依赖注入的方式

构造器注入（constructor injection）

public class Product {
  private Category category;
  public Product(Category category) {
    this.category = category;
  }
}

Set 注入

public class Product {
  private Category category;
  public void setCategory(Category category) {
    this.category = category;
  }
}

静态工厂方法注入

示例工厂方法注入