DEV Community: Djordje Bajic

I started YT channel!

Djordje Bajic — Wed, 16 Dec 2020 22:11:47 +0000

Hello Programmer, Developers, Administrators, DevOps people and whatever you like to be called.

I started YT channel a couple of months ago.

IT'S ABOUT JAVA. VERY INOVATIVE, VERY NEW, MUCH WOW, SOMETHING WORLD DID NOT SEE.

Jokes aside.

If you are willing, take a look, leave a comment about what should be improved, what you like...etc.

Link: https://www.youtube.com/channel/UC0Ws7Fn3fTjZ9eKH87R_rKA

Gimme some love, gimme some hate, whatever is on your mind.

Stay safe and positive (you see what i did there),

George / Djordje

Apache Camel #4 - Processors

Djordje Bajic — Thu, 03 Dec 2020 18:18:21 +0000

Hello Devs!

Long time no new article!

Guess i have to fix that.

Today we are talking about processors in Apache Camel routes.

Processors are a part of camel which enables us to write our custom components and business logic and implement it in the routes.

There are two ways of using processors.

Creating a class and implementing Processor with process method. This way we can easily write a test and separate processor logic from route itself. It looks something like this in the route.

.process(new CustomProcessor())

Processor itself will look something like this:

public class CustomProcessor implements Processor {

    @Override
    public void process(Exchange exchange) {
         exchange.getIn().setBody("test");
    }
}

Functional way.

.process(exchange -> exchange.getIn().setBody("test"))

Even though this way is easier that first, it couples processor logic to route and you could only test it if you test whole route.

My YT: https://www.youtube.com/channel/UC0Ws7Fn3fTjZ9eKH87R_rKA

That would be all for today!
Stay safe,stay cool!

George / Djordje

I wrote my first eBook!

Djordje Bajic — Sun, 15 Dec 2019 21:05:18 +0000

Hello world!

I am proud to announce that my ebook "How I Became a programmer" is (self) published on Amazon. This book is about my story how I got into the IT industry and what I think beginners need to do in order to get their first programming job.

If anyone is interested in reading it go to this link and purchase it.

In case that you have any questions feel free to contact me on: okand_anvandare@protonmail.com

Cheers!

Djordje

Apache Camel #4 - Bean Validation

Djordje Bajic — Sun, 25 Aug 2019 06:38:44 +0000

There is a lot of cases where we needed to write validation for data input. This "problem" can be easily solved in Camel by using Bean Validation component.

Imagine we have a JSON input in our route and we want to validate payload.

{
     "name":"Jane Doe",
     "cardNumber":"377198642272436",
     "email":"jane@doe.com",
     "paid":true,
     "price":1.25
}

To do that, we first we must unmarshall that payload to POJO.
But first, we must create a class with the same parameters as JSON and add Hibernate Validation annotations.

 @NotNull
 @Length(min = 1, max = 60)
 private String name;

 @CreditCardNumber
 private String cardNumber;

 @Email
 private String email;

 @NotNull
 private boolean paid;

 @Min(0.1)
 private int price;

And then we add this to our Camel route.

   //define a datasource for the class you want to validate.
   GsonDataSource dataSource = new GsonDatasource(JsonDto.class);

   //unmarshal JSON to POJO
   .unmarshall(dataSource)

   //Validate data
   .to("bean-validator:someLabelHere)

When that unmarshalled data is sent to bean validator, that objects will be validated by annotations we set for JsonDto fields.

Thank you for your attention.

Apache Camel #3 - RabbitMq

Djordje Bajic — Sun, 18 Aug 2019 18:58:46 +0000

Hello there again!

It passed 2 months since my last article, so I decided to write a new one.

Today we will focus on RabbitMq and what we can do with it using Camel.

Dependencies

Maven repository -> Camel RabbitMq

Connection to RabbitMq

When using SpringBoot:

Create a class with @Configuration annotation.
Create a method which will return ConnectionFactory and annotate it with @Bean.
Instance a connection factory and set properties.

@Bean
public ConnectionFactory rabbitConnectionFactory() {
    ConnectionFactory connectionFactory = new ConnectionFactory();
    connectionFactory.setHost("localhost);
    connectionFactory.setPort(5672);
    connectionFactory.setUsername("Username");
    connectionFactory.setPassword("Password);

    return connectionFactory;
}

*note: You can use application properties to connect to the server.

If you are using pure Camel:

Using RabbitMq

Now that we successfully connected to RabbitMq it's time to start consuming/producing messages to queue/exchange.

Camel RabbitMq component documentation.

Consuming Message from the queue:

We will set the rabbitMq component to fetch from the queue which is bind to exchange.
Log message body received.

public void configure() {

from("rabbitmq:exchangeA?queue=QueueA&amp;declare=true")
.routeId("RabbiqMqConsumer")
.log("Message received: ${body}");

Producing Message to exchange:

We will create a route.
Set message body.
Send a message to the exchange.

public void configure() {

 from("timer:fooo?period=10000")
 .routeId("RabbiqMqProducer)
 .setBody().constant("{\"foo\":\"bar\"}")
 .log("Message to be sent: ${body}")
 .to("rabbitmq:exchangeB");

Aand that's all folks, if anyone have some question, feel free to ask me via DM or just leave a comment.

Apache Camel #2 - Calling Rest API

Djordje Bajic — Thu, 30 May 2019 18:45:31 +0000

Hello!

This is the second text about Apache Camel, there will be a lot more in the future. Purpose of this articles is to present people the real power of Camel, maybe some of you will find a use case where you can use this framework instead of writing boilerplate code over and over.

Today we will use Camel to call API endpoint and handle some of the exceptions.

Dependencies

Camel http dependency

Routes

Scheduler route

If you remember from introduction, this is a scheduler route, it will trigger a message every 120 seconds and send it to "direct:httpRoute" route. I am using synchronous "direct" component, there is also asynchronous "seda" component.

@Override"
public void configure() {

    from("timer:scheduler?period=120000")
            .log("Scheduled job!")
            .to("direct:httpRoute");

}

Http route

This is a HTTP client route, it will call the bittrex rest API and get crypto currencies and log the response.

@Override
public void configure() {

    from("direct:httpRoute")
            .log("Http Route started")
            .setHeader(Exchange.HTTP_METHOD).constant(HttpMethod.GET)
            .to("https://api.bittrex.com/api/v1.1/public/getcurrencies")
            .log("Response : ${body}");

}

Error Handlers

If you want to cover some exceptions there is a two options.

Default error handler
onException clause to handle specific class exceptions.

@Override
public void configure() {

    errorHandler(deadLetterChannel("mock:errorHandler"));

    onException(HttpOperationFailedException.class)
            .log("${exception}")
            .to("mock:errorHandler");

    from("direct:httpRoute")
            .log("Http Route started")
            .setHeader(Exchange.HTTP_METHOD).constant(HttpMethod.GET)
            .to("https://api.bittrex.com/api/v1.1/public/getcurrencies")
            .log("Response : ${body}");

}

Results

This is all for this tutorial, if something is not clear, feel free to contact me I will gladly answer any question.

Thanks!

How many developers are musicians?

Djordje Bajic — Sun, 26 May 2019 09:20:35 +0000

Hey!

How many of you play an instrument?
Do you play in a band?

if (you do) {
please leave a comment with a link to your music.
} else {
listen to music from comments!
}

This way I want to learn more about bands you guys play in, maybe some of that music will be on my playlist in the future.

Thanks!

Apache Camel #1 - Introduction to Apache Camel

Djordje Bajic — Sat, 25 May 2019 15:27:22 +0000

Hello World!

This is my first post so I decided to write about the framework I use a lot in the last couple of months.

Apache Camel is a very powerful integration framework, it is used as a mediation engine between two systems, it has a great community, large codebase with over 200 components which can be used out of the box and of course it is written in Java.

On project official website you can find documentation and all info about releases.

Camel Context

Context is a heart of camel applications and it represents runtime system.

Camel Route

Sample route:

Explanation:

As you probably noticed class Route extends the RouteBuilder class, from which you will override configuration and write your route in it.

I used JavaDsl in this route, you can use any other dsl that camel supports.

errorHandler(deadLetterChannel("mock:errorRoute")) - This is error handler for this particular route, if any exception occurs message will be sent to deadletter mock queue "errorRoute".

from("timer:timerName?period=5000") - "from" is like an endpoint in camel context. In this particular case, it is timer component(scheduler) which will trigger route execution every 5 seconds, timer name is "timerName". You can check more about that on this link.

log("Route started!") - this is a camel's log component which will print text in console.

to("mock:anotherRouter") - "to" represents on which endpoint, queue or route message will be sent. "mock:anotherRoute" represents a mock queue on which message will be sent.

These are the most basic things about Camel.

If you are interested in learning a little more about Apache Camel feel free to contact me here or on gitter -> @djoleb.

Thanks!