All About Android Overview

Outline
Java network programming overview
Android Overview
Android Emulator Overview
Project Overview
Getting Started

Java Network Programming
• Java.net.* programming model
– Blocking model, you wait until work is done, maybe
forever
– One thread required per connection
– Socket exposes input and output stream

• Java.nio.* programming model
– Introduced in Java 1.4, non-blocking IO
– New Interface: SocketChannel (in java.nio.channels)
– Reading/writing via Buffer objects rather than
input/output streams
– Select() implemented

Java.net.* Socket API
• Part of the java.net package
– import java.net.*;

• Provides two classes of sockets for TCP
– Socket : client side of socket
– ServerSocket : server side of socket

• Provides one socket type for UDP
– DatagramSocket

Java.net.Socket
• Making a connection
Socket s = new Socket(“hostname”, port);
• The constructor not only creates a socket, but
makes a TCP connection.
• Socket exposes input and output stream.

s.getOutputStream()
s.getInputStream()

• Most of the time you'll chain the input/output
stream to some other input/output stream or
reader object to more easily handle the data.

Java.net.Socket
• Create a print stream for writing
– OutputStream rawOut =
socket.getOutputStream();
– PrintStream pout = new PrintStream(rawOut);
• Create a data output stream for writing
– BufferedOutputStream buffOut = new
BufferedOutputStream(rawOut);
– out =new DataOutputStream(buffOut);

• Create a data input stream for reading
DataInputStream din =
new DataInputStream(socket.getInputStream());
Java.net.ServerSocket
• Server Side socket
• To support multiple clients servers have
at least one thread per clien
ServerSocket svr = new ServerSocket(port);
while (Socket s = svr.accept())
new EchoThread(s).start();
Java.net and Thread
class EchoThread extends Thread {
EchoThread(Socket s) { ... }
public void run() {
// waits for data and reads it in until connection dies
// readLine() blocks until the server receives a new line from client
String s;
while ((s = in.readLine()) != null) {
out.println(s);
}

Reference for Java Network Programming
• http://java.sun.com/docs/books/tutorial/net
working/sockets/index.html

Android
• Software platform on mobile device by Open
Handset Alliance (Google)
• Developing language is Java
• Linux kernel (Open Source)
• Provides a development kit (SDK)
• Emulator support with some limitation

Developing Android Application
• There are four building blocks to an Android
application:

– Activity
– Service
– Broadcast Intent Receiver
– Content Provider

• http://code.google.com/android/intro/anatomy.html

Developing Android Application
– Controls a single screen
– Usually starts up with an app, multiple Activity(screen) is
associated to an app
– Intent is used to move from screen to screen
– A Service is code that is long-lived and runs without a UI
– E.g. Network I/O, playback of media files

• Not using these components correctly can result in the system killing
the application's process while it is doing important work.

Project 1
– Develop a file sharing application where updates get
synchronized when users come across within
communication range

– Implement service discovery
– Establish a TCP connection between every pair of
nodes in range
– Due Feb 5. 2 weeks from now.

Getting Started
• Setting up the environment (Installation)
– Section 3.1 of the project document
– Use the pre-installed binaries on AFS
– Copy the binaries from AFS
– Install yourself

• Need eclipse, Java SDK 1.5/1.6, android SDK,
eclipse plug-in

Getting Started
• Starting the project on Eclipse
– Download project file
– Open the project in Eclipse (read the documentation)

• Running the local server
– Local server controls the connection between Android
emulators
– Implemented in Ruby binds port 10001 ~ 10010
– Need eventmachine Ruby lib
– setenv RUBYLIB
/afs/cs.cmu.edu/project/cmcl-srini-4/15-
446/android/eventmachine-0.12.2/lib

Emulator

Emulator
• Running the emulator
– Stand-alone (./emulator)
– Eclipse Plug-in (Just ‘Run’ it as Android application)

• Binds to port 5554~5580
– Don’t run on shared machines

• adb (Android Debugging Bridge)
– Using adb, we can connect to android’s shell
– Logcat (demo)

Running multiple emulators
• Manual mode will let you do this
– Menu: Run  Run Configurations
– Go to Android Applications on the left tab and
select FileSharerActivityProject
– Click on Target tab and select “maunal” mode
– When you run you can specify to launch a new
emulator or use existing ones to run the app

• To use adb you have to specify the emulator
device name if there are multiple emulators
• #adb –s emulator-5554 shell

Configurations
• XML file defines a connectivity
<?xml version="1.0" encoding="UTF-8" ?>
<connectivity time="2" nodes="2">
<connect node1="0" node2="1" at="1" />
</connectivity>

Project API
• Broadcast Interface
– BroadcastReceiveCallBack
– CS446Bcast

• Socket API (blocking IO)
– CS446ServerSocket
– CS446Socket
– getMyID() returns the ID of the emulator

Broadcast Interface
• BroadcastReceiveCallBack
– BcastMsgReceived(byte []msg, int srcID) gets
called when a broadcast message is received from
srcID. Msg is the byte array of the content.
– open() : returns CS446Bcast
– send(byte [] msg): sends a broadcast message

Socket
• CS446ServerSocket
– There can be only one server socket. ServerSocket
always binds to port 0.
– open(): returns a CS446ServerSocket
– accept(): Listens for a incoming connection and
returns a CS446Socket when a connection is
established
– close(): closes the socket
– isClosed(): returns boolean

Socket
– CS446Socket(int peerID): opens a socket and makes a
connection to peerID, always use local port 1 remote
port 0 when making a active connection
– void close()
– int getLocalPort()
– int getPort()
– int getPeerID()
– int getLocalID()
– OutputStream getOutputStream()
– InputStream getInputStream()

2nd part of project 1
• You will be given a workload of users updating
file.
• You will need to keep a version vector and
synchronize the content.
• Details will be posted soon