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Introduction to Custom Ant Tasks

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❶One such type is the simple task, where you define the task with an action closure.

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Build Events
Writing Your Own Task
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I will adopt this pattern for the discussion, using element name "helloworld" and a Java package and classname of org. The declaration and use of a package is highly encouraged.

If you are a weekend coder and do not know what to use as a package name, use something like "org. If you define a constructor, it should be a public, no-arg constructor. In fact, Ant will call your init method prior to calling your other methods to deal with nested elements and attributes and such to do initialization work, so you can dispense with explicitly defined constructors entirely. The second argument in the log method is the priority level that the message is emitted at.

This is an optional argument. If you use the log "some message" version, you get an "INFO" level message. Possible values are available in a set of constants in the Project class. I have saved my source file underneath a "src" folder, and I am compiling this file into the "classes" folder. Strictly speaking, this step is optional, but creating a jar file for your Ant task will enhance portability and ease-of-use.

Also, you have a few choices to register your task with Ant in the next step, but the easiest choice, in my opinion, involves the use of a properties file. Save this as a properties file. I will use "MyAntTasks. Now, create a standard jar file which includes your class file and this properties file. On a command line, you might do this:. With this jar file available, you are nearly ready to use your custom task in your own build.

The final step is to register your task name and class file so Ant knows where to pass control to at the proper time. Because you have a jar file with a properties file, this is rather simple. You started this article with a build. Ant is capable of generating build events as it performs the tasks necessary to build a project. Listeners can be attached to Ant to receive these events. To use build events you need to create an ant Project object.

You can then call the addBuildListener method to add your listener to the project. Your listener must implement the org. The listener will receive BuildEvents for the following events. If you are interested in those events, all you need to do is to implement the new interface instead of BuildListener and register the listener, of course.

If you wish to attach a listener from the command line you may use the -listener option. This listener is included with Ant, as is the default listener, which generates the logging to standard output.

A listener must not access System. Accessing these streams can cause an infinite loop in Ant. Depending on the version of Ant, this will either cause the build to terminate or the JVM to run out of Stack space.

A logger, also, may not access System. It must use the streams with which it has been configured. Writing an adapter to your favourite log library is very easy. Just implement the BuildListener interface, instantiate your logger and delegate the message to that instance.

When starting your build provide your adapter class and the log library to the build classpath and activate your logger via -listener option as described above. The other way to extend Ant through Java is to make changes to existing tasks, which is positively encouraged. Both changes to the existing source and new tasks can be incorporated back into the Ant codebase, which benefits all users and spreads the maintenance load around.

Tools like the Kotlin compiler provide incrementality as a built-in feature. The way this is typically implemented is that the tool stores some analysis data about the state of the previous execution in some file. If such state files are relocatable , then they can be declared as outputs of the task. Indeed, when the task is loaded from cache, any such state files must be cleaned up to prevent stale state to confuse the tool during the next execution.

Gradle can ensure such stale files are removed if they are declared via task. The API for exposing command line options is an incubating feature. Sometimes a user wants to declare the value of an exposed task property on the command line instead of the build script.

Being able to pass in property values on the command line is particularly helpful if they change more frequently. The task API supports a mechanism for marking a property to automatically generate a corresponding command line parameter with a specific name at runtime.

Exposing a new command line option for a task property is straightforward. You just have to annotate the corresponding setter method of a property with Option.

An option requires a mandatory identifier. Additionally, you can provide an optional description. A task can expose as many command line options as properties available in the class. The URL to be verified is configurable through the property url. The setter method for the property is annotated with Option.

All options declared for a task can be rendered as console output by running the help task and the --task option. The option uses a double-dash as prefix e. A single dash does not qualify as valid syntax for a task option.

The option argument follows directly after the task declaration e. Multiple options of a task can be declared in any order on the command line following the task name. Getting back to the previous example, the build script creates a task instance of type UrlVerify and provides a value from the command line through the exposed option. Gradle limits the set of data types that can be used for declaring command line options.

The use on the command line differ per type. Describes an option with the value true or false. Passing the option on the command line does not require assigning a value. For example --enabled equates to true. The absence of the option uses the default values assign to the property; that is false for boolean and null for the complex data type. Describes an option with an arbitrary String value.

Passing the option on the command line requires a key-value pair of option and value separated by an equals sign e. Describes an option as enum. The enum has to be passed on the command line as key-value pair similar to the String type e. The provided value is not case sensitive. Describes an option that can takes multiple values of a given type.

The values for the option have to be provided as distinct declarations e. Other notations like comma-separated lists or multiple values separated by a space character are currently not supported. Expected values for such an option can be documented programmatically with the help of the annotation OptionValues.

This annotation may be assigned to any method that returns a List of one of the supported data types. In addition, you have to provide the option identifier to indicate the relationship between option and available values. Passing a value on the command line that is not supported by the option does not fail the build or throw an exception. This example demonstrates the use of multiple options for a single task.

The task implementation provides a list of available values for the option output-type. Command line options using the annotations Option and OptionValues are self-documenting.

You will see declared options and their available values reflected in the console output of the help task. The output renders options in alphabetical order. Command line options can only be declared for custom tasks via annotation. When assigning an option on the command line then the task exposing the option needs to be spelled out explicitly e. As can be seen from the discussion of incremental tasks , the work that a task performs can be viewed as discrete units i.

Many times, these units of work are highly independent of each other, meaning they can be performed in any order and simply aggregated together to form the overall action of the task. In a single threaded execution, these units of work would execute in sequence, however if we have multiple processors, it would be desirable to perform independent units of work concurrently.

By doing so, we can fully utilize the available resources at build time and complete the activity of the task faster. The Worker API provides a mechanism for doing exactly this. It allows for safe, concurrent execution of multiple items of work during a task action. But the benefits of the Worker API are not confined to parallelizing the work of a task.

You can also configure a desired level of isolation such that work can be executed in an isolated classloader or even in an isolated process. Furthermore, the benefits extend beyond even the execution of a single task. In other words, once a task has submitted its work to be executed asynchronously, and has exited the task action, Gradle can then begin the execution of other independent tasks in parallel, even if those tasks are in the same project.

In order to submit work to the Worker API, two things must be provided: The implementation is simply a class that extends java. This class should have a constructor that is annotated with javax.

Inject and accepts parameters that configure the class for a single unit of work. When a unit of work is submitted to the WorkerExecutor , an instance of this class will be created and the parameters configured for the unit of work will be passed to the constructor. The configuration of the worker is represented by a WorkerConfiguration and is set by configuring an instance of this object at the time of submission. However, in order to submit the unit of work, it is necessary to first acquire the WorkerExecutor.

To do this, a constructor should be provided that is annotated with javax. Inject and accepts a WorkerExecutor parameter. Gradle will inject the instance of WorkerExecutor at runtime when the task is created. Note that one element of the WorkerConfiguration is the params property. These are the parameters passed to the constructor of the unit of work implementation for each item of work submitted. Any parameters provided to the unit of work must be java.

Once all of the work for a task action has been submitted, it is safe to exit the task action. The work will be executed asynchronously and in parallel up to the setting of max-workers. Of course, any tasks that are dependent on this task and any subsequent task actions of this task will not begin executing until all of the asynchronous work completes.

However, other independent tasks that have no relationship to this task can begin executing immediately. If any failures occur while executing the asynchronous work, the task will fail and a WorkerExecutionException will be thrown detailing the failure for each failed work item. This will be treated like any failure during task execution and will prevent any dependent tasks from executing. In some cases, however, it might be desirable to wait for work to complete before exiting the task action.

This is possible using the WorkerExecutor. As in the case of allowing the work to complete asynchronously, any failures that occur while executing an item of work will be surfaced as a WorkerExecutionException thrown from the WorkerExecutor.

Note that Gradle will only begin running other independent tasks in parallel when a task has exited a task action and returned control of execution to Gradle. This means that Gradle will not allow other tasks to begin executing and will wait for the task action to complete before doing so.

Gradle provides three isolation modes that can be configured on a unit of work and are specified using the IsolationMode enum:.


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Developing with Apache Ant Writing Your Own Task. It is very easy to write your own task: Create a Java class that extends or another class that was designed to be extended.; For each attribute, write a setter method. The setter method must be a public void method that takes a single argument. The name of the method must begin with set, followed by the attribute name.

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Introduction to Custom Ant Tasks. When I realized the task day that I was going to need to create a new custom Ant task, I was excited by the potential task post fodder.

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Tutorial: Writing Tasks. This document provides a step by step tutorial for writing tasks. Content. Set up the build environment; Write the Task; Use the Task. Create your own Ant task: Custom Task «Ant «Java When I realized the writing day that I was going to need to create a new custom Ant task, I was excited by the potential writing custom .

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