Java Microservices: Code Examples, Tutorials, and More
What Is a Microservice?
Microservices are small, autonomous programs that function as both data producers and data consumers, particularly between service boundaries within a virtualized cloud environment. 100–200 individual microservices might be used to render a single Amazon web page, for example. Microservices are a new type of vector into secured networked assets.
Microservices can be coded in a variety of languages that are often, but not always, dependent upon the cloud infrastructure in which the microservice resides. In addition, there is no reason why a microservice programmed in C# can’t be designed to talk to another microservice written in Python. The most common languages used to create microservices are Python, Java, Ruby, C#, PHP, JavaScript, Elixir, and Go.
At a fundamental level, microservices expose a limited API, which provides a simple set of related functionalities that, by design, are “loosely coupled” with other collaborating services. Coupling refers to the degree of direct knowledge that one component has of another. Messages consist of instructions bound in metadata and encoded in a data-interchange format such as JSON. Other components such as testing or monitoring stubs are also typically present in a particular microservice.
To better understand microservices, you need to understand some of the basic jargon.
The fundamental components of a microservice consists of
- Message Dispatcher or more simply, a Producer, which publishes messages to a service bus;
- An Event Listener or Consumer, which receives messages from service bus; and
- Business logic (the data that passes between Producers and Consumers).
In addition, most microservice implementations rely upon some type of message broker — typically a library that provides a message queue and an exchange. You can think of a message queue as a buffer or an array of n length. An exchange consists of the logic that receives messages from producers and pushes them into the correct queue(s). There are different classes of exchanges but we won’t detail them here.
Let’s look at some pictures to better understand these relationships.
A producer is simply a service that sends data. We’ll signify it as a circle with a P inside.
A consumer is a service that receives and performs some operation on data such as rendering a PDF file. We’ll represent this as a circle with a C inside.
An exchange pushes data from the producer into a queue. We’ll use a yellow circle with an X inside to represent this.
We’ll represent a queue as a row of blue boxes.
One of the two most common microservice patterns are work queues, which distribute tasks among different workers. We can represent this pattern as follows:
The producer, in this case, might be a web-based button that submits customer information that is acted upon in some fashion by the back-end consumers.
The second most common pattern is known as publish/subscribe or PubSub. This pattern allows consumers to subscribe to data or events created by a producer. The pattern is shown below.
Unlike message queues, where data is pushed to specific consumers, the PubSub pattern allows the producer to queue data without knowing which, if any, consumers will receive the data. Consumers, depending upon their mission, can subscribe to many producers.
Other microservice patterns exist, but these two are far and away the most common messaging patterns in use in the AWS cloud. In most cases, these patterns rely upon one or more RPC calls. We’ll get to RPC in a moment.
Microservices allow flexibility in terms of infrastructure and deployment; application traffic is routed to collections of services that may be distributed across CPU’s, disks, machines and networks as opposed to a single monolithic platform designed to manage all traffic. In a fashion similar to the object-oriented (OO) notion of encapsulation, the primary advantages of loosely coupled microservices is that deployment times are reduced, since theoretically any cooperating microservice contract can be replaced with an alternative that provides the same service(s) without redeploying or re-architecting any other collaborating microservice. Additionally, as mentioned earlier, microservices in a loosely coupled system are less constrained to the same platform, language, operating system, or build environment.
Microservices are increasingly used in the development world as developers work to create larger, more complex applications that are better developed and managed as a combination of smaller services that work cohesively together for larger, application-wide functionality.
Tools are rising to meet the need to think about and build apps using a piece-by-piece methodology that is, frankly, less mind-boggling than considering the whole of the application at once. Today, we’ll take a look at microservices, the benefits of using this capability, and a few code examples.
What Are Microservices?
Microservices are a form of service-oriented architecture style (one of the most important skills for Java developers) wherein applications are built as a collection of different smaller services rather than one whole app. Instead of a monolithic app, you have several independent applications that can run on their own and may be created using different coding or programming languages. Big and complicated applications can be made up of simpler and independent programs that are executable by themselves. These smaller programs are grouped together to deliver all the functionalities of the big, monolithic app.
Microservices captures your business scenario, answering the question “What problem are you trying to solve?” It is usually developed by an engineering team with only a few members and can be written in any programming language as well as utilize any framework. Each of the involved programs is independently versioned, executed, and scaled. These microservices can interact with other microservices and can have unique URLs or names while being always available and consistent even when failures are experienced.
What Are the Benefits of Microservices?
There are several benefits to using microservices. For one, because these smaller applications are not dependent on the same coding language, the developers can use the programming language that they are most familiar with. That helps developers come up with a program faster with lower costs and fewer bugs. The agility and low costs can also come from being able to reuse these smaller programs on other projects, making it more efficient.
Examples of Microservices Frameworks for Java
There are several microservices frameworks that you can use for developing for Java. Some of these are:
- Spring Boot: This is probably the best Java microservices framework that works on top of languages for Inversion of Control, Aspect Oriented Programming, and others.
- Jersey: This open-source framework supports JAX-RS APIs in Java is very easy to use.
- Swagger: Helps you in documenting API as well as gives you a development portal, which allows users to test your APIs.
Others that you can consider include: Dropwizard, Ninja Web Framework, Play Framework, RestExpress, Restlet, Restx, and Spark Framework.
How to Create Using DropWizard
DropWizard pulls together mature and stable Java libraries in lightweight packages that you can use for your own applications. It uses Jetty for HTTP, Jersey for REST, and Jackson for JSON, along with Metrics, Guava, Logback, Hibernate Validator, Apache HttpClient, Liquibase, Mustache, Joda Time, and Freemarker.
Microservices With Spring Boot
Spring Boot gives you Java application to use with your own apps via an embedded server. It uses Tomcat, so you do not have to use Java EE containers. A sample Spring Boot tutorial is at this link.
You can find all Spring Boot projects here, and you will realize that Spring Boot has all the infrastructures that your applications need. It does not matter if you are writing apps for security, configuration, or big data; there is a Spring Boot project for it.
Spring Boot projects include:
- Spring IO Platform: Enterprise-grade distribution for versioned applications.
- Spring Framework: For transaction management, dependency injection, data access, messaging, and web apps.
- Spring Cloud: For distributed systems and used for building or deploying your microservices.
- Spring Data: For microservices that are related to data access, be it map-reduce, relational or non-relational.
- Spring Batch: For high levels of batch operations.
- Spring Security: For authorization and authentication support.
- Spring REST Docs: For documenting RESTful services.
- Spring Social: For connecting to social media APIs.
- Spring Mobile: For mobile Web apps.
