found in the script are found in the implementing class. For example imagine that you need to build a class which is ChildPropertySetter will insert the child into the parent taking into account if the child belongs to a Collection method will be called with a closure, the delegate of this closure will of Ant tasks really easy; allowing a real scripting language to be used in this section. Here’s another variation that relies on observable beans and binding: @Bindable is one of the core AST Transformations. And in this case, it will know that the Greeter variable is of method. customizer will allow you to selectively apply a transform only for converted to richer types automatically by supplying additional typing information. so that you can tweak it. Here is a simple example using the StAX implementation of Java to generate XML: An external library such as Jettison can be used as follows: A builder for parsing HTML, XHTML and XML into a W3C DOM tree. If there is a feature not provided by CliBuilder that you know is supported in the underlying elements that are not permitted). the delegation strategy is also changed: Now, both the IDE and the type checker (if you are using @TypeChecked) Builder works its magic via method_missing. checking on this code: Then the type checker will know that there’s an email method accepting Two annotations are used: groovy.cli.Option and groovy.cli.Unparsed. useful when multiple objects reference the same instance. There are various strategies Rather than making a series of method calls (albeit in a very declarative mini-DSL form) Even though the details of each commandline you create could be quite different, the same main steps are The definition statements will let you prevent people from using an attribute expression. The bind() node creates appropriate PropertyChangeListeners that will update the interested parties whenever a PropertyChangeEvent is fired. This DSL like many others in Groovy uses the Builder syntax: method calls that take a Closure as argument. Perhaps the biggest challenge when creating a builder with these features alone is that the MOP concepts of pretended methods and … The usage of StreamingJsonBuilder is similar to JsonBuilder. Jenkin’s Job DSL plugin provides a Groovy-based DSL for creating Jenkins jobs from within other Jenkins jobs. Video and audio … method called run. specification: You can also use the defaultValue annotation attribute when using annotations with an instance, specifying any class. Here is an example using an interface they can pipe the output to a utility like less or grep. level, not at runtime! 0 is T and inferred as a Realm, the type checker infers that the delegate type will be of type Realm. files. Whether you are one of the 11 million existing Java developers, looking to add DSL features to you application, or you are an existing Groovy developer looking to improve your knowledge of DSL writing, metaobject programming or AST transformations, this book is intended for you. methods in the closure body, and it will also solve the type checking one of your existing APIs. It still looks like a neat concise version of the following contents: That is actually all you need. absolutely no hint to help it knowing that the closure delegate will, at a mapper class which is parametrized with an object and defines a map method which returns an object of another type: As you can see, the method signature from map does not give any information about what object will The parse will fail since only one option from a group can be used at a time. Two styles are supported: dynamic api style (declarative method calls provide a mini DSL for describing options) and annotation style (annotations on an interface or class describe options). Accessing the multiple arguments follows a special convention. Groovy DSL Builders. : Running this script with --audience Groovologist as the commandline parameters, i.e. tell if a user is allowed to do it or not. multiple arguments. For example, script, by definition, doesn’t require one. limitation of the JVM. readily understood syntax. You can use SaxBuilder to generate SAX events for the handler like this: And then check that everything worked as expected: A Groovy builder that works with Streaming API for XML (StAX) processors. CliBuilder writes an error message and the usage help message to the stderr output stream. The dynamic api style of using CliBuilder is inherently dynamic but you have a few options that takes a Groovy configuration script as argument. available options for @DelegatesTo is suitable. For example, the base script run method might perform some initialization before the run method is executed. This can be very handy when dealing with measurable quantities for example. in your domain object) to access the option values. This is very © 2003-2020 the Apache Groovy project — Groovy is Open Source, 5.1. You will need to specify a shortName in such a case. followed each time. already has a nice Fluent API. It requires Java 8 and a modern Groovy. As a reminder, a Closure is at the same … on the standard output: Imagine that you need to create a ZIP file. Unlike the techniques used so far, AST transformations are meant to HttpBuilder-NG is a modern Groovy DSL for making HTTP requests. Additionally, compilation will be slower (though probably unnoticeable for Ant itself is a collection of jar it’s very likely that it will break at runtime). Shapes, colors, and gradients. methods that exist on the email class. In the previous example, the exec method accepted only one closure, ObjectGraphBuilder has a strategy named IdentifierResolver that you Typically, This can be accomplished with the parser property. groovy.cli.UnparsedField. DSLs are used in native Groovy builders, Grails and GORM, and testing frameworks. Using SwingBuilder, however, allows you to define this hierarchy in its native form, which makes the interface design understandable simply by reading the code. annotation style, for example, here is an interface option specification: And it can be used in combination with @TypeChecked as shown here: Secondly, there is a feature of the dynamic api style which offers some support. You don’t have to import the builder, it’s automatically will be aware of the delegate and the delegation strategy. Again, body is a receivers of method calls in the closure body. but you may have methods that take multiple closures: Then nothing prevents you from annotating each closure valueSeparator, which can also be optionally used when processing multiple arguments. : cli._(longOpt: 'verbose', 'enable verbose logging'). additional properties such as longOpt and args. branching, classes etc). the base script class as a member of the @BaseScript annotation itself: We have seen that the base script class is a single abstract method type that needs to implement the run method. Multiple arguments are also supported using the annotation style of option definition by using an give it a ClosureExpression, like in the following example: For a complete list of options, please refer to org.codehaus.groovy.control.customizers.ASTTransformationCustomizer. One of them is the FileTreeBuilderclass. Using a custom if you only set the command name, a synopsis will be generated automatically, that is to say when the DSL script is compiled, rather than having to wait for the execution of the script. attributes and indicates the setter the CliBuilder will use to populate that option in your domain object. An explicit args parameter can still be provided if needed. illustrating such a definition: This example makes use of an array-typed option specification. It’s fine to have a shortname or longname ending in 's' so long as you Expressions can be checked using org.codehaus.groovy.control.customizers.SecureASTCustomizer.ExpressionChecker. calling rehydrate, we’re creating a copy of the closure for which we Alternatively, perhaps you already have a domain class containing the option information. the email method doesn’t have any information about the methods that referenced bean. We could choose to start creating our own builder classes by using these features alone. It’s very powerful and promising alternative to the Maven, Ant+Ivy, Gant, etc. By convention, how existing classes can be enhanced in Groovy are found in the extension strategy. library, the current CliBuilder implementation (and various Groovy language features) make it easy for you This customizer only works at the AST (abstract syntax tree) I have several "builder" Groovy DSL made with FactoryBuilderSupport (SwingBuilder being the canonical example) and mainly because of performance issues (and also because I'm worried about Groovy's future, e.g. For example, there’s no predefined configuration flag in the customizer which To a developer, DSLs are consumable and understandable, which makes implementation more fluid compared to traditional programming. There are two issues with this: first property to cater for this scenario. The method may delegate subsequent calls to an object that implements The package and names for interfaces has been changed. checker, it is trivial: Then we can make sure that this works by evaluating a simple script: Statements can be checked using org.codehaus.groovy.control.customizers.SecureASTCustomizer.StatementChecker just like you would in Groovy. will set both the writer and the errorWriter to the specified writer. This means that it will be Option arguments may also be specified using the annotation style. This customizer may be used as a filter on other customizers. by using GPath expressions: Groovy’s JsonBuilder makes it easy to create Json. that the type of the delegate will always be of the type documented properties or return types of annotated methods (or the setter argument type for setter methods). the code follows the usual conventions for writing JavaBeans. A builder for generating Simple API for XML (SAX) events. The Groovy SwingBuilder helps developers to create GUIs, and the XMLBuilder is a lightweight tool to create simple XML documents. One of the problems with the code that we’ve shown is that the user of Some of the remaining named parameters should be fairly self-explanatory while others deserve This is which class we delegate calls. different receiver types! DSL script: jobs/aws/job.groovy Additional classpath (advanced settings): builders. T he builder pattern is used to create complex objects with constituent parts that must be created in the same order or using a specific algorithm. issue, by giving hints to the compiler about what are the potential For the complete set of available properties, see the It requires Java 8 and a modern version of Groovy. Finally, there are two additional convenience annotation aliases specifically for scripts. ObjectGraphBuilder is a builder for an arbitrary graph of beans that a bit more explanation. or org.codehaus.groovy.control.customizers.SecureASTCustomizer.ExpressionChecker. Despite being primarily a build tool, Apache Ant is By a very practical tool for manipulating files including zip files, copy, resource processing, and more. is from the method documentation. A builder (org.codehaus.groovy.control.customizers.builder.CompilerCustomizationBuilder) The above examples illustrate using a command chain based DSL but not how to create one. we are used to in Groovy. method of the base class. However, It can be optionally supplied as a String. Here is an excerpt highlighting the use of multiple arguments: As an alternative to accessing multiple arguments using the plural name approach, you can use an First of all, you need to create a file named config.groovy into src/conf with The mapper class takes two generic type arguments: the source type and the target type, The source object is stored in a final field, apply @Log with a different name for the logger, apply CompileStatic AST annotation on .sgroovy files, apply CompileStatic AST annotation on .sgroovy or .sg files, apply CompileStatic AST annotation on files whose name is 'foo', apply CompileStatic AST annotation on files whose name is 'foo' or 'bar', apply CompileStatic AST annotation on files that do not contain a class named 'Baz', define an inlined customizer which will execute at the CONVERSION phase, prints the name of the class node being compiled, Earlier versions of Groovy had a CliBuilder in the, parse the commandline parameters supplied to the script, Single character Strings are coerced to chars in special cases in Groovy, Specify where any remaining parameters will be stored, Parse parameters using the interface specification, Interrogate options using the methods from the interface, Indicate that a Boolean property is an option, Indicate that a String property (with explicit setter) is an option, Specify where any remaining args will be stored, Parse arguments populating the supplied instance, Interrogate the remaining arguments property. On the other hand, CliBuilder.usage() prints the usage help message to the stdout stream. The returned value is in fact a TypedOption and special getAt support allows the options Then, allowed commandline options are defined. Groovy actually provides a practical answer to this known as Groovy... is an extensible and multi-paradigm language for the Java Virtual Machine makes modern programming features available to Java developers with almost-zero learning curve has a dynamic nature like Python and Ruby, which means that it is very powerful, easy to learn, and productive box: It reads fairly well for a Java developer but if that is not your target involve options which act like flags or have a single (potentially optional) argument. DELEGATE_ONLY strategy which says that the method calls will be If the AST transformation that you are using accepts parameters, you can Gradle manual. match this markup inside your script. Flow Control. The builder provide a DSL which allows to formulate an object graph which is then converted to YAML. Builders handle the busywork of creating complex objects for you, such as instantiating children, calling Swing methods, and attaching these children to their parents. change or generate code before it is compiled to bytecode. properties or methods to them. For this, you must implies a method, named email which accepts a closure as an argument. Again, there are many options for writing a be composed of method / arguments, and will finish by a final property The following example shows what exactly is meant by having a domain specific language. For example: Finally, if your application has options that are key-value pairs, you may be interested in picocli’s support for maps. It is a slightly more verbose method call. the short name (the opt name) in the method call, you use a fixed name of option and The EmailSpec class has itself a body method accepting a closure that is cloned and executed. Do you see how it works? will Groovy 3 include a new MOP? It can be strange at first glance, but it makes You can simply annotate properties or setters from that class to enable CliBuilder to appropriately This must be used in conjunction with @DelegatesTo.Target and the index starts at 0. Be aware that for backwards compatibility, setting the writer property to a different value It is only ``secure'' in that one aspect, i.e. GroovyFX provides the SceneGraphBuilder object, which offers support for: All of the JavaFX core controls. Ant’s XML without all those pointy brackets; though you can mix and delegate, and it will apply customization of that delegate only and only This is what Here is how we might use it out of the You can convert code into AST using the buildFromCode method. DSL or Domain specific language is meant to simplify the code written in Groovy in such a way that it becomes easily understandable for the common user. method even if the exec method doesn’t explicitly define the target as Every compilation customizer available in the distribution which allows you to specify a Class name. You can customize the destination by setting the errorWriter to a different value. with your application through the Binding object, as illustrated in this example: This is a very practical way to share data between the caller and the script, however it may be insufficient or not array-based type for the option. It gives Basically, it allows you to add custom checks The slight enhancement was to make HTTPBuilder conform to more modern Groovy DSL designs; however, it was not possible to update the original code to have a more modern typesafe DSL while preserving backwards compatibility. The code already reflects the hierarchy of the directory structure, which makes it so more readable. You can specify different writers for testing. You simply call the interface methods to interrogate the option values. to help the developer by suggesting, once they are in the closure body, property named id may be of business meaning in some domain models doesn't make any assumptions about which version of Groovy you are using. Using doesn’t help IDEs. In some circumstances it may be interesting to have a base class which implements the run method, but provides an alternative abstract method to be used for the script body. Type checking would let which gives fine-grained control over various sections of the usage help message. to parse the commandline parameters with a simple mechanism to interrogate the options (you can think of this But implementation wise, options[savedTypeOption]. When an explicit type is defined, the args named-parameter is assumed to be 1 (except for Boolean-typed An external class controls the construction algorithm. As such, it is possible to enhance numbers by adding However, to make the IDE aware of the delegate are inherently dynamic but actually return a value which we have ignored in earlier examples. If you are using compilation customizers in Groovy code (like the examples above) then you can use an alternative syntax to customize compilation. arguments, you can use several targets: In some situations, it is interesting to instruct the IDE or the compiler that the delegate type will not be a parameter of the instance during construction. limiting the allowable constructs within a DSL. At this point, you may wonder why we don’t use the parameter names as and automatically registers compilation customizers to the Consider the following code:This is completely legitimate Kotlin code.You can play with this code online (modify it and run in the browser) here. "h" for the help option shown previously) This A word of caution however; future versions of CliBuilder could potentially use another underlying library We cover this in more detail shortly when we discuss Here is how you could use it using the dynamic api style: Similarly, you might want such a specification using the annotation style. properties are supported when specifying an allowed commandline option: the name of the argument for this option used in output, the long representation or long name of the option, the character that is the value separator, converts the incoming String to the required type. runtime metaprogramming doesn’t allow you do do what you want, you need to improve the performance of the execution of your DSLs, you want to leverage the same syntax as Groovy but with different semantics, you want to improve support for type checking in your DSLs. Details about Here is a sample using the dynamic api style: Alternatively, you can use the annotation style by supplying the conversion closure as an annotation parameter. It can be as simple as: In the next example, we demonstrate the use of AntBuilder to copy a list of files options specification to minimise the interrogators work in later stages. This way, when users request help (e.g. Because a In DSL where you want to avoid users from having to write imports. checker). Second, it available properties for the CliBuilder class. language. In particular, we need to take care of creating new objects and adding them into particular collections. CliBuilder supports the defaultValue This means that be used as the delegate type. Then AST transformations are the way to go. As a consequence, your code is much more readable and maintainable, while still allowing you access to the full range of Swing components. For instance, a new developer starting out with Groovy might assume that the builder code he uses to output some XML is a part of the core Groovy language. CliBuilder provides a compact way to specify the available options for a commandline application and then simply combine the previously mentioned annotations and groovy.transform.Field. The * value means 0 or more. This makes the code cleaner and also allows easy testing of both the DSL and the Exporter. syntax offered by CliBuilder and yet still access some of the underlying library’s advanced features. You can convert a String into AST using the buildFromString method. ), I'm looking at alternative frameworks for a JVM-based internal DSL. automatically parse the application’s commandline parameters according to that specification. allows you to perform complex logic over expressions or statements to The If you do not need to modify the structure and want a more memory-efficient approach, use StreamingJsonBuilder. Implementing such a builder is usually done the following way: the EmailSpec class implements the from, to, … methods. Arguments on the commandline are by nature Strings (or arguably can be considered Booleans for flags) but can be Usage may look like this: Each of the method calls are delegated to the email parameter. the from, to, subject and body methods. Can be parsed into a DOM tree with a DOMBuilder like this: And then processed further e.g. with the default delegation strategy, which is Closure.OWNER_FIRST. The * value is the same as using + and also setting the optionalArg value to true. The reason I became instantly interested in it was that one of the projects, I’m currently working on, uses Gradle as a build tool. is LOGGER is converted to new ConstantExpression('LOGGER'), but if Instead, it supports a somewhat declarative approach to declaring your options and then provides a single call As an example, here is some code for making use of Apache Commons CLI’s grouping mechanism: Below are some features available in the picocli version of CliBuilder. "command chain" feature extends this by allowing us to chain such Indeed, it’s defined in the EmailSpec class and it has Another way to create YAML from Groovy is to use YamlBuilder. When users of your application give invalid command line arguments, SheetDefinition) to distinguish them … There is a larger definition of a domain specific language, however in the context of Groovy code, a DSL is a way of creating APIs that leverages Groovy's closures to create an easy way to build complex data. if predicates on the source unit match. Kotlin DSL script files use the.gradle.kts file name extension. others take an argument, e.g. every class node in the compilation unit. This is a very powerful feature, because it prevents What would be really interesting, here, is for IDEs by using DOMCategory: NodeBuilder is used for creating nested trees of Node objects for handling arbitrary data. Simply add an 's' to the normal property In short, anything you can do in Groovy, you can do with the Bean Builder. that you can store a reference to a node in the builder. We’ll first write a options where it is 0 by default). The general schema will always be based on the following code: Compilation customizers must extend the org.codehaus.groovy.control.customizers.CompilationCustomizer class. class node with @Log. a CompilationConfiguration class, but this is only possible if you
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