Access to Remote Data ( ) Frank Ducrest

Access to Remote Data 2 Generic Connection Framework hierarchy of interfaces and classes for managing remote connections and I/O includes ➢ Connector – connection factory class ➢ Connection – generic interface for connections ➢ DatagramConnection – interface that defines datagram connections (UDP) ➢ StreamConnection – interface that defines stream connections (TCP)

Generic Connection Framework (continued) includes (continued) ➢ StreamConnectionNotifier – interface for stream connection listeners ➢ ContentConnection – interface for support of transmission of content ➢ Datagram – interface for a single datagram ● reduces connections with remote objects to ➢ creating a URL with the socket, address and name ➢ invoking the Connector.open method to receive a Connection subclass object ➢ use that object to work with the connection Access to Remote Data 3

URL Uniform Resource Locator; subset of URI (Uniform Resource Identifier) used to specify a location of an available resource a string that looks like this ➢ scheme specifies the protocol to be used ➢ user and are optional and used only if necessary ➢ :port is optional; protocol default used if absent ➢ /path is optional; listening service default used if absent ➢ ;parameters is optional and used only if necessary Access to Remote Data 4

Connection Schemes all Java ME platforms must support HTTP and HTTPS see text page 298, table 12-1 for a listing Connection Implementations see text page 298, table 12-2 for Java Me connection implementations Access to Remote Data 5

Reading a File Over a Network very similar to input from a local file uses ContentConnection and Connector instead of FileConnection Connector is used to create a ContentConnection object, which is used to create the input stream object example ContentConnection cc = (ContentConnection)Connector.open(fileURL); DataInputStream dis = cc.openDataInputStream(); Access to Remote Data 6

Example of Reading a File Across a Network import javax.microedition.midlet.*; import javax.microedition.io.*; import java.io.*; public class ReadOverNetworkMidlet extends MIDlet { private static final String fileURL = " private ContentConnection cc = null; private DataInputStream dis = null; public void startApp() { connectToFile(); readFromFile(); closeFile(); destroyApp(true); notifyDestroyed(); } public void pauseApp() { } public void destroyApp(boolean unconditional) { } Access to Remote Data 7

Example of Reading a File Across a Network (continued) private void connectToFile() { try { cc = (ContentConnection)Connector.open(fileURL); dis = cc.openDataInputStream(); System.out.println("Connected"); } catch (Exception e) { System.out.println("Connection exception"); e.printStackTrace(); } private void closeFile() { try { dis.close(); cc.close(); System.out.println("Closed"); } catch (Exception e) { System.out.println("Closing exception"); e.printStackTrace(); } Access to Remote Data 8

Example of Reading a File Across a Network (continued) private void readFromFile() { System.out.println("in readFromfile"); try { System.out.println("Numbers in:"); int len = (int)cc.getLength(); if (len > 0) { byte[] data = new byte[len]; dis.readFully(data);// read entire file String s = new String(data); System.out.println(s); // output all read Access to Remote Data 9

Example of Reading a File Across a Network (continued) // parse integers from string read in and sum int sum = 0; int i = 0, j = 0; while (j < s.length()-1) { j = s.indexOf("\n", i); try { int n = Integer.parseInt(s.substring(i, j)); sum += n; i = j+1; } catch (Exception e) { j = s.length(); } System.out.println("sum = " + sum); } } catch(Exception e) { System.out.println("readFromfile exception"); e.printStackTrace(); } System.out.println("out readFromfile"); } Access to Remote Data 10

Example of Reading a File Across a Network (continued) mydata.txt example run Connected in readFromfile Numbers in: sum = 460 out readFromfile Closed Access to Remote Data 11

Sockets a socket is one end of a link between two computers link is bi-directional link usually in the form of a client / server pair example: normal http port is 80 is sent by the client browser as Access to Remote Data 12

Socket Time Client Example /* Some Public Time Servers: time-a.nist.gov NIST, Gaithersburg, Maryland time-b.nist.gov NIST, Gaithersburg, Maryland time-a.timefreq.bldrdoc.gov NIST, Boulder, Colorado time-b.timefreq.bldrdoc.gov NIST, Boulder, Colorado time-c.timefreq.bldrdoc.gov NIST, Boulder, Colorado utcnist.colorado.edu University of Colorado, Boulder time.nist.gov NCAR, Boulder, Colorado time-nw.nist.gov Microsoft, Redmond, Washington nist1.datum.com Datum, San Jose, California nist1.dc.glassey.com Abovenet, Virginia nist1.ny.glassey.com Abovenet, New York City nist1.sj.glassey.com Abovenet, San Jose, California nist1.aol-ca.truetime.com True Time, Sunnyvale, California nist1.aol-va.truetime.com True Time, Virginiat */ import javax.microedition.midlet.*; import javax.microedition.io.*; import java.io.*; public class TimeMidlet extends MIDlet { public void pauseApp() { } public void destroyApp(boolean unconditional) { } Access to Remote Data 13

Socket Time Client Example (continued) public void startApp() { String url = "socket://time-a.nist.gov:13"; StreamConnection c = null; InputStream i = null; byte[] b = new byte[50]; try { c = (StreamConnection)Connector.open(url); i = c.openInputStream(); int bytes = i.read(b); String s = new String(b); System.out.println("All info received: " + s); int start = s.indexOf(" ")+1; System.out.println("Date: " + s.substring(start,start+8)); System.out.println("Time: " + s.substring(start+9,start+17) + " UTC"); i.close(); c.close(); } catch (Exception e) { e.printStackTrace(); } Access to Remote Data 14

Socket Time Client Example (continued) destroyApp(true); notifyDestroyed(); } Example Run All info received: :43: UTC(NIST Date: Time: 16:43:09 UTC Access to Remote Data 15

Socket Time Client Example /* Some Public Time Servers: time-a.nist.gov NIST, Gaithersburg, Maryland time-b.nist.gov NIST, Gaithersburg, Maryland time-a.timefreq.bldrdoc.gov NIST, Boulder, Colorado time-b.timefreq.bldrdoc.gov NIST, Boulder, Colorado time-c.timefreq.bldrdoc.gov NIST, Boulder, Colorado utcnist.colorado.edu University of Colorado, Boulder time.nist.gov NCAR, Boulder, Colorado time-nw.nist.gov Microsoft, Redmond, Washington nist1.datum.com Datum, San Jose, California nist1.dc.glassey.com Abovenet, Virginia nist1.ny.glassey.com Abovenet, New York City nist1.sj.glassey.com Abovenet, San Jose, California nist1.aol-ca.truetime.com True Time, Sunnyvale, California nist1.aol-va.truetime.com True Time, Virginiat */ import javax.microedition.midlet.*; import javax.microedition.io.*; import java.io.*; public class TimeMidlet extends MIDlet { public void pauseApp() { } public void destroyApp(boolean unconditional) { } Access to Remote Data 16 Socket Client Example import javax.microedition.midlet.*; import javax.microedition.io.*; import java.io.*; public class Midlet extends MIDlet { StreamConnection c = null; InputStream i = null; OutputStream o = null; byte[] b = new byte[200]; int bytes = 0; private void read() { try { bytes = i.read(b); System.out.println("First Read: " + new String(b)); } catch (Exception e) { System.out.println("Read Problem: "); e.printStackTrace(); } public void pauseApp() { } public void destroyApp(boolean unconditional) { }

Socket Client Example (continued) public void startApp() { String url = "socket://mailer.louisiana.edu:25"; try { c = (StreamConnection)Connector.open(url); i = c.openInputStream(); o = c.openOutputStream(); read(); byte[] mailfrom = ("mail from: o.write(mailfrom); read(); byte[] addressee = ("rcpt to: o.write(addressee); read(); byte[] data = ("data\n").getBytes(); o.write(data); read(); Access to Remote Data 17 Socket Time Client Example import javax.microedition.midlet.*; import javax.microedition.io.*; import java.io.*; public class Midlet extends MIDlet { StreamConnection c = null; InputStream i = null; OutputStream o = null; byte[] b = new byte[200]; int bytes = 0; private void read() { try { bytes = i.read(b); System.out.println("First Read: " + new String(b)); } catch (Exception e) { System.out.println("Read Problem: "); e.printStackTrace(); } public void pauseApp() { } public void destroyApp(boolean unconditional) { }

Socket Time Client Example (continued) public void startApp() { String url = "socket://mailer.louisiana.edu:25"; try { c = (StreamConnection)Connector.open(url); i = c.openInputStream(); o = c.openOutputStream(); byte[] mailfrom = ("mail from: o.write(mailfrom); read(); byte[] addressee = ("rcpt to: o.write(addressee); read(); byte[] data = ("data\n").getBytes(); o.write(data); read(); Access to Remote Data 18 Socket Client Example (continued) byte[] subject = ("subject: Test \n").getBytes(); o.write(subject); byte[] toaddressee = ("To: " + addressee + "\n").getBytes(); o.write(toaddressee); byte[] message = ("This is a test\n over 3\nlines.\n").getBytes(); o.write(message); byte[] eom = (".\n").getBytes(); o.write(eom); read(); i.close(); o.flush(); o.close(); c.close();

Socket Client Example (continued) } catch (Exception e) { System.out.println("general problem"); e.printStackTrace(); } destroyApp(true); notifyDestroyed(); } Example Run Access to Remote Data 19 Socket Client Example (continued) byte[] subject = ("subject: Test \n").getBytes(); o.write(subject); byte[] toaddressee = ("To: " + addressee + "\n").getBytes(); o.write(toaddressee); byte[] message = ("This is a test\n over 3\nlines.\n").getBytes(); o.write(message); byte[] eom = (".\n").getBytes(); o.write(eom); read(); i.close(); o.flush(); o.close(); c.close(); } catch (Exception e) { System.out.println("general problem"); e.printStackTrace(); } destroyApp(true); notifyDestroyed(); }

Datagrams used for short messages no sequencing or flow control Connector class is used to make connections Datagram class objects encapsulate the datagram DatagramConnection or UDPDatagramConnection objects are used to send and receive Datagram objects Access to Remote Data 20

Datagram Client Example in the the example: ➢ the client sends a datagram to a datagram server; the data in the datagram is a pronoun (“Dud”) ➢ the server uses the data in the datagram to form a reply to the client in the form “Yo, “ plus the data from the client's datagram and a quote read from a file import javax.microedition.midlet.*; import javax.microedition.io.*; public class DatagramClientMidlet extends MIDlet { public void pauseApp() { } public void destroyApp(boolean unconditional) { } Access to Remote Data 21

Datagram Client Example (continued) public void startApp() { byte[] b = new byte[256]; String url = "datagram://...ip-or-url...:4445"; DatagramConnection dgc = null; byte[] m = ("Dud\n").getBytes(); try { dgc =(DatagramConnection)Connector.open(url); Datagram d = dgc.newDatagram(m, m.length); dgc.send(d); d = dgc.newDatagram(b, 256); dgc.receive(d); String s = new String(d.getData()); System.out.println("incomming datagram data: " + s.substring(0, d.getLength()-1)); System.out.println( "incomming datagram buffer length: " + d.getLength()); } catch (Exception e) {} Access to Remote Data 22 Socket Client Example import javax.microedition.midlet.*; import javax.microedition.io.*; import java.io.*; public class Midlet extends MIDlet { StreamConnection c = null; InputStream i = null; OutputStream o = null; byte[] b = new byte[200]; int bytes = 0; private void read() { try { bytes = i.read(b); System.out.println("First Read: " + new String(b)); } catch (Exception e) { System.out.println("Read Problem: "); e.printStackTrace(); } public void pauseApp() { } public void destroyApp(boolean unconditional) { }

Datagram Client Example public void startApp() { byte[] b = new byte[256]; String url = "datagram://...ip-or-url...:4445"; DatagramConnection dgc = null; byte[] m = ("Dud\n").getBytes(); try { dgc =(DatagramConnection)Connector.open(url); Datagram d = dgc.newDatagram(m, m.length); dgc.send(d); d = dgc.newDatagram(b, 256); dgc.receive(d); String s = new String(d.getData()); System.out.println("incomming datagram data: " + s.substring(0, d.getLength()-1)); System.out.println( "incomming datagram buffer length: " + d.getLength()); } catch (Exception e) {} Access to Remote Data 23 Datagram Client Example (continued) finally { try { if (dgc == null) dgc.close(); } catch (Exception e) { e.printStackTrace(); } destroyApp(true); notifyDestroyed(); } Example Run incomming datagram data: Yo, Dud, Life is wonderful. Without it we'd all be dead. incomming datagram buffer length: 57