Abstraction layer project for HTTP client calls and two adapters for external projects.
In a current project I need an abstraction layer for HTTP client calls. I also want to easily replace the client implementation to unit test my project.
The project where this is needed itself is a library. So it should be easily reusable and bring no extra baggage.
Say you have a project and use library A for HTTP client calls. Now you add a new dependency to a library for a REST service you want to use - and this library depends on HTTP client library B. You end up with two dependencies who do exactly the same thing. Who needs that?
If the REST library would just depend on an API project you could use an existing adapter implementation for library A or quickly write one yourself. Problem solved.
Since this project is currently intended for my java-lib-for-wunderlist project, I keep the usage chapter very short. It basicly works like log4j or slf4j. You depend on the facade project (see Maven) and only use the HTTPClient interface for HTTP calls.
The field initialization looks like this:
private HTTPClient httpClient = HTTPClientFactory.create();During compile time this code is perfectly fine. When running the program a concrete implementation of the HTTPClient interface is needed. For that you additionally depend on an adapter implementation (e.g. http4j-apache). In your library project you do not want to have a compile dependency to an adapter implementation, but with a test dependency you actually can run and test your code.
If you have multiple adapter projects in your classpath you can select a specific one by setting the Java system property jochor.servicefactory.de.jochor.lib.http4j.StaticHTTPClientBinder to the full qualified name of the service class.
System.setProperty("jochor.servicefactory.de.jochor.lib.json4j.StaticHTTPClientBinder", "de.jochor.lib.http4j.junit.HTTPClientJUnit");Normally this is only necessary if you need different implementation during testing and runtime.
<dependency>
<groupId>de.jochor.lib.http</groupId>
<artifactId>http4j</artifactId>
<version>0.3.2</version>
</dependency><dependency>
<groupId>de.jochor.lib.http</groupId>
<artifactId>http4j-apache</artifactId>
<version>0.3.2</version>
</dependency><dependency>
<groupId>de.jochor.lib.http</groupId>
<artifactId>http4j-junit</artifactId>
<version>0.3.2</version>
</dependency><repository>
<id>jochor-public-releases</id>
<url>http://maven.jochor.de/content/repositories/public-releases/</url>
</repository><repository>
<id>jochor-public-releases</id>
<url>http://maven.jochor.de/content/repositories/public-snapshots/</url>
</repository>