Enforce Coding Style with CheckStyle
Enforce Coding Style with CheckStyle
The world of programming is tricky and it gets trickier when it
comes to employing a standard. A standard may mean a standard in
application architecture or a standard in the development
pattern. Also one of the most important things that companies
want to enforce is a coding standard. Many wonder about the
advantage of doing this. To me this means better understanding
and better maintainability of the source code. By following a
coding standard, you ensure that the source code is predictable
in its semantics and understood in the same manner across the
development team. The importance of having this visibility may
not be imminent to the small size projects and a small size team
but as the scope of the project is spanned across multiple
teams, the coding standard becomes an important issue. In this
article, we explore one such coding style checker
component called Checkstyle and see how it helps you define and
enforce a Java coding standard across the project teams.
CheckStyle Starter
With the above background in mind, we will now have an
introduction to the Checkstyle component. Well, Checkstyle is an
open source project hosted by Sourceforge. It is a component
targeted to define and enforce coding standards for Java
language based applications. You can get the binary version from
the following website:
http://checkstyle.sourceforge.net/
In general, Checkstyle helps you to do the following things:
- Checking Javadoc comments
- Checking for Naming conventions
- Checking for Import statements
- Check for size violations
- Check for whitespaces
- Check for Modifiers
- Check for Coding problems
- Checking for Class design
- And other miscellaneous checks
We will now explore how Checkstyle attempts to do the
style checking.
Working of Checkstyle
First of all, Checkstyle allows you to define the coding
standards in the form of a XML file. The Checkstyle component
parses the information provided in the configuration XML file
and then checks any particular Java application against the
defined standards. Upon failure in some checks, the Checkstyle
can produce non-conformation reports in a file.
In essence, the Checkstyle XML configuration file follows a DTD
defined within the Checkstyle binary distribution. The
Checkstyle configuration consists of <module> elements
with one or more <property> elements defined within it.
Each <module> has a name attribute associated with it. The
Checkstyle attempts to load a class defined by the name
attribute. For example,
<module name=”RedundantThrows”>
will ask Checkstyle to load a class named RedundantThrows from
the classpath. Now the question is what if this class has a
package structure. The answer is that you can predefine the
package names in a separate XML file called
checkstyle_packages.xml. As an example, all the default
Checkstyle classes are packaged in
com.puppycrawl.tools.checkstyle package. So the
checkstyle_packages.xml file defines the following:
<checkstyle-packages>
<package name="com.puppycrawl.tools.checkstyle">
<package name="checks"/>
</package>
</checkstyle-packages>
To sum up the general rule of thumb in Checkstyle configuration is that:
- The class that handles any particular type of code checking is called a
module.
- The name of the class to invoke is defined as the name attribute of the
<module> elements in the main checkstyle configuration file.
- The class name can be a fully qualified name of the class or may be only
the name of the class in case using the pre-specified packages.
- In case, you are using pre-specified package mechanism, the package names
need to be defined in the checkstyle_packages.xml file.
- This gives us the flexibility to plug-in our own custom Checker classes
doing some specific things.
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