Lombok 构建器检查非空且不为空

Question

我有一个 class 变量，我不希望它为 null 或空。有没有办法使用 Lombok 构建器来设置属性？我可以使用 @NonNull 但我无法验证它是否为空。显然，另一种选择是编写我自己的构建器来完成所有这些检查。例如：

class Person {
    @NonNull
    private String firstName;
    @NonNull
    private String lastName;

    public static class PersonBuilder() {
        // .
        // .
        // .
        public Person build() {
            //do checks for empty etc and return object
        }
    }
}

Answer 1

构建器注释应该可以解决您的问题：

@Builder
class Person {
    @NonNull
    private String firstName;
    @NonNull
    private String lastName;
}

生成的代码是：

class Person {
    @NonNull
    private String firstName;
    @NonNull
    private String lastName;

    @ConstructorProperties({"firstName", "lastName"})
    Person(@NonNull String firstName, @NonNull String lastName) {
        if(firstName == null) {
            throw new NullPointerException("firstName");
        } else if(lastName == null) {
            throw new NullPointerException("lastName");
        } else {
            this.firstName = firstName;
            this.lastName = lastName;
        }
    }

    public static Person.PersonBuilder builder() {
        return new Person.PersonBuilder();
    }

    public static class PersonBuilder {
        private String firstName;
        private String lastName;

        PersonBuilder() {
        }

        public Person.PersonBuilder firstName(String firstName) {
            this.firstName = firstName;
            return this;
        }

        public Person.PersonBuilder lastName(String lastName) {
            this.lastName = lastName;
            return this;
        }

        public Person build() {
            return new Person(this.firstName, this.lastName);
        }

        public String toString() {
            return "Person.PersonBuilder(firstName=" + this.firstName + ", lastName=" + this.lastName + ")";
        }
    }
}

在这种情况下，null 验证将在对象构造期间进行。

Answer 2

Maxim Kirilov 的回答不完整。它不检查 blank/empty 个字符串。

我以前遇到过同样的问题，我意识到除了使用来自 Lombok 的 @NonNull 和 @Builder 之外，还可以使用私有访问修饰符重载构造函数，您可以在其中执行验证。像这样：

private Person(final String firstName, final String lastName) {
    if(StringUtils.isBlank(firstName)) {
        throw new IllegalArgumentException("First name can't be blank/empty/null"); 
    }
    if(StringUtils.isBlank(lastName)) {
        throw new IllegalArgumentException("Last name can't be blank/empty/null"); 
    }
    this.firstName = firstName;
    this.lastName = lastName;
}

此外，当 String 具有空白、空值或 null 值时，抛出 IllegalArgumentException 更有意义（而不是 NPE）。

Answer 3

我做了这样的事情，

class Person {
    private String mFristName;
    private String mSecondName;

    @Builder
    Person(String firstName, String secondName) {
        mFristName = PreCondition.checkNotNullOrEmpty(firstName);
        mSecondName = PreCondition.checkNotNullOrEmpty(secondName);
    }
}

class PreCondition {

    static <T> T checkNotNullOrEmpty(T instance) {
        if (instance == null || (instance instanceof String && ((String) instance).isEmpty())) {
            throw new NullOrEmptyException();
        }
        return instance;
    }

    static class NullOrEmptyException extends RuntimeException {
        NullOrEmptyException() {
            super("Null or Empty");
        }
    }
}

Answer 4

你试过“@NotEmpty”吗？它在 javax.validation.constraints 包

中

https://javaee.github.io/javaee-spec/javadocs/javax/validation/constraints/NotEmpty.html

Lombok 构建器检查非空且不为空

Lombok builder to check non null and not empty

java

builder

lombok