SMILA/Development Guidelines

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This page covers a collection of development guidelines whose compliance should ensure that SMILA appears as a unified product rather than as a loose collection of parts worked on by a variety of individuals each with their own styles and ways of working. Furthermore it contains information on the used software components and requirements and provides descriptions (how-tos) of common tasks (e.g. setting up the development environment).


How-to manuals

Find a list of How-To manuals at SMILA How-to manuals.

Development requirements


The officially Java version needed for this project is Java 1.7.

OSGi runtime

The OSGi implementation of Equinox of Eclipse 3.7 or later and the corresponding OSGi specification(s).

Development conventions

Description of make.xml

For a description of the build file make.xml refer to Introduction to make.xml.

Continuous integration

Each developer should check his code before committing it to subversion regarding:

The failed JUnit tests are reported at the end of the build output.

Furthermore the full JUnit reports are generate under and the error messages from the JUnit reports are stored under

Everyone should monitor the trunk at the build server and if there is a "red" build everyone should look if he has committed the error.

If the error could not be solved within the next build, the developer should inform the developer team that there is a problem with the build and that he is working on the solution.

File header & copyright notice

For guidelines on file header and copyright notices see Project Guidelines.

Eclipse code formatter profile

The Eclipse code formatter file is available in trunk at SMILA.builder/eclipse-formatter/Eclipse-formatter-Brox-3.2-3.3.xml.

To import the Eclipse code formatter profile:

  1. Select Window > Preferences in Eclipse and switch to the Java > Code Style > Formatter preferences page.
  2. Click the Import button and select the downloaded formatter file.
formatter vs. save actions
most source files have been edited with the save action turned on: "remove trailing white spaces on all lines". If you dont have this set then formatting the whole file will result in a lot white space of changes, which is cumbersome as is clutters diffs and poses problems to patches. So please turn this feature on.


Each Eclipse project (bundles) should follow the SMILA Coding Conventions.

We use different checkstyle rules for "normal" bundles and test bundles. So there are two files containing the Checkstyle configurations in the trunk that you have to import (see below).

Eclipse checkstyle plugin

The eclipse-cs Checkstyle plugin integrates the source code analyzer Checkstyle into Eclipse IDE. By using this plugin your code is constantly inspected for problems. Within the Eclipse workbench you are notified of problems via the Eclipse Problems View and source code annotations just as you would see with compiler errors or warnings. The Checkstyle Eclipse plugin can be obtained from the update site: Instructions about how to set up the Checkstyle plugin for your project can be obtained from here.

Setup checkstyle configuration

  1. Click Window > Preferences in Eclipse.
  2. Select the Checkstyle preference page and click the New button.
  3. Select External Configuration File as Type and point to the location of the file
    (if using checkstyle 4.x) SMILA.Builder/checkstyle/smila_checkstyle.xml.
    (if using checkstyle 5.x - recommended) SMILA.Builder/checkstyle/smila_checkstyle-5.xml.
  4. This Checkstyle configuration profile should be named (while importing): "SMILA Checkstyle" and it should be set as default.
  5. Select External Configuration File as Type and point to the location of the file
    (if using checkstyle 4.x) SMILA.Builder/checkstyle/smila-test_checkstyle.xml.
    (if using checkstyle 5.x - recommended) SMILA.Builder/checkstyle/smila-test_checkstyle-5.xml.
  6. This Checkstyle configuration profile should be named (while importing): "SMILA Test Checkstyle".


Most checkstyle warnings will be self-explaining. But there are two metrics considering method complexity that should be pointed to here explicitly, in case you got appropriate warnings:

Reduce javadoc overhead

Instead of writing member variable comments as

 * switch to true to add newlines for better readability, but poorer performance. 
 private final boolean _printPretty;

it's more readable and clearer to write such javadoc comments as one line:

 /** switch to true to add newlines for better readability, but poorer performance. */
 private final boolean _printPretty;

Creation of bundles

For information on creating and integrating bundles refer to the following pages:

Naming conventions for launch files (.launch)

It is a good thing to share your launches and many do so already which helps greatly to run tests quickly from within Eclipse. However, in order that at least I don't get confused, we need to define a naming scheme for the .launch files!

Preliminary convention: <bundle name>[_config name].launch

The [config name] part is optional and needed when several .launch files exist for the same bundle but with different settings.

Generated source code goes into code/gen source folder (like Jaxb)

All generated source code (eg. JAXB) goes into the distinct source code folder code/gen. Where possible all generated classes should also have their own package. Reasons:

  • Separate generated source code from handwritten code
  • Easier filtering for Checkstyle

(see Setup for JAXB code generation for details specific to creating crawler configurations.)

Logging guidelines

In SMILA apache commons logging is used with log4j. The are located in SMILA.application. Here are some guidelines how and when logging should be used:

  • use local Log instances in each class where you want to log:
private final Log _log = LogFactory.getLog(MyClass.class);
  • always check log level before logging 'debug' and 'info', e.g.
if (_log.isDebugEnabled()) {
    _log.debug("Your debug message", e);

For 'warn' and 'error' messages the log level check can be omitted.

  • do not log exceptions before throwing new exceptions, e.g.
if( paramXY == null ) {
    if (_log.isErrorEnabled()) {
        _log.error("paramXY is not set");
    throw new NullPointerException("paramXY is not set");

I advise against this as it only causes the same message to be repeated at least twice, namely when the exception is created and then when the exception is logged itself. IMO it is sufficient to have a verbose error msg and this then is reported along with the stack trace when the exception is logged. if the exception is handled then this message is even confusing b/c u have ERROR log entry but wonder: what happened then? if u deem the condition so extraordinary and dangerous we could log it as WARN, but since we don't log the eception here it should not be level ERROR.

Even worse than this is sometimes the habit to log an exception before (re)throwing or wrapping it, which I have seen often (in general, not this project in particular). this then has the effect that u have the same exception logged several times which makes the log very verbose and confusing. as u think u have lot of problems/exception when it fact it is only that one case.
Log and throw makes only sense in a client-server architecture. We have no clients except Jconsole and the JmxAgent, and these clients use JMX for the commmuncation, thus Exceptions are not "forwarded".

I think we should use the Rule: Never log and throw. Because the "process" that catches the exception is responsible for logging.

see: Mail thread

When to use what log level and what information to provide?

FATAL designates very severe error events that will presumably lead the application to abort.
ERROR designates error events that might still allow the application to continue running.
WARN designates potentially harmful situations.
INFO for the "high level" information. For example - interesting runtime events (startup/shutdown).
DEBUG only for the software developer interesting messages (detailed information on the flow through the system).

A good resource on how to use the levels in regard to the Enterprise context offers JCL Best Practices.

Read here further about Useful Log Messages for Smila.

Used technologies

OSGi related information