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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In a previous blog post we learned how to use HandlerDecorator.prepend to add common handlers via the registry in our application. The type of handlers suitable for this approach were handlers that had common functionality for the rest of the handlers. If we want to add a Chain implementation, containing handlers and maybe even path information, we cannot use the prepend method, must write our own implementation of the HandlerDecorator interface. This can be useful when we want to re-use a Chain in multiple applications. We write a module that adds the Chain implementation to the registry and we don't have to write any code in the handlers section for the Chain to work. This blog post is inspired by a conversation on the Ratpack Slack channel recently. First we create a simple handler that renders a result:
// File: src/main/groovy/com/mrhaki/ratpack/Ping.groovy
package com.mrhaki.ratpack
import ratpack.groovy.handling.GroovyChainAction
/**
* Implementation of a {@link ratpack.handling.Chain} interface
* by extending {@link GroovyChainAction}, so
* we can use Groovy DSL support in the
* {@link Ping#execute} method.
*/
class Ping extends GroovyChainAction {
@Override
void execute() throws Exception {
// What we normally would write
// in the handlers{} section
// of Ratpack.groovy.
path('pingpong') {
render 'Ratpack rules!'
}
}
}
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In our Ratpack application we can have handlers that need to be invoked for every request. For example the handler needs to set a response header and will use the Context.next() method to continue with the rest of the handlers. When we have such a handler we can use the all method of a Chain instance. This happens in the handlers section of our application definition. We can also register such handlers directly in the registry. We can even use a Module to register the handler implementation. To register a handler in the registry we must use the HandlerDecorator interface. The interface has a method prepend that will encapsulate a Handler implementation and makes it available before any other handlers.
In the following sample we have a Handler implementation that checks if the RequestId object is available. If so then the value is set as a response header:
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