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Getting started with Dropwizard: Connecting to external REST Web-services using Jersey Client

Here is a link to my Getting Started with Dropwizard course on Udemy. Only $10! Imagine a situation that you would like to create a currency conversion API using Dropwizard, but exchange rates are fickle and change on daily if not hourly basis. So, you need an external source of exchange rate data and luckily, Google search returns a list of such APIs. In this tutorial will connect to Open Exchange Rates which has a free option.

To use the API one needs to obtain a free API key which is an alphanumeric string supplied as part of request string when accessing the API. Here is the description of how to obtain the key. From this moment it is supposed that you have obtained the key, otherwise you will be unable to follow the examples from this tutorial.

Let’s play a little with the API before we start writing the actual code. First, one can obtain the list of supported currencies, this can be accomplished by navigating the following URL

https://openexchangerates.org/api/currencies.json?app_…

Start building JVM microservices with DropWizard

Here is a link to my Getting Started with Dropwizard course on Udemy. Only $10! A full-profile application server, such as Glassfish  are Wildfly, was conceived to integrate a lot of frameworks that could be used separately with a lightweight server such as Jetty otherwise. However, the benefit was that all parts were assembled for you and you didn’t need to iron out the wrinkles you might encounter gluing various frameworks together. Also, an application server saves a developer from writing code that not pertain to the business domain: the application server copes with multithreading, provides a persistence solution, simplifies receiving messages from JMS queues and so on. It should be noted, that one can use a web-profile application server, such as Tomcat along with Spring to solve the same problems. The difference is that Spring mostly does not abide by standards of enterprise Java.

Using an application server solves a lot of developer’s problems, although when an application grow…

Getting started with Dropwizard: Connecting to a Database using Hibernate

Here is a link to my Getting Started with Dropwizard course on Udemy. Only $10! In the previous installments of this series we discussed how to create a Dropwizard application using Maven archetype and how to use a YAML file to set configuration parameters for the application. In this tutorial we'll create a simple application that exposes an Employee Directory via REST API. For simplicity reasons our representations will not contain hyperlinks, that is we'll talk about Level 2 of Richardson Maturity Model. The sources for the tutorial can be found here.

We'll begin with adding parameters of database connection including credentials, connection URI and database driver name to the application's configuration file. The snippet below shows how to configure the database connection.

MySQL RDBMS was used for our example, but some other DBMS can be used. As we'll use Hibernate to talk to our database, switching databases is a snap, it's only necessary to change t…

Introduction to Hypertext Application Language (HAL)

Principles of REST architectural style were put forth by Dr. Roy Fielding in his thesis “Architectural Styles and the Design of Network-based Software Architectures”. One of the main principles of the style is that REST applications should be hypermedia driven, that is the change of an application's state or, in other words, transition from one resource to another, should be done by following the links. The rationale behind this principle is that all possible operations with the resource can be discovered without the need of any out-of-band documentation and if some URI changes, there is no need to change the client as it is server's responsibility to generate URIs and insert them into representations. This principle is also called Hypermedia As The Engine Of An Application state (HATEOAS). While the Thesis gives the prescription to use hyperlinks in the representations of resources, Hypertext Application Language (HAL) is one possible recipe for how to do design representa…