Creating a Windowed Browser | Real World XML (2nd Edition)

Converting the code we've written to display a document in a window isn't difficult because that code was purposely written to store the output in an array of strings and because I can display those strings in a Java window. In this example, I'll upgrade that code to a new program, browser.java, that will use Java to display XML documents in a window.

Here's how it works. I start by parsing the document the user wants to parse in the main method:

 public static void main(String args[]) {    displayDocument(args[0]);    .    .    .

Then I'll create a new window using the techniques we saw in the previous chapter. Specifically, I'll create a new class named AppFrame , create an object of that class, and display it:

 public static void main(String args[]) {     displayDocument(args[0]);  AppFrame f = new AppFrame(displayStrings, numberDisplayLines);   f.setSize(300, 500);   f.addWindowListener(new WindowAdapter() {public void   windowClosing(WindowEvent e) {System.exit(0);}});   f.show();  }

The AppFrame class is specially designed to display the output strings in the displayStrings array in a Java window. To do that, I pass that array and the number of lines to display to the AppFrame constructor, and I store them in this new class:

 class AppFrame extends Frame  {  String displayStrings[];   int numberDisplayLines;  public AppFrame(String[] strings, int number)     {  displayStrings = strings;   numberDisplayLines = number;  }         .         .         .

All that's left is to display the strings in the displayStrings array. When you display text in a Java window, you're responsible for positioning that text as you want it. To display multiline text, we'll need to know the height of a line of text in the window, and you can find that with the Java FontMetrics class's getHeight method.

Here's how I display the output text in the AppFrame window. I create a new Java Font object using Courier font, and I install it in the Graphics object passed to the paint method. Then I find the height of each line of text:

 public void paint(Graphics g)  {  Font font = new Font("Courier", Font.PLAIN, 12);   g.setFont(font);   FontMetrics fontmetrics = getFontMetrics(getFont());   int y = fontmetrics.getHeight();  .     .     .

Finally, I loop over all lines of text using the Java Graphics object's drawString method:

 public void paint(Graphics g)  {     Font font = new Font("Courier", Font.PLAIN, 12);     g.setFont(font);    FontMetrics fontmetrics = getFontMetrics(getFont());    int y = fontmetrics.getHeight();  for(int index = 0; index < numberDisplayLines; index++){   y += fontmetrics.getHeight();   g.drawString(displayStrings[index], 5, y);   }  }

You can see the result in Figure 11-3. As you see in this figure, ch11_01.xml is displayed in our windowed browser.

Figure 11-3. A graphical browser.

graphics/11fig03.gif

Here's the code for this example, ch11_05.java:

Listing ch11_05.java

 import javax.xml.parsers.*; import org.w3c.dom.*; import java.awt.*; import java.awt.event.*; public class ch11_05 {     static String displayStrings[] = new String[1000];     static int numberDisplayLines = 0;     public static void displayDocument(String uri)     {         try {         DocumentBuilderFactory dbf =             DocumentBuilderFactory.newInstance();         DocumentBuilder db = null;         try {             db = dbf.newDocumentBuilder();         }         catch (ParserConfigurationException pce) {}         Document document = null;             document = db.parse(uri);             display(document, "");         } catch (Exception e) {             e.printStackTrace(System.err);         }     }     public static void display(Node node, String indent)     {         if (node == null) {             return;         }         int type = node.getNodeType();         switch (type) {             case Node.DOCUMENT_NODE: {                 displayStrings[numberDisplayLines] = indent;                 displayStrings[numberDisplayLines] += "<?xml version=\"1.0\" encoding=\""+                   "UTF-8" + "\"?>";                 numberDisplayLines++;                 display(((Document)node).getDocumentElement(), "");                 break;              }              case Node.ELEMENT_NODE: {                  displayStrings[numberDisplayLines] = indent;                  displayStrings[numberDisplayLines] += "<";                  displayStrings[numberDisplayLines] += node.getNodeName();                  int length = (node.getAttributes() != null) ? node.getAttributes().  getLength() : 0;                  Attr attrs[] = new Attr[length];                  for (int loopIndex = 0; loopIndex < length; loopIndex++) {                      attrs[loopIndex] = (Attr)node.getAttributes().item(loopIndex);                   }                  for (int loopIndex = 0; loopIndex < attrs.length; loopIndex++) {                      Attr attr = attrs[loopIndex];                      displayStrings[numberDisplayLines] += " ";                      displayStrings[numberDisplayLines] += attr.getNodeName();                      displayStrings[numberDisplayLines] += "=\"";                      displayStrings[numberDisplayLines] += attr.getNodeValue();                      displayStrings[numberDisplayLines] += "\"";                  }                  displayStrings[numberDisplayLines] +=">";                  numberDisplayLines++;                  NodeList childNodes = node.getChildNodes();                  if (childNodes != null) {                      length = childNodes.getLength();                      indent += "    ";                      for (int loopIndex = 0; loopIndex < length; loopIndex++ ) {                         display(childNodes.item(loopIndex), indent);                      }                  }                  break;              }              case Node.CDATA_SECTION_NODE: {                  displayStrings[numberDisplayLines] = indent;                  displayStrings[numberDisplayLines] += "<![CDATA[";                  displayStrings[numberDisplayLines] += node.getNodeValue();                  displayStrings[numberDisplayLines] += "]]>";                  numberDisplayLines++;                  break;              }              case Node.TEXT_NODE: {                  displayStrings[numberDisplayLines] = indent;                  String newText = node.getNodeValue().trim();                  if(newText.indexOf("\n") < 0 && newText.length() > 0) {                      displayStrings[numberDisplayLines] += newText;                      numberDisplayLines++;                  }                  break;              }              case Node.PROCESSING_INSTRUCTION_NODE: {                  displayStrings[numberDisplayLines] = indent;                  displayStrings[numberDisplayLines] += "<?";                  displayStrings[numberDisplayLines] += node.getNodeName();                  String text = node.getNodeValue();                  if (text != null && text.length() > 0) {                      displayStrings[numberDisplayLines] += text;                  }                  displayStrings[numberDisplayLines] += "?>";                  numberDisplayLines++;                  break;             }         }         if (type == Node.ELEMENT_NODE) {             displayStrings[numberDisplayLines] = indent.substring(0, indent.length() - 4);             displayStrings[numberDisplayLines] += "</";             displayStrings[numberDisplayLines] += node.getNodeName();             displayStrings[numberDisplayLines] +=">";             numberDisplayLines++;             indent+= "    ";         }     }     public static void main(String args[]) {         displayDocument(args[0]);         AppFrame f = new AppFrame(displayStrings, numberDisplayLines);         f.setSize(300, 500);         f.addWindowListener(new WindowAdapter() {public void             windowClosing(WindowEvent e) {System.exit(0);}});         f.show();     } } class AppFrame extends Frame {     String displayStrings[];     int numberDisplayLines;     public AppFrame(String[] strings, int number)     {         displayStrings = strings;         numberDisplayLines = number;     }     public void paint(Graphics g)     {         Font font = new Font("Courier", Font.PLAIN, 12);         g.setFont(font);         FontMetrics fontmetrics = getFontMetrics(getFont());         int y = fontmetrics.getHeight();         for(int index = 0; index < numberDisplayLines; index++){             y += fontmetrics.getHeight();             g.drawString(displayStrings[index], 5, y);         }     } }

Now that we're parsing and displaying XML documents in windows , there's no reason to restrict ourselves to displaying the text form of an XML document. Take a look at the next topic.