在这篇文章中，我们将学习如何使用Java Architecture for XML Binding（JAXB）将XML转换为Java对象。
Java Architecture for XML Binding (JAXB)是一个Java标准，它定义了Java对象如何从XML转换到XML。它使用一套标准的映射。

在JAXB术语中，将XML转换为Java对象被称为JAXB Unmarshalling。JAXB API提供了UnMarshaller接口，我们可以将对象解读为一个XML文档。
查看如何将Java对象转换为XML - JAXB Marshalling

让我们看看将XML文档转换为Java对象的步骤。

• 创建POJO或绑定模式并生成类
• 创建JAXBContext对象
• 创建Unmarshaller对象
• 调用unmarshal方法
• 使用POJO的getter方法来访问数据

Unmarshaller例子。将XML文档转换为Java对象

XML文档

这里是我们要转换为Java对象的XML文件。

<?xmlversion="1.0"encoding="UTF-8"standalone="yes"?>
<ns2:bookstore
 xmlns:ns2="net.javaguides.javaxmlparser.jaxb">
 <bookList>
  <book>
   <author>Joshua Bloch</author>
   <title>Effective Java</title>
   <publisher>Amazon</publisher>
   <isbn>978-0134685991</isbn>
  </book>
  <book>
   <author>Kathy Sierra</author>
   <title>Head First Java, 2nd Edition</title>
   <publisher>amazon</publisher>
   <isbn>978-0596009205</isbn>
  </book>
 </bookList>
 <location>Newyorkt</location>
 <name>Amazon Bookstore</name>
</ns2:bookstore>

创建POJO类并添加JAXB注解

一些基本的和有用的JAXB注解是。

1. @XmlRootElement。这是在JAXB中使用的Object必须有的注解。它定义了XML内容的根元素。
2. @XmlType。它将类映射到XML模式类型。我们可以用它来排列XML中的元素。
3. @XmlTransient。这将确保Object属性不被写入XML中。
4. @XmlAttribute: 这将创建Object属性作为一个属性。
5. @XmlElement(name = “ABC”): 这将创建名称为 "ABC "的元素。

Book POJO类

package net.javaguides.javaxmlparser.jaxb;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;

@XmlRootElement(name = "book")
@XmlType(propOrder = {
    "author",
    "name",
    "publisher",
    "isbn"
})
public class Book {

    private String name;
    private String author;
    private String publisher;
    private String isbn;

    @XmlElement(name = "title")
    public String getName() {
        return name;
    }

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

    public String getAuthor() {
        return author;
    }

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

    public String getPublisher() {
        return publisher;
    }

    public void setPublisher(String publisher) {
        this.publisher = publisher;
    }

    public String getIsbn() {
        return isbn;
    }

    public void setIsbn(String isbn) {
        this.isbn = isbn;
    }
}

Bootstore POJO类

package net.javaguides.javaxmlparser.jaxb;

import java.util.List;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElementWrapper;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement(namespace = "net.javaguides.javaxmlparser.jaxb")
public class Bookstore {

    @XmlElementWrapper(name = "bookList")
    @XmlElement(name = "book")
    private List < Book > bookList;
    private String name;
    private String location;

    public void setBookList(List < Book > bookList) {
        this.bookList = bookList;
    }

    public List < Book > getBooksList() {
        return bookList;
    }

    public String getName() {
        return name;
    }

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

    public String getLocation() {
        return location;
    }

    public void setLocation(String location) {
        this.location = location;
    }
}

Unmarshaller类 - 在Java中转换XML为对象

package net.javaguides.javaxmlparser.jaxb;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

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

/**
* Unmarshaller Class - Convert XML to Object in Java
* @author Ramesh Fadatare
*
*/
public class BookMain {
    private static final String BOOKSTORE_XML = "bookstore-jaxb.xml";

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

        List < Book > bookList = new ArrayList < Book > ();

        // create books
        Book book1 = new Book();
        book1.setIsbn("978-0134685991");
        book1.setName("Effective Java");
        book1.setAuthor("Joshua Bloch");
        book1.setPublisher("Amazon");
        bookList.add(book1);

        Book book2 = new Book();
        book2.setIsbn("978-0596009205");
        book2.setName("Head First Java, 2nd Edition");
        book2.setAuthor("Kathy Sierra");
        book2.setPublisher("amazon");
        bookList.add(book2);

        // create bookstore, assigning book
        Bookstore bookstore = new Bookstore();
        bookstore.setName("Amazon Bookstore");
        bookstore.setLocation("Newyorkt");
        bookstore.setBookList(bookList);

        convertXMLToObject();
    }

    private static Bookstore convertXMLToObject() {
        try {
            JAXBContext context = JAXBContext.newInstance(Bookstore.class);
            Unmarshaller un = context.createUnmarshaller();
            Bookstore bookstore = (Bookstore) un.unmarshal(new File(BOOKSTORE_XML));
            List < Book > list = bookstore.getBooksList();
            for (Book book: list) {
                System.out.println("Book: " + book.getName() + " from " + book.getAuthor());
            }
        } catch (JAXBException e) {
            e.printStackTrace();
        }
        return null;
    }
}

输出

Book: Effective Java from Joshua Bloch
Book: Head First Java, 2nd Edition from Kathy Sierra