Question

可能重复：
Guice with parents

class Book{string title;}
class ChildrensBook extends Book{}
class ScienceBook extends Book{}

我想将书名注入子类中，例如，childrensBook应该被赋予标题＆＃34;爱丽丝梦游仙境＆＃34;并且ScienceBook应该得到＆＃34;关于物种起源＆＃34;。我如何用Guice实现这一目标？

（请注意，我不想覆盖子类中的title字段）

Answer 1

之前曾问及answered here：

埋藏在Guice最佳实践的Minimize Mutability部分，您会找到以下指南：

子类必须使用所有依赖项调用super()。这使得构造函数注入繁琐，特别是作为注入基础班级变化。

在实践中，以下是使用构造函数注入的方法：

public class TestInheritanceBinding {
   static class Book {
      final String title;
      @Inject Book(@Named("GeneralTitle") String title) {
         this.title = title;
      }
   }
   static class ChildrensBook extends Book {
      @Inject ChildrensBook(@Named("ChildrensTitle") String title) {
         super(title);
      }
   }
   static class ScienceBook extends Book {
      @Inject ScienceBook(@Named("ScienceTitle") String title) {
         super(title);
      }
   }

   @Test
   public void bindingWorked() {
      Injector injector = Guice.createInjector(new AbstractModule() {
         @Override protected void configure() {
            bind(String.class).
            annotatedWith(Names.named("GeneralTitle")).
            toInstance("To Kill a Mockingbird");
            bind(String.class).
            annotatedWith(Names.named("ChildrensTitle")).
            toInstance("Alice in Wonderland");
            bind(String.class).
            annotatedWith(Names.named("ScienceTitle")).
            toInstance("On the Origin of Species");
         }
      });
      Book generalBook = injector.getInstance(Book.class);
      assertEquals("To Kill a Mockingbird", generalBook.title);
      ChildrensBook childrensBook = injector.getInstance(ChildrensBook.class);
      assertEquals("Alice in Wonderland", childrensBook.title);
      ScienceBook scienceBook = injector.getInstance(ScienceBook.class);
      assertEquals("On the Origin of Species", scienceBook.title);
   }
}

Answer 2

您最好的选择可能是使用不同的参数注释编写子类构造函数 - 类似于

class ChildrensBook extends Book {
  @Inject ChildrensBook (@AliceInWonderland String title) {
     super(title);
  }
}

使用Guice，如何注入超类的构造函数参数？

2 个答案: