Victor Ng

Jython and Java Integration

Java integration is the heart of Jython application development. Most Jython developers are either Python developers that are looking to make use of the vast library of tools that the JVM has to offer, or Java developers that would like to utilize the Python language semantics without migrating to a completely different platform. The fact is that most Jython developers are using it so that they can take advantage of the vast libraries available to the Java world, and in order to do so there needs to be a certain amount of Java integration in the application. Whether you plan to use some of the existing Java libraries in your application, or you’re interested in mixing some great Python code into your Java application, this chapter is geared to help with the integration.

Modules and Packages for Code Reuse

Up until this chapter, we have been looking at code at the level of the interactive console and simple scripts. This works well for small examples, but when your program gets larger, it becomes necessary to break programs up into smaller units. In Jython, the basic building block for these units in larger programs is the module.

Object-Oriented Jython

This chapter is going to cover the basics of object-oriented programming. We’ll start with covering the basic reasons why you would want to write object-oriented code in the first place, and then cover all the basic syntax, and finally we’ll show you a non-trivial example.

Operators, Expressions, and Program Flow

The focus of this chapter is an in-depth look at each of the ways that we can evaluate code, and write meaningful blocks of conditional logic. We’ll cover the details of many operators that can be used in Python expressions. This chapter will also cover some topics that have already been discussed in more meaningful detail such as the looping constructs, and some basic program flow.

Data Types and Referencing

Programming languages and applications need data. We define applications to work with data, and we need to have containers that can be used to hold it. This chapter is all about defining containers and using them to work with application data. Whether the data we are using is coming from a keyboard entry or if we are working with a database, there needs to be a way to temporarily store it in our programs so that it can be manipulated and used. Once we’re done working with the data then these temporary containers can be destroyed in order to make room for new constructs.

Simple Web Applications

One of the major benefits of using Jython is the ability to make use of Java platform capabilities programming in the Python programming language instead of Java. In the Java world today, the most widely used web development technique is the Java servlet. Now in JavaEE, there are techniques and frameworks used so that we can essentially code HTML or other markup languages as opposed to writing pure Java servlets. However, sometimes writing a pure Java servlet still has its advantages. We can use Jython to write servlets and this adds many more advantages above and beyond what Java has to offer because now we can make use of Python language features as well. Similarly, we can code web start applications using Jython instead of pure Java to make our lives easier. Coding these applications in pure Java has proven sometimes to be a difficult and sometimes grueling task. We can use some of the techniques available in Jython to make our lives easier. We can even code WSGI applications with Jython making use of the modjy integration in the Jython project.

Testing and Continuous Integration

Nowadays, automated testing is a fundamental activity in software development. In this chapter, you will see a survey of the tools available for Jython in this field. These tools range from common tools used in the Python world to aid with unit testing, to more complex tools available in the Java world that can be extended or driven using Jython.

Databases and Jython: Object Relational Mapping and Using JDBC

In this chapter, we will look at zxJDBC package, which is a standard part of Jython since version 2.1 and complies with the Python 2.0 DBI standard. zxJDBC can be an appropriate choice for simple one-off scripts where database portability is not a concern. In addition, it’s (generally) necessary to use zxJDBC when writing a new dialect for SQLAlchemy or Django. (But that’s not strictly true: you can use pg8000, a pure Python DBI driver, and of course write your own DBI drivers. But please don’t do that.) So knowing how zxJDBC works can be useful when working with these packages. However, it’s too low level for us to recommend for more general usage. Use SQLAlchemy or Django if at all possible. Finally, JDBC itself is also directly accessible, like any other Java package from Jython. Simply use the java.sql package. In practice this should be rarely necessary.

Scripting With Jython

In this chapter, we will look at scripting with Jython. For our purposes, we will define “scripting” as the writing of small programs to help out with daily tasks. These tasks are things like deleting and creating directories, managing files and programs, and anything else that feels repetitive that you might be able to express as a small program. In practice, however, scripts can become so large that the line between a script and a full sized program can blur.

Using Jython in an IDE

In this chapter, we will discuss developing Jython applications using two of the most popular integrated development environments, Eclipse and Netbeans. There are many other development environments available for Python and Jython today; however, these two are perhaps the most popular and contain the most Jython-specific tools. Eclipse has had a plug-in known as PyDev for a number of years, and this plug-in provides rich support for developing and maintaining Python and Jython applications alike. Netbeans began to include Python and Jython support with version 6.5 and later. The Netbeans IDE also provides rich support for development and maintenance of Python and Jython applications.