JAXB，如何在解组时验证可空字段和必填字段

JAXB是Java体系结构的一部分，用于将Java对象与XML文档之间进行相互转换。在使用JAXB解组（unmarshal）过程中，我们可以通过使用注解来验证可空字段和必填字段的合法性。本文将介绍如何在JAXB中实现这一功能，并提供相应的案例代码。

java
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Unmarshaller;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;
@XmlRootElement
@XmlType(propOrder = {"name", "age"})
public class Person {
    private String name;
    private int age;
    @XmlElement(required = true)
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @XmlElement(required = true)
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public static void main(String[] args) throws JAXBException {
        String xml = "John Doe";
        JAXBContext jaxbContext = JAXBContext.newInstance(Person.class);
        Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
        Person person = (Person) unmarshaller.unmarshal(new StringReader(xml));
    }
}

java
import javax.validation.constraints.NotNull;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Unmarshaller;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;
import javax.xml.validation.ConstraintValidator;
import javax.xml.validation.ConstraintValidatorContext;
import java.io.StringReader;
@XmlRootElement
@XmlType(propOrder = {"name", "age"})
public class Person {
    @NotNull
    private String name;
    @NotNull
    private Integer age;
    @XmlElement(required = true)
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @XmlElement(required = true)
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    public static class NotNullValidator implements ConstraintValidator {
        @Override
        public void initialize(NotNull constraintAnnotation) {
        }
        @Override
        public boolean isValid(Object value, ConstraintValidatorContext context) {
            return value != null;
        }
    }
    public static void main(String[] args) throws JAXBException {
        String xml = "John Doe";
        JAXBContext jaxbContext = JAXBContext.newInstance(Person.class);
        Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
        Person person = (Person) unmarshaller.unmarshal(new StringReader(xml));
    }
}