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如何使用java注釋讀取xsi:type

Java

BIG陽(yáng) 2023-09-20 15:33:14

我想將基于 jaxb 的 xml 文件讀入我的面向?qū)ο蠼Y(jié)構(gòu)。可以說(shuō)這是我的 xml 文件： <?xml version="1.0" encoding="utf-8" standalone="yes"?> <children xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> <child xsi:type="girl"> <age>12</age> <isdancing>true</isdancing> </child> <child xsi:type="boy"> <age>10</age> <issoccerplayer>true</issoccerplayer> </child> </children>Children是某種包含多個(gè)子元素的包裝元素。孩子可以是 xsi : type 指定的男孩或女孩。這兩個(gè)類有一些共同的元素（如age）和一些不同（排除）的元素（如isdancing或issoccerplayer）要讀取文件，我有這個(gè)方法： public static void main( String[] args ) throws JAXBException { JAXBContext jaxbContext; jaxbContext = JAXBContext.newInstance(Children.class); Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller(); File file = new File("C:/test.xml"); if (!file.exists()) System.out.println("File does not exist"); Children children = (Children) jaxbUnmarshaller.unmarshal(file); System.out.println(children.toString()); }我的孩子們的班級(jí)是這樣的： @XmlRootElement(name="children") @XmlAccessorType(XmlAccessType.FIELD) public class Children { @XmlElement(name="child") private List<Child> childrenList; public List<Child> getChildren() { return childrenList; } public void setChildren(List<Child> children) {this.childrenList = children;} @Override public String toString() { return ReflectionToStringBuilder.toString(this); } }我的孩子班看起來(lái)像這樣： @XmlAccessorType(XmlAccessType.FIELD) public class Child { @XmlAttribute(name="xsi:type") private XsiType xsiType; private int age; @XmlElement(name = "isdancing") private boolean isDancing; } }我現(xiàn)在的問(wèn)題是，輸出正常，但 Child-class 的元素 xsiType 始終為 null，否則最終會(huì)出現(xiàn) IllegalAnnotationExceptions，這與 XmlTest.model.Child.xsiType 相關(guān)所以我預(yù)計(jì)設(shè)置任何類型的 @Xml-Annotation 都會(huì)出現(xiàn)錯(cuò)誤。有人可以幫我找出錯(cuò)誤嗎？目標(biāo)是迭代孩子列表并在運(yùn)行時(shí)（基于 xsiType）決定這是女孩還是男孩。

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3 回答

千巷貓影

TA貢獻(xiàn)1829條經(jīng)驗(yàn) 獲得超7個(gè)贊

你不需要你的XsiType課。您可以直接使用String。

在你的Child類中xsiType，屬性應(yīng)該如下所示。

@XmlAttribute(name?=?"type",?namespace?=?"?
private?String?xsiType;

注意：在@XmlAttribute注釋中

使用name = "type"（不帶前綴xsi:）
指定namespaceXML 中給定的參數(shù)xmlns:xsi="..."

順便說(shuō)一句：?您最好使用常量，
而不是鍵入字符串。所以你的改進(jìn)代碼會(huì)是這樣的："http://www.w3.org/2001/XMLSchema-instance"XMLConstants.W3C_XML_SCHEMA_INSTANCE_NS_URI

@XmlAttribute(name?=?"type",?namespace?=?XMLConstants.W3C_XML_SCHEMA_INSTANCE_NS_URI)
private?String?xsiType;

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慕無(wú)忌1623718

TA貢獻(xiàn)1744條經(jīng)驗(yàn) 獲得超4個(gè)贊

xsi 類型通常用于表達(dá)對(duì)具體類型的引用。Jaxb 可以使用 xsi 類型，無(wú)需進(jìn)一步的解決方法。

創(chuàng)建一個(gè)Boy和一個(gè)Girl擴(kuò)展的類Children。（您可能需要使用調(diào)整類型名稱@XmlType）。這樣，所有具有的元素都xsi:type=Girl將綁定到該類Girl

@XmlAccessorType(XmlAccessType.FIELD)

@XmlSeeAlso({ Boy.class, Girl.class }) // Either use @XmlSeeAlso to register classes in the JaxbContext

// or add them to the context directly

public class Child {

private int age;

@XmlElement(name = "isdancing")

private boolean isDancing;

@XmlElement(name = "issoccerplayer")

private boolean isSoccerPlayer;

// Getter and setter for all fields

}

@XmlType(name = "boy") // can be omitted if default value matches with the default value

public class Boy extends Child {

}

@XmlType(name = "girl")

public class Girl extends Child {

}

完整的獨(dú)立示例：

package jaxb;

import java.io.File;

import java.io.StringReader;

import java.util.List;

import javax.xml.bind.JAXBContext;

import javax.xml.bind.JAXBException;

import javax.xml.bind.Unmarshaller;

import javax.xml.bind.annotation.XmlAccessType;

import javax.xml.bind.annotation.XmlAccessorType;

import javax.xml.bind.annotation.XmlElement;

import javax.xml.bind.annotation.XmlRootElement;

import javax.xml.bind.annotation.XmlSeeAlso;

import javax.xml.bind.annotation.XmlType;

public class Inheritance {

public static void main(String[] args) throws JAXBException {

JAXBContext jaxbContext;

jaxbContext = JAXBContext.newInstance(Children.class);

Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();

String x = "<?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"yes\"?>\r\n"

+ " <children xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\">\r\n"

+ " <child xsi:type=\"girl\">\r\n" + " <age>12</age>\r\n"

+ " <isdancing>true</isdancing>\r\n" + " </child>\r\n"

+ " <child xsi:type=\"boy\">\r\n" + " <age>10</age>\r\n"

+ " <issoccerplayer>true</issoccerplayer>\r\n" + " </child>\r\n" + " </children>";

Children children = (Children) jaxbUnmarshaller.unmarshal(new StringReader(x));

System.out.println(children.getChildren().toString());

}

@XmlRootElement(name = "children")

@XmlAccessorType(XmlAccessType.FIELD)

public static class Children {

@XmlElement(name = "child")

private List<Child> childrenList;

public List<Child> getChildren() {

return childrenList;

}

public void setChildren(List<Child> children) {

this.childrenList = children;

}

@XmlAccessorType(XmlAccessType.FIELD)

@XmlSeeAlso({ Boy.class, Girl.class })

public static class Child {

private int age;

@XmlElement(name = "isdancing")

private boolean isDancing;

@XmlElement(name = "issoccerplayer")

private boolean isSoccerPlayer;

// Getter and setter for all fields

}

@XmlType(name = "boy")

public static class Boy extends Child {

}

@XmlType(name = "girl")

public static class Girl extends Child {

}

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慕哥6287543

TA貢獻(xiàn)1831條經(jīng)驗(yàn) 獲得超10個(gè)贊

第二種方法的干凈解決方案（基于單獨(dú)的類文件）：

public class App

{

public static void main(String[] args) throws JAXBException

{

JAXBContext jaxbContext = JAXBContext.newInstance(Children.class);

Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();

File file = new File("C:/test2.xml");

Children children = (Children) jaxbUnmarshaller.unmarshal(file);

for (Child c : children.getChildren()) {

if (c instanceof Boy) {

System.out.println(((Boy)c).toString());

} else if (c instanceof Girl){

System.out.println(((Girl)c).toString());

}

Children.java

@XmlRootElement(name="children")

@XmlAccessorType(XmlAccessType.FIELD)

public class Children {

@XmlElement(name="child")

private List<Child> childrenList;

public List<Child> getChildren() { return childrenList; }

public void setChildren(List<Child> children) {this.childrenList = children;}

@Override

public String toString() { return ReflectionToStringBuilder.toString(this); }

}

Boy.java

@XmlType(name="boy")

public class Boy extends Child {

@XmlElement(name = "issoccerplayer")

private boolean isSoccerPlayer;

public boolean isSoccerPlayer() { return isSoccerPlayer; }

public void setSoccerPlayer(boolean isSoccerPlayer) { this.isSoccerPlayer = isSoccerPlayer; }

@Override

public String toString() { return ReflectionToStringBuilder.toString(this); }

}

Girl.java

@XmlType(name="girl")

public class Girl extends Child {

@XmlElement(name = "isdancing")

private boolean isDancing;

public boolean isDancing() { return isDancing; }

public void setDancing(boolean isDancing) { this.isDancing = isDancing; }

@Override

public String toString() { return ReflectionToStringBuilder.toString(this); }

}

Child.java

@XmlAccessorType(XmlAccessType.FIELD)

@XmlSeeAlso({ Boy.class, Girl.class })

public abstract class Child {

private int age;

public int getAge() { return age; }

public void setAge(int age) { this.age = age; }

}

輸出應(yīng)該是：

de.home.myproject.XmlTest.model.Girl@12edcd21[isDancing=true,age=12]

de.home.myproject.XmlTest.model.Boy@27bc2616[isSoccerPlayer=true,age=10]

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如何使用java注釋讀取xsi:type

如何使用java注釋讀取xsi:type

3 回答

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