在我們的實際應用中，Xml中的結構往往不止這麼簡單，一般都會有2，3層。也就是說如果對映成物件就是聚合（組合）的情況 。

就用我們上一章的例子繼續來講，簡單我們的Book的author現在不止是一個String型別的名子，他是一個物件Author，幷包含作者的相關個人資訊。那我們怎麼做列？

直接看程式碼

package com.jaxb.first;

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

@XmlRootElement(name = "book")
// If you want you can define the order in which the fields are written
// Optional
@XmlType(propOrder = { "name", "author", "publisher", "isbn" })
public class Book {

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

	// If you like the variable name, e.g. "name", you can easily change this
	// name for your XML-Output:
	public String getName() {
		return name;
	}

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


	public Author getAuthor() {
		return author;
	}

	public void setAuthor(Author 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;
	}

}
 

package com.jaxb.first;

import javax.xml.bind.annotation.XmlAttribute;

public class Author {

	
	private String name;
	private int age;
	
	@XmlAttribute
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	
	
	
}
 

package com.jaxb.first;

import java.util.ArrayList;

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

@XmlRootElement(namespace="abc")
public class Bookstore {

	// XmLElementWrapper generates a wrapper element around XML representation
	@XmlElementWrapper(name = "bookList")
	// XmlElement sets the name of the entities
	@XmlElement(name = "book")
	private ArrayList<Book> bookList;
	private String name;
	private String location;

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

	public ArrayList<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;
	}
}
 

package com.jaxb.first;

import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
import java.util.ArrayList;

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

import com.sun.xml.bind.marshaller.NamespacePrefixMapper;

public class BookMain {

	private static final String BOOKSTORE_XML = "./bookstore-jaxb.xml";

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

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

		// create books
		Book book1 = new Book();
		book1.setIsbn("978-0060554736");
		book1.setName("The Game");
		Author a = new Author();
		a.setAge(28);
		a.setName("Gosling");
		book1.setAuthor(a);
		book1.setPublisher("Harpercollins");
		bookList.add(book1);

		Book book2 = new Book();
		book2.setIsbn("978-3832180577");
		book2.setName("Feuchtgebiete");
		Author a2 = new Author();
		a2.setAge(32);
		a2.setName("James Green");
		book2.setAuthor(a2);
		book2.setPublisher("Dumont Buchverlag");
		bookList.add(book2);

		// create bookstore, assigning book
		Bookstore bookstore = new Bookstore();
		bookstore.setName("Fraport Bookstore");
		bookstore.setLocation("Frankfurt Airport");
		bookstore.setBookList(bookList);

		// create JAXB context and instantiate marshaller
		JAXBContext context = JAXBContext.newInstance(Bookstore.class);
		Marshaller m = context.createMarshaller();
		NamespacePrefixMapper mapper = new PreferredMapper();
		m.setProperty("com.sun.xml.bind.namespacePrefixMapper", mapper);

		m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);
		m.marshal(bookstore, System.out);

		Writer w = null;
		try {
			w = new FileWriter(BOOKSTORE_XML);
			m.marshal(bookstore, w);
		} finally {
			try {
				w.close();
			} catch (Exception e) {
			}
		}

		// get variables from our xml file, created before
		System.out.println();
		System.out.println("Output from our XML File: ");
		Unmarshaller um = context.createUnmarshaller();
		Bookstore bookstore2 = (Bookstore) um.unmarshal(new FileReader(
				BOOKSTORE_XML));

		for (int i = 0; i < bookstore2.getBooksList().toArray().length; i++) {
			System.out.println("Book " + (i + 1) + ": "
					+ bookstore2.getBooksList().get(i).getName() + " from "
					+ bookstore2.getBooksList().get(i).getAuthor());
		}

	}

	public static class PreferredMapper extends NamespacePrefixMapper {
		@Override
		public String getPreferredPrefix(String namespaceUri,
				String suggestion, boolean requirePrefix) {
			return "pre";
		}

		
	}
}

看下輸出結果：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<pre:bookstore xmlns:pre="abc">
    <bookList>
        <book>
            <name>The Game</name>
            <author name="Gosling">
                <age>28</age>
            </author>
            <publisher>Harpercollins</publisher>
            <isbn>978-0060554736</isbn>
        </book>
        <book>
            <name>Feuchtgebiete</name>
            <author name="James Green">
                <age>32</age>
            </author>
            <publisher>Dumont Buchverlag</publisher>
            <isbn>978-3832180577</isbn>
        </book>
    </bookList>
    <location>Frankfurt Airport</location>
    <name>Fraport Bookstore</name>
</pre:bookstore>

Output from our XML File: 
Book 1: The Game from [email protected]
Book 2: Feuchtgebiete from [email protected]

OK 是我們想要的格式吧。 那麼事情就解決了

   值 得注意的是：如果你要對屬性做註解，必須將註解寫在屬性的get方法上， 就如我們Author類中的 @XmlAttribute那樣，否則執行的時候他會提示：the same element name xxx..