It would be nice to decouple components in client applications the way that we have become accustom to doing in server side applications and providing a way to use mock implementations for unit testing.

Fortunately it is fairly straightforward to configure a Java SE client application to use a dependency injection framework such as Weld.

The first step is to include the weld-se jar as a dependency in your project. The weld-se jar is basically the Weld framework repackaged along with its other dependencies as a single jar file which is about 4MB.

    <dependency>
        <groupId>org.jboss.weld.se</groupId>
        <artifactId>weld-se</artifactId>
        <version>2.2.11.Final</version>
    </dependency>

Implement a singleton which will create and initialize the Weld container and provide a method to access a bean from the container.

import org.jboss.weld.environment.se.Weld;
import org.jboss.weld.environment.se.WeldContainer;


public class CdiContext {

    public static final CdiContext INSTANCE = new CdiContext();

    private final Weld weld;
    private final WeldContainer container;

    private CdiContext() {
        this.weld = new Weld();
        this.container = weld.initialize();
        Runtime.getRuntime().addShutdownHook(new Thread() {
            @Override
            public void run() {
                weld.shutdown();
            }
        });
    }

    public <T> T getBean(Class<T> type) {
        return container.instance().select(type).get();
    }
}

Once you have the context you can then use it to instantiate a bean which in turn will inject any dependencies into the bean.

import java.util.HashMap;
import java.util.Map;


public class MainClass {
    protected String baseDir;
    protected String wldFileLocation;
    protected String dataFileDir;
    protected int timeInterval = 15;
    protected String outputFileDir;

    public void run() throws Exception {
        CdiContext context = CdiContext.INSTANCE;

        //Get an isntance of the bean from the context
        IMatcher matcher = context.getBean(IMatcher.class);

        matcher.setCommodityTradeTimeMap( getDateTranslations(1, "6:30:00 AM", "6:35:00 AM", "6:45:00 AM") );

        matcher.matchTrades(wldFileLocation, dataFileDir, timeInterval, outputFileDir);

    }

What is great is that there are no annotations required on the interfaces or their implementing classes. Weld will automatically find the implementation and inject it in the class where defined. ie. there were no annotations required on the IDataFileReader interface or its implementing classes in order to @Inject it into the Matcher class. Likewise neither the IMatcher interface nor the Matcher class require annotations in order to be instantiated by the CdiContext above.

public class Matcher implements IMatcher {

    //Framework will automatically find and inject
    //an implementation of IDataFileReader

    @Inject
    protected IDataFileReader dataFileReader;

twitter: @RobTerpilowski
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