The Java Tutorials have been written for JDK 8.Java教程是为JDK 8编写的。Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.本页中描述的示例和实践没有利用后续版本中引入的改进，并且可能使用不再可用的技术。See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.有关Java SE 9及其后续版本中更新的语言特性的摘要，请参阅Java语言更改。
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.有关所有JDK版本的新功能、增强功能以及已删除或不推荐的选项的信息，请参阅JDK发行说明。
Every web page is composed of a series of nested objects. These objects make up the Document Object Model (DOM). A Java applet can traverse and modify objects of its parent web page using the Common DOM API.
Consider an example of a Java applet that dumps the contents of its parent web page.
In order to traverse and manipulate the DOM tree, you must first obtain a reference to the Document object for the web page. You can do so by using the getDocument method in the com.sun.java.browser.plugin2.DOM class. Here is a code snippet that retrieves a reference to a Document object in the DOMDumpstart method. See inline comments in the code.
public void start() {
try {
// use reflection to get document
Class c =
Class.forName("com.sun.java.browser.plugin2.DOM");
Method m = c.getMethod("getDocument",
new Class[] { java.applet.Applet.class });
// cast object returned as HTMLDocument;
// then traverse or modify DOM
HTMLDocument doc = (HTMLDocument) m.invoke(null,
new Object[] { this });
HTMLBodyElement body =
(HTMLBodyElement) doc.getBody();
dump(body, INDENT);
} catch (Exception e) {
System.out.println("New Java Plug-In not available");
// In this case, you could fallback to the old
// bootstrapping mechanism available in the
// com.sun.java.browser.plugin.dom package
}
}Now that you have a reference to the Document object, you can traverse and modify the DOM tree using the Common DOM API. The DOMDump applet traverses the DOM tree and writes its contents to the Java Console log.
private void dump(Node root, String prefix) {
if (root instanceof Element) {
System.out.println(prefix +
((Element) root).getTagName() +
" / " + root.getClass().getName());
} else if (root instanceof CharacterData) {
String data =
((CharacterData) root).getData().trim();
if (!data.equals("")) {
System.out.println(prefix +
"CharacterData: " + data);
}
} else {
System.out.println(prefix +
root.getClass().getName());
}
NamedNodeMap attrs = root.getAttributes();
if (attrs != null) {
int len = attrs.getLength();
for (int i = 0; i < len; i++) {
Node attr = attrs.item(i);
System.out.print(prefix + HALF_INDENT +
"attribute " + i + ": " +
attr.getNodeName());
if (attr instanceof Attr) {
System.out.print(" = " +
((Attr) attr).getValue());
}
System.out.println();
}
}
if (root.hasChildNodes()) {
NodeList children = root.getChildNodes();
if (children != null) {
int len = children.getLength();
for (int i = 0; i < len; i++) {
dump(children.item(i), prefix +
INDENT);
}
}
}
}Open AppletPage.htmlDOMDump applet running. Check the Java Console log for a dump of the DOM tree of the web page.
Download the source code for the DOM Dump example to experiment further.