JAXB XML和Bean互相转换

JAXB（Java Architecture for XML Binding) 是一个业界的标准，是一项可以根据XML Schema产生Java类的技术。该过程中，JAXB也提供了将XML实例文档反向生成Java对象树的方法，并能将Java对象树的内容重新写到XML实例文档。是JDK的组成部分

JDK中JAXB相关的重要Class和Interface：

JAXBContext类，是应用的入口，用于管理XML/Java绑定信息。

Marshaller接口，将Java对象序列化为XML数据。

Unmarshaller接口，将XML数据反序列化为Java对象。

当使用 @XmlRootElement 注释对顶层类或枚举类型进行注释时，类型值被表示为 XML 文档中的 XML 元素。

JAXB Annotation

• @XmlRootElement   // xml 文件的根元素 将Java类或枚举类型映射到XML元素(必须使用 指定xml跟元素)
• @XmlElement    //将Java类的一个属性映射到与属性同名的一个XML元素
• @XmlAccessorType  // 控制默认情况下是否对字段或 Javabean 属性进行系列化（必须使用 指定如何转化）。
• @XmlTransient
• @XmlJavaTypeAdaptor:参考Using JAXB 2.0's XmlJavaTypeAdapter

XmlAccessorType 
默认规则：
默认情况下，如果包中不存在 @XmlAccessorType，那么假定使用以下包级别注释。
@XmlAccessorType(XmlAccessType.PUBLIC_MEMBER)
默认情况下，如果类中不存在 @XmlAccessorType，并且没有任何超类是使用 @XmlAccessorType 注释的，则假定在类中使用以下默认注释：
@XmlAccessorType(XmlAccessType.PUBLIC_MEMBER)
可能值：
FIELD:    JAXB 绑定类中的每个非静态、非瞬态字段将会自动绑定到 XML，除非由 XmlTransient 注释。
NONE:     所有字段或属性都不能绑定到 XML，除非使用一些 JAXB 注释专门对它们进行注释。
PROPERTY: JAXB 绑定类中的每个获取方法/设置方法（get/set方法）对将会自动绑定到 XML，除非由 XmlTransient 注释。
PUBLIC_MEMBER:每个公共获取方法/设置方法对和每个公共字段将会自动绑定到 XML，除非由 XmlTransient 注释。

Java Bean转换成XML实例：

实体类：

@XmlRootElement(name = "person")
@XmlAccessorType(XmlAccessType.FIELD)
public class Person {

    private String name;
    private Integer age;


    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

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

转换代码：

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;

public class JAXBTest {
    public static void main(String[] args) throws JAXBException {
        JAXBContext context = JAXBContext.newInstance(Person.class);

        Marshaller marshaller = context.createMarshaller();
        Unmarshaller unmarshaller = context.createUnmarshaller();

        Person person = new Person();
        person.setAge(11);
        person.setName("测试");
        marshaller.marshal(person, System.out);
        System.out.println();
    }
}

输出结果：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?><person><name>测试</name><age>11</age></person>

XML转换成Bean实例：

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Unmarshaller;
import java.io.StringReader;

public class JAXBTest {
    public static void main(String[] args) throws JAXBException {
        JAXBContext context = JAXBContext.newInstance(Person.class);

        Unmarshaller unmarshaller = context.createUnmarshaller();

        String xml = "<person><age>11</age><name>测试</name></person>";
        Person person = (Person) unmarshaller.unmarshal(new StringReader(xml));
        System.out.println(person.getAge());
    }
}

XML转换成Bean是有命名空间的情况：

public class JAXBTest {
    public static void main(String[] args) throws JAXBException {
        JAXBContext context = JAXBContext.newInstance(Person.class);

        Unmarshaller unmarshaller = context.createUnmarshaller();

        String xml = "<person xmlns="http://test.org/"><age>11</age><name>测试</name></person>";
        Person person = (Person) unmarshaller.unmarshal(new StringReader(xml));
        System.out.println(person.getAge());
    }
}

会报错：

Exception in thread "main" javax.xml.bind.UnmarshalException: 意外的元素 (uri:"http://test.org/", local:"person")。所需元素为<{}person>
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallingContext.handleEvent(UnmarshallingContext.java:726)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.Loader.reportError(Loader.java:247)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.Loader.reportError(Loader.java:242)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.Loader.reportUnexpectedChildElement(Loader.java:109)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallingContext$DefaultRootLoader.childElement(UnmarshallingContext.java:1131)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallingContext._startElement(UnmarshallingContext.java:556)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallingContext.startElement(UnmarshallingContext.java:538)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.SAXConnector.startElement(SAXConnector.java:153)
    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.startElement(AbstractSAXParser.java:509)
    at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.scanStartElement(XMLNSDocumentScannerImpl.java:374)
    at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl$NSContentDriver.scanRootElementHook(XMLNSDocumentScannerImpl.java:613)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:3132)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(XMLDocumentScannerImpl.java:852)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:602)
    at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(XMLNSDocumentScannerImpl.java:112)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:505)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:841)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:770)
    at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:141)
    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1213)
    at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:643)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal0(UnmarshallerImpl.java:243)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal(UnmarshallerImpl.java:214)
    at javax.xml.bind.helpers.AbstractUnmarshallerImpl.unmarshal(AbstractUnmarshallerImpl.java:157)
    at javax.xml.bind.helpers.AbstractUnmarshallerImpl.unmarshal(AbstractUnmarshallerImpl.java:214)

一种处理方法就是XML转换成Bean的时候忽略命名空间：

import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Unmarshaller;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParserFactory;
import javax.xml.transform.Source;
import javax.xml.transform.sax.SAXSource;
import java.io.StringReader;

public class JAXBTest {
    public static void main(String[] args) throws JAXBException, ParserConfigurationException, SAXException {

        JAXBContext jaxbContext = JAXBContext.newInstance(Person.class);
        Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
        String xml = "<person xmlns="http://test.org/"><age>11</age><name>测试</name></person>";
        StringReader reader = new StringReader(xml);
        SAXParserFactory sax = SAXParserFactory.newInstance();
        sax.setNamespaceAware(false);//设置忽略明明空间
        XMLReader xmlReader = sax.newSAXParser().getXMLReader();
        Source source = new SAXSource(xmlReader, new InputSource(reader));

        Person person = (Person) unmarshaller.unmarshal(source);
        System.out.println(person.getAge());
    }
}

如果我们的根元素没有子元素并且里面有值 而且我们需要解析XML获取这个值的时候 一种解决办法：修改我们的Bean注解 这样就能正确转化成Bean

import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlValue;

@XmlRootElement(name = "string")
public class XMLToBeanlVo {
    private String stringValue;

    @XmlValue
    public String getStringValue() {
        return stringValue;
    }

    public void setStringValue(String stringValue) {
        this.stringValue = stringValue;
    }
}

将xml中多个相同的元素解析成java中的list

<?xml version="1.0" encoding="GBK" ?>
<reports>
<report>
<name>test</name>
<mobile>13810000001</mobile>
</report>
<report>
<name>test</name>
<mobile>13810000002</mobile>
</report>
</reports>

java实体类：

@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement(name = "reports")
public class XmlVo {
    @XmlElement(name = "report")
    private List<DetailXmlVo> report;

    public List<DetailXmlVo> getReport() {
        return report;
    }

    public void setReport(List<DetailXmlVo> report) {
        this.report = report;
    }
}

public class DetailXmlVo {
    private String name;
    private String mobile;
}

参考：https://www.cnblogs.com/Nouno/p/5728112.html