) { return this.registeredThreads.remove(ct); } //distributes a message to all the threads located registerThreads //using the addMessage(Message) method public void pushToAll(Message m) { for(ChatThread ct : this.registeredThreads) { ct.addMessage(m); } } //shuts down all the threads in registeredThreads b calling their //shutdown() method public void shutdownThreads() { for(ChatThread ct : this.registeredThreads) { ct.shutdown(); } } } ///the worker thread import java.util.concurrent.*; import java.io.*; import java.nio.*; import java.nio.channels.*; public class ChatThread extends Thread { //queue of messages private BlockingQueue<Message> queue; //channel to use private SocketChannel channel; //controller that was set in the constructor private ChatController controller; //shutdown flag; run checks if it should return based on it private boolean shutdown = false; //makes a new ChatThread object public ChatThread(SocketChannel sc, ChatController cc) { this.channel = sc; this.controller = cc; this.queue = new LinkedBlockingQueue<Message>(); } //used to run as thread public void run() { try { this.channel.configureBlocking(false); } catch(IOException ioe) { } while(!shutdown) { try { if(!this.channel.isConnected()) { throw new IOException("Disconnected"); } this.readMessage(); this.pushMessages(); TimeUnit.SECONDS.sleep(1); } catch(IOException ioe) { System.out.println(ioe); shutdown(); break; } catch(InterruptedException ie) { } } } //read the message from the channel or return if there is nothing to read //i.e. non-blocking; assumes channel is already non-blocking public void readMessage() throws IOException { if(!this.channel.isConnected()) { throw new IOException("Disconnected"); } System.out.println("Reading"); try { ByteBuffer buffer = ByteBuffer.allocate(1024); StringBuilder strBuild = new StringBuilder(); buffer.clear(); boolean readMessage = false; while(this.channel.read(buffer) > 0) { buffer.flip(); for(int i = 0; i < buffer.limit(); i++) { strBuild.append((char) buffer.get(i)); } buffer.clear(); readMessage = true; } System.out.println("Done Reading"); if(readMessage) { this.controller.pushToAll(new Message(strBuild.toString())); } } catch(IOException ioe) { System.out.println(ioe); throw ioe; } } //pushes all messages currently in queue and pushes //them out to the clients with ObjectOutputStreams //(temp sets blocking to true) public void pushMessages() throws IOException { System.out.println("Pushing messages"); try { if(!this.channel.isConnected()) { throw new IOException("Disconnected"); } this.channel.configureBlocking(true); while(this.queue.size() > 0) { Message m = this.queue.poll(); ObjectOutputStream oos = new ObjectOutputStream(this.channel.socket().getOutputStream()); oos.writeObject(m); } this.channel.configureBlocking(false); } catch(IOException ioe) { System.out.println(ioe); throw ioe; } } //adds Message m to queue(BlockingQueue) public boolean addMessage(Message m) { boolean answer = this.queue.offer(m); System.out.println("Got a message"); return answer; } //shuts down this thread by stting the shutdown flag to true //and also unregisters this from the conroller public void shutdown() { //deregister this.controller.unregister(this); this.shutdown = true; } } ///message class, used only internal so far public class Message extends Object implements java.io.Serializable { private String data; public Message(String s) { this.data = s; } public String getData() { return data; } }

I guess I didn't see that, thanks

Any open source Java project that wouldn't mind someone who has a reasonable amount of experience(Intermediate?)? I would really like a chance to use Java networking(esp java.nio) and become more proficient in it. If at all possible, I prefer smaller groups. (people < 20)

THX

I would like to ask about any open source Java project that wouldn't mind someone who has a reasonable amount of experience(Intermediate?). I would really like a chance to use Java networking(esp java.nio) and become more proficient in it.

Thanks