java如何在JAXB集合解组中使用setter

1 周，5 日 Questions & Answers 381

我不想将XML反序列化到我的POJO中，但有些地方做错了

我的POJO课程：

@Builder @ToString @AllArgsConstructor @NoArgsConstructor @XmlRootElement(name="taxi") @XmlAccessorType(XmlAccessType.PROPERTY) @XmlType(propOrder = {"id", "name", "phone", "citiesId"}) public class TaxiEntity { @Getter @Setter private Integer id; @Getter @Setter private String name; @Getter @Setter private String phone; @Singular("city") private Set<Integer> citiesId = new HashSet<>(); @XmlElementWrapper(name="cities_id") @XmlElement(name="city_id") public void setCitiesId(Set<Integer> citiesId) { System.out.println("setCitiesId()"); this.citiesId = citiesId; } public Set<Integer> getCitiesId() { System.out.println("getCitiesId()"); return new HashSet<>(citiesId); } }

编组示例：

JAXBContext context = JAXBContext.newInstance(TaxiEntity.class); TaxiEntity entity = TaxiEntity.builder(). id(5). name("my city"). phone("12345678"). city(1). city(5). build(); Marshaller marshaller = context.createMarshaller(); marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE); marshaller.marshal(entity, new File("entity.xml"));

XML输出：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <taxi> <id>5</id> <name>my city</name> <phone>12345678</phone> <cities_id> <city_id>1</city_id> <city_id>5</city_id> </cities_id> </taxi>

解组示例：

JAXBContext context = JAXBContext.newInstance(TaxiEntity.class); Unmarshaller unmarshaller = context.createUnmarshaller(); TaxiEntity entity = (TaxiEntity) unmarshaller.unmarshal(new File("entity.xml")); System.out.println(entity);

控制台输出：

getCitiesId() getCitiesId() TaxiEntity(id=5, name=my city, phone=12345678, citiesId=[]) Process finished with exit code 0

如您所见，citiesId为空。这是因为JAXB解组调用getter（在我的例子中是字段的副本）并尝试将值设置到集合的副本中。如何让它创建一个集合并通过setter进行设置

另外，在我真正的业务对象中，我在getter中从DB实体收集ID，并且不能在getter中返回集合

谢谢

# 1 楼答案

上次编辑-

import java.io.File;
import java.util.Set;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElementWrapper;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;

import lombok.Builder;
import lombok.Singular;
import lombok.ToString;

@Builder
@ToString
@XmlRootElement(name = "taxi")
@XmlType(name="taxi", propOrder = { "id", "name", "phone", "citiesId" })
public class TaxiEntity {
    
    private Integer id;
    private String name;
    private String phone;

    @Singular("city")
    private Set<Integer> citiesId;

    public TaxiEntity() {
        
    }
    
    public TaxiEntity(Integer id, String name, String phone, Set<Integer> citiesId) {
        
        System.out.println("Hello");
        this.id = id;
        this.name = name;
        this.phone = phone;
        this.citiesId = citiesId;
    }

    
    @XmlElementWrapper(name = "cities_id")
    @XmlElement(name = "city_id")
    public void setCitiesId(Set<Integer> citiesId) {
        System.out.println("I should be calling during deserialization" + citiesId);
        
        this.citiesId = citiesId;
    }

    @XmlElement
    public void setId(Integer id) {
        this.id = id;
    }
    
    @XmlElement
    public void setName(String name) {
        this.name = name;
    }
    
    @XmlElement
    public void setPhone(String phone) {
        this.phone = phone;
    }

    
    public Integer getId() {
        return id;
    }
    public String getName() {
        return name;
    }
    public String getPhone() {
        return phone;
    }
    
    public Set<Integer> getCitiesId() {
        
        System.out.println("Calling getter " + this.citiesId);
        
        return citiesId;
    }
    
    

    public static void main(String[] args) {

        try {
            JAXBContext context = JAXBContext.newInstance(TaxiEntity.class);
            Marshaller marshaller = context.createMarshaller();
            marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);

            Unmarshaller unmarshaller = context.createUnmarshaller();            

            TaxiEntity entity = TaxiEntity.builder().id(5).name("my city").phone("12345678").city(1).city(5).build();

            marshaller.marshal(entity, new File("C:/whee/entity.xml"));
            
            System.out.println("Unmarshalling now    ");
            
            TaxiEntity taxEntityWithSettersGetters = (TaxiEntity) unmarshaller.unmarshal(new File("C:/whee/entity.xml"));
            
            System.out.println(taxEntityWithSettersGetters);
            
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

打印输出：

Hello
Calling getter [1, 5]
Unmarshalling now    
Calling getter null
I should be calling during deserialization[]
Calling getter [1, 5]
TaxiEntity(id=5, name=my city, phone=12345678, citiesId=[1, 5])

在解组过程中，JAXB会检查集合是否为空，是否为空（它会第一次调用setter将其初始化为空），您可以在日志中看到这一点

但是，之后，它将使用其内部逻辑来填充集合（集合），通过使用您拥有的Setter初始化其类型（新集合）*，并使用集合。添加（xyz）；加上（1），然后加上（5）

调用的JAXB逻辑可以在类中找到：

public abstract class Lister<BeanT,PropT,ItemT,PackT> {

//StartPack正在调用以初始化集合集，使其为空

public T startPacking(BeanT bean, Accessor<BeanT, T> acc) throws AccessorException {
    T collection = acc.get(bean);
    if(collection==null) {
        collection = ClassFactory.create(implClass);
        if(!acc.isAdapted())
            acc.set(bean,collection);
    }
    collection.clear();
    return collection;
}

//正确的方法是，这会在之后（在任何实体逻辑之前）调用，以执行addToPack（1）、addToPack（5）和<；-现在你的布景有[1,5]

public void addToPack(T collection, Object o) {
    collection.add(o);
}

然后，你在日志中看到，它调用getCitiesId（），你会神奇地看到它有[1,5]

这就是JAXB处理集合的方式。所有其他元素，它们的适当设置器被称为

见JAXB does not call Setter method

你需要想出一种不同的方法来做这件事，而不是依赖于getter/setter。它完成了从XML文件中解组对象的工作，其余的逻辑可以用外部方法编写

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java如何在JAXB集合解组中使用setter

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