吉斯注射

Question

我有一個類：

public class FizzBuzz { 
    @Named("Red") private String redService; 

    public static void main(String[] args) { 
     GuiceTest testApp = new GuiceTest(); 

     testApp.run(); 
    } 

    private void run() { 
     Injector inj = Guice.createInjector(new MyModule()); 

     redService = (String)inj.getInstance(String.class); 

     // Should print "red-service" but is instead an empty string! 
     System.out.println("redService = " + redService); 
    } 

    // ... Rest of class omitted for brevity 
} 

public class MyModule extends AbstractModule { 
    @Override 
    protected void configure() { 
     bind(String.class).annotatedWith(Names.named("Red")).toInstance("red-service"); 
    } 
} 

在我的模塊我指示吉斯綁定所有String.class實例@Named「紅」字符串實例「紅色服務」，但我在輸出的打印語句中沒有看到。我如何錯誤地使用Guice？

Answer 1

讓我總結出一些已經在這裏提出的意見......

1. 你忘了@Inject註釋
2. 我會強烈建議保持吉斯/注射器FizzFuzz之外。使用靜態主要方法來引導您的應用程序（不是運行（））。
3. 將字符串綁定到常量可以通過bindConstant輕鬆完成。

THS給你帶來的東西是這樣的：

public class FizzFuzz { 
    @Inject 
    @Named("red") 
    private String service; 

    public static void main(String[] args) { 
     FizzFuzz fizzFuzz = Guice.createInjector(new AbstractModule() { 
      @Override 
      protected void configure() { 
       bindConstant().annotatedWith(Names.named("red")).to("red-service"); 
      }  
     }).getInstance(FizzFuzz.class); 

     System.out.println(fizzFuzz.service); 
    } 
} 

Answer 2

您忘記了@Inject之前@Named("Red")。 另外使用bindConstant（）可以預見這種事情。

P.S.你爲什麼收到String而不是FizzBuzz？

Answer 3

它應該是相當多用我的方式。
創建第一註記

@Retention(RetentionPolicy.RUNTIME) 
public @interface InjectSetting { 
    String value(); 
} 

創建吉斯模塊

@Slf4j 
public class SettingModule extends AbstractModule { 
    private final Properties properties; 

    private SettingModule(Properties properties) { 
     this.properties = properties; 
    } 

    @Override 
    protected void configure() { 
     binder().bindListener(Matchers.any(), listener(((type, encounter) -> { 
      for (Field field : type.getRawType().getDeclaredFields()) { 
       if (field.isAnnotationPresent(InjectSetting.class)) { 
        field.setAccessible(true); 

        encounter.register(injector(instance -> { 
         try { 
          Object value = properties.get(
            field.getAnnotation(InjectSetting.class).value()); 

          field.set(instance, parse(value, field)); 
         } catch (IllegalAccessException e) { 
          binder().addError(e); 
         } 
        })); 
       } 
      } 
     }))); 
    } 

    TypeListener listener(BiConsumer<TypeLiteral<?>, TypeEncounter<?>> consumer) { 
     return consumer::accept; 
    } 

    MembersInjector<Object> injector(Consumer<Object> consumer) { 
     return consumer::accept; 
    } 

    Object parse(Object value, Field field) { 
     Type type = field.getType(); 

     if(type == boolean.class) 
      value = Boolean.parseBoolean(value.toString()); 
     else if(type == int.class) 
      value = Integer.parseInt(value.toString()); 

     return value; 
    } 

    public static Module of(String propertiesPath, String... more) { 
     Properties properties = new Properties(); 

     try { 
      properties.load(Files.newInputStream(Paths.get(propertiesPath, more))); 
     } catch(Exception e) { 
      log.error("can't load config file {}", propertiesPath); 
      throw new RuntimeException(e); 
     } 

     return new SettingModule(properties); 
    } 
} 

然後注入你的領域

@InjectSetting("database.port") 
private int port;