Guice - Hello World!
這個範例主要了解Guice如何實做Dependency Injection(DI)。
準備
- 至Guice官網下載lib包。我下載了 guice-4.0-beta.zip。
- 建立一個Eclipse Java Project並把壓縮的內容解壓到Project libs目錄。
- 將guice-4.0-beta.tar與javax.inject.jar加入build path中。
第一隻Guice程式
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!