在java中有没有办法检查一个类是否为空?

yzuktlbb  于 2022-12-25  发布在  Java
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Sorry if the title is a bit confusing, I didn't really know how to word what I wanted to ask.
Basically, I am making an api call to a database that returns data as such:
[{"profiles":{"testexample":{"addresses":[{"city":"***","street1":"***","street2":"apt 320"}],"addressType":"HOME","city":"***","dateOfBirth":"***","emailAddress1":"***","emailAddress2":"***","emailAddresses":[{"email":"***","preferred":1,"type":"BUSINESS"},{"email":"***","preferred":0,"type":"PERSONAL"}],"firstName":"***","lastName":"***","phoneNumber":"***","phoneNumbers":[],"phoneType":"HOME","postalCode":"***","preferred":1,"street1":"***","street2":"***"}]
The code I have below works fine when the database returns a non-empty profiles {}. I have the following Java classes that looks like the following:

public class Account {

    @JsonProperty("profiles")
    private Profiles profiles;

    @JsonProperty("profiles")
    public Profiles getProfiles() {
        return profiles;
    }

    @JsonProperty("testexample")
    public void setProfiles(Profiles profiles) {
        this.profiles = profiles;
    }

}
public class Profiles {

    @JsonProperty("testexample")
    private Profile testExample;

    @JsonProperty("testexample")
    public Profile getTestExample() {
        return testExample;
    }

    @JsonProperty("testexample")
    public void setTestExample(Profile testExample) {
        this.testExample = testExample;
    }

}
public class Profile {

    @JsonProperty("dateOfBirth")
    private String dateOfBirth;

    @JsonProperty("dateOfBirth")
    public String getDateOfBirth() {
        return dateOfBirth;
    }
    @JsonProperty("dateOfBirth")
    public void setDateOfBirth(String dateOfBirth) {
        this.dateOfBirth = dateOfBirth;
    }

}

So what I want to do when I get the data is check whether the getProfiles() returns empty, so I don't make the calls to anything within that object.

Please note, for the sake of simplicity I omitted other parts of the classes to focus primarily on what I wanted

This is what I have so far, and it works when the profiles {} is not empty

Account response = access.lookup(id, type); //This is to grab the response from the database, which is working.

response.getProfiles(); //This is the part that works when it has a profiles {} not empty, but fails on empty.

So what happens is that I don't get an error for response.getProfiles(), but if I tried to do response.getProfiles().getDateOfBirth(), it won't work because it will give a null pointer exception since the dateOfBirth isn't there.
I want to avoid calling anything within response.getProfiles() by skipping it if it's empty.

sulc1iza

sulc1iza1#

你需要一些基本的空值检查。最基本的方法是分配一个新变量并检查。

Profiles profiles = account.getProfiles();
if(profiles != null) {
   //dosomething with profiles.getDateOfBirth()
}

更“现代”的函数式Java方法是使用Optional类。

String dateOfBirth = Optional.ofNullable(account.getProfiles())
    .map(profile -> profile.getDateOfBirth)
    .orElse(null);

(关于您的示例的注意事项:在Account类中,您有以下代码。

@JsonProperty("testexample")
public void setProfiles(Profiles profiles) {
    this.profiles = profiles;
}

这似乎是一个不正确的@JsonProperty注解,可能会导致一些问题。也就是说,没有必要注解getter和setter。字段上的一个注解就足够了。)

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