我需要解析 archetype-catalog.xml 的内容文件到 Java 对象结构。为此，我想我会使用旧的 JAXB。所以，我寻找了 xsd xml 文件的定义并从中生成 jaxb 类:

原型(prototype)目录.java

import java.util.ArrayList;
import java.util.List;
import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlType;


/**
 *  0.0.0+
 * 
 * <p>Java class for ArchetypeCatalog complex type.
 * 
 * <p>The following schema fragment specifies the expected content contained within this class.
 * 
 * <pre>
 * &lt;complexType name="ArchetypeCatalog">
 *   &lt;complexContent>
 *     &lt;restriction base="{http://www.w3.org/2001/XMLSchema}anyType">
 *       &lt;all>
 *         &lt;element name="archetypes" minOccurs="0">
 *           &lt;complexType>
 *             &lt;complexContent>
 *               &lt;restriction base="{http://www.w3.org/2001/XMLSchema}anyType">
 *                 &lt;sequence>
 *                   &lt;element name="archetype" type="{http://maven.apache.org/plugins/maven-archetype-plugin/archetype-catalog/1.0.0}Archetype" maxOccurs="unbounded" minOccurs="0"/>
 *                 &lt;/sequence>
 *               &lt;/restriction>
 *             &lt;/complexContent>
 *           &lt;/complexType>
 *         &lt;/element>
 *       &lt;/all>
 *     &lt;/restriction>
 *   &lt;/complexContent>
 * &lt;/complexType>
 * </pre>
 * 
 * 
 */
@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "ArchetypeCatalog", propOrder = {

})
public class ArchetypeCatalog {

    protected ArchetypeCatalog.Archetypes archetypes;

    /**
     * Gets the value of the archetypes property.
     * 
     * @return
     *     possible object is
     *     {@link ArchetypeCatalog.Archetypes }
     *     
     */
    public ArchetypeCatalog.Archetypes getArchetypes() {
        return archetypes;
    }

    /**
     * Sets the value of the archetypes property.
     * 
     * @param value
     *     allowed object is
     *     {@link ArchetypeCatalog.Archetypes }
     *     
     */
    public void setArchetypes(ArchetypeCatalog.Archetypes value) {
        this.archetypes = value;
    }


    /**
     * <p>Java class for anonymous complex type.
     * 
     * <p>The following schema fragment specifies the expected content contained within this class.
     * 
     * <pre>
     * &lt;complexType>
     *   &lt;complexContent>
     *     &lt;restriction base="{http://www.w3.org/2001/XMLSchema}anyType">
     *       &lt;sequence>
     *         &lt;element name="archetype" type="{http://maven.apache.org/plugins/maven-archetype-plugin/archetype-catalog/1.0.0}Archetype" maxOccurs="unbounded" minOccurs="0"/>
     *       &lt;/sequence>
     *     &lt;/restriction>
     *   &lt;/complexContent>
     * &lt;/complexType>
     * </pre>
     * 
     * 
     */
    @XmlAccessorType(XmlAccessType.FIELD)
    @XmlType(name = "", propOrder = {
        "archetype"
    })
    public static class Archetypes {

        protected List<Archetype> archetype;

        /**
         * Gets the value of the archetype property.
         * 
         * <p>
         * This accessor method returns a reference to the live list,
         * not a snapshot. Therefore any modification you make to the
         * returned list will be present inside the JAXB object.
         * This is why there is not a <CODE>set</CODE> method for the archetype property.
         * 
         * <p>
         * For example, to add a new item, do as follows:
         * <pre>
         *    getArchetype().add(newItem);
         * </pre>
         * 
         * 
         * <p>
         * Objects of the following type(s) are allowed in the list
         * {@link Archetype }
         * 
         * 
         */
        public List<Archetype> getArchetype() {
            if (archetype == null) {
                archetype = new ArrayList<Archetype>();
            }
            return this.archetype;
        }

    }

}

原型(prototype).java

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlType;


/**
 * 
 *              Informations to point to an Archetype referenced in the catalog.
 *          
 * 
 * <p>Java class for Archetype complex type.
 * 
 * <p>The following schema fragment specifies the expected content contained within this class.
 * 
 * <pre>
 * &lt;complexType name="Archetype">
 *   &lt;complexContent>
 *     &lt;restriction base="{http://www.w3.org/2001/XMLSchema}anyType">
 *       &lt;all>
 *         &lt;element name="groupId" type="{http://www.w3.org/2001/XMLSchema}string" minOccurs="0"/>
 *         &lt;element name="artifactId" type="{http://www.w3.org/2001/XMLSchema}string" minOccurs="0"/>
 *         &lt;element name="version" type="{http://www.w3.org/2001/XMLSchema}string" minOccurs="0"/>
 *         &lt;element name="repository" type="{http://www.w3.org/2001/XMLSchema}string" minOccurs="0"/>
 *         &lt;element name="description" type="{http://www.w3.org/2001/XMLSchema}string" minOccurs="0"/>
 *       &lt;/all>
 *     &lt;/restriction>
 *   &lt;/complexContent>
 * &lt;/complexType>
 * </pre>
 * 
 * 
 */
@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "Archetype", propOrder = {

})
public class Archetype {

    protected String groupId;
    protected String artifactId;
    protected String version;
    protected String repository;
    protected String description;

    /**
     * Gets the value of the groupId property.
     * 
     * @return
     *     possible object is
     *     {@link String }
     *     
     */
    public String getGroupId() {
        return groupId;
    }

    /**
     * Sets the value of the groupId property.
     * 
     * @param value
     *     allowed object is
     *     {@link String }
     *     
     */
    public void setGroupId(String value) {
        this.groupId = value;
    }

    /**
     * Gets the value of the artifactId property.
     * 
     * @return
     *     possible object is
     *     {@link String }
     *     
     */
    public String getArtifactId() {
        return artifactId;
    }

    /**
     * Sets the value of the artifactId property.
     * 
     * @param value
     *     allowed object is
     *     {@link String }
     *     
     */
    public void setArtifactId(String value) {
        this.artifactId = value;
    }

    /**
     * Gets the value of the version property.
     * 
     * @return
     *     possible object is
     *     {@link String }
     *     
     */
    public String getVersion() {
        return version;
    }

    /**
     * Sets the value of the version property.
     * 
     * @param value
     *     allowed object is
     *     {@link String }
     *     
     */
    public void setVersion(String value) {
        this.version = value;
    }

    /**
     * Gets the value of the repository property.
     * 
     * @return
     *     possible object is
     *     {@link String }
     *     
     */
    public String getRepository() {
        return repository;
    }

    /**
     * Sets the value of the repository property.
     * 
     * @param value
     *     allowed object is
     *     {@link String }
     *     
     */
    public void setRepository(String value) {
        this.repository = value;
    }

    /**
     * Gets the value of the description property.
     * 
     * @return
     *     possible object is
     *     {@link String }
     *     
     */
    public String getDescription() {
        return description;
    }

    /**
     * Sets the value of the description property.
     * 
     * @param value
     *     allowed object is
     *     {@link String }
     *     
     */
    public void setDescription(String value) {
        this.description = value;
    }

}

对象工厂.java

import javax.xml.bind.JAXBElement;
import javax.xml.bind.annotation.XmlElementDecl;
import javax.xml.bind.annotation.XmlRegistry;
import javax.xml.namespace.QName;


@XmlRegistry
public class ObjectFactory {

    private final static QName _ArchetypeCatalog_QNAME = new QName("http://maven.apache.org/plugins/maven-archetype-plugin/archetype-catalog/1.0.0", "archetype-catalog");


    public ObjectFactory() {
    }

    /**
     * Create an instance of {@link ArchetypeCatalog }
     * 
     */
    public ArchetypeCatalog createArchetypeCatalog() {
        return new ArchetypeCatalog();
    }

    /**
     * Create an instance of {@link Archetype }
     * 
     */
    public Archetype createArchetype() {
        return new Archetype();
    }

    /**
     * Create an instance of {@link ArchetypeCatalog.Archetypes }
     * 
     */
    public ArchetypeCatalog.Archetypes createArchetypeCatalogArchetypes() {
        return new ArchetypeCatalog.Archetypes();
    }

    /**
     * Create an instance of {@link JAXBElement }{@code <}{@link ArchetypeCatalog }{@code >}}
     * 
     */
    @XmlElementDecl(namespace = "http://maven.apache.org/plugins/maven-archetype-plugin/archetype-catalog/1.0.0", name = "archetype-catalog")
    public JAXBElement<ArchetypeCatalog> createArchetypeCatalog(ArchetypeCatalog value) {
        return new JAXBElement<ArchetypeCatalog>(_ArchetypeCatalog_QNAME, ArchetypeCatalog.class, null, value);
    }

}

然而，当实际分解 example 时文件进行测试，我得到以下信息:

堆栈跟踪:

Exception in thread "main" java.lang.RuntimeException: an error occurred while unmarshalling xml into com.catalogupdater.plugin.jaxb.ArchetypeCatalog object
    at com.catalogupdater.plugin.converter.JAXBConverter.stringToObject(JAXBConverter.java:48)
    at Main.main(Main.java:60)
Caused by: javax.xml.bind.UnmarshalException: unexpected element (uri:"http://maven.apache.org/plugins/maven-archetype-plugin/archetype-catalog/1.0.0", local:"archetype-catalog"). Expected elements are (none)

任何建议这里出了什么问题？ 亲切的问候

编辑: 以下是我正在使用的完整解码逻辑:

   public static <T> T stringToObject( final String textClazz, final Class<T> clazz )
   {
      T returnedValue = null;
      try
      {
         final JAXBContext jaxbContext = JAXBContext.newInstance( clazz );
         final Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
         final StringReader reader = new StringReader( textClazz );
         returnedValue = ( T ) unmarshaller.unmarshal( reader );
      }
      catch ( final JAXBException e )
      {
         throw new RuntimeException(
               "an error occurred while unmarshalling xml into " + clazz.getCanonicalName() + " object", e );
      }
      return returnedValue;
   }

最佳答案

你应该这样做:

     final JAXBContext jaxbContext = JAXBContext.newInstance( clazz.getPackage().getName() );
     final Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
     final StringReader reader = new StringReader( textClazz );
     returnedValue = ( T ) unmarshaller.unmarshal( reader ).getValue();

显然，如果您只是创建 JAXBContext你的clazz , ObjectFactory不被考虑。 ObjectFactory是所谓的“XML 注册表”，它说明哪个类应该用于哪个根元素。

你从解码中得到的是 JAXBContext<SomeType>其中包含 SomeType 类型的值(在您的情况下为 ArchetypeCatalog)以及根元素的名称。您可以通过 getValue() 获取您感兴趣的值.

您在回答中所做的也有效，但这不是这样做的“JAXB 方式”。

您已经添加了 @XmlRootElement手动注释这肯定不利于生成的代码。您可以通过插件添加它，例如 jaxb2-annotate-plugin (免责声明:我是作者)。

但最终你应该更好地使用 ObjectFactory因为这是它的用途。长期坚持标准模式会更好。

关于java - 使用 JAXB 解码 xml 文件，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/41649702/