java有没有办法在没有反射的情况下访问方面的目标对象字段（给定getter切入点）？

Question

我正试图用AspectJ解决以下问题

给定一个带有null@Embedded field的实体类，当试图使用getter访问该字段时，如果该字段为null，则首先实例化它。ie：这将确保getXXXX永远不会返回空值

例如：

@Entity
public class MyClass {

        @Id
    private long id;

    @Embedded
    private Validity validity;
}


And Validity:

@Embeddable
public class Validity{
    private long from;
    private long to;
}

然而，我很难想出如何最好地写出before（）建议。理想情况下，我会尽量避免使用反射，以免减慢速度，但到目前为止，我能想到的最好办法是：

// define a pointcut for any getter method of a field with @Embedded of type Validity with any name in com.ia.domain package
pointcut embeddedGetter() : get( @javax.persistence.Embedded com.ia.domain.Validity com.ia.domain..* );

before() : embeddedGetter(){
    String fieldName = thisJoinPoint.getSignature().getName();
    Object obj = thisJoinPoint.getThis();

    // check to see if the obj has the field already defined or is null
    try{
        Field field = obj.getClass().getDeclaredField(fieldName);
        field.setAccessible(true);
        if( field.get(obj) == null )
            field.set(obj, new com.ia.domain.Validity() );
    }
    catch( IllegalAccessException | NoSuchFieldException e){}
}

但我的建议是使用反射来访问字段值。有没有办法做到这一点而不反思

Answer 1

根据around建议，您可以仅在需要初始化时进行反射：

Object around(): embeddedGetter() {
    Object value = proceed();
    if (value == null) {
        String fieldName = thisJoinPoint.getSignature().getName();
        Object obj = thisJoinPoint.getThis();

        try{
            Field field = obj.getClass().getDeclaredField(fieldName);
            field.setAccessible(true);
            field.set(obj, value = new Validity() );
        }
        catch( IllegalAccessException | NoSuchFieldException e){e.printStackTrace();}           
    }
    return value;
}