These guidelines gives some recommendations for those who want to adapt the current code and/or send in new plugins. They should be regarded as recommendations, not rules, but following them will make life easier for both parties.
Furthermore they give guidelines for how to adapt the current code to the design that are already decided and used in the NetarchiveSuite software. This relates to the design described in the System Design document.
Guidelines on Unit tests can be found in Old unit test guidelines.
The coding style was decided in 2014 to be the default Eclipse formatter setting (as of 4.4) with the following additions:
- Line width set to 120 characters (as Java is considered a bit too verbose for the default to work well)
- Indentation is 4 spaces. No tabs.
Source can be formatted by maven using
Note: In order for IntelliJ and Eclipse to format sources interchangeably the import sorting order must be the same. For simplicity we went with the Eclipse defaults.
All imports are declared explicitly unless there is more than 99 classes used in a package (so no * by default) - this has the advantage of being unambigious. We use the following ordering (empty lines included):
- import static *
- import java.*
- import javax.*
- import all other
- import dk.netarkivet.*
Codestyles changes should be initiated in Eclipse and copied to other IDE's.
- Use File->Import->General->Preferences to import eclipse-xml-settings.epf in build-tools/src/main/resources
- Use Preferences->Java->Code Style->Formatter->[Import] to import eclipse-formatter-settings.xml in build-tools/src/main/resources
(README.txt in the root Maven project contains the latest instructions)
- See IntelliJ IDEA 13: Importing Code Formatter Settings from Eclipse for instructions on how to use build-tools/src/main/resource/eclipse-xml-settings.epf.
- Currently importorder is not imported, so these are maintain separatly in IntelliJ . IntelliJ can also export it codestyle, see Copying Code Style Settings.
Or by running the
./precommit.sh script, which includes a step to update file heades.
NetarchiveSuite was designed in another age with a lot of central methods elsewhere being called to provide a given service. It has since been learned that quality improves if it is possible to test individual components on their own without having the full system available, and a good way to do that in Java is to provide external dependencies explicitly in the class constructor, as it allows for providing exactly what is needed in the given situation.
When conversion is complete, it may be realistic to use a dependency injection framework to make this easier to manage.
The Provider<X> interface provides a get() method returning X. This allows for lazy initialization and/or providing an unknown number of X'es.
Nested class definitions
Declare nested classes as static whenever possible. This avoids an unnecessary link back to the outer class, and in particular makes it possible to serialized the inner class even if the outer class is not serializable. The "invisible" link to the outer class found in a non-static inner class can also lead to unexpected memory leaks, as an inner instance may outlive its outer instance and keep it artificially alive through its implicit link. Nested class definitions appear at the beginning of the enclosing class before (static) variables.
The general rule is "put declarations only at the beginning of blocks". We allow one exception from this rule, namely declarations that 1) initialize the variable and 2) depend on previous calculations are allowed be further down the block. Example:
Public methods should always check that their arguments follow the JavaDoc restriction with respect to being null, empty, non-negative etc. The ArgumentNotValid class has a number of useful methods for this.
JavaDoc is strongly encouraged, as the code might explain what happens, but not the why; the JavaDoc must describe the intent of the function, including assumptions and invariants as well as expectations of the arguments. Please add and improve as needed.
We use the apache.commons.logging framework for logging (currently version 1.0.4), which gives us one unified interface that can be realized with different underlying systems.
However, currently the monitoring component requires the underlying implementation to be Jdk14 logging, since it exposes log messages using a LogHandler implementation for the Jdk14 framework. To use another logging framework, this method would need to be redefined for that framework (for instance an appender for Log4J).
Getting a logger
Retrieving an logger is a straightforward matter. Each class uses the logger interface to obtain a logger, using the class name to identify the logger.
Using the logger
Logging messages are generated using the level specific logging methods:
- log.fatal("Error situations where the application can not recover" ,Throwable);
- log.warn("Error situations where the application may continue to operate" ,Throwable);
- log.info("Information about major modules/functionalities. Like Application data loaded, Application services started. also used, where log.config() was used before" ,Throwable)
- log.debug("Major functionalities within individual packages and classes are reported; Also used for tracing. Information within each method may be displayed" ,Throwable)
- log.trace("Detailed tracing information" ,Throwable)
When we used java.util.logging, we used these levels
- logger.severe("Error situations where the application can not recover")
- logger.warning("Error situations where the application may continue to operate")
- logger.info("Information about major modules/functionalites. Like Application data loaded, Application services started")
- logger.config("Only used to report application configuration information")
- logger.fine("Major functionalities within indvidual packages and classes are reported")
- logger.finer("Used for tracing. Information within each method may be displayed")
- logger.finest("Detailed tracing information")
- logger.log( FINER, "Exception logging", exception)
The logging levels and handlers are defined using a configuration filelog.prop=. The loglevels mentioned in this configuration file uses loglevels defined by java.util.logging.Level
An example file:
In order to load the configuration file add the following to the java command lines: