Castor XML 之映射模式

Castor XML 的映射模式可以满足内省模式所不能处理的需求。

在映射模式下，Java 类及属性与XML 文档的元素、属性之间的绑定关系是写在XML形式的文件里的。

下面是Java 类：

public class Author {
	private String firstName, lastName;

	public Author() {
	}

	public Author(String firstName, String lastName) {
		this.firstName = firstName;
		this.lastName = lastName;
	}

	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}

	public void setLastName(String lastName) {
		this.lastName = lastName;
	}

	public String getFirstName() {
		return firstName;
	}

	public String getLastName() {
		return lastName;
	}
}

public class Book {
	private String isbn;
	private String title;
	private List<Author> authors;

	public Book() {
	}

	public Book(String isbn, String title, List<Author> authors) {
		this.isbn = isbn;
		this.title = title;
		this.authors = authors;
	}

	public Book(String isbn, String title, Author author) {
		this.isbn = isbn;
		this.title = title;
		this.authors = new LinkedList<Author>();
		authors.add(author);
	}

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

	public String getIsbn() {
		return isbn;
	}

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

	public String getTitle() {
		return title;
	}

	public void setAuthors(List<Author> authors) {
		this.authors = authors;
	}

	public List<Author> getAuthors() {
		return authors;
	}

	public void addAuthor(Author author) {
		authors.add(author);
	}
}

要解组的数据文件：

<?xml version="1.0" encoding="UTF-8"?>
<book>
	<authors>
		<author>
			<name first="Douglas" last="Preston" />
		</author>
		<author>
			<name first="Lincoln" last="Child" />
		</author>
	</authors>

	<book-info>
		<isbn>9780446618502</isbn>
		<title>The Book of the Dead</title>
	</book-info>
</book>

Author类的映射文件：

<?xml version="1.0"?>
<!DOCTYPE mapping PUBLIC "-//EXOLAB/Castor Mapping DTD Version 1.0//EN"
                         "http://castor.org/mapping.dtd">

<mapping>
	<class name="liuwh.learn.databind.castor.test3.Author">
		<field name="FirstName" type="java.lang.String">
			<bind-xml name="first" node="attribute" location="name" />
		</field>

		<field name="LastName" type="java.lang.String">
			<bind-xml name="last" node="attribute" location="name" />
		</field>
	</class>
</mapping>

Book类的映射文件

<?xml version="1.0"?>
<!DOCTYPE mapping PUBLIC "-//EXOLAB/Castor Mapping DTD Version 1.0//EN"
                         "http://castor.org/mapping.dtd">

<mapping>
	<!--  name 属性中指定完全限定的 Java 类名 -->
	<class name="liuwh.learn.databind.castor.test3.Book">
		<!-- xml 属性指定这个类要映射到的 XML 元素 -->
		<map-to xml="book" />

		<!-- name 指定POJO的属性名，不是成员变量名。Castor调用set[PropertyName]()设置值 -->
		<!-- type指定数据类型，必须是全限定类名 -->
		<field name="Title" type="java.lang.String">
			<!-- node 指定是绑定到属性(attribute)还是绑定到元素(element) -->
			<bind-xml name="title" node="element" location="book-info" />
		</field>

		<field name="Isbn" type="java.lang.String">
			<bind-xml name="isbn" node="element" location="book-info" />
		</field>
		<field name="Authors" type="liuwh.learn.databind.castor.test3.Author"
			collection="arraylist">
			<!--
				一个类中的一个字段并不直接映射到与这个类对应的 XML 元素中的数据 — 就需要在 bind-xml 元素中使用 location 属性
				如果绑定到元素数据，它就应该是目标元素的父 元素；如果绑定到属性数据，它就应该是包含这个属性的 元素。
			-->
			<bind-xml name="author" location="authors" />
		</field>
	</class>
</mapping>

根据映射文件解组的代码：

public class BookMapUnmarshaller {
	public static void main(String[] args) {
		Mapping mapping = new Mapping();

		try {
			mapping.loadMapping("book_map.xml");
			mapping.loadMapping("author_map.xml");
			
			XMLContext context = new XMLContext();
			context.addMapping(mapping);

			Unmarshaller unmarshaller = context.createUnmarshaller();

			FileReader reader = new FileReader("bookdata.xml");
			Book book = (Book) unmarshaller.unmarshal(reader);

			System.out.println("Book ISBN: " + book.getIsbn());
			System.out.println("Book Title: " + book.getTitle());
			List authors = book.getAuthors();

			for (Iterator i = authors.iterator(); i.hasNext();) {
				Author author = (Author) i.next();
				System.out.println("Author: " + author.getFirstName() + " "
						+ author.getLastName());
			}

		} catch (Exception e) {
			System.err.println(e.getMessage());
			e.printStackTrace(System.err);
		}
	}
}

输出的结果：
2011-6-2 10:43:54 org.exolab.castor.mapping.Mapping setBaseURL
信息: book_map.xml is not a URL, trying to convert it to a file URL
2011-6-2 10:43:54 org.exolab.castor.mapping.Mapping loadMapping
信息: Loading mapping descriptors from book_map.xml
2011-6-2 10:43:54 org.exolab.castor.mapping.Mapping loadMapping
信息: Loading mapping descriptors from author_map.xml
Book ISBN: 9780446618502
Book Title: The Book of the Dead
Author: Douglas Preston
Author: Lincoln Child


根据映射文件编组的代码：

public class BookMapMarshaller {
	public static void main(String[] args) {
		List<Author> authors = new ArrayList<Author>();
		Author author = new Author("liu", "yi");
		authors.add(author);
		Author author2 = new Author("liu", "er");
		authors.add(author2);

		Book book = new Book("isbn123456", "<<深入计算机操作系统>>", authors);

		Mapping mapping = new Mapping();

		try {
			mapping.loadMapping("book_map.xml");
			mapping.loadMapping("author_map.xml");

			XMLContext context = new XMLContext();
			context.addMapping(mapping);

			Marshaller marshaller = context.createMarshaller();

			FileWriter writer = new FileWriter("map_marshaller.xml");

			marshaller.setWriter(writer);
			marshaller.marshal(book);

		} catch (Exception e) {
			System.err.println(e.getMessage());
			e.printStackTrace(System.err);
		}
	}
}

编组生成的XML文件：

<?xml version="1.0" encoding="UTF-8"?>
<book>
	<book-info>
		<title>&lt;&lt;深入计算机操作系统&gt;&gt;</title>
		<isbn>isbn123456</isbn>
	</book-info>
	<authors>
		<author>
			<name first="liu" last="yi" />
		</author>
		<author>
			<name first="liu" last="er" />
		</author>
	</authors>
</book>

使用映射文件也很简单。
具体的映射规则以后再写。