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Java Programming Unit 10 Stock Price Quotes with URL, Sockets, and RMI (c) Yakov Fain 2014

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Page 1: JavaProgramming$$ Unit10$ - myflex.orgmyflex.org/yf/java/slides/Unit10.pdfWhat’s$Socket (c)$Yakov$Fain$$2014$ The$package$java.net$includes$classes$Socket$and$ ServerSocket. $ A$socketis$a

Java  Programming    Unit  10  

Stock  Price  Quotes  with  URL,  Sockets,  and  RMI    

(c)  Yakov  Fain    2014  

Page 2: JavaProgramming$$ Unit10$ - myflex.orgmyflex.org/yf/java/slides/Unit10.pdfWhat’s$Socket (c)$Yakov$Fain$$2014$ The$package$java.net$includes$classes$Socket$and$ ServerSocket. $ A$socketis$a

GeFng  Stock  Quotes  From  Yahoo!  

(c)  Yakov  Fain    2014  

1.  Visit  hJp://finance.yahoo.com,  enter  AAPL  -­‐  the  symbol  of  the  Apple’s  stock,  and  press  the  buJon  Get  Quotes  .    Note  the  URL.  Change  it  to  hJp://finance.yahoo.com/q?s=AAPL            

2.   To  get  the  price  quote  programma&cally  create  an  instance  of  the  URL  object  and  open  the  stream:    url = new URL(”http://finance.yahoo.com/q?s=AAPL”);!

InputStream in = url.getInputStream();! BufferedReader buff= new BufferedReader(new InputStreamReader(in));!

           One  way  of  geFng  the  stock  info  from  Yahoo!  is  to  read  the  en^re  Web  page:     String theWholePage;! Srting txt;! while (txt =buff.readLine() != null ){! theWholePage=theWholePage + txt;! } !

       …and  then  parse  it  trying  to  find  the  fragment  with  the  AAPL  price.  

Page 3: JavaProgramming$$ Unit10$ - myflex.orgmyflex.org/yf/java/slides/Unit10.pdfWhat’s$Socket (c)$Yakov$Fain$$2014$ The$package$java.net$includes$classes$Socket$and$ ServerSocket. $ A$socketis$a

An  alterna^ve  URL  for  stock  quotes  

(c)  Yakov  Fain    2014  

The  previous  solu^on  produces  lots  of  text  to  filter  out.  Here  you  can  get  the  quotes  for  AAPL  or  any  other  stock  symbol  in  the  CSV  format:    hJp://quote.yahoo.com/d/quotes.csv?s=AAPL&f=sl1d1t1c1ohgv&e=.csv          The  classes  StringTokenizer  or  Scanner  can  help  you  in  parsing  the  received  String    with  comma-­‐separated  values.  

The  textbook  has  a  sample  code  (pg.  191  –  193)  that  uses  the  stock  symbol  MOT,  which  used  to  represent  Motorola.  Since  the  MOT  stock  symbol  has  been  recently  modified,    use  MSI  for  Motorola  or  any  other  valid  stock  symbol,  e.g.  AAPL  for  Apple.    

Page 4: JavaProgramming$$ Unit10$ - myflex.orgmyflex.org/yf/java/slides/Unit10.pdfWhat’s$Socket (c)$Yakov$Fain$$2014$ The$package$java.net$includes$classes$Socket$and$ ServerSocket. $ A$socketis$a

Walkthrough  1  •  Review    with  the  instructor  the  code  of  the  program  StockQuote.java  

from  Eclipse  project  Lesson18    

•  Go  to  the  Eclipse  menu  Run  Configura^ons  and  enter  AAPL  in  the  field  Program  Arguments    

•  Run  the  program  and  observe  the  current  price  of  the  stock    

•  Change  the  stock  symbol  to  be  IBM  and  re-­‐run  the  program  to  see  the  latest  price  of  IBM  stock    

•  Run  the  same  program  through  a  debugger      placing  a  breakpoint  at  line  26.    Debug  the  program  and  watch  the  work    of  the  class  StringTokenizer!

(c)  Yakov  Fain    2014  

Page 5: JavaProgramming$$ Unit10$ - myflex.orgmyflex.org/yf/java/slides/Unit10.pdfWhat’s$Socket (c)$Yakov$Fain$$2014$ The$package$java.net$includes$classes$Socket$and$ ServerSocket. $ A$socketis$a

Programming  Sockets  

(c)  Yakov  Fain    2014  

Page 6: JavaProgramming$$ Unit10$ - myflex.orgmyflex.org/yf/java/slides/Unit10.pdfWhat’s$Socket (c)$Yakov$Fain$$2014$ The$package$java.net$includes$classes$Socket$and$ ServerSocket. $ A$socketis$a

What’s  Socket  

(c)  Yakov  Fain    2014  

The  package  java.net  includes  classes  Socket  and  ServerSocket.      A  socket  is  a  connec%on  end-­‐point  in  IP  networking.      The  TCP/IP  protocol  maintains  a  socket  connec^on  for  the  whole  period  of  communica^on,  while  UDP  is  a  connec^onless  protocol,  which  sends  data  in  small  chunks  called  datagrams.    The  socket  address  is  a  pairof  IP  address  and  port.      An  instance  of  the  ServerSocket  class  becomes    a  server  that  listens  to  the  specified  port    for  requests.    

Page 7: JavaProgramming$$ Unit10$ - myflex.orgmyflex.org/yf/java/slides/Unit10.pdfWhat’s$Socket (c)$Yakov$Fain$$2014$ The$package$java.net$includes$classes$Socket$and$ ServerSocket. $ A$socketis$a

Sockets:  the  Client  and  the  Server  

(c)  Yakov  Fain    2014  

The  following  two  lines  create  a  server  that  is  listening  to  port  3000:    ServerSocket serverSocket = new ServerSocket(3000); Socket client = serverSocket.accept(); The  client  program  creates  an  instance  of  the  class  Socket  poin^ng  at  the  computer/port  on  which  the  ServerSocket  is  running:      Socket clientSocket = new Socket("124.67.98.101", 3000);!  WebSocket  is  an  new  HTML5  standard  of  communica^on  over  the  Internet.  More  details  here:  http://enterprisewebbook.com/ch8_websockets.html    

Page 8: JavaProgramming$$ Unit10$ - myflex.orgmyflex.org/yf/java/slides/Unit10.pdfWhat’s$Socket (c)$Yakov$Fain$$2014$ The$package$java.net$includes$classes$Socket$and$ ServerSocket. $ A$socketis$a

GeFng  Stock  Quotes  with  Sockets  JVM  1  (the  server):    1.  Start  the  ServerSocket  on  some  port   new ServerSocket(3000);!

2.  Put  it  in  a  listening  mode  with  accept().  3.  Process  the  request  and  return  the  result  to  the  client  via  the  stream.  

(c)  Yakov  Fain    2014  

JVM  2  (the  client):    1.  Connect  to  the  server  socket  by  instan^a^ng  the  class  Socket   clientSocket = new Socket(“124.67.98.101”, 3000);!2.  Get  the  reference  to  the  server’s  stream           outbound = clientSocket.getOutputStream();!3.  Send  your  requests  to  this  stream.  4.  Process  server’s  responses  

Page 9: JavaProgramming$$ Unit10$ - myflex.orgmyflex.org/yf/java/slides/Unit10.pdfWhat’s$Socket (c)$Yakov$Fain$$2014$ The$package$java.net$includes$classes$Socket$and$ ServerSocket. $ A$socketis$a

Walkthrough  2  

•  Review  with  instructor  the  code  of  the  program  StockQuoteServer  and  Client  from  Eclipse  project  Lesson18  

•  Follow  the  instruc^ons  from  the  TRY  IT  sec^on  to  Lesson  18  to  test  the  client-­‐server  communica^ons  using  sockets.  

(c)  Yakov  Fain    2014  

Page 10: JavaProgramming$$ Unit10$ - myflex.orgmyflex.org/yf/java/slides/Unit10.pdfWhat’s$Socket (c)$Yakov$Fain$$2014$ The$package$java.net$includes$classes$Socket$and$ ServerSocket. $ A$socketis$a

Non-­‐Blocking  Sockets  

(c)  Yakov  Fain    2014  

If  our  stock  server  needs  to  process  mul^ple  requests,  the  StockQuoteServer  would  need  to  create  a  new  thread  for  each  request.    Each  thread  introduces  an  overhead  limi^ng  the  number  requests  that  can  be  processed  concurrently.    The  package  java.nio    includes    a  number  of  classes  that  support  non-­‐blocking  i/o  in  general  and  non-­‐blocking  sockets  in  par^cular.  which  allows  i/o  communica^ons  on  the  socket  channel  without  blocking  the  processes  using  it.    You  can  read  a  short  tutorial  on  non-­‐blocking  I/O  by  Jacob  Jenkov:  hJp://tutorials.jenkov.com/java-­‐nio/index.html      

Page 11: JavaProgramming$$ Unit10$ - myflex.orgmyflex.org/yf/java/slides/Unit10.pdfWhat’s$Socket (c)$Yakov$Fain$$2014$ The$package$java.net$includes$classes$Socket$and$ ServerSocket. $ A$socketis$a

Remote  Method  Invoca^on  (RMI)  

(c)  Yakov  Fain  2013  

RMI  allows  JVMs  communicate  with  each  other.      With  sockets,  the  Java  client  was  directly  connec^ng  to  Java  server  running  on  a  different  JVM.    With  RMI,  Java  client  will  make  a  method  call  that  looks    as  if  this  method  is  running  in  the  same  JVM,  but  it’s  not.      Only  a  proxy  (a  stub)  of  the  remote  method  exists  in  the    client’s  JVM.              

Page 12: JavaProgramming$$ Unit10$ - myflex.orgmyflex.org/yf/java/slides/Unit10.pdfWhat’s$Socket (c)$Yakov$Fain$$2014$ The$package$java.net$includes$classes$Socket$and$ ServerSocket. $ A$socketis$a

Finding  Remote  Objects  

(c)  Yakov  Fain  2013  

RMI  clients  find  remote  services  by  using  a  naming  service,  which  must  run  on  a  known  host  and  port  number.    The  RMI  server  can  start  its  own  registry  that  offers  naming  services  for  RMI  clients.  The  behavior  of  the  registry  is  defined  by  the  interface  java.rmi.registry.Registry      By  default,  the  RMI  registry  runs  on  port  1099    The  client  obtains  a  reference  to  a  remote  object  by  looking  up  its  name  in  the  registry.  This  lookup  returns  to  the  client  a  remote  reference  a.k.a.  stub.    The  method  lookup() takes  the  service  name  URL  as  an  argument  in  the  following  format:                rmi://<host_name>[:<name_service_port>]/<service_name>            

Page 13: JavaProgramming$$ Unit10$ - myflex.orgmyflex.org/yf/java/slides/Unit10.pdfWhat’s$Socket (c)$Yakov$Fain$$2014$ The$package$java.net$includes$classes$Socket$and$ ServerSocket. $ A$socketis$a

RMI  Players  

(c)  Yakov  Fain  2013  

Page 14: JavaProgramming$$ Unit10$ - myflex.orgmyflex.org/yf/java/slides/Unit10.pdfWhat’s$Socket (c)$Yakov$Fain$$2014$ The$package$java.net$includes$classes$Socket$and$ ServerSocket. $ A$socketis$a

Developing  and  Running  an  app  using  RMI  

(c)  Yakov  Fain  2013  

•  Declare  a  remote  Java  interface    •  Implement  the  remote  interface  in  a  Java  class    •  Computer  A:  Start  the  registry  and  register  the  RMI  server  with  it    •  Computer  B:  Start  the  server      •  Computer  C:  Start  a  Java  client  that  will  look  up  the  service  in  the  registry  A  to  get  stubs  from  the  server  B  and  calls  remote  methods.      

Page 15: JavaProgramming$$ Unit10$ - myflex.orgmyflex.org/yf/java/slides/Unit10.pdfWhat’s$Socket (c)$Yakov$Fain$$2014$ The$package$java.net$includes$classes$Socket$and$ ServerSocket. $ A$socketis$a

Walkthrough  3    

(c)  Yakov  Fain  2013  

 1.  Download  and  import  the  project  Lesson25  and  review  the  code  with  the  instructor.      2.  Add  the  following  statement  at  the  line  12  of  StartServer.java:  LocateRegistry.createRegistry(1099); !  3.  Add  the  import  statement  for  LocateRegistry!  4.  Run  StartServer  and  it  should  give  a  prompt  <QuoteService>  server  is  ready    5.Run  configura^on  for  Client.java  to  specify  one  program  argument:  AAPL    6.  Run  the  Client  and  you  should  get  the  random  price  quote  like    The  price  of  AAPL  is:  $1.3335365174267477  

Page 16: JavaProgramming$$ Unit10$ - myflex.orgmyflex.org/yf/java/slides/Unit10.pdfWhat’s$Socket (c)$Yakov$Fain$$2014$ The$package$java.net$includes$classes$Socket$and$ ServerSocket. $ A$socketis$a

Homework  

1.  Study  the  materials  from  Lesson  18  and  lesson  25  from  the  textbook.      

 

(c)  Yakov  Fain    2014  

Page 17: JavaProgramming$$ Unit10$ - myflex.orgmyflex.org/yf/java/slides/Unit10.pdfWhat’s$Socket (c)$Yakov$Fain$$2014$ The$package$java.net$includes$classes$Socket$and$ ServerSocket. $ A$socketis$a

Addi^onal  Reading/Watching  •  Read  about  working  with  Yahoo  stock  quote  data  feed  

hJp://www.gummy-­‐stuff.org/Yahoo-­‐data.htm  .    

•  RMI:  hJp://docs.oracle.com/javase/tutorial/rmi/      

•  Watch  the  video  on  code  refactoring  and  tes^ng:  hJp://www.java-­‐tv.com/2013/10/23/tes^ng-­‐and-­‐refactoring-­‐legacy-­‐code-­‐2/      

•  Watch  the  video  about  automated  tes^ng:  hJp://www.infoq.com/presenta^ons/Tes^ng-­‐Java.    Create  a  project  that  uses  unit  tests  with  JUnit.    

    (c)  Yakov  Fain    2014  


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