java - JAXB读取XML文档

Question

我正在尝试读取 XML 文档并将其解码为 Java Bean。我已经解决了阅读部分，但遇到了一个问题。我基本上试图解码 XML 文档的所有子节点，根是“目录”。如何使用 XMLDecoder 执行此操作？

XML解码器:

private static Book jaxbXMLToObject() {
    try {
        JAXBContext context = JAXBContext.newInstance(Book.class);
        Unmarshaller un = context.createUnmarshaller();
        Book book = (Book) un.unmarshal(new File("PATH"));
        return book;
    } catch (JAXBException e) {
        e.printStackTrace();
    }
    return null;
}

我正在尝试阅读以下文档

    <?xml version="1.0"?>
    <catalog>
       <book id="1">
          <author>Isaac Asimov</author>
          <title>Foundation</title>
          <genre>Science Ficition</genre>
          <price>164</price>
          <publish_date>1951-08-21</publish_date>
          <description>Foundation is the first novel in Isaac Asimovs Foundation Trilogy (later expanded into The Foundation Series). Foundation is a cycle of five interrelated short stories, first published as a single book by Gnome Press in 1951. Collectively they tell the story of the Foundation, an institute to preserve the best of galactic civilization after the collapse of the Galactic Empire.</description>
       </book>
   </catalog>

并将其解析为 Book 对象

@XmlRootElement(name = "book")
@XmlType(propOrder = {"id", "price", "title", "author", "genre", "description"})
public class Book {
    private int id;
    private int price;
    private String title;
    private String author;
    private String genre;
    private String description;
    private Date publish_date;

    public Book() {

    }

......我收到错误:jjavax.xml.bind.UnmarshalException: unexpected element (uri:"", local:"catalog"). Expected elements are <{}book>

如何仅使用 JAXB 访问子节点？

更新

目录类别:

@XmlRootElement(name = "catalog")

    public class Catalog {
        @XmlElement(name = "book")
        List<Book> books;

        public List<Book> getBooks() {
            return books;
        }

        public void setBooks(List<Book> books) {
            this.books = books;
        }
    }

图书类别:

@XmlAccessorType(XmlAccessType.FIELD)
public class Book {
    @XmlAttribute
    int id;
    private int price;
    private String title;
    private String author;
    private String genre;
    private String description;
    private Date publish_date;

    public Book() {

    }

    public Book(int id, int price, String title, String genre, String description, Date publicationDate) {
        this.id = id;
        this.price = price;
        this.title = title;
        this.genre = genre;
        this.description = description;
        this.publish_date = publicationDate;
    }

    public int getId() {
        return id;
    }

    public int getPrice() {
        return price;
    }

    public String getTitle() {
        return title;
    }

    public String getGenre() {
        return genre;
    }

    public String getDescription() {
        return description;
    }

    public Date getPublicationDate() {
        return publish_date;
    }

    public void setId(int id) {
        this.id = id;
    }

    public void setPrice(int price) {
        this.price = price;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public void setGenre(String genre) {
        this.genre = genre;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public void setPublish_date(String publish_date) {
        this.publish_date = new Date();
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public Date getPublish_date() {
        return publish_date;
    }

    public String toJSON() {
        ObjectMapper mapper = new ObjectMapper();

        try {
            return mapper.writeValueAsString(this);
        } catch (IOException e) {
            e.printStackTrace();
        }

        return null;
    }

    @Override
    public String toString() {
        return "Book{" +
                "id=" + id +
                ", price=" + price +
                ", title='" + title + '\'' +
                ", genre='" + genre + '\'' +
                ", description='" + description + '\'' +
                ", publicationDate=" + publish_date +
                '}';
    }
}

DAO:

public class BooksDAO {

    public BooksDAO() {
    }

    public List<Book> getBooks() {
        Catalog catalog = jaxbXMLToObject();
        return catalog.getBooks();
    }

    private static Catalog jaxbXMLToObject() {
        try {
            return JAXB.unmarshal(new File("PATH"), Catalog.class);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

Answer 1

正如 JB Nizet 已经指出的那样，您肯定需要一个封闭的 Catalog 对象。以下是能够使用 JAXB 解码所提供的 XML 文档并从中提取书籍的最低限度:

public class ReadXMLUsingJAXB {

    static class Catalog {
        @XmlElement(name = "book")
        List<Book> books;
    }

    @XmlAccessorType(XmlAccessType.FIELD)
    static class Book {
        @XmlAttribute
        int id;
        String author;
        String title;
        String genre;
        int price;
        Date publish_date;
        String description;
    }

    private static Book firstBookFromXML() {
        Catalog catalog = JAXB.unmarshal(new File("PATH"), Catalog.class);
        return catalog.books.get(0);
    }

    public static void main(String[] args) {
        Book book = firstBookFromXML();
        System.out.println(book.id + ", " + book.author + ", " + book.title 
                + ", " + book.genre + ", " + book.price 
                + ", " + book.publish_date + ", " + book.description);
    }

}

这里值得一提的是:

1. @XmlAccessorType - Catalog 不需要注释，因为只有一个字段用 @XmlElement 注释。
2. 选择 FIELD 作为访问类型时，所有字段都会被考虑在内，无论其可见性如何，除非使用 @XmlTransient 进行注释。
3. 图书 ID 是文档中的一个属性，因此必须使用 @XmlAttribute 进行声明。
Catalog.books 上的
4. @XmlElement 对于反射(reflect)图书元素的名称是必要的。 JAXB 默认使用字段(或属性)名称，该名称将是 books，因此与元素不匹配。

如前所述，演示代码是最低限度的，应该进行更改以满足您的需求(即字段可见性、正确的构造函数、getters、equals、hashCode、toString 等)