java - JAXB - 防止可空属性 xmlns :xsi ="http://www.w3.org/2001/XMLSchema-instance" xsi:nil ="true"

Question

这是我的问题:我需要在 XML 中显示 by 对象的名称标签，但没有可空属性:简而言之，如 <name/> 。这是该对象的代码。如果 name 为空，我会得到标签 <name xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/> ，但是附加的属性可能会给客户端带来问题。

正如我所读到的，从语义上讲，以这种方式表示空值确实有意义(使用 @XmlElement(nillable=true) )。

    package com.mns.mnsutilities.jaxb.model;

    import java.util.ArrayList;
    import java.util.List;

    import javax.xml.bind.annotation.XmlAttribute;
    import javax.xml.bind.annotation.XmlElement;
    import javax.xml.bind.annotation.XmlElementWrapper;
    import javax.xml.bind.annotation.XmlRootElement;
    import javax.xml.bind.annotation.XmlTransient;
    import javax.xml.bind.annotation.XmlType;


    @XmlRootElement(name="Emp_MNS")
    @XmlType(propOrder= {"name", "age", "role", "gender", "addressesList"})
    public class Employee {
        private int id;
        private String gender;
        private int age;
        private String name;
        private String role;
        private String password;
        private List<Address> addressesList;

        public Employee() {}

        public Employee(int id, String gender, int age, String name, String role,
                String password) {
            super();
            this.id = id;
            this.gender = gender;
            this.age = age;
            this.name = name;
            this.role = role;
            this.password = password;
        }

        public Employee(int id, String gender, int age, String name, String role,
                String password, List<Address> addressesList) {
            super();
            this.id = id;
            this.gender = gender;
            this.age = age;
            this.name = name;
            this.role = role;
            this.password = password;
            this.addressesList = addressesList;
        }

        @XmlAttribute
        public int getId() {
            return id;
        }
        public void setId(int id) {
            this.id = id;
        }
        @XmlElement(name = "gen", nillable=true)
        public String getGender() {
            return gender;
        }
        public void setGender(String gender) {
            this.gender = gender;
        }
        public int getAge() {
            return age;
        }
        public void setAge(int age) {
            this.age = age;
        }
        @XmlElement(nillable=true)
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        public String getRole() {
            return role;
        }
        public void setRole(String role) {
            this.role = role;
        }
        @XmlTransient
        public String getPassword() {
            return password;
        }
        public void setPassword(String password) {
            this.password = password;
        }
        @XmlElementWrapper( name="addresses" )
        @XmlElement(name = "address")
        public List<Address> getAddressesList() {
            if(addressesList == null){
                addressesList = new ArrayList<>();
            }
            return addressesList;
        }

        public void setAddressesList(List<Address> addressesList) {
            this.addressesList = addressesList;
        }

        @Override
        public String toString() {
            return "Employee [id=" + id + ", gender=" + gender + ", age=" + age
                    + ", name=" + name + ", role=" + role + ", password="
                    + password + ", addressesList=" + addressesList + "]";
        }
    }

Answer 1

扩展 Ian Roberts 的评论，您可以利用字段访问并使属性将 "" 字段值视为 null。

@XmlRootElement(name="Emp_MNS")
@XmlAccessorType(XmlAccessType.FIELD)
public class Employee {

    private String name = "";

    public String getName() {
        if(name.length() == 0) {
            return null;
        }
        return name;
    }

    public void setName(String name) {
        if(null == name) {
            this.name = "";
        } else {
            this.name = name;
        }
    }