Introduce Guice with Example

The motivation of Guice

Guice alleviates the need for factories and the user of new operator in Java

Make youself confident with Java's type safe nature.

Helps you design better API

Easy tests

Less boilerplate code

Works on Java SE, Java EE, Android and GWT

Let me give you a little taste of Guice by an example.

public interface Shorter {
    String shortenUrl(String text);
}

 

public class UrlShortener implements Shorter {

    public String shortenUrl(String text) {
        // Local or remote URL shorted service request here
        return "short-url";
    }
}

 

public interface WeiboSender {

    void send(String text);
}

 

public class WeiboBrowserSender implements WeiboSender {

    @Override
    public void send(String text) {
        // Send weibo.
        System.out.println("Weibo was sent out: " + text);
    }
}

 

import com.google.inject.Inject;

/**
 * Weibo client for posting, first it will try to shorten url, then send the weibo out.
 * <p/>
 * User: George Sun
 * Date: 7/12/13
 * Time: 7:25 PM
 */
public class WeiboClient {
    private WeiboSender sender;
    private UrlShortener urlShortener;

    // Note the Inject here, this is the key of this example.
    @Inject
    public WeiboClient(WeiboSender sender, UrlShortener urlShortener) {
        this.sender = sender;
        this.urlShortener = urlShortener;
    }

    public void postWeibo(String text) {
        String weiboText = getWeiboText();
        if (weiboText.length() > 140) {
            weiboText = urlShortener.shortenUrl(weiboText);
        }

        if (weiboText.length() <= 140) {
            sender.send(weiboText);
        }
    }

    private String getWeiboText() {
        return "Sample Weibo text here.";
    }
}

 

import com.google.inject.AbstractModule;

/**
 * Tell Guice what to inject, then Guice will inject instances when needed.
 * <p/>
 * User: George Sun
 * Date: 7/12/13
 * Time: 7:40 PM
 */
public class WeiboModule extends AbstractModule {

    @Override
    protected void configure() {
        bind(WeiboSender.class).to(WeiboBrowserSender.class);
        bind(Shorter.class).to(UrlShortener.class);
    }
}

 

import com.google.inject.Guice;
import com.google.inject.Injector;

/**
 * Driver class.
 * <p/>
 * User: George Sun
 * Date: 7/12/13
 * Time: 7:44 PM
 */
public class Main {

    public static void main(String[] args) {
        Injector injector = Guice.createInjector(new WeiboModule());
        WeiboClient weiboClient = injector.getInstance(WeiboClient.class);

        String sample = "Sample weibo text here.";
        weiboClient.postWeibo(sample);
    }
}

 
For complete reference and documents, visit Guice project home .