简单管理系统的开发流程

1、定义好数据层

选择一个存储方式（XML）

创建users.xml

<?xml version="1.0" encoding="UTF-8"?>

<users> 

</users>

2、创建DAO完成对用户对象的CRUD

Data Access Object -->DAO

DAO所做的事情是完成对用户对象的增删改查，常规的说，每一个对象都有一个DAO。

public class UserDao {
	public static final String USER_XML = "users";
	private Document ud;
	
	public UserDao() {
		ud = XMLUtil.getUserDocument();
	}
	
	private void write() {
		XMLUtil.write2XML(ud,USER_XML);
	}
	
	private Element loadElementByUsername(String username) {
		String path = "/users/user[username='"+username+"']";
		Element e = (Element)ud.selectSingleNode(path);
		return e;
	}
	
	private User element2User(Element e) {
		User u = new User();
		u.setNickname(e.elementText("nickname"));
		u.setPassword(e.elementText("password"));
		u.setUseranme(e.elementText("username"));
		return u;
	}
	
	public void add(User user) {
		if(user.getUseranme()==null||"".equals(user.getUseranme())) throw new ExpException("用户名不能为空");
		User u = this.load(user.getUseranme());
		if(u!=null) throw new ExpException("用户已经存在！不能继续添加");
		Element e = ud.getRootElement().addElement("user");
		e.addElement("username").addText(user.getUseranme());
		e.addElement("password").addText(user.getPassword());
		e.addElement("nickname").addText(user.getNickname());
		write();
	}
	
	public void delete(String username) {
		//1、获取根节点
		Element root = ud.getRootElement();
		//2、获取username的节点
		Element e = loadElementByUsername(username);
		root.remove(e);
		write();
	}
	
	public void update(User user) {
		//1、根据username获取节点
		Element e = loadElementByUsername(user.getUseranme());
		if(e==null) throw new ExpException("要更新的用户不存在");
		//2、为这个节点修改数据
		e.element("password").setText(user.getPassword());
		e.element("nickname").setText(user.getNickname());
		write();
	}
	
	public User load(String username) {
		Element e = loadElementByUsername(username);
		if(e==null) return null;
		User u = element2User(e);
		return u;
	}
	
	@SuppressWarnings("unchecked")
	public List<User> list() {
		String path = "/users/user";
		List<Element> eles = ud.selectNodes(path);
		List<User> users = new ArrayList<User>();
		for(Element e:eles) {
			users.add(element2User(e));
		}
		return users;
	}

3、编写一个XML的工具类来完成对XML的操作

public class XMLUtil {
	private static Document userDocument;
	
	public static Document getUserDocument() {
		//如果document存在直接返回
		if(userDocument!=null) return userDocument;
		//如果不存在就创建对象
		try {
			SAXReader reader = new SAXReader();
			//System.out.println(XMLUtil.class.getResource(""));
			//System.out.println(XMLUtil.class.getClassLoader().getResource(""));
			userDocument = reader.read(XMLUtil.class.getClassLoader().getResourceAsStream("xml/users.xml"));
			return userDocument;
		} catch (DocumentException e) {
			e.printStackTrace();
		}
		return null;
	}
	
	public static void write2XML(Document d,String name) {
		XMLWriter out = null;
		try {
			String path = XMLUtil.class.getClassLoader().getResource("xml/"+name+".xml").getPath();
			path = path.replace("bin","src");
			out = new XMLWriter(new FileWriter(path),OutputFormat.createPrettyPrint());
			out.write(d);
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			try {
				if(out!=null) out.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}

4、编写XML的单例模式

单例模式指的是所有的对象只有一个，这样可以提高访问的效率。

private static Document userDocument;
	
	public static Document getUserDocument() {
		//如果document存在直接返回
		if(userDocument!=null) return userDocument;
		//如果不存在就创建对象
		try {
			SAXReader reader = new SAXReader();
			//System.out.println(XMLUtil.class.getResource(""));
			//System.out.println(XMLUtil.class.getClassLoader().getResource(""));
			userDocument = reader.read(XMLUtil.class.getClassLoader().getResourceAsStream("xml/users.xml"));
			return userDocument;
		} catch (DocumentException e) {
			e.printStackTrace();
		}
		return null;
	}