如何使用AspectJ处理通用结果？

Question

我有一个方面(用aspectj语法public aspect ....编写)，它操作许多返回Collection的方法的结果，以便对结果进行分页。

我不能(或者我不知道如何)在建议中使用泛型，所以无论我在哪里调用建议的方法，我都会得到警告

unchecked conversion when advice applied at shadow method-call(java.util.Collection ...), expected java.util.Collection<T> but advice uses java.util.Collection [Xlint:uncheckedAdviceConversion]

我怎么才能摆脱这个？

斯特凡诺

-添加方面代码摘录

public aspect PaginationSupportAspect extends ServiceSupportAspect {

    private static final Logger log = LoggerFactory.getLogger(PaginationSupportAspect.class);

    private pointcut paginate(Criteria criteria) : call(Collection org.jcz.persistence.Service+.*(Criteria));

    @SuppressWarnings({ "unchecked", "rawtypes" })
    Collection around(Criteria criteria, Service service) : paginate(criteria) && target(service) {
        log.trace(String.format("Executing <%s> @ <%s>", this.getClass(), thisJoinPoint.toLongString()));

        return doPaginate(proceed(criteria, service), criteria.getPagination(), service);
    }

    /**
     * 
     * @param source
     * @param criteria
     * @return
     */
    private <T extends EntitySupport> Collection<T> doPaginate(Collection<T> source, Pagination pagination, Service<T> service) {
        // IMPLEMENTATION OMITTED BECAUSE IT'S QUITE LONG

        // What it does is to create another Collection<T> that holds the pagination coordinates (page number, size, count) 
        // and only the elements of the requested page
    }

}

使用实例

Collection<MyEntity> entities = myEntityService.findAll(criteria);

这就是我得到警告的地方

Answer 1

坏消息是:我不知道如何避免这种警告，因为我不太精通Java泛型，特别是不熟悉AspectJ，因为并不是所有您可能期望的都是语法允许的，例如将target()绑定到参数化类型(因为类型擦除限制)。

您可能与这一个邮件列表中的AspectJ有相同的问题。

好消息是:我终于用一个最少的代码示例来重现您的问题，使用了许多虚拟类，并对您如何在应用程序中使用它们做了一些有根据的猜测：

虚拟/助手类/方面：

package org.jcz.persistence;
public class EntitySupport {}

package org.jcz.persistence;
public class MyEntity {}

package org.jcz.persistence;
public class Pagination {}

package org.jcz.persistence;

public class Criteria {
    public Pagination getPagination() {
        return new Pagination();
    }
}

package org.jcz.persistence;

import java.util.ArrayList;
import java.util.Collection;

public class Service<T> {
    public Collection<T> findAll(Criteria criteria) {
        return new ArrayList<T>();
    }
}

package org.jcz.persistence;
public abstract aspect ServiceSupportAspect {}

您的方面，略有改变：

package org.jcz.persistence;

import java.util.ArrayList;
import java.util.Collection;

import org.apache.log4j.Logger;

public aspect PaginationSupportAspect extends ServiceSupportAspect {
    private static final Logger log = Logger.getLogger(PaginationSupportAspect.class);

    private pointcut paginate(Criteria criteria) :
        call(Collection org.jcz.persistence.Service+.*(Criteria)) && args(criteria);

    @SuppressWarnings({ "unchecked", "rawtypes" })
    Collection around(Criteria criteria, Service service) : paginate(criteria) && target(service) {
        log.trace(String.format("Executing <%s> @ <%s>", this.getClass(), thisJoinPoint.toLongString()));
        return doPaginate(proceed(criteria, service), criteria.getPagination(), service);
    }

    private <T extends EntitySupport> Collection<T> doPaginate(
            Collection<T> source, Pagination pagination, Service<T> service)
    {
        System.out.println("doPaginate");
        return new ArrayList<T>();
    }
}

，现在是一个小型驱动程序，用于复制Xlint警告：

import java.util.Collection;

import org.jcz.persistence.Criteria;
import org.jcz.persistence.MyEntity;
import org.jcz.persistence.Service;

public class Application {
    public static void main(String[] args) {
        Service<MyEntity> myEntityService = new Service<MyEntity>();
        Criteria criteria = new Criteria();
        Collection<MyEntity> entities = myEntityService.findAll(criteria);
        System.out.println("Found entities: " + entities);
    }
}

也许其他人能做些我做不到的事。我能做的就是复制它。我会把安迪·克莱门特引向这篇文章。祝好运!