在 Java 中对抽象泛型类变量进行方法调用

如何解决在 Java 中对抽象泛型类变量进行方法调用

老实说，我很难解决这个问题。假设我们有一个基类：

public abstract class Work {
}

还有两个实现：

public class SimpleWork extends Work {
    }

public class HardWork extends Work {
    }

现在我想要具有通用工作类型的抽象工作执行者：

public abstract class AbstractWorkExecuter<TWork extends Work> {

    public abstract WorkResult executeWork(TWork work);
}

以及执行器的两个实现：

public class SimpleWorkExecuter extends AbstractWorkExecuter<SimpleWork> {
    
        public abstract WorkResult executeWork(SimpleWork work);
    }

public class HardWorkExecuter extends AbstractWorkExecuter<HarkWork> {
    
        public abstract WorkResult executeWork(HardWork work);
    }

然后我需要创建一些工厂来实现我需要的执行器：

public class WorkExecutorFactory {
    public static AbstractWorkExecuter<?> create(String type) {
        if (type.equals("simple")) {
            return new SimpleWorkExecuter();
        } else {
            return new HardWorkExecuter();
        }
    }
}

现在我想使用所有这些：

public static void main (String args []) {
    Work work = new SimpleWork();

    //This line works fine
    AbstractWorkExecuter<?> workExecuter = WorkExecutorFactory.create("simple");
    //There is the problem
    workExecuter.executeWork(work);     
}

Eclipse 中的最后一行显示如下异常：

The method executeWork(capture#2-of ?) in the type AbstractWorkExecuter<capture#2-of ?> is not applicable for the arguments (Work)

那么，我应该怎么做才能让它发挥作用？我想避免使用原始类型。需要提及的是，我不知道我可能需要什么实现，并且在这个示例中，实际项目的实现比两个多得多。提前致谢。

解决方法

你不能用字符串来做到这一点。没有足够的静态类型信息来确保编译时的类型正确性。

创建工厂，为您提供所需类型的实例。例如：

class WorkExecutorFactory<T> {
  private final Supplier<T> supplier;

  private WorkExecutorFactory(Supplier<T> supplier) {
    this.supplier = supplier;
  }

  T create() { return supplier.get(); }

  static final WorkExecutorFactory<SimpleWork> SIMPLE_FACTORY = new WorkExecutorFactory<>(SimpleWorkExecuter::new);
}

然后你可以使用SIMPLE_FACTORY.create()（它携带它创建的事物的类型信息）而不是WorkExecutorFactory.create("simple")。

@Aleks，你的方法是正确的，一般来说都是关于依赖注入，非常广泛的主题。

您的问题根本不需要定义要使用的执行程序。只有使用类型和反射 Java 才能匹配、实例化和运行每一个工作。

public class Test {

    // the core team define some basic names
    interface Work {}
    interface WorkExecutor<T extends Work> {
        default void executeWork(T work) {
            System.out.printf("%s run %s%n",this.getClass().getName(),work.getClass().getName());
        }
    }

    // some dev team create simple works
    static class SimpleWork implements Work {}

    // some dev team create hard works
    static class HardWork implements Work {}

    // some dev team create simple executors
    static class SimpleWorkExecutor implements WorkExecutor<SimpleWork> { }

    // some dev team create hard executors
    static class HardWorkExecutor implements WorkExecutor<HardWork> { }

    // (extra requirement) some dev team create aditional (sidecars) hard executors
    static class SideCarHardWorkExecutor implements WorkExecutor<HardWork> { }


    @SneakyThrows
    public static void main(String... args) {

        // somewhere somebody define works
        List<Work> works = asList(new SimpleWork(),new HardWork());

        // for each work to do
        for(Work w: works) {

            final String validExecutorType = WorkExecutor.class.getName() + "<" + w.getClass().getName() + ">";

            // find all available workers,simply ensure the jar,class,... are loaded (websphere,jboss,java -jar...)
            // NOTE: reflection could be hard,use a good reflection dependency injection library!
            for (Class<?> clazz : Test.class.getDeclaredClasses())
                if(Arrays.stream(clazz.getGenericInterfaces()).map(Type::getTypeName).anyMatch(validExecutorType::equals)) {
                    ((WorkExecutor<?>) clazz.newInstance()).executeWork(cast(w));
                    // you can break or continue doing the work with other available worker executors
                }

        }

    }

    private static <T extends Work> T cast(Work w) {
        return (T) w;
    }

}

带输出

Test$SimpleWorkExecutor run Test$SimpleWork
Test$SideCarHardWorkExecutor run Test$HardWork
Test$HardWorkExecutor run Test$HardWork

仅包含/放置类，匹配将自动进行。

注意：for 循环体特定于所使用的 DI 库，在实际项目中使用之前了解并练习。