jdom解析xml

A typical Java application is a domain-specific XML editor:

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• nobody wants to write the markup by hand
• general-purpose XML editors are too clunky
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We generalize the business card language to allow collections of business cards:

<cards> <card> <name>John Doe</name> <title>CEO, Widget Inc.</title> <email>[e-mail]</email> <phone>[phone]</phone> <logo url="widget.gif" /> </card> <card> <name>Michael Schwartzbach</name> <title>Associate Professor</title> <email>[e-mail]</email> <phone>[phone]</phone> <logo url="http://www.brics.dk/~mis/portrait.gif" /> </card> <card> <name>Anders Møller</name> <title>Research Assistant Professor</title> <email>[e-mail]</email> <phone>[phone]</phone> <logo url="http://www.brics.dk/~amoeller/am.jpg"/> </card> </cards>

We then write a Java ​​program​​ to edit such collections.

First, we need a high-level representation of a business card:

class Card { public String name, title, email, phone, logo; public Card(String name, String title, String email, String phone, String logo) { this.name = name; this.title = title; this.email = email; this.phone = phone; this.logo = logo; } }

An XML document must then be translated into a vector of such objects:

Vector doc2vector(Document d) { Vector v = new Vector(); Iterator i = d.getRootElement().getChildren().iterator(); while (i.hasNext()) { Element e = (Element)i.next(); String phone = e.getChildText("phone"); if (phone==null) phone=""; Element logo = e.getChild("logo"); String url; if (logo==null) url = ""; else url = logo.getAttributeValue("url"); Card c = new Card(e.getChildText("name"), // exploit schema, e.getChildText("title"), // assume validity e.getChildText("email"), phone, url); v.add(c); } return v; }

And back into an XML document:

Document vector2doc() { Element cards = new Element("cards"); for (int i=0; i<cardvector.size(); i++) { Card c = (Card)cardvector.elementAt(i); if (c!=null) { Element card = new Element("card"); Element name = new Element("name"); name.addContent(c.name); card.addContent(name); Element title = new Element("title"); title.addContent(c.title); card.addContent(title); Element email = new Element("email"); email.addContent(c.email); card.addContent(email); if (!c.phone.equals("")) { Element phone = new Element("phone"); phone.addContent(c.phone); card.addContent(phone); } if (!c.logo.equals("")) { Element logo = new Element("logo"); logo.setAttribute("url",c.logo); card.addContent(logo); } cards.addContent(card); } } return new Document(cards); }

A little logic and some GUI then completes the editor:

Compile with: javac -classpath xerces.jar:jdom.jar BCedit.java

This example contains some general observations:

• • 
    
• XML documents are parsed via JDOM into domain-specific data structures
• if the input is known to validate according to some schema, then many runtime errors can be assumed never to occur
• how do we ensure that the output of vector2doc is valid according to the schema? (well-formedness is for free) 
  - that's a current research challenge!

• import java.awt.*;
  import java.awt.event.*;
  import java.io.*; 
  import java.util.*;
  import org.jdom.*; 
  import org.jdom.input.*; 
  import org.jdom.output.*; 
  
  class Card {
  public String name, title, email, phone, logo;
  
  public Card(String name, String title, String email, String phone, String logo) {
  this.name = name;
  this.title = title;
  this.email = email;
  this.phone = phone;
  this.logo = logo;
    }
  }
  
  public class BCedit extends Frame implements ActionListener {
  Button ok = new Button("ok");
  Button delete = new Button("delete");
  Button clear = new Button("clear");
  Button save = new Button("save");
  Button quit = new Button("quit");
  TextField name = new TextField(20);
  TextField title = new TextField(20);
  TextField email = new TextField(20);
  TextField phone = new TextField(20);
  TextField logo = new TextField(20);
  Panel cardpanel = new Panel(new GridLayout(0,1));
  String cardfile;
  Vector cardvector;
  int current = -1;
  
  public static void main(String[] args) { new BCedit(args[0]); }
  
  Vector doc2vector(Document d) {
  Vector v = new Vector();
  Iterator i = d.getRootElement().getChildren().iterator();
  while (i.hasNext()) {
  Element e = (Element)i.next();
  String phone = e.getChildText("phone");
  if (phone==null) phone="";
  Element logo = e.getChild("logo");
  String url;
  if (logo==null) url=""; else url=logo.getAttributeValue("url");
  Card c = new Card(e.getChildText("name"),
  e.getChildText("title"),
  e.getChildText("email"),
  phone,
  url);
  v.add(c);
      }
  return v;
    }
  
  Document vector2doc() {
  Element cards = new Element("cards");
  for (int i=0; i<cardvector.size(); i++) {
  Card c = (Card)cardvector.elementAt(i);
  if (c!=null) {
  Element card = new Element("card");
  Element name = new Element("name");
  name.addContent(c.name);
  card.addContent(name);
  Element title = new Element("title");
  title.addContent(c.title);
  card.addContent(title);
  Element email = new Element("email");
  email.addContent(c.email);
  card.addContent(email);
  if (!c.phone.equals("")) {
  Element phone = new Element("phone");
  phone.addContent(c.phone);
  card.addContent(phone);
          }
  if (!c.logo.equals("")) {
  Element logo = new Element("logo");
  logo.setAttribute("url",c.logo);
  card.addContent(logo);
          }
  cards.addContent(card);
        }
      }
  return new Document(cards);
    }
  
  void addCards() {
  cardpanel.removeAll();
  for (int i=0; i<cardvector.size(); i++) {
  Card c = (Card)cardvector.elementAt(i);
  if (c!=null) {
  Button b = new Button(c.name);
  b.setActionCommand(String.valueOf(i));
  b.addActionListener(this);
  cardpanel.add(b);
        }
      }
  this.pack();
    }
  
  public BCedit(String cardfile) {
  super("BCedit");
  this.cardfile=cardfile;
  try {
  cardvector = doc2vector(new SAXBuilder().build(new File(cardfile)));
      } catch (Exception e) {e.printStackTrace();}
  this.setLayout(new BorderLayout());
  ScrollPane s = new ScrollPane();
  s.setSize(200,0);
  s.add(cardpanel);
  this.add(s,BorderLayout.WEST);
  Panel l = new Panel(new GridLayout(5,1));
  l.add(new Label("Name"));                  
  l.add(new Label("Title"));                  
  l.add(new Label("Email"));                  
  l.add(new Label("Phone"));                  
  l.add(new Label("Logo"));                  
  this.add(l,BorderLayout.CENTER);
  Panel f = new Panel(new GridLayout(5,1));
  f.add(name);    
  f.add(title);    
  f.add(email);    
  f.add(phone);    
  f.add(logo);    
  this.add(f,BorderLayout.EAST);
  Panel p = new Panel();
  ok.addActionListener(this);
  p.add(ok);
  delete.addActionListener(this);
  p.add(delete);
  clear.addActionListener(this);
  p.add(clear);
  save.addActionListener(this);
  p.add(save);
  quit.addActionListener(this);
  p.add(quit);
  this.add(p,BorderLayout.SOUTH);
  addCards();
  this.show();
    }
  
  public void actionPerformed(ActionEvent event) {
  Card c;
  String command = event.getActionCommand();
  if (command.equals("ok")) {
  c = new Card(name.getText(),
  title.getText(),
  email.getText(),
  phone.getText(),
  logo.getText());
  if (current==-1) {
  cardvector.add(c);
         } else {
  cardvector.setElementAt(c,current);
         }
  addCards();
       } else if (command.equals("delete")) {
  if (current!=-1) {
  cardvector.setElementAt(null,current);
  addCards();
          }
       } else if (command.equals("clear")) {
  current = -1;
  name.setText("");
  title.setText("");
  email.setText("");
  phone.setText("");
  logo.setText("");
       } else if (command.equals("save")) {
  try {
  new XMLOutputter().output(vector2doc(),new FileOutputStream(cardfile));
          } catch (Exception e) {e.printStackTrace();}
       } else if (command.equals("quit")) {
  System.exit(0);
       } else {
  current = Integer.parseInt(command);
  c = (Card)cardvector.elementAt(current);
  name.setText(c.name);
  title.setText(c.title);
  email.setText(c.email);
  phone.setText(c.phone);
  logo.setText(c.logo);
       }
    }
  }

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