嵌套对象空检查

问题描述

我知道许多方法来检查嵌套对象中是否存在 NullPointerException ，因为对于Java 8，最简单的方法是应用 Optional< param> .或使用简单的if代码(例如

I know many ways how to check on nested objects for a NullPointerException, as for Java 8 the simplest is to apply the Optional<param>.or to use a simple if code such as

if(foo.bar() != null && foo.getBar().getObject()!=null){
    foo.getBar().getObject().getWhatever();
}

好吧，我的问题是，在不知道内部类/方法名称的情况下，是否有一种简便的方法可以做到这一点

well my question is is there an easy way to do so in one method without knowing the names of the inner classes/methods

更清楚地说，我有一个像这样的代码

to be more clear i have a code which is like this

contract.getContactInfo().getPosition()
contract.getEntitledPerson().getEmail()

我想做一个这样的例子

excel.setCell(name1,contract.getContactInfo().getPosition());
excel.setCell(name2,contract.getEntitledPerson().getEmail());

如果它仅适用于2个嵌套对象或仅2个setter，但对于50个excel单元格(有时带有5或6个嵌套对象)而言，这是一个真正的噩梦

if its for only 2 nested objects or only 2 setters that's fine but get it for a 50 excel cells with sometimes 5 or 6 nested objects its a real nightmare to do so

可以说像setCell方法

something lets say like the setCell method

public setCell(String name,Object object){
     return object; // make sure no nested object is null
}

我希望我的问题足够清楚.请记住，我不能简单地更改嵌套对象，因为其遗留代码已在很多地方使用！有什么想法吗?

i hope my question is clear enough. keep in mind i cant simply change the nested objects since its legacy code and being used in a lot of places! any ideas ?

推荐答案

正如您在问题中提到的那样，请使用 Optional ，但这更为宽松.

As you mentioned yourself in the question, use Optional, but it's more lenghty.

excel.setCell(name1, Optional.of(contract).map(Contract::getContactInfo).map(ContactInfo::getPosition).orElse(null));
excel.setCell(name2, Optional.of(contract).map(Contract::getEntitledPerson).map(Person::getEmail).orElse(null));

像这样格式化时更容易阅读:

Which is more easily read when formatted like this:

excel.setCell(name1, Optional.of(contract)
                             .map(Contract::getContactInfo)
                             .map(ContactInfo::getPosition)
                             .orElse(null));
excel.setCell(name2, Optional.of(contract)
                             .map(Contract::getEntitledPerson)
                             .map(Person::getEmail)
                             .orElse(null));

如果您的目标是最小的代码，则只需捕获 NullPointerException .在我看来，这有点骇人听闻，但是可以解决问题.

If your goal is smallest code, you could just catch the NullPointerException. It's a bit of a hack, in my opinion, but it'll do the trick.

首先，一个辅助方法:

public static <T> T nullGuard(Supplier<T> supplier) {
    try {
        return supplier.get();
    } catch (@SuppressWarnings("unused") NullPointerException ignored) {
        return null;
    }
}

然后包装有问题的表达式:

Then you wrapper the expression in question:

excel.setCell(name1, nullGuard(() -> contract.getContactInfo().getPosition()));
excel.setCell(name2, nullGuard(() -> contract.getEntitledPerson().getEmail()));

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