hibernate 通用 dao 重载 removeById

Question

我在我的 java 项目中实现休眠 ORM。 我从github 下载了源代码 我已经编译了示例中包含的 hibernate-maven-web。 现在让我们假设我想在其中一个实现中重载方法 例如 CitizenDAOImpl.java 在我进行更改之前，它看起来像这样。

package sample.googlecode.genericdao.oldworld.dao;

import org.springframework.stereotype.Repository;

import sample.googlecode.genericdao.oldworld.model.Citizen;

/**
 * <p>
 * This is the implementation of the Citizen DAO. You can see that we don't
 * actually have to implement anything, it is all inherited from GenericDAOImpl
 * through BaseDAO. We just specify the entity type (Citizen) and its identifier
 * type (Long).
 * 
 * <p>
 * The @Repository allows Spring to recognize this as a managed component (so we
 * don't need to specify it in XML) and also tells spring to do DAO exception
 * translation to the Spring exception hierarchy.
 * 
 * @author dwolverton
 * 
 */
@Repository
public class CitizenDAOImpl extends BaseDAO<Citizen, Long> implements CitizenDAO {


}

我所做的只是重写将调用超类的 removeById。 稍后我打算添加一些加密功能，所以 id 都会被打乱。

package sample.googlecode.genericdao.oldworld.dao;

import org.springframework.stereotype.Repository;

import sample.googlecode.genericdao.oldworld.model.Citizen;

/**
 * <p>
 * This is the implementation of the Citizen DAO. You can see that we don't
 * actually have to implement anything, it is all inherited from GenericDAOImpl
 * through BaseDAO. We just specify the entity type (Citizen) and its identifier
 * type (Long).
 * 
 * <p>
 * The @Repository allows Spring to recognize this as a managed component (so we
 * don't need to specify it in XML) and also tells spring to do DAO exception
 * translation to the Spring exception hierarchy.
 * 
 * @author dwolverton
 * 
 */
@Repository
public class CitizenDAOImpl extends BaseDAO<Citizen, Long> implements CitizenDAO {

    @Override
    public boolean removeById(java.io.Serializable id) {
        return super.removeById(id);
    }
}

当我运行 mvn clean install 时出现错误

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.
1:compile (default-compile) on project hibernate-maven-web: Compilation failure
[ERROR] /C:/Dev/spike/hibernate-maven-web/src/main/java/sample/googlecode/generi
cdao/oldworld/dao/CitizenDAOImpl.java:[26,24] name clash: removeById(java.io.Ser
ializable) in sample.googlecode.genericdao.oldworld.dao.CitizenDAOImpl and remov
eById(ID) in com.googlecode.genericdao.dao.hibernate.GenericDAO have the same er
asure, yet neither overrides the other
[ERROR] -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e swit
ch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please rea
d the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureExc
eption

我知道它的模糊调用以及 BaseDAO 和 CitizenDAO 在某些时候确实继承了 GenericADO。 在这种情况下有什么好的解决方案？ 谢谢

Answer 1

实际上你的方法并没有覆盖超类方法，你应该使用 Long id 而不是 Serializable id 作为参数使其被覆盖。

超类是一个有界泛型类，因为它对 ID 的泛型类型有ID extends Serializable 限制。请注意，通用信息不会存储在运行时中，并且会被删除。这只是一个编译时间信息。详情请见https://docs.oracle.com/javase/tutorial/java/generics/erasure.html。

这里您的自定义方法不会覆盖超类方法，而且，这两个方法都是通用的并且具有相同的擦除。所以在运行时，在擦除之后，这些方法将具有相同的签名，JVM 会混淆要调用哪一个。这就是编译器因错误而失败的原因。