Property dependencies

The build system allows reporting dependencies for environment and execution level properties. Properties are used to determine various aspects of the associated environment.

Such properties can be:

• Current Java Runtime version.
• Underlying operating system type.
• Value of an execution user parameter.
• Other custom defined properties.

These can be useful when a build task depends on a given configuration of the environment. In case these change, the task will be rerun with an appropriate delta.

Both the environment property (EnvironmentProperty) and execution property (ExecutionProperty) interfaces define a function (getCurrentValue) that is responsible for calculating their value based on the appropriate context. The calculated values should adhere to the equality functions of Object.

The property interface implementations should adhere to the hashCode and equals contract of Object as well. Clients can implement their own versions of these properties at will.

public String run(TaskContext taskcontext) throws Exception {
	String exuserparam = taskcontext.getTaskUtilities()
			.getReportExecutionDependency(
					new UserParameterExecutionProperty("execution.user.parameter"));
	String envuserparam = taskcontext.getTaskUtilities()
			.getReportEnvironmentDependency(
					new UserParameterEnvironmentProperty("environment.user.parameter"));
	//do something more meaningful with the values
	return exuserparam + envuserparam;
}

In the above example we retrieve the values of the specified user parameter based properties, and right away report them as dependencies using the function given in the task utilities. The TaskContext.reportEnvironmentDependency or TaskContext.reportExecutionDependency functions could've been used as well to do that.

In order to retrieve a property value without reporting it, you can use the ExecutionContext.getExecutionPropertyCurrentValue and SakerEnvironment.getEnvironmentPropertyCurrentValue functions.

When you report a property dependency, it will be checked again when the next build is run. If it changes, the task will be reinvoked with an appropriate delta.