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How to implement Cache Aside Pattern with Spring?

ProblemYou want to boost application performance by loading data from a cache and prevent the network trip to the persistent store (and also the query execution). This can be achieved by loading data from a cache. However, you want to load data on demand or lazily. Also, you want the application to control the cache data management – loading, eviction, and retrieval. Forces Improve performance by loading data from cache lazily.Application code controls cache data management.The underlying caching system does not provide read-through, write-through/write-behind strategies (strange really ??).
Solution Use cache aside design pattern to solve the problems outlined above. This is also one of many caching patterns/strategies. I believe it is named in this because aside from managing the data store, application code is responsible for managing the cache also.
Let's now try to understand how this caching technique works and then explore how it solves the problems.
ReadCache MissThe applic…
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How to Stand up a Spring Cloud Config Server?

Setup and Configure Spring Cloud Config Server Project

Spring Cloud Config Server is just another Spring Boot application. It provides several infrastructure micro services to centralize access to configuration information backed by a version controlled (well at least in the case of default GIT storage) repository.

Step 1 - Create a Spring Boot project in STS with the dependencies shown in Figure 2.


Click on 'Finish' to complete the creation of the Spring Boot project in STS.
The build.gradle file is shown in listing below. There is only one dependency to the Spring Cloud Config Server. Also Spring Cloud release train 'Dalston.SR1'.
Step 2 - Annotate the class containing main method
The next step is to annotate the ConfigServerInfraApplication class with @EnableConfigServer
That's all is needed on the Java side to start the configuration server.


Step 3 - Final step, create the configuration file.
Finally, create a file named bootstrap.yml and configure it as shown in …

Upgrading Lead Microservice - Use MariaDB and Flyway with Spring Boot

So far I have been using an in-memory H2 database or Mockito for testing the lead microservice. To make the transition towards using the Spring Cloud Config server, I need to upgrade the micro-application to use MariaDB. I will be adding the configuration in the application.yml  the file which in the subsequent post will move over to the config server store. I will also be using Flyway to make it easy to maintain the database schema changes in future. I will use this post to introduce Flyway in the mix. Spring Boot also provides first class integration with Flyway. I am using Flyway as its really quick and easy to get started, minimal learning curve (no DSL) and I am comfortable with it having used it in the past.

Assumptions

MariaDB 10 is installedBasic familiarity with FlywayHeidi SQL client is installed.
Step 1 - Update build.gradle to include the MariaDB JDBC and Flyway dependencies.
Do not forget to do a Gradle refresh on your IDE (I am using STS 3.8.4 on Java 8)

Step 2 - Rename the…

Why do you need Spring Cloud Config server?

Last month I wrote a primer on concepts around 12 factor app. Before getting into the details of the Spring Cloud Config Server, I must refresh on the principle #3 from the list presented in that post.

3 – ConfigurationStore config in the environments
Configuration information must be separate from the source code. This may seem so obvious, but often we are guilty of leaving critical configuration parameters in the scattered in the code. Instead, applications should have environment specific configuration files. The sensitive information like database password or API key should be stored in these environment configuration files in encrypted format.
 The key takeaways from this postulate for a cloud-native microservices application are:
Do not store configuration as part of the deployable unit (in the case of lead microservice - inside the jar or war if you are still deploying war like the good old days). Instead, store it in an external location and make it easily accessible during run-…

Unit Test - Microservices - Business Layer

In this post, I am going to show how to unit test the business layer of the lead microservice that I am developing. A couple of things to keep in mind to write the unit test for the business layer.

These tests run must very fast for quick feedback.Only the business layer is involved and hence the web layer and repository layer should not be started. In other words, the Spring web tier beans should not be created and neither any database connections should be used. (This helps to achieve #1). The repository layer will be mocked using Mockito.The fluent assert from AssertJ library will be used.  The source code of the lead business unit test is shown in listing below.
Most of the test methods are straight forward. However, the testDelete the method needs some explanation. Here the findOne method is mocked/stubbed. This ensures that correct lead object is returned by the stub method. The other thing to note is that the verify the method for saving method captures the internal Lead objec…

Complete Unit tests - Microservices - Repository Layer

In the previous post, I introduced the unit tests for the repository layer of the lead microservice. In this short post, I will do some cleanup, add all the unit tests. Finally, I replaced all the JUNIT asserts with AssertJ asserts. AssserJ is also recommended by the Spring champions over at Pivotal.


AssertJ - provides fluent assertions for Java. Testing improvements in Spring Boot

Ok thats it for now. In the next post I will show how to unit test the business / service layer of the lead microservice.

Microservice - Unit Test - Repository Layer

Now that we have completed the first round of development of our lead microservice, it is time to focus on some testing. I will follow a bottom-up approach and start by writing unit tests for the repository layer.

In order to write unit tests, I will make use of the Spring Test Framework and Spring Boot Test support. Spring Boot makes it extremely easy to unit test slices of the application. We can use @DataJpaTest and just unit test the database layer with an embedded database like H2. However, there are some gotchas (I do not know exactly what at this moment), the @DataJpaTest does not work if you have extended the Spring Data JPA to add a custom method for all the repositories. The problem I found was that the when running the Spring Boot application, everything works fine and the custom method works fine and the query returns the correct results. However, when the unit test is run, Spring Data JPA fails, complaining that it is not able to find an attribute for the entity/type.

So…