-
Notifications
You must be signed in to change notification settings - Fork 1
Creating a basic service
This article explains how to create a FREME basic service. It will create a filter that is executed before every API request. The filter writes a message to the logger for every API request. You can find the whole source code in the logging-filter project in the freme-example GitHub repository.
Every basic service consists at least of a pom.xml to provide the maven configuration, a Java source code file that implements the service and a Spring XML configuration file to load the basic service. This section explains these three components in the example.
pom.xml is an Apache Maven configuration file that mainly pulls in the required dependencies. Like every basic service it inherits from the artifact eu.freme.bservices.basic-services-parent. This simplifies the Maven setup of basic services a lot because all common configuration can be done in the parent artifact. Further it defines a dependency on the test-helper artifact because this will be needed later on in this tutorial.
ExampleLoggingFilter.java contains the source codes of the example logging filter. Here is the source code:
@Component
public class ExampleLoggingFilter extends GenericFilterBean {
Logger logger = Logger.getLogger(ExampleLoggingFilter.class);
@Override
public void doFilter(ServletRequest req, ServletResponse res,
FilterChain chain) throws IOException, ServletException {
if (req instanceof HttpServletRequest) {
HttpServletRequest httpRequest = (HttpServletRequest) req;
String uri = httpRequest.getRequestURI();
logger.info("Detect HTTP request to endpoint " + uri);
}
chain.doFilter(req, res);
}
}
ExampleLoggingFilter is implemented as a standard filter in the Spring MVC framework. Therefore it extends GenericFilterBean and is defined as a Spring Bean by the @Component annotation. Then it creates the logger. FREME uses Apache Log4j framework for logging.
Every Spring MVC filter overrides the method doFilter. It is executed upon every HTTP request, before the request is processed by the controller. It contains only a short source code that converts the request to an HttpServletRequest and logs the URI to the logger. Then it calls chain.doFilter() which is required by the Spring MVC framework so the request is passed to the next filter in the filter chain.
The Spring XML configuration is provided by the file example-logger.xml. As all Spring configurations it resides in the resource folder "spring-configurations". It instructs the Spring application context to perform a component scan on the package eu.freme.bservices.example.loggingfilter. Through this configuration Spring will find the Bean defined by ExampleLoggingFilter.java and initialize the filter.
Now we have an implementation of the filter that is ready for inclusion into any FREME package. This section of the article shows how to write a simple FREME package to start the filter. The files described here are not necessarily part of a FREME basic service. They are contained in the example only for demonstration purposes.
package.xml defines a very simple FREME package. First like all FREME packages it loads freme-common.xml. Then it loads test-helper.xml. Further the package imports example-logger.xml to initialize the logging filter created in this guide.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd">
<import resource="classpath:spring-configurations/freme-common.xml" />
<import resource="classpath:spring-configurations/test-helper.xml" />
<import resource="classpath:spring-configurations/example-logger.xml" />
</beans>
From within your IDE you can now run the main class eu.freme.common.starter.FREMEStarter. This starter class looks for a file called package.xml located in the root of the Java class path. So it will start the package.xml file described above.
The test-helper basic service creates an REST endpoint on /mockups/file. When FREME is started you can call the REST endpoint by opening http://localhost:8080/mockups/file/http-response.txt with a web browser. The mockup endpoint returns the file http-response.txt. So it sends "hello world" to the web browser. Usually this functionality is used to create mockup endpoints for unit testing but here we use it so we can create an API endpoint without programming.
Now you can take a look at the console output of FREME. In the log stream you can find the message
ExampleLoggingFilter: Detect HTTP request to URI /mockups/file/http-response.txt
This message was generated by the example logging filter.