lunes, agosto 13, 2018

Java Iterator to Java 8 Stream

Sometimes during my work, I need to integrate with other libraries which they return an Iterator object instead of a list. This is fine from the point of view of libraries but it might be a problem when you want to use Java 8 streams on the returned iterator. There is one way to transform the Iterator to Iterable and then easily to stream.

Since all the time I need to remember how to do it, I decided to share the snippet here.

In the example, first of all, we have an Iterator class. Since Iterator cannot be used as a stream but an Iterable can do, we just create a new Iterable class which overrides its iterator() method to return the Iterator we want to stream.

Then we have an Iterable which is not streamable yet. So what we need to do is to use StreamSupport class to convert the Iterable to a Stream.

And that's all then you can use all streaming operations without any problem.

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jueves, junio 07, 2018

Spring Boot + Cockroach DB in Kubernetes/OpenShift

In my previous post, I showed why CockroachDB might help you if you need a cloud native SQL database for your application. I explained how to install it in Kubernetes/OpenShift and how to validate that the data is replicated correctly.

In this post, I am going to show you how to use Cockroach DB in a Spring Boot application. Notice that Cockroach DB is compatible with PostgresSQL driver, so in terms of configuration is almost the same.

In this post, I assume that you have already a Cockroach DB cluster running in Kubernetes cluster as explained in my previous post.

For this example, I am using Fabric8 Maven Plugin to smoothly deploy a Spring Boot application to Kubernetes without having to worry so much about creating resources, creating Dockerfile and so on. Everything is automatically created and managed.

For this reason, pom.xml looks like:

Notice that apart from defining Fabric8 Maven Plugin I am also defining to use Spring Data JPA to make the integration between Spring Boot and JPA easier from the point of view of the developer.

Then you need to create a JPA entity and Spring Data Crud repository to interact with JPA.

Also, we need to create a controller who is responsible to get incoming requests, use the repository to make queries to DB and return results back to the caller.

Finally, you need to configure JPA to use the desired driver and dialect. In case of Spring Boot this is done in file.

The most important part here is that we need to use the PostgeSQL94 dialect. Notice that in url, we are using the postgresql jdbc url form. That's fine, since Cockroach uses the Postgres driver.

Now we need to create the database (customers) and the user (myuser) as configured in To make it so, you just need to run cockroach shell and run some SQL commands:

Finally, you can deploy the application by running mvn clean fabric8:deploy. After that, the first time might take longer since needs to pull Docker images, you can start sending queries to the service.

As you can see it is really easy to start using a cloud-native DB like Cockroach DB in Spring Boot. If you want you can do exactly the same as in my previous post and start running queries to each of the nodes to validate that data is available correctly.


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martes, mayo 29, 2018

CockroachDB. A cloud native SQL database in Kubernetes.

CockroachDB 2.0 has just been released. For those who don't know what it is, it can be summarized as a SQL database for the cloud era. One of the best things about CockroachDB is that it automatically scales, rebalances and repairs itself without sacrificing the SQL language. Moreover, Cockroach implements ACID transactions,  so your data is always in a known state.

In this post, I am going to explain how to install it in Kubernetes/OpenShift, insert some data and validate that it has been replicated in all nodes. In next post, I am going to show you how to use it with Spring Boot + JPA.

The first thing you need to have is a Kubernetes/OpenShift cluster to be used. You can use Minikube or Minishift for this purpose. In my case, I am using Minishift but I will provide equivalent commands for Minikube.

After having everything installed, you need to launch the Cockroach cluster.

In case of Kuberneteskubectl create -f

In case of OpenShiftoc apply -f

Then you need to initialize the cluster:

In case of Kuberneteskubectl create -f

In case of OpenShift: oc apply -f

Then let's configure the cluster so we can access the admin UI:

In case of Kuberneteskubectl port-forward cockroachdb-0 8080

In case of OpenShift: oc expose svc  cockroachdb-public --port=8080 --name=r1

Now let's create a database and a table and see how it is replicated across all the cluster easily. Cockroach comes with a service that offers a load-balanced virtual IP for clients to access the database.

In case of Kubernetes: kubectl run cockroachdb -it --image=cockroachdb/cockroach --rm --restart=Never -- sql --insecure --host=cockroachdb-public

In case of OpenShift: oc run cockroachdb -it --image=cockroachdb/cockroach --rm --restart=Never     -- sql --insecure --host=cockroachdb-public

And finally in the opened console just type some SQL calls:

create database games;
use games;
create table game (id int, title varchar(30));
insert into game values (1, 'The Secret of Monkey Island');

So far, we have a new database, table, and entry in CockroachDB. Open admin UI, push Databases and you'll see something like this:

You can see that the database and the table have been created. Now let's see how we can know that everything has been replicated correctly. Push Overview and you'll see something like:

So pay attention to Replicas column. In all nodes, the number is exactly the same number, this means that all data in the cluster has been replicated X times.

Now let's increase by one the number of replicas and just refresh the page to see that the new node initially has not the same replica count.

In case of Kuberneteskubectl scale statefulset cockroachdb --replicas=4

In case of OpenShift: oc scale statefulset cockroachdb --replicas=4

Another thing you can do is to just enter each container and validate that when connecting to localhost, the inserted data is there.

In case of Kuberneteskubectl exec -it cockroachdb-0 /bin/bash

In case of OpenShiftoc exec -it cockroachdb-0 /bin/bash

Then inside the container just run: ./cockroach dump games --insecure

And you will see that CLI connects by default to the current node (localhost) and dumps the content of games db.

Repeat the same with other nodes cockroachdb-1 and cockroachdb-2 and you should see exactly the same.

So as you can see, it is really easy to use SQL in scale way thanks to Cockroach DB. In next post, we are going to see how to integrate Spring Boot + JPA with Cockroach DB, and deploying it into Kubernetes. 

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lunes, marzo 26, 2018

Arquillian Chameleon. Simplifying your Arquillian tests.

Arquillian Chameleon was born to simplify the configuration of Arquillian tests. I am proud to announce that with version 1.0.0.CR2 we have not only simplified how to configure Arquillian tests but also how to write them.

With this new release, three new simplifications have been added:
  • You only need to use 1 (or at most 2 dependencies just in case you want to use auto-deployment feature)
  • It is not necessary to add any dependency to define which application server you want to use to run tests. Even not necessary to use arquillian.xml file to define it.
  • It is not necessary to use ShrinkWrap to build your package. You can still use it, but you can delegate the process of creating the package to a custom SPI.
So let's start.


You only need to add one dependency you don't need to add Arquillian dependency + container dependency anymore.

Definition of container 

Now to define a container you just need to use a special runner and special annotation:

You just need to use ArquillianChameleon runner and the special annotation @ChameleonTarget to define which container you want to use. In this example, Wildfly 11 with the managed mode is configured.

When running this test, classpath is going to be configured with Arquillian Wildfly dependency, download the application server and behave as any other Arquillian test.


Arquillan allows you to define a Java SPI to describe how the archive should be created. This effectively means that no @Deployment method is required if you provide an implementation which automatically creates the deployment file.

Arquillian Chameleon provides at this time two implementations:
  1. File which deploys an already created file. You need to set the location of the file.
  2. Maven which runs using embedded Maven the build of the project and the generated archive is used as deployment archive.
For this example, I am going to use a multi-module project as an example, but notice that if you create a none multimodule project, then defaults works perfectly.

Notice that depending on the method you choose (File or Maven) you need to add the implementation on classpath.

In this case, I choose to use the Maven approach which means that the archive is generated by building all project.

Two things that are specific to this test and needs to be customized (instead of defaults) because of the example.

First one is the pom location. By default, the @MavenBuild annotation uses the pom.xml where the test is executed. In case of multimodule project, you don't want to run the build from module where test is defined but from the root of the project, so you get a complete archive with all dependencies. For this case you need to set it where is located.

The second one is where is the archive generated to be used to deploy. By default, you don't need to specify anything since in case of none multimodule project you are only generating one file. But in case of multimodule projects, you are generating multiple archives, so you need to specify which module contains the final archive.

And that's all, when you run this test, Arquillian will download Wildfly, start it, runs the build to get the final deployment file (such as .war), deploy it and finally run the test.

Notice that also there is @DeploymentParameters annotation which is not mandatory to be used, but allows you to configure the deployment as you do with @Deployment annotation, such as setting a deployment name or changing the mode from a container (the default one) to as client.


You can see that everything has been simplified a lot. The idea is to offer a similar experience that you get when running a Spring tests.

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lunes, febrero 12, 2018

Repeatable Annotations in Java 8

With Java 8 you are able to repeat the same annotation to a declaration or type. For example, to register that one class should only be accessible at runtime by specific roles, you could write something like:

Notice that now @Role is repeated several times. For compatibility reasons, repeating annotations are stored in a container annotation, so instead of writing just one annotation you need to write two, so in the previous case, you need to create @Role and @Roles annotations.

Notice that you need to create two annotations, one which is the "plural" part of the annotation where you set return type of value method to be an array of the annotation that can be used multiple times. The other annotation can be used multiple time in the scope where it is defined and must be annotated with @Repeatable annotation.

This is how I did all the time since Java 8 allows to do it. But last week, during a code review my mate George Gastaldi pointed me out how they are implementing these repeatable annotations in javax.validation spec.  Of course, it is not completely different but I think that looks pretty much clear from point of view implementation since everything is implemented within the same archive and also, in my opinion, the name looks much natural. 

Notice that now everything is placed in the same archive. Since usually you only need to refer to @Role class, and not @Roles (now @Role.List) annotation you can hide this annotation as an inner annotation. Also in case of defining several annotations, this approach makes everything look more compact, instead of having of populating the hierarchy with "duplicated" classes serving the same purpose, you only create one.

Of course, I am not saying that the approach of having two classes is wrong, at the end is about preferences since both are really similar. But after implementing repeatable annotations in this way, I think that it is cleaner and compact solution having everything defined in one class.

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lunes, enero 08, 2018

Secret Rotation for JWT tokens

When you are using JSON Web Token (JWT), or any other token technology that requires to sign or encrypt payload information, it is important to set an expiration date to the token, so if the token expires, you can either assume that this might be considered a security breach and you refuse any communication using this token, or you decide to enable the token by updating it with new expiry date.

But it is also important to use some kind of secret rotation algorithm, so the secret used to sign or encrypt a token is periodically updated, so if the secret is compromised the tokens leaked by this key is less. Also in this way you are decreasing the probability of a secret being broken.

There are several strategies for implementing this, but in this post, I am going to explain how I implemented secret rotation in one project I developed some years ago to sign JWT tokens with HMAC algorithm.

I am going to show how to create a JWT token in Java.

Notice that what you need to do here is creating an algorithm object setting HMAC algorithm and set a secret that is used to sign and verify instance.

So what we need is to rotate this algorithm instance every X minutes, so the probability of breaking the secret, and that the broken secret is still valid, becomes very low.

So how to rotate secrets? Well, with a really simple algorithm that everyone (even if you are not a crypto expert) can understand. Just using time.

So to generate the secret, you need a string, in the previous example was secret String, of course, this is not so secure, so the idea is to compose this secret string by a root (something we called the big bang part) + a shifted part time. In summary the secret is <bigbang>+<timeInMilliseconds>

Bing bang part has no mystery, it is just a static part, for example, my_super_secret.

The interesting part is the time part. Suppose you want to renew secret every second. You only need to do this:

I am just putting 0s to milliseconds part, so if I run this I get something like:


Notice that although between second and third print, it has passed 50 milliseconds, the time part is exactly the same. And it will be the same during the same second.

Of course, this is an extreme example where the secret is changed every second but the idea is that you remove the part of the time that you want to ignore, and fill it with 0s. For this reason, first, you are dividing the time and then multiply by the same number.

For example, suppose that you want to rotate the secret every 10 minutes you just need to divide and multiply for 600000.

There are two problems with this approach that can be fixed although one of them is not really a big issue.

The first one is that since you are truncating the time if you want to change the secret every minute and for example, the first calculation occurs in the middle of a minute, then for just this initial case, the rotation will occur after 30 seconds and not 1 minute. Not a big problem and in our project, we did nothing to fix it.

The second one is what's happening with tokens that were signed just before the secret rotation, they are still valid and you need to be able to verify them too, not with the new secret but with previous one.

To fix this, what we did was to create a valid window, where the previous valid secret was also maintained. So when the system receives a token, it is verified with the current secret, if it passes then we can do any other checks and work with it, if not then the token is verified by the previous secret. If it passes, the token is recreated and signed with the new secret, and if not then obviously this token is invalid and must be refused.

To create the algorithm object for JWT you only need to do something like:

What I really like about this solution is:

  • It is clean, no need for extra elements on your system.
  • No need for triggered threads that are run asynchronously to update the secret.
  • It is really performant, you don't need to access an external system.
  • Testing the service is really easy.
  • The process of verifying is responsible for rotating the secret.
  • It is really easy to scale, in fact, you don't need to do anything, you can add more and more instances of the same service and all of them will rotate the secret at the same time, and all of them will use the same secret, so the rotating process is really stateless, you can scale up or down your instances and all instances will continue to be able to verify tokens signed by other instances.

But of course there are some drawbacks:

  • You still need to share a part of the secret (the big bang part) to each of the services in a secure way. Maybe using Kubernetes secrets, Vault from Hashicorp or if you are not using microservices, you can just copy a file into a concrete location and when the service is up and running, read the big bang part, and then just remove it.
  • If your physical servers are in different time zones, then using this approach might be more problematic. Also, you need that the servers are more or less synchronized. Since you are storing the previous token and current token, it is not necessary that they are synced in the same second and some seconds delay is still possible without any issue.

So we have seen a really simple way of rotating secrets so you can keep your tokens safer. Of course, there are other ways of doing the same. In this post, I just have explained how I did it in a monolith application we developed three years ago, and it worked really well.

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miércoles, enero 03, 2018

Cloud Native Applications with JWT

A native cloud application is an application that is developed for a cloud computing environment.

There is no specific answer to the question "what is a cloud-native application" but different concepts that must be met. 

One of the most important in my opinion is the ability to scale up and down at a rapid rate. And this means that our applications cannot have any state on each of the servers since if one server goes down or is scaled down, then the state stored in that server will be lost.

This is very well summarized at where it is explained with a shopping cart example. In monolith approach, you store the products of the shopping cart in a server session, if the server went down then all products of shopping cart were lost as well. In a cloud-native app, where server instances can be scaled up and down quickly, it is important to not have this stateful behavior on your services and design them to be stateless.

There are different approaches to achieve this goal of implementing a stateless architecture but they can be summarized into two categories:
  • Use a distributed in-memory key/value data store like Infinispan.
  • Use a token which acts as a session between client and server using for example JWT.
In this post, I am going to introduce you the later approach.

JSON Web Token (JWT) is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object.  

This information can be verified and trusted because it is digitally signed. JWTs can be signed using a secret using HMAC or a public/private key pair using RSA.

JSON Web Tokens consist of three Base64Url strings separated by dots which are: Header.Payload.Signature

So the idea basic idea for implementing stateless architecture on backend using JWT is the next one:
  1. When the user adds the first product, the backend service generates a new JWT token with the product added and sent it back to the frontend.
  2. When the user adds a new product, it sends the product to add and also the JWT token that was sent before by backend.
  3. Then the backend verifies that the token has not been modified (verifying the signature), then it gets the products from JWT payload added previously and add the new one to the list. Finally, it creates a new token with previous and new products and it sent it back to the frontend.
  4. The same process is repeated all the time.

So as you can see, now it is not necessary to maintain any state or add any new database service on backend side, you just need to sent back and forward the JWT token with the products inside.

I have recorded a video of a simple shopping cart example where I show the stateless nature of the solution. It can be seen at:

Also if you want to check the project that I used for recording you can take a look at

Notice that this is just a simple post so you can get the basic idea. But you need to take into consideration next things to use it in production:
  1. Use HTTPS instead of HTTP
  2. JWT just signs the token, if you want extra protection apart from HTTPS, use JWE to encrypt the payload of JWT token as well.
  3. Fingerprinting the token to avoid any man-in-the-middle attack and use these parameters as authentication parameters for the token.
  4. JWT can be used for passing authentication and authorization things as well.
You can watch my talk at JavaZone where I introduce some of these techniques:

The good part of JWT approach is that it simplifies a lot the deployment of the service, you don't need to deploy or configure any other distributed database to share the content across the cluster, which minimizes the problems related to the network for communicating to the distributed database or misconfiguring of any of the nodes.

The drawback is that the client needs to be aware to receive and sent back the token and deal with it. In backend side, you need to sign and verify every token all the time.

Note that this approach might work in some cases and might get into some troubles in others (for example if there are parallel connections to backend all of them modifying the token). This post just shows an example of how I implemented this stateless thing in a project with specific requirements, but in other cases it might be wrong to do it. A real shopping cart implementation would have some problems, but for the sake of simplicity and having a business model that everyone undertands, I decided to implement it in this way.

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martes, enero 02, 2018

Writing end to end test for a microservices architecture

UPDATE: I was not really sure if I should call this post with e2e tests since I knew it can get some confusions, but I couldn0t think about any other name. After reading I can be sure that what I am describing here is how to do Narrow Integration Test.

One of the main aspects of microservices architecture is that the application is formed as a collection of loosely coupled services each one deployable independently and communicated each other with some kind of light protocol.

It is because of microservices architecture is a distributed system that makes writing end to end tests really hard. Suppose next simple example provided by Red Hat as an example of microservices architecture (

Now suppose that you want to write an end to end test for Cart Service. You will quickly see that it is not easy at all, let me enumerate some of the reasons:

  • Cart Service needs to know how to boot up Pricing Service, Catalog Service, and MongoDB (and if you want to involve the front-end as well then Coolstore GW and WebUI).
  • Cart Service needs to prepare some data (fixtures) for both of external services.
  • You communicate with services using a network. It might occur that some tests fail not because of a real failure but because of an infrastructure problem or because the other services have any bug. So the probability of these tests become flaky and start failing not because any changed introduced in current service is higher.
  • In more complex cases running these tests might be expensive, in terms of cost (deploying to the cloud), time (booting up all the infrastructure and services) and maintenance time.
  • Difficult to run them in developer machine, since you need all the pieces installed on the machine.

For this reason, the end to end tests is not the best approach for testing a microservice, but you still need a way to test from the beginning to the end of the service.

It is necessary to find a way to "simulate" these external dependencies without having to inject any mock object. What we need to do is cheat the service under test so it really thinks it is communicating with the real external services, when in reality it is not.

The method that allows us to do it is Service Virtualiztion.  Service virtualization is a method to emulate the behavior of component applications such as API based.

You can think about service virtualization as mocking approach you used to implement in OOP but instead of simulating at the object level, you simulate at the service level. It is mocking for the enterprise.

There are a lot of service virtualization tools out there, but in my experience, in the JVM ecosystem, one of the tools that work better is Hoverfly.

Let's see how an "end-to-end" test looks like for Cart Service.

This service is implemented using Spring Boot, so we are using Spring Boot Test framework. The important part here is that the URL where Catalog service is deployed is specified by using CATALOG_ENDPOINT property.  And for this test, it is set to catalog.

The next important point is the Hoverfly class rule section. In that rule next things are specified:
  1. An Http proxy is started before the test and all outgoing traffic from JVM is redirected to that proxy.
  2. It records that when a request to host catalog is done and the path is /api/products it must return a success result with given json document.

The test itself just uses TestRestTemplate (it is a rest client) and validates that you can add some elements to the cart.

Notice that you don't need to configure where the Http proxy is started or configure any port because Hoverfly automatically configures JVM network parameters so any network communication goes through Hoverfly proxy.

So notice that now you don't need to know how to boot up Catalog service nor how to configure it with correct data.

You are testing the whole service within its boundaries, from incoming messages to outgoing messages to other services, without mocking any internal element.

Probably you are wondering "What's happening in case of current  service has also a dependency on a database server?"

In this case, you do as usual since the service itself knows which database server is using and the kind of data it requires, you only need to boot up the database server, populate required data (fixtures) and execute tests. For this scenario I suggest you using Arquillian Cube Docker to bootup database service from a Docker container so you don't need to install it on each machine you need to run tests and Arquillian Persistence Extension for maintaining the database into a known state.

In next example of rating service, you can see briefly how to use them for persistence tests:

With this approach, you are ensuring that all inner components of the service work together as expected and avoiding the flakiness nature of end to end tests in microservices.

So end to end tests in any microservice is not exactly the same of an end to end test in a monolith application, you are still testing the whole service, but just keeping a controlled environment, where test only depends on components within the boundary of service.

How contract tests fit on this? Well actually everything showed here can be used in consumer and provider side of contract testing to avoid having to boot up any external service.  In this way, as many authors conclude, if you are using contract tests, these are becoming the new end to end tests.