JAVA AJAX聊天室

package dwr.classes; import java.util.ArrayList; import java.util.Hashtable; import util.StaticUserList; import beans.Message; public class DWRChat { private static ArrayList<Message> commonMessages = new ArrayList<Message>(); private static Hashtable<String, ArrayList<Message>> singleMessageHash = new Hashtable<String, ArrayList<Message>>(); @SuppressWarnings("unchecked") public ArrayList<Message> getPrivateMessages(String username) { if (singleMessageHash.get(username) != null) { return singleMessageHash.get(username); } return null; } public ArrayList<Message> getCommonMessages() { return commonMessages; } public void sendMessage(Message message) { if (!message.getTarget().equals("all")) { ArrayList<Message> tosave = singleMessageHash.get(message .getTarget()); if (tosave == null) { tosave = new ArrayList<Message>(); singleMessageHash.put(message.getTarget(), tosave); } tosave.add(message); } else if (message.getTarget().equals("all")) { commonMessages.add(message); } } public ArrayList<String> getUserList(String[] oldusers) { Hashtable<String, String> userhash = StaticUserList.getUserlist(); ArrayList<String> olduserlist = new ArrayList<String>(); ArrayList<String> userlist = new ArrayList<String>(); for (String username : oldusers) { olduserlist.add(username); } for (String username : userhash.values()) { userlist.add(username); } for (String username : userlist) { if (!olduserlist.contains(username)) { return userlist; } } for (String username : olduserlist) { if (!userlist.contains(username)) { return userlist; } } return null; } }