在spring中自动将空列表转换为null

Question

我想让所有DAO方法返回一个空集合而不是null.我怎么能用AOP弹簧做到这一点？

Answer 1

这应该工作:

@Aspect
@Service
public class DaoAspect {

    @Around("execution(java.util.List com.example.*Dao.get*())")
    public Object aroundGetDaoMethods(ProceedingJoinPoint joinPoint) throws Throwable {
        final Object retVal = joinPoint.proceed();
        return retVal != null ? retVal : Collections.emptyList();
    }

}

调整切入点以仅匹配您希望拦截的方法.您还需要添加AspectJ JAR:

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-aop</artifactId>
    <version>3.1.2.RELEASE</version>
</dependency>
<dependency>
    <groupId>org.aspectj</groupId>
    <artifactId>aspectjrt</artifactId>
    <version>1.6.6</version>
</dependency>
<dependency>
    <groupId>org.aspectj</groupId>
    <artifactId>aspectjweaver</artifactId>
    <version>1.6.6</version>
</dependency>

并启用CLASSPATH扫描:

<aop:aspectj-autoproxy/>