Using Jython to Speed Development Don Coleman, Aaron Mulder, Tom Purcell Chariot Solutions

Using Jython to Speed Development

• Don Coleman, Aaron Mulder, Tom Purcell Chariot Solutions

Goal

Who are we?

• We are J2EE Architects

• We write commercial Java software

• We use Jython as a tool for developing and testing Java software

Presentation Agenda

• About Jython

• Language Overview
• Using the Interactive Interpreter

• Server Side Jython

• Accessing Databases
• Accessing EJBs
• PyServlet
• Embedded Jython

• Advanced Jython

About Jython

What is Jython?

• Jython is an implementation of the Python language that runs on the JVM

• Jython excels at scripting and is excellent for exploring and debugging code

• Jython's interpreted nature allows you to work with Java without a compiler and manipulate live objects on the fly

• Jython gives you the power of Java + Python

What is Python?

• Python is a mature language that ...

• has clear syntax

• is easy to learn

• is easy to use

• is object oriented

• is powerful

Installing Jython

• Install JDK 1.4

• Download Jython from http://www.jython.org

• cd to the directory with jython-21.class

• Start the installer $ java -cp . jython-21

Sample Code

• class Greeter:

• def sayHello(self, name = None):

• if name == None:

• print "Hello"

• else:

• print "Hello, %s" % name

• def sayGoodbye(self):

• print "Goodbye"

Why would you use Jython?

• Live interaction with Java for experimentation

• Testing and debugging

• Write quick scripts without needing to compile

• Quick runtime tests

• BigDecimal("0").equals(BigDecimal("0.00"))

• Inspecting private variables or methods

• Rapid development

• Embedded scripting

Interactive Command Line

• $ jython

• >>> print “Hello world!”

• Hello world!

• >>>

• Use CTRL+D to exit on UNIX

• Use CTRL+Z to exit on Windows

Language Overview

Language Overview

• supports modules, classes and methods

• dynamic typing (don't declare variable types)

• familiar control structures (for, if, while ...)

• uses # for comments

• built-in collection types (lists, dictionaries)

• indentation for code blocks { not braces }

• no semicolons to indicate end of line;

• omits “new” keyword (“o = Object()”)

Variable Assignment and Printing

• >>> s = 17

• >>> print s

• 17

• >>> s = “JavaOne”

• >>> print s

• JavaOne

• >>>

Creating a method

• >>> def add(a,b):

• ... return a + b

• ...

• >>> add(4,5)

• 9

• >>>

Creating a class

• >>> class Calc:

• ... def add(self, a, b)

• ... return a + b

• ...

• >>> c = Calc()

• >>> c.add(4,5)

• 9

• >>>

Lists

• Lists are like arrays and ArrayLists

• >>> l = []

• >>> l.append(1)

• >>> l.append('string')

• >>> l.append(12.3)

• >>> print l

• [1, 'string', 12.3]

• >>> len(l)

• 3

• >>> l[2]

• 12.3

Dictionaries

• Dictionaries are similar to HashMaps

• >>> dict = {}

• >>> dict['color'] = 'red'

• >>> dict[17] = 'seventeen'

• >>> dict

• {'color':'red', 17:'seventeen'}

• >>> dict['color']

• 'red'

• >>>

Loops / Iterators

• >>> l = ['spam','bacon','eggs']

• >>> for item in l:

• ... print item

• ...

• spam

• bacon

• eggs

• >>>

Using Java in Jython

• >>> from java.lang import *

• >>> System.getProperty(“user.home”)

• '/home/dcoleman'

• >>> from java.math import BigDecimal

• >>> b = BigDecimal(“17”)

• >>> b

• 17

• >>>

Jython Modules

• A module is a collection of jython code

• May contain, code, methods, classes

• Import modules import module from module import object

• Run modules like a script

• $ jython module.py

Inheriting from Java

• from javax.swing import *

• from java.awt import Color

• class GreenPanel(JPanel):

• def __init__(self):
• self.background = Color.green
• def toString(self):
• return "GreenPanel"

• if __name__ == "__main__":

• f = Jframe("Green", size=(200,200))
• f.getContentPane().add(GreenPanel())
• f.show()

Server-Side Jython

Database Access

• Can use standard JDBC calls in Jython

• There's a more “pythonic” DB API called zxJDBC, included with Jython 2.1

• Use whichever you're comfortable with, though zxJDBC is a little more compact

JDBC Example

• from java.lang import *

• from java.sql import *

• Class.forName("org.hsqldb.jdbcDriver")

• conn = DriverManager.getConnection( "jdbc:hsqldb:demo", "sa", "")

• stmt = conn.createStatement()

• rs = stmt.executeQuery("SELECT code, desc FROM states")

• while rs.next():

• print rs.getString("code"),rs.getString("desc")

• rs.close()

• stmt.close()

• conn.close()

zxJDBC Example

• from com.ziclix.python.sql import zxJDBC

• from pprint import pprint

• conn = zxJDBC.connect("jdbc:hsqldb:demo", "sa", "", "org.hsqldb.jdbcDriver")

• cursor = conn.cursor()

• cursor.execute("SELECT code, desc FROM states")

• data = cursor.fetchall()

• cursor.close()

• conn.close()

• pprint(data)

A Jython EJB Client

• Set up the classpath, jndi.properties like normal, then...

• >>> from javax.naming import *

• >>> c = InitialContext()

• >>> home = c.lookup("Demo")

• >>> demo = home.create()

• >>> demo.setFoo("Jython")

• >>> demo.getFoo()

• 'Jython'

• >>> demo.getDate()

• Tues Jun 10 11:45:17 PST 2003

PyServlet

• Jython includes a servlet that executes *.py scripts

• Similar to the way *.jsp files are executed

• Just need to map the servlet in the web.xml file

• Can provide “python.home” and “python.path” init-params to customize the Jython libs and configuration

Mapping PyServlet

• PyServlet

• org.python.util.PyServlet

• 1

• PyServlet

• *.py

Embedded Jython

• Can execute Jython within a servlet or EJB container

• Jython can load resource references, local EJB references, etc. like any other component

• Can set up a client to interact with the Jython in the server, just like the normal interpreter

• Probably need to customize the environment to make additional JARs visible to Jython

Demo

Advanced Jython

PyUnit

• PyUnit is based on the JUnit Framework

• Test are generally shorter with PyUnit

• Ability to access private methods

• Ant integration (using JUnit task)

PyUnit

• import unittest

• class DemoTestCase(unittest.TestCase):

• def testBar(self):

• self.assertEquals(5, len("hello"))

• if __name__ == '__main__':

• unittest.main()

Accessing non-public code

• Edit the Jython registry file

• The registry is a text file in the Jython installation directory

• # Setting this to false will allow Jython to provide access to

• # non-public fields, methods, and constructors of Java objects.

• python.security.respectJavaAccessibility = false

Compiling Jython to Java

• allows Jython code to run in Java

• jythonc is the compiler .py > .java > .class

• jython.jar must be in the classpath

• special @sig comment to declare the method's signature in Java

Jython Standard Libraries

• Jython includes a rich set of built-in libraries

• You can run most Python code except where - modules implemented in C - modules that target a particular platform - modules where JVM lacks functionality

Code Completion

• Jython Console with Code Completion

• http://don.freeshell.org/jython

Conclusion

Q&A

Links...

• This presentation is available from http://www.chariotsolutions.com/presentations.html

• Jython www.jython.org

• Python www.python.org

• Jython Console http://don.freeshell.org/jython

• Jython Essentials by Samuele Pedroni & Noel Rappin http://www.oreilly.com/catalog/jythoness/

• JEdit http://www.jedit.com

• Eclipse Python Integration http://www.python.org/cgi-bin/moinmoin/EclipsePythonIntegration