= Command Mode Applications

Camel Quarkus is typically used for creating integration applications that run as long living processes.
In this chapter, we are going to have a look at a slightly different use case:
utilizing Camel Quarkus for writing programs that exit by themselves after performing some desired tasks.

== Where can this be useful?

The enterprise is full of scheduled batch processing. Say, some system exports some sort of reports daily at 4 a.m.
Those need to be transformed (e.g. XML -> Excel) and transferred somewhere else (e.g. via mail, FTP, etc.)

Camel is a perfect match for doing the transformation and the transfer.
However, having a service running 24/7 for doing something useful just once a day would probably be an overkill.
Combining a https://en.wikipedia.org/wiki/Cron[Cron job] (or a similar scheduling technology)
with a command line utility may suit much better in situations like this.

== How to write a command line tool with Camel Quarkus

There is just one thing where it would differ from a stock Camel Quarkus application:
setting an exit condition in `application.properties`.

The rest of the application - most notably the xref:manual::routes.adoc[Route]
that performs the actual data transformation and transfer - will look the same like with a traditional Camel service.

== A minimal Hello World!

Let's go through a minimal example that just prints `Hello World!` to
the console and exits.

The route definition could look like the following:

[source,java]
----
import org.apache.camel.builder.RouteBuilder;

@ApplicationScoped
public class CamelRoute extends RouteBuilder {

    @Override
    public void configure() {
        from("timer:hello?delay=-1&repeatCount=1")
                .setBody().constant("Hello World!")
                .to("log:hello");
    }
}
----

Note that we use the xref:reference/extensions/timer.adoc[timer] component to trigger the route execution.
The URI parameter `delay=-1` causes the timer to be triggered with no initial delay
and `repeatCount=1` ensures that the route is executed just once.

But doing just the above would not make our application exit by itself.
The `camel.main.durationMax*` family of configuration options (available via `camel-quarkus-core`) offers a way to solve that.
E.g. we can set the following in `application.properties`

[source,properties]
----
camel.main.durationMaxMessages = 1
----

to make the application exit after the route has processed a single
message.

We need to add the dependencies for `timer` and `log` components:

[source,xml]
----
<dependency>
    <groupId>org.apache.camel.quarkus</groupId>
    <artifactId>camel-quarkus-core</artifactId>
</dependency>
<dependency>
    <groupId>org.apache.camel.quarkus</groupId>
    <artifactId>camel-quarkus-log</artifactId>
</dependency>
<dependency>
    <groupId>org.apache.camel.quarkus</groupId>
    <artifactId>camel-quarkus-timer</artifactId>
</dependency>
----

When invoking the application on the command line, you should see
something like the following:

[source,shell]
----
]$ java -jar target/*-runner.jar
2020-07-15 11:32:13,577 INFO  [org.apa.cam.qua.cor.CamelBootstrapRecorder] (main) bootstrap runtime: org.apache.camel.quarkus.main.CamelMainRuntime
2020-07-15 11:32:13,623 INFO  [org.apa.cam.mai.BaseMainSupport] (main) Auto-configuration summary:
2020-07-15 11:32:13,623 INFO  [org.apa.cam.mai.BaseMainSupport] (main)  camel.main.durationMaxMessages=1
2020-07-15 11:32:13,700 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (main) Apache Camel 3.4.0 (camel-1) is starting
2020-07-15 11:32:13,701 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (main) StreamCaching is not in use. If using streams then its recommended to enable stream caching. See more details at http://camel.apache.org/stream-caching.html
2020-07-15 11:32:13,709 INFO  [org.apa.cam.imp.eng.InternalRouteStartupManager] (main) Route: route1 started and consuming from: timer://hello
2020-07-15 11:32:13,714 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (main) Total 1 routes, of which 1 are started
2020-07-15 11:32:13,715 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (main) Apache Camel 3.4.0 (camel-1) started in 0.014 seconds
2020-07-15 11:32:13,718 INFO  [org.apa.cam.mai.MainSupport] (camel-main) Waiting until: 1 messages has been processed
2020-07-15 11:32:13,719 INFO  [io.quarkus] (main) camel-quarkus-integration-test-main-command-mode 1.1.0-SNAPSHOT on JVM (powered by Quarkus 1.6.0.Final) started in 0.592s.
2020-07-15 11:32:13,720 INFO  [io.quarkus] (main) Profile prod activated.
2020-07-15 11:32:13,721 INFO  [io.quarkus] (main) Installed features: [camel-core, camel-log, camel-main, camel-policy, camel-support-common, camel-timer, cdi]
2020-07-15 11:32:13,725 INFO  [hello] (Camel (camel-1) thread #0 - timer://hello) Exchange[ExchangePattern: InOnly, BodyType: String, Body: Hello World!]
2020-07-15 11:32:13,729 INFO  [org.apa.cam.mai.MainLifecycleStrategy] (Camel (camel-1) thread #0 - timer://hello) Duration max messages triggering shutdown of the JVM.
2020-07-15 11:32:13,730 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (Camel (camel-1) thread #1 - CamelMainShutdownCamelContext) Apache Camel 3.4.0 (camel-1) is shutting down
2020-07-15 11:32:13,740 INFO  [org.apa.cam.mai.MainLifecycleStrategy] (Camel (camel-1) thread #1 - CamelMainShutdownCamelContext) CamelContext: camel-1 has been shutdown, triggering shutdown of the JVM.
2020-07-15 11:32:13,741 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (Camel (camel-1) thread #1 - CamelMainShutdownCamelContext) Apache Camel 3.4.0 (camel-1) uptime 0.041 seconds
2020-07-15 11:32:13,741 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (Camel (camel-1) thread #1 - CamelMainShutdownCamelContext) Apache Camel 3.4.0 (camel-1) is shutdown in 0.011 seconds
2020-07-15 11:32:13,745 INFO  [io.quarkus] (main) camel-quarkus-integration-test-main-command-mode stopped in 0.005s
----

== Command line parameters

That was really trivial. How about greeting a person whose name is passed via a command line parameter?
We can use https://quarkus.io/guides/config[Quarkus MicroProfile Config] for that:

[source,java]
----
import jakarta.enterprise.context.ApplicationScoped;
import org.apache.camel.builder.RouteBuilder;
import org.eclipse.microprofile.config.inject.ConfigProperty;

@ApplicationScoped
public class CamelRoute extends RouteBuilder {

    @ConfigProperty(name = "greeted.subject", defaultValue = "World")
    String greetedSubject;

    @Override
    public void configure() {
        from("timer:hello?delay=-1")
                .setBody().constant("Hello " + greetedSubject + "!")
                .to("log:hello");
    }
}
----

For the `@ConfigProperty` annotation to work, the `CamelRoute` class needs to be annotated with `@ApplicationScoped`.

Having the above in place, we can call the application with the `-Dgreeted.subject=Joe` parameter at the command line and voilà

[source,shell]
----
$ java -Dgreeted.subject=Joe -jar target/quarkus-app/quarkus-run.jar
2020-07-15 11:42:18,770 INFO  [org.apa.cam.qua.cor.CamelBootstrapRecorder] (main) bootstrap runtime: org.apache.camel.quarkus.main.CamelMainRuntime
2020-07-15 11:42:18,816 INFO  [org.apa.cam.mai.BaseMainSupport] (main) Auto-configuration summary:
2020-07-15 11:42:18,816 INFO  [org.apa.cam.mai.BaseMainSupport] (main)  camel.main.durationMaxMessages=1
2020-07-15 11:42:18,892 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (main) Apache Camel 3.4.0 (camel-1) is starting
2020-07-15 11:42:18,893 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (main) StreamCaching is not in use. If using streams then its recommended to enable stream caching. See more details at http://camel.apache.org/stream-caching.html
2020-07-15 11:42:18,902 INFO  [org.apa.cam.imp.eng.InternalRouteStartupManager] (main) Route: route1 started and consuming from: timer://hello
2020-07-15 11:42:18,907 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (main) Total 1 routes, of which 1 are started
2020-07-15 11:42:18,908 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (main) Apache Camel 3.4.0 (camel-1) started in 0.015 seconds
2020-07-15 11:42:18,911 INFO  [org.apa.cam.mai.MainSupport] (camel-main) Waiting until: 1 messages has been processed
2020-07-15 11:42:18,914 INFO  [io.quarkus] (main) camel-quarkus-integration-test-main-command-mode 1.1.0-SNAPSHOT on JVM (powered by Quarkus 1.6.0.Final) started in 0.569s.
2020-07-15 11:42:18,915 INFO  [io.quarkus] (main) Profile prod activated.
2020-07-15 11:42:18,915 INFO  [io.quarkus] (main) Installed features: [camel-core, camel-log, camel-main, camel-policy, camel-support-common, camel-timer, cdi]
2020-07-15 11:42:18,919 INFO  [hello] (Camel (camel-1) thread #0 - timer://hello) Exchange[ExchangePattern: InOnly, BodyType: String, Body: Hello Joe!]
2020-07-15 11:42:18,921 INFO  [org.apa.cam.mai.MainLifecycleStrategy] (Camel (camel-1) thread #0 - timer://hello) Duration max messages triggering shutdown of the JVM.
2020-07-15 11:42:18,922 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (Camel (camel-1) thread #1 - CamelMainShutdownCamelContext) Apache Camel 3.4.0 (camel-1) is shutting down
2020-07-15 11:42:18,931 INFO  [org.apa.cam.mai.MainLifecycleStrategy] (Camel (camel-1) thread #1 - CamelMainShutdownCamelContext) CamelContext: camel-1 has been shutdown, triggering shutdown of the JVM.
2020-07-15 11:42:18,933 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (Camel (camel-1) thread #1 - CamelMainShutdownCamelContext) Apache Camel 3.4.0 (camel-1) uptime 0.040 seconds
2020-07-15 11:42:18,933 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (Camel (camel-1) thread #1 - CamelMainShutdownCamelContext) Apache Camel 3.4.0 (camel-1) is shutdown in 0.011 seconds
2020-07-15 11:42:18,937 INFO  [io.quarkus] (main) camel-quarkus-integration-test-main-command-mode stopped in 0.005s
----

== Compiling the command line utility to a native executable

xref:first-steps.adoc#_native_mode[As usual with Camel Quarkus], the application can be compiled to native executable by activating the `native` profile.
GraalVM with `native-image` command installed and `GRAALVM_HOME` environment variable set is required for that, see https://quarkus.io/guides/building-native-image[Building a native executable] section of the Quarkus documentation.

[source,shell]
----
export GRAALVM_HOME=...
mvn clean package -Pnative
----

The basic command line application compiled into a Linux native
executable has about 33 Megabytes.

Running it is easy:

[source,shell]
----
$ target/*runner -Dgreeted.subject=Joe
2020-07-15 12:19:22,810 INFO  [org.apa.cam.qua.cor.CamelBootstrapRecorder] (main) bootstrap runtime: org.apache.camel.quarkus.main.CamelMainRuntime
2020-07-15 12:19:22,811 INFO  [org.apa.cam.mai.BaseMainSupport] (main) Auto-configuration summary:
2020-07-15 12:19:22,811 INFO  [org.apa.cam.mai.BaseMainSupport] (main)  camel.main.durationMaxMessages=1
2020-07-15 12:19:22,812 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (main) Apache Camel 3.4.0 (camel-1) is starting
2020-07-15 12:19:22,812 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (main) StreamCaching is not in use. If using streams then its recommended to enable stream caching. See more details at http://camel.apache.org/stream-caching.html
2020-07-15 12:19:22,812 INFO  [org.apa.cam.imp.eng.InternalRouteStartupManager] (main) Route: route1 started and consuming from: timer://hello
2020-07-15 12:19:22,812 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (main) Total 1 routes, of which 1 are started
2020-07-15 12:19:22,812 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (main) Apache Camel 3.4.0 (camel-1) started in 0.000 seconds
2020-07-15 12:19:22,812 INFO  [io.quarkus] (main) camel-quarkus-integration-test-main-command-mode 1.1.0-SNAPSHOT native (powered by Quarkus 1.6.0.Final) started in 0.007s.
2020-07-15 12:19:22,813 INFO  [io.quarkus] (main) Profile prod activated.
2020-07-15 12:19:22,812 INFO  [hello] (Camel (camel-1) thread #0 - timer://hello) Exchange[ExchangePattern: InOnly, BodyType: String, Body: Hello Joe!]
2020-07-15 12:19:22,813 INFO  [io.quarkus] (main) Installed features: [camel-core, camel-log, camel-main, camel-policy, camel-support-common, camel-timer, cdi]
2020-07-15 12:19:22,813 INFO  [org.apa.cam.mai.MainSupport] (camel-main) Waiting until: 1 messages has been processed
2020-07-15 12:19:22,813 INFO  [org.apa.cam.mai.MainLifecycleStrategy] (Camel (camel-1) thread #0 - timer://hello) Duration max messages triggering shutdown of the JVM.
2020-07-15 12:19:22,813 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (Camel (camel-1) thread #1 - CamelMainShutdownCamelContext) Apache Camel 3.4.0 (camel-1) is shutting down
2020-07-15 12:19:22,813 INFO  [org.apa.cam.mai.MainLifecycleStrategy] (Camel (camel-1) thread #1 - CamelMainShutdownCamelContext) CamelContext: camel-1 has been shutdown, triggering shutdown of the JVM.
2020-07-15 12:19:22,813 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (Camel (camel-1) thread #1 - CamelMainShutdownCamelContext) Apache Camel 3.4.0 (camel-1) uptime 0.001 seconds
2020-07-15 12:19:22,813 INFO  [org.apa.cam.imp.eng.AbstractCamelContext] (Camel (camel-1) thread #1 - CamelMainShutdownCamelContext) Apache Camel 3.4.0 (camel-1) is shutdown in 0.000 seconds
2020-07-15 12:19:22,813 INFO  [io.quarkus] (main) camel-quarkus-integration-test-main-command-mode stopped in 0.000s
----

== Source code

The sources of the application used in this section are based on the `main-command-mode` integration test in the Camel Quarkus source tree:
https://github.com/apache/camel-quarkus/tree/main/integration-tests/main-command-mode[https://github.com/apache/camel-quarkus/tree/main/integration-tests/main-command-mode]

Bonus: The integration test module shows a way how to test command line applications.

== Full control over starting Camel by invoking `CamelMainApplication` directly.

If you need to perform some custom logic before starting Camel (or even not starting it at all),
you can do so by implementing a `@QuarkusMain` class and starting `CamelMainApplication` yourself
after your custom logic is executed.

E.g. you may want to output a joke instead of starting Camel each year on April 1st:

[source,java]
----
import io.quarkus.runtime.Quarkus;
import io.quarkus.runtime.annotations.QuarkusMain;
import org.apache.camel.quarkus.main.CamelMainApplication;
import java.time.LocalDate;

@QuarkusMain
public class Main {
    public static void main(String... args) {
        /* Your custom logic is executed before Camel is started */
        LocalDate now = LocalDate.now();
        if (now.getDayOfMonth() == 1 && now.getMonthValue() == 4) {
            System.out.println("Haha!");
            return;
        }

        /* Start Quarkus and the Camel Quarkus runtime */
        Quarkus.run(CamelMainApplication.class, args);
    }
}
----

[NOTE]
====
It is recommended to perform very little logic in Java `main()` method.
====

Read more about Quarkus command mode applications in https://quarkus.io/guides/command-mode-reference[Quarkus command mode guide].
