ICOM 4015-Advanced Programming. Spring Instructor: Dr. Amir H. Chinaei. TAs: Hector Franqui, Jose Garcia, and Antonio Tapia. Reference: Big Java

Transcription

1 ICOM 4015-Advanced Programming Spring 2014 Instructor: Dr. Amir H. Chinaei TAs: Hector Franqui, Jose Garcia, and Antonio Tapia Reference: Big Java By Hortsmann, Ed 4 Lab 7 Continuation of HTTP and Introduction to Sockets Department of Electrical and Computer Engineering University of Puerto Rico at Mayagüez

2 Before the Lab: 1- Read about Sockets in the Java Tutorials 2- Read about Threads in the Java Tutorials 3- Read about String manipulation methods, such as trim(), split() and replace() During the Lab: 1- Login to the computer (1 minute) 2- More about HTTP requests (50 minutes) - In the previous lab, we began our study of HTTP requests. Using them, we were able to enter a chat room and register a user in a chat application. - Today, we are going to continue our study by going deeper into how communication occurs between clients and servers. - We already know that: o In almost every circumstance, clients always begin communication. This communication is normally called a request. o The server is to answer the client s request. The server, under almost every circumstance, must answer to the client. This answer is normally called a response. The server may give two types of responses: A handshake is a response the server gives when the client sends data to it. Normally, the handshake is just an acknowledge to the client to let it know it received data successfully. A data response is a response when the server returns data that the client requested. o There are many ways or mediums for servers and clients to exchange information. This ways or mediums are called protocols. We are studying the HTTP protocol right now. o However, HTTP is just a way to exchange data. The server and the client must agree on what data they exchange. There are many ways to do this. In particular, a commonly used standard is JSON, which you used in the past lab. o What data do servers and client exchanges? On normal operations, it is just a bunch of strings. o These strings contain text that must follow a format in order for the server and client understand what each wants to say (much as humans do). However, we as programmers specify and implement that format and process the text to extract the information we need. o This is what we are going to do today.

3 - Now, we are going to revisit very similar functionality to what we did in last lab. The application has been simplified: there is only one chat room for everyone that enters the app. - We want the server to know (in other words send to the server information) when: o When a new user registers o When we send a message o When we exit the room - We want to know from the server: o A new user (other user) registers o A new message is sent by other user - We are going to implement this functionality by sending Strings to the server whose text values are written in the following format: o registeruser?<username> o sendmessage?<username>;<message> o removeuserrequest?<username> o newuserrequest o newmessagerequest - Note: In the previous format, anything enclosed on < and > brackets denotes a variable. If the username variable is Jose, then the format would be registeruser?jose. - The server is to respond, correspondingly using String with text values in the following format: o userregistered o messagereceived o removalsuccess o <username1;message1,username2;message2,...,usernamen, messagen> OR nonewmessage (if no message has arrived) o <username1,username2,...,usernamen> OR nonewuser (if no user has been registered) - Go to and download the project zip file. It should have the name ICOM4015Lab7-1.zip. Save it in any place you want, as long as you remember the location. - Import the project in Eclipse by clicking File > Import... > General > Existing Project into Workspace > Select archive file and browse to the location where you stored the zip file. - Click Finish.

4 - Once imported, open the class ChatEngine.java. NOTE: Read all steps up to the point where you are supposed to show code to your instructor before proceeding. o Look for the method enterroom(string username). o Read the code and understand the comments. Finish its implementation by completing the code there. Notice the String message is following the format specified above! o Now, basing your work in what you have done in the enterroom() method, finish the implementation the sendmessage(string message) and removeuser() methods. - Show your work to the instructor (20 points) - Now, look at the method hasnewuserarrived(). What should it do? o This method must return true if there s a new user from the server. In other words, if we sent a specific request to the server inquiring if there are new users, we should receive an answer. If this answer is negative, we must return false. o If there s a new user, assign the server s response to the instance variable newuser. Trim the server s response. o Now, finish the implementation of this method basing yourself on the format. - Implement now, in a very similar way, the hasnewmessagearrived() method. o If there are new messages, assign the server s answer to instance variable newmessage. - If everything is correctly implemented, you should run the class ChatRunner.java and see what happens. You should be able to connect to a chat room and chat with other users. - If so, show your work to the instructor (20 points) 3- Introduction to Sockets (70 minutes) - HTTP is a great way to communicate, but is not the only one. - Actually, HTTP works over something called a socket. Your TA should give a brief talk about Sockets and Threads (10 minutes). - In this part of the lab, we are modifying the chat application to work with sockets and not HTTP requests. - Furthermore, we are going to build the server of the chat application. o Notice that in the previous part, the server was already implemented. The reason why you don t see it is because it s not written in Java, but in

5 Javascript. Javascript is nothing like Java, just the name and the syntax looks kind of similar. o The server made in Javascript was based on a technology called Node.js. It s excellent for this kind of applications. o We could also build this server in Java and using HTTP requests, by using something called a Web Socket. However, it s preferred you understand the behavior of sockets in general, as that will help you understand by your own the web socket. - Go to and download the project zip file. It should have the name ICOM4015Lab7-2.zip. Download it to any place you want. - Import the project in Eclipse by File > Import... > General > Existing Project into Workspace > Select archive file. Now browse to the location you downloaded the zip file. - Once imported, go to the ChatEngine.java class. o At the beginning of the file, add to your instance fields the following variables: private Socket clientsocket; private PrintWriter out; private BufferedReader in; o Now, go to the enterroom() method. Initialize the clientsocket instance variable. Initialize using the already existing server and port variables. Initialize the PrintWriter out variable. Use the clientsocket s output stream for initializing the PrintWriter. Initialize the BufferedReader in variable. Use the clientsocket s input stream for initializing the BufferedReader. o Go to the removeuser() method. Close the clientsocket at the end of this method. o Go to the sendrequest() method. o Notice that this method has been changed. We are going to change only this method and leave the rest of the program as it is whenever possible. Send the parameters variable through the socket by printing to the out variable (Hint: much like System.out...). Assign the response of the server to a new String variable. Wait for this new variable to not be null. When it s not null, return it. - Show your work to the instructor (20 points)

6 - Now, we are going to work with the server. Create a new class and name it SocketServer. - Add the following code to your class: public class SocketServer { private static ArrayList<String> registeredusers, sentmessages; private static boolean newuser, newmessage; private static int newusersfetched, newmessagesfetched, sentmessagespos; private static class ServerThread implements Runnable { private Socket socket; public ServerThread(Socket socket) { this.socket = socket; System.out.println("Socket public void run() { public static void main(string[] args) throws IOException { boolean listening = true;

7 newmessage = newuser = false; registeredusers = new ArrayList<String>(); sentmessages = new ArrayList<String>(); newmessagesfetched = newusersfetched = sentmessagespos = 0; ServerSocket serversocket = new ServerSocket(8080); while (listening) { System.out.println("Listening on "); (new Thread(new ServerThread(serverSocket.accept()))).start(); - Let s start by going to the run() method inside the ServerThread inner class. o The run() method will specify what a thread will do when it s executed. o Initialize the following variables using the same code you used in the enterroom() method of the ChatEngine class. Of course, make sure socket s variable name agrees... PrintWriter out =... BufferedReader in =... o Note: Declaring these will make Eclipse complain and ask you for a try block. Keep the rest of the code inside the try block. o Declare a new String, input. o Now we must check what the value of input is. Remember the format? The client will send us some strings in a specific format. We now must interpret that format and answer the client correspondingly. o Copy the following code after you declare the input variable: do { if (input.contains("registeruser")) { String[] splitresult = input.split(... )

8 String username =... registeredusers.add(...); output = "..."; newuser = true; out.println(output); // Rest of code here... while ((input = in.readline())!= null); socket.close(); o Inside the if statement: Basing yourself on the format, process the string input. You want the username part of that String. You must use the split() method to obtain the username part. HINT: What divides the username from the other string, registeruser? Replace the... with that divider. You must precede the divider by two backslashes. If the divider is x, your method should look like input.split( \\x ); The username is now on the second element of the array Add the user to the registeredusers ArrayList. Replace the... with the name of the corresponding variable. Answer the client by telling it that the user was registered (Hint: remember the format...). Replace the... with the text in the appropriate format. o Add an else if statement and check if input contains information for sending a message (Hint: what is the format for the client to send a message?) In a very similar way to the previous method, implement the server action for when a client sends a message.

9 Remember to split the incoming input String. You may need to do two splits. o Add another else if statement and check if the input contains information for removing a user. In a very similar way to the previous two, implement this method. Notice some points: Now we must remove a user, not add it. Removing a user means the client is closing. Close the socket too. Even if there s no new user added, the variable newuser must be set to true (why?) - Show your work to the instructor (20 points) - The next step is to implement the functionality to let the client know if new messages or new users have arrived. - Copy the following code after your last else if statement: else if (input.contains("newuserrequest")) { if (newuser == true) { if (newusersfetched < registeredusers.size()) { else { // Your code to prepare the response and send here newuser = false; newusersfetched = 0; // Your code for notifying no new users here else { // Your code for notifying no new users here else if (input.contains("newmessagerequest")) {

10 if (newmessage == true) { if (newmessagesfetched < registeredusers.size()) { // Your code to prepare the response and send here else { newmessage = false; newmessagesfetched = 0; sentmessagespos = sentmessages.size(); // Your code for notifying no new messages here else { // Your code for notifying no new messages here - For the new user request action, do the following: o Increment the amount of newusersfetched variable. o Declare a new String variable, result. o Iterate over the whole registeredusers ArrayList and add to the result variable each element of registeredusers followed by a comma,. o Write the result into the socket. o In the other else statements, write to the socket the value that indicates the client there s no new users (Hint: the format...) - In a very similar way, implement the new message request action. o Notice the following points: Instead of iterating from zero, you should start at the variable sentmessagepos. Instead of adding a, following each message, you should add the following: %MessageSeparator% - Show your work to the instructor (20 points).

11 - Now, run your server first by right clicking the SocketServer.java class in the Package Explorer and selecting Run As > Java Application. - Right click the ChatRunner.java class and run it by selecting Run As > Java Application. - Test your chat client. It should work for just one user. If it does, then try opening another chat client by right-clicking the ChatRunner.java class and selecting Run As > Java Application. - If everything works, you should see exactly the same behavior as with the HTTP chat server. - Show you work to the instructor (20 points) After the Lab: 1- Investigate a little bit about inner classes 2- Think on how today s lab can help you to develop Project 2

12 Evaluating Lab 6 Write Your Section# here:.. Please evaluate the quality of the lab and performance of the instructors by filling up the following table and give it to your lab representative. (Choose 5 as the highest and 1 as the lowest grade). The lab started on time SHARP. Items The instructor was able to help you during the HTTP part and answer questions. The instructor gave an understandable presentation of Socket and Threads and followed timeline. The instructor was able to help you during the implementation of the server in the Sockets part. The instructor overall followed the specified timeline for each step You found the lab today overall Great (helpful, fruitful, interesting, etc.). Evaluating Lab 6 Write Your Section# here:.. Please evaluate the quality of the lab and performance of the instructors by filling up the following table and give it to your lab representative. (Choose 5 as the highest and 1 as the lowest grade). The lab started on time SHARP. Items The instructor was able to help you during the HTTP part and answer questions. The instructor gave an understandable presentation of Socket and Threads and followed timeline. The instructor was able to help you during the implementation of the server in the Sockets part. The instructor overall followed the specified timeline for each step You found the lab today overall Great (helpful, fruitful, interesting, etc.).

13