java - SelectionKey iterator.remove() throws UnsupportedOperationException and infinite loop -

i have method opens connection, queries site, gets number of pages , uses nio concurrently retrieve of pages. first query done using urlconnection , works fine. running in 2 issues when try use nio selectors , channels:

1) if don't remove key iterator, in runs in infinite loop printing size() , sending queries. if try remove key, unsupportedoperationsexception. bah!

2) need deregister channel op_write after i've written socket? if so, can call channel.register(selector, selectionkey.op_read) remove interest in writing?

public void test() throws ioexception { // create selector selector selector = selector.open(); system.out.println("opened");  // number of pages url itemurl = new url(item_url); urlconnection conn = itemurl.openconnection(); conn.setdooutput(true); outputstreamwriter out = new outputstreamwriter(conn.getoutputstream()); // out.write(getheaderstring(itemurl)); out.write(new query("", "internal hard drives", false, false, true, false, -1, 7603, 1, 14, -1, "", "price", 1).tostring()); out.close();  jsonreader in = new jsonreader(new inputstreamreader(conn.getinputstream())); jsonparser parser = new jsonparser(); jsonobject tempobj = (jsonobject) parser.parse(in); pages.setnumofpages(getnumberofiterations(tempobj.get("paginationinfo"))); system.out.println("pages: " + pages.getnumofpages());      // each page, create channel, attach selector interest in read     // typically <= pages.getnumberofpages troubleshoot, i'm limiting once. (int = 1; <= 1; i++) {     socketchannel channel = socketchannel.open();     channel.configureblocking(false);     channel.connect(new inetsocketaddress(itemurl.gethost(), 80));     channel.register(selector, selectionkey.op_write | selectionkey.op_read); } selector.select(); set<selectionkey> sk = selector.keys();  while (!sk.isempty()) {     system.out.println(sk.size());     iterator<selectionkey> iterator = sk.iterator();     while (iterator.hasnext()) {     selectionkey key = iterator.next();              iterator.remove();     if (key.isreadable()) {         socketchannel channel = (socketchannel) key.channel();         bytebuffer buf = bytebuffer.allocate(8192);         channel.read(buf);         buf.flip();         product p = parse(buf, product.class);         if (p != null) {         finalitems.add(p);         system.out.println("item added!");         key.cancel();         }     } else if (key.iswritable()) {         socketchannel channel = (socketchannel) key.channel();         system.out.println(itemurl);         system.out.println(new query("", "internal hard drives", false, false, true,             false, -1, 7603, 1, 14, -1, "", "price", 1).tostring());         channel.write(bytebuffer.wrap(new query("", "internal hard drives", false,             false, true, false, -1, 7603, 1, 14, -1, "", "price", 1).tostring()             .getbytes()));      }     }     selector.select();     sk = selector.keys(); } } 

from http://docs.oracle.com/javase/6/docs/api/java/nio/channels/selector.html#keys()

"the key set not directly modifiable. key removed after has been cancelled , channel has been deregistered. attempt modify key set cause unsupportedoperationexception thrown."

you want using selector.selectedkeys();

"keys may removed from, not directly added to, selected-key set. attempt add object key set cause unsupportedoperationexception thrown."

selector.select(); set<selectionkey> sk = selector.selectedkeys(); 

and can use iterator.remove()

a example posted here http://tutorials.jenkov.com/java-nio/selectors.html @ bottom of page