Groovy

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Vert.x for Groovy

If you are using Maven or Gradle, add the following dependency to the dependencies section of your project descriptor to access the Vert.x Core API and enable the Groovy support:

Maven (in your pom.xml):

<dependency>
<groupId>io.vertx</groupId>
<artifactId>vertx-core</artifactId>
<version>4.3.8</version>
</dependency>
<dependency>
 <groupId>io.vertx</groupId>
 <artifactId>vertx-lang-groovy</artifactId>
 <version>4.3.8</version>
</dependency>

Gradle (in your build.gradle file):

compile "io.vertx:vertx-core:4.3.8"
compile "io.vertx:vertx-lang-groovy:4.3.8"

Verticles

Writing Verticles

There are two alternatives to create Verticles in Groovy:

a plain Groovy script a Groovy class implementing the Verticle interface or extending the AbstractVerticle class

For example, the next snippet is a valid Groovy verticle:

println "Hello from vertx"

On deployment, by default, Vert.x executes the script. Optionally, your script can provide the startVertx and stopVertx methods. Theses methods are called respectively when the verticle starts and stops:

void vertxStart() {
println "starting"
}

void vertxStop() {
println "stopping"
}

Such methods are synchronous, after the method is called the verticle is considered started or stopped.

Alternatively, you can extend the AbstractVerticle class and implement the start and stop methods:

import io.vertx.core.AbstractVerticle;

class HelloWorldHttpVerticle extends AbstractVerticle {

void start() {
 println("Starting")
}

void stop() {
  println("Stopping")
}
}

When Vert.x deploys the verticle it will call the start method, and when the method has completed the verticle will be considered started.

You can also optionally override the stop method. This will be called by Vert.x when the verticle is undeployed and when the method has completed the verticle will be considered stopped.

Like before such methods are synchronous, after the method is called the verticle is considered started or stopped.

Accessing the vertx instance from a verticle

Regardless the way you use to implement your verticle, you access the vert.x instance using the vertx variable / field.

Access to the vert.x instance in a Groovy script

vertx.deployVerticle("another_verticle.groovy")

Access to the vert.x instance in a Groovy class

import io.vertx.core.AbstractVerticle;

class HelloWorldHttpVerticle extends AbstractVerticle {

  void start() {
    vertx.deployVerticle("another_verticle.groovy")
  }
}

Asynchronous Verticle start and stop

Sometimes you want to do something in your verticle start-up which takes some time and you don’t want the verticle to be considered deployed until that happens. For example you might want to deploy other verticles in the start method.

You can’t block waiting for the other verticles to deploy in your start method as that would break the Golden Rule.

So how can you do this?

The way to do it is to implement the asynchronous start method. This version of the method takes a Promise as a parameter. When the method returns the verticle will not be considered deployed.

Some time later, after you’ve done everything you need to do (e.g. start other verticles), you can call complete on the Promise (or fail) to signal that you’re done. Similarly, there is an asynchronous version of the stop method too.

You use this if you want to do some verticle cleanup that takes some time.

When your Verticle is implemented as a script, asynchronous start and stop are implemented as follows:

import io.vertx.core.Promise

void vertxStart(Promise<Void> promise) {
println "starting"
vertx.deployVerticle("v.rb"){ res ->
  if (res) {
    promise.complete()
  } else {
    promise.fail(res.cause())
  }
}
}

void vertxStop(Promise<Void> future) {
println "stopping"
promise.complete()
}

The objects of AsyncResult or it’s subclasses are coerced to Boolean according to (Groovy-Truth, so that an instance of AsyncResult or Future evaluates to true if succeeded, or to false otherwise. That allowes to write more readable code like res ? doSuccess() : doFail().

If your verticle extends AbstractVerticle, you override the start and stop methods:

import io.vertx.core.Future
import io.vertx.core.AbstractVerticle

class HelloWorldHttpVerticle extends AbstractVerticle {
void start(Promise<Void> future) {
  println "starting"
  vertx.deployVerticle("v.rb",
  { res ->
    if (res.succeeded()) {
      future.complete()
    } else {
      future.fail(res.cause())
    }
  })
 }

void stop(Promise<Void> future) {
 println("stopping")
 future.complete()
}
}

You don’t need to manually undeploy child verticles started by a verticle, in the verticle’s stop method. Vert.x will automatically undeploy any child verticles when the parent is undeployed.

Passing configuration to a verticle

Configuration in the form of Map can be passed to a verticle at deployment time:

def config = [
name:"tim",
directory:"/blah"
]
def options = [ "config" : config ];
vertx.deployVerticle("com.mycompany.MyOrderProcessorVerticle", options);

This configuration is then available via the Context, The configuration is returned as a Map object so you can retrieve data as follows:

println vertx.getOrCreateContext().config()["name"]

The configuration can also be a JsonObject object.

Accessing environment variables in a Verticle

Environment variables and system properties are accessible using the Java API:

println System.getProperty("foo")
println System.getenv("HOME")

JSON

To manipulate JSON object, Vert.x proposes its own implementation of JsonObject and JsonArray. This is because, unlike some other languages, Java does not have first class support for JSON.

When developping a vert.x application with Groovy, you can rely on these two classes, or use the (JSON support from Groovy. This section explains how to use the Vert.x classes.

Most vert.x methods taking a JSON object as argument in their Java version, take a map instead.

Data object conversion

Class annotated with @DataObject used in Vert.x API can be converted back and forth to maps thanks to the Groovy as operator.

import io.vertx.core.http.HttpServerOptions
import io.vertx.core.net.PemKeyCertOptions

// Instead of this
def server = vertx.createHttpServer(new HttpServerOptions()
   .setUseAlpn(true)
   .setSsl(true)
   .setKeyStoreOptions(new JksOptions().setPath("/path/to/my/keystore")))

// You can convert a map literal to HttpServerOptions
server = vertx.createHttpServer([
   "userAlpn":        true,
   "ssl":             true,
   "keyStoreOptions": ["path":"/path/to/my/keystore"]
   ] as HttpServerOptions)

JSON objects

The JsonObject class represents JSON objects.

A JSON object is basically just a map which has string keys and values can be of one of the JSON supported types (string, number, boolean).

JSON objects also support null values.

Creating JSON objects

Empty JSON objects can be created with the default constructor.

You can create a JSON object from a string or g-string JSON representation as follows:

def object = new JsonObject("{\"foo\":\"bar\"}")
def object2 = new JsonObject("""
{
"foo": "bar"
}
""")

In Groovy it’s also convenient to create a JSON object from a map:

def map = [ "foo" : "bar" ]
def json = new JsonObject(map)

Nested maps are transformed to nested JSON objects.

It can be achieved using a Groovy cast as well:

def map = [ "foo" : "bar" ]
def json = map as JsonObject

Putting entries into a JSON object

Use the put methods to put values into the JSON object.

The method invocations can be chained because of the fluent API:

def object = new JsonObject()
object.put("foo", "bar").put("num", 123).put("mybool", true)

The Groovy subscript operator works too:

def object = new JsonObject()
object["foo"] = "bar"
object["num"] = 123
object["mybool"] = true

Getting values from a JSON object

You get values from a JSON object using the getXXX methods, for example:

def val1 = jsonObject.getString("some-key")
def val2 = jsonObject.getInteger("some-other-key")

The Groovy subscript operator works too:

def val1 = jsonObject["some-key"]
def val2 = jsonObject["some-other-key"]

Encoding the JSON object to a String

You use encode to encode the object to a String form. There is also a encodePrettily that makes the output pretty (understand multi-line and indented).

JSON arrays

The JsonArray class represents JSON arrays.

A JSON array is a sequence of values (string, number, boolean).

JSON arrays can also contain null values.

Creating JSON arrays

Empty JSON arrays can be created with the default constructor.

You can create a JSON array from a string JSON representation or a list as follows:

def object = new JsonArray("[\"foo\", \"bar\"]")
def object2 = new JsonObject("""
[
"foo", "bar"
]
""")

In Groovy it’s also convenient to create a JSON array from a list:

def list = [ "foo", "bar" ]
def json = new JsonArray(list)

Nested maps are transformed to nested JSON objects.

It can be achieved using a Groovy cast as well:

def list = [ "foo", "bar" ]
def json = map as JsonArray

Adding entries into a JSON array

You add entries to a JSON array using the add methods.

def array = new JsonArray()
array.add("foo").add(123).add(false)

The left shift operator can be used as well:

def array = new JsonArray()
array << "foo"
array << 123
array << false

Getting values from a JSON array

You get values from a JSON array using the getXXX methods, for example:

def val = array.getString(0)
def intVal = array.getInteger(1)
def boolVal = array.getBoolean(2)

The Groovy subscript operator works too:

def val = array[0]
def intVal = array[1]
def boolVal = array[2]

Encoding the JSON array to a String

You use encode to encode the array to a String form. There is also a encodePrettily that makes the output pretty (understand multi-line and indented).

Kotlin coroutines

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