Using Jython to Speed Development

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Using Jython to Speed Development

• Don Coleman, Aaron Mulder, Tom PurcellChariot
  Solutions

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Goal
Use Jython to make software development easier.
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Who are we?

• We are J2EE Architects
• We write commercial Java software
• We use Jython as a tool for developing and
  testing Java software

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Presentation Agenda

• About Jython
• Language Overview
• Using the Interactive Interpreter
• Server Side Jython
• Accessing Databases
• Accessing EJBs
• PyServlet
• Embedded Jython
• Advanced Jython

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About Jython
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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

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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

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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

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Sample Code

• class Greeter
• def sayHello(self, name None)
• if name None
• print "Hello"
• else
• print "Hello, s" name
• def sayGoodbye(self)
• print "Goodbye"

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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

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Interactive Command Line

• jython
• gtgtgt print Hello world!
• Hello world!
• gtgtgt
• Use CTRLD to exit on UNIX
• Use CTRLZ to exit on Windows

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Language Overview
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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())

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Variable Assignment and Printing

• gtgtgt s 17
• gtgtgt print s
• 17
• gtgtgt s JavaOne
• gtgtgt print s
• JavaOne
• gtgtgt

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Creating a method

• gtgtgt def add(a,b)
• ... return a b
• ...
• gtgtgt add(4,5)
• 9
• gtgtgt

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Creating a class

• gtgtgt class Calc
• ... def add(self, a, b)
• ... return a b
• ...
• gtgtgt c Calc()
• gtgtgt c.add(4,5)
• 9
• gtgtgt

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Lists

• Lists are like arrays and ArrayLists
• gtgtgt l
• gtgtgt l.append(1)
• gtgtgt l.append('string')
• gtgtgt l.append(12.3)
• gtgtgt print l
• 1, 'string', 12.3
• gtgtgt len(l)
• 3
• gtgtgt l2
• 12.3

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Dictionaries

• Dictionaries are similar to HashMaps
• gtgtgt dict
• gtgtgt dict'color' 'red'
• gtgtgt dict17 'seventeen'
• gtgtgt dict
• 'color''red', 17'seventeen'
• gtgtgt dict'color'
• 'red'
• gtgtgt

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Loops / Iterators

• gtgtgt l 'spam','bacon','eggs'
• gtgtgt for item in l
• ... print item
• ...
• spam
• bacon
• eggs
• gtgtgt

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Using Java in Jython

• gtgtgt from java.lang import
• gtgtgt System.getProperty(user.home)
• '/home/dcoleman'
• gtgtgt from java.math import BigDecimal
• gtgtgt b BigDecimal(17)
• gtgtgt b
• 17
• gtgtgt

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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

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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()

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Server-Side Jython
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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

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JDBC Example

• from java.lang import
• from java.sql import
• Class.forName("org.hsqldb.jdbcDriver")
• conn DriverManager.getConnection(
  "jdbchsqldbdemo", "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()

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zxJDBC Example

• from com.ziclix.python.sql import zxJDBC
• from pprint import pprint
• conn zxJDBC.connect("jdbchsqldbdemo", "sa",
  "", "org.hsqldb.jdbcDriver")
• cursor conn.cursor()
• cursor.execute("SELECT code, desc FROM states")
• data cursor.fetchall()
• cursor.close()
• conn.close()
• pprint(data)

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A Jython EJB Client

• Set up the classpath, jndi.properties like
  normal, then...
• gtgtgt from javax.naming import
• gtgtgt c InitialContext()
• gtgtgt home c.lookup("Demo")
• gtgtgt demo home.create()
• gtgtgt demo.setFoo("Jython")
• gtgtgt demo.getFoo()
• 'Jython'
• gtgtgt demo.getDate()
• Tues Jun 10 114517 PST 2003

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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

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Mapping PyServlet

• ltweb-appgt
• ltservletgt
• ltservlet-namegtPyServletlt/servlet-namegt
• ltservlet-classgt
• org.python.util.PyServlet
• lt/servlet-classgt
• ltload-on-startupgt1lt/load-on-startupgt
• lt/servletgt
• ltservlet-mappinggt
• ltservlet-namegtPyServletlt/servlet-namegt
• lturl-patterngt.pylt/url-patterngt
• lt/servlet-mappinggt
• lt/web-appgt

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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

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Demo
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Advanced Jython
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PyUnit

• PyUnit is based on the JUnit Framework
• Test are generally shorter with PyUnit
• Ability to access private methods
• Ant integration (using JUnit task)

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PyUnit

• import unittest
• class DemoTestCase(unittest.TestCase)
• def testBar(self)
• self.assertEquals(5, len("hello"))
• if __name__ '__main__'
• unittest.main()

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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

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Compiling Jython to Java

• allows Jython code to run in Java
• jythonc is the compiler .py gt .java gt .class
• jython.jar must be in the classpath
• special _at_sig comment to declare the method's
  signature in Java

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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

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Code Completion

• Jython Console with Code Completion
• http//don.freeshell.org/jython

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Conclusion
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QA
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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/c
  gi-bin/moinmoin/EclipsePythonIntegration

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