Guice - Hello World!

這個範例主要了解Guice如何實做Dependency Injection(DI)。

  1. Guice官網下載lib包。我下載了 guice-4.0-beta.zip。
  2. 建立一個Eclipse Java Project並把壓縮的內容解壓到Project libs目錄。
  3. 將guice-4.0-beta.tar與javax.inject.jar加入build path中。

範例程式包含介面IPrintServer、實作類別ConsolePrinter、用戶端PrinterClient與Guice所需要的configuration模組PrinterModule。

PrintService介面:

package org.tonylin.practice.guice;

public interface IPrintService {
	void print(String ... strs);
}
ConsolePrinter提供Console類型服務的PrintService:
package org.tonylin.practice.guice;

public class ConsolePrinter implements IPrintService {

	@Override
	public void print(String... strs) {
		for( String str : strs ){
			System.out.println(str);
		}
	}
}
PrinterClient是使用到PrintService的用戶端,我們必須針對提供注入服務的函式宣告為@Inject:
package org.tonylin.practice.guice;

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

public class PrinterClient {
	private IPrintService mPrintService = null;
	
	
	@Inject
	public void setPrintService(IPrintService aPrintService){
		mPrintService = aPrintService;
	}
	
	public IPrintService getPrintService(){
		return mPrintService;
	}
	
	public void print(String ... strs){
		mPrintService.print(strs);
	}
	
	public static void main(String[] args) {
		Injector injector = Guice.createInjector(new PrinterModule());
		PrinterClient printerClient = injector.getInstance(PrinterClient.class);
		printerClient.print("test1", "test2");
	}

}
PrinterModule負責建立PrinterClient與實際提供服務類別的連結,在這裡我透過System Propertes去決定我所要注入給PrinterClient的IPrintService實體:
package org.tonylin.practice.guice;

import com.google.inject.Binder;
import com.google.inject.Module;

public class PrinterModule implements Module {
	@Override
	public void configure(Binder binder) {
	    binder.bind(IPrintService.class).to(ConsolePrinter.class);
	}
}

執行PrinterClient的main可以發現test1與test2字串顯示在螢幕上。

友藏內心獨白: 照這樣看來Guice是蠻簡單的!