In a previous post we have seen how to execute a Groovy script in our source directories. But what if we want to use the Groovy command line to execute a Groovy script? Suppose we want to evaluate a small Groovy script expressed by a String value, that we normally would invoke like $ groovy -e "println 'Hello Groovy!'". Or we want to use the command line option -l to start Groovy in listening mode with a script to handle requests. We can achieve this by creating a task with type JavaExec or by using the Gradle javaexec method. We must set the Java main class to groovy.ui.Main which is the class that is used for running the Groovy command line.
In the following sample build file we create a new task runGroovyScript of type JavaExec. We also create a new dependency configuration groovyScript so we can use a separate class path for running our Groovy scripts.
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When we use the Context.render method Ratpack's rendering mechanism kicks in. The type of the argument we pass to the render method is used to look up the correct renderer. The renderer implements the Renderer interface and provides the real output. We can add functionality that can work with the object of the Renderer implementation before the actual output is created. We do this by adding a class or object to the registry that implements the RenderableDecorator interface. The interface has a method decorate that accepts the Context and object that needs to be rendered. The code is invoked after the Context.render method, but before the Renderer.render method. This is especially useful when we use template renderers with a view model and with a RenderableDecorator implementation we can augment the view model with some general attributes. Suppose we have a Ratpack application that uses the Groovy text template engine provided by the TextTemplateModule. The module adds a Renderer for TextTemplate objects. Let's write a RenderableDecorator implementation for the TextTemplate, where we add an extra attribute createdOn to the view model:
// File: src/main/groovy/com/mrhaki/ratpack/CreatedOnRendererDecorator.groovy
package com.mrhaki.ratpack
import ratpack.exec.Promise
import ratpack.groovy.template.TextTemplate
import ratpack.handling.Context
import ratpack.render.RenderableDecorator
import java.time.Clock
import java.time.LocalDateTime
import java.time.format.DateTimeFormatter
/**
* Add extra attribute to view model for all TextTemplate renderers.
*/
class CreatedOnRendererDecorator implements RenderableDecorator {
/**
* Apply this decorator for TextTemplate renderers.
*
* @return TextTemplate class.
*/
@Override
Class getType() {
return TextTemplate
}
/**
* Add an extra attribute createdOn to the view model with the current
* date and time.
*
* @param context Context to get Clock instance for this Ratpack application from.
* @param template Template with view model to extend.
* @return Promise with new TextTemplate instance with the extended view model.
*/
@Override
Promise decorate(final Context context, final TextTemplate template) {
final footerModel = [createdOn: createdOn(context)]
return Promise.value(
new TextTemplate(
template.model + footerModel,
template.id,
template.type))
}
/**
* Create formatted date/time String based on
* the Clock available on the Ratpack registry.
*
* @param context Context to get Clock instance from.
* @return Formatted date/time String.
*/
private String createdOn(final Context context) {
final Clock clock = context.get(Clock)
final LocalDateTime now = LocalDateTime.now(clock)
final DateTimeFormatter formatter =
DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
return formatter.format(now)
}
}
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We learned about externalised configuration in a previous blog post. Ratpack provides support out of the box for several formats and configuration sources. For example we can use files in YAML, properties or JSON format, arguments passed to the application, system properties and environment variables. We can add our own configuration source by implementing the ratpack.config.ConfigSource interface. We must override the method loadConfigData to load configuration data from a custom source and convert it to a format that can be handled by Ratpack.
We are going to write a custom ConfigSource implementation that will get configuration data from a database. We assume the data is in a table with the name CONFIGURATION and has the columns KEY and VALUE. The format of the key is the same as for Java properties files.
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In a previous post we learned about the get and getAll methods to get objects from the registry. Ratpack also provides the first method to get objects from the registry. This method accepts a Function that is applied to the elements of a given type. The first element where the Function returns a non null value is returned encapsulated in an Optional object. If the Function returns a null value for all elements than Optional.empty() is returned.
package com.mrhaki.ratpack
import ratpack.registry.Registry
import ratpack.registry.RegistrySpec
import spock.lang.Specification
class FindFirstRegistrySpec extends Specification {
Registry registry
def setup() {
// Setup registry with two objects of type User.
registry = Registry.of { RegistrySpec registrySpec ->
registrySpec.add(new User(username: 'mrhaki'))
registrySpec.add('hubert')
registrySpec.add(new User(username: 'hubert'))
registrySpec.add('mrhaki')
}
}
def "find User where username starts with mr"() {
when:
// First element that returns a non null value
// is return encapsulated in an Optional.
final Optional user = registry.first(User) { user ->
// If username property starts with
// "mr" than return user as non null value.
user.username.startsWith("mr") ? user : null
}
then:
user.get().username == 'mrhaki'
}
}
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Grails 3.1 allows us to build a runnable WAR file for our application with the package command. We can run this WAR file with Java using the -jar option. In Grails 3.0 the package command also created a JAR file that could be executed as standalone application. Let's see how we can still create the JAR with Grails 3.1.
First we use the package command to create the WAR file. The file is generated in the directory build/libs. The WAR file can be run with the command java -jar sample-0.1.war if the file name of our WAR file is sample-0.1.war. It is important to run this command in the same directory as where the WAR file is, otherwise we get an ServletException when we open the application in our web browser (javax.servlet.ServletException: Could not resolve view with name '/index' in servlet with name 'grailsDispatcherServlet').
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Interesting links for week 5 2016:
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In a previous post we learned how to save the application PID in a file when we start our Grails application. We can also save the port number the application uses in a file when we run our Grails application. We must use the class EmbeddedServerPortFileWriter and add it as a listener to the GrailsApp instance. By default the server port is saved in a file application.port. But we can pass a custom file name or File object to the constructor of the EmbeddedServerPortFileWriter class.
In the following example we use the file name application.server.port to store the port number:
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The Spring Cloud project has several sub projects. One of them is the Spring Cloud Config Server. With the Config Server we have a central place to manage external properties for applications with support for different environments. Configuration files in several formats like YAML or properties are added to a Git repository. The server provides an REST API to get configuration values. But there is also a good integration for client applications written with Spring Boot. And because Grails (3) depends on Spring Boot we can leverage the same integration support. Because of the Spring Boot auto configuration we only have to add a dependency to our build file and add some configuration.
Before we look at how to use a Spring Cloud Config server in our Grails application we start our own server for testing. We use a local Git repository as backend for the configuration. And we use the Spring Boot CLI to start the server. We have the following Groovy source file to enable the configuration server:
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To get objects from the registry or context we specify the type of the object we want. Ratpack will find the object(s) that match the given type. If we use the get method then the last object added to the registry with the given type is returned. To get multiple objects we use the getAll method. The methods returns an Iterable with the found objects where the last added objects are returned as first elements.
In the following example specification we have a Registry with some objects, of which two are of type User. Next we use the get and getAll methods to get the objects.
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We can use the wiretap method of the Promise interface to listen in on results. We write an Action implementation which has the result of a Promise encapsulated in a Result object. The wiretap method can be used to do something with a Promise value without interrupting a method chain.
In the following example we tap in on Promise results:
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In a Spock specification we write our assertion in the then: or expect: blocks. If we need to write multiple assertions for an object we can group those with the with method. We specify the object we want write assertions for as argument followed by a closure with the real assertions. We don't need to use the assert keyword inside the closure, just as we don't have to use the assert keyword in an expect: or then: block.
In the following example specification we have a very simple implementation for finding an User object. We want to check that the properties username and name have the correct value.
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Interesting links for week 4 2016:
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