怎样把Document对象直接变成输出流，写入一个空文件变成XML文档？

Question

给你个Class，传给它一个PrintWriter，然后再调用一下write方法（参数是利用DOM生成的Node对象）
就OK了
import org.w3c.dom.*;import java.io.*;public class XMLDocumentWriter {    PrintWriter out;    public XMLDocumentWriter(PrintWriter out) {
        this.out = out;
    }    public void close() {
        out.close();
    }    public void write(Node node) {
        write(node, "");
    }    public void write(Node node, String indent) {
        switch (node.getNodeType()) {
        case Node.DOCUMENT_NODE: {
            Document doc = (Document) node;
            out.println(indent + "<?xml version='1.0'?>");
            Node child = doc.getFirstChild();
            while (child != null) {
                write(child, indent);
                child = child.getNextSibling();
            }
            break;
        }        case Node.DOCUMENT_TYPE_NODE: {
            DocumentType doctype = (DocumentType) node;            out.println("!DOCTYPE " + doctype.getName() + ">");
            break;
        }
        case Node.ELEMENT_NODE: {
            Element elt = (Element) node;
            out.print(indent + "<" + elt.getTagName());
            NamedNodeMap attrs = elt.getAttributes();
            for (int i = 0; i < attrs.getLength(); i++) {
                Node a = attrs.item(i);
                out.print(" " + a.getNodeName() + "='"
                        + fixup(a.getNodeValue()) + "'");            }
            out.println(">");
            String newindent = indent + "    ";
            Node child = elt.getFirstChild();
            while (child != null) {
                write(child, newindent);
                child = child.getNextSibling();
            }
            out.println(indent + "</" + elt.getTagName() + ">");
            break;
        }
        case Node.TEXT_NODE: {
            Text textNode = (Text) node;
            String text = textNode.getData().trim();
            if ((text != null) && text.length() > 0)
                out.println(indent + fixup(text));
            break;
        }
        case Node.PROCESSING_INSTRUCTION_NODE: {
            ProcessingInstruction pi = (ProcessingInstruction) node;
            out.println(indent + "<?" + pi.getTarget() + " " + pi.getData()
                    + "?>");
            break;
        }
        case Node.CDATA_SECTION_NODE: {
            CDATASection cdata = (CDATASection) node;
            out.println(indent + "<" + "![CDATA[" + cdata.getData() + "]]"
                    + ">");
            break;
        }
        case Node.COMMENT_NODE: {
            Comment c = (Comment) node;
            out.println(indent + "<!-- " + c.getData() + "-->");
            break;
        }
        default:
            System.out.println("Ignoring node: " + node.getClass().getName());
            break;
        }    }    String fixup(String s) {
        StringBuffer sb = new StringBuffer();
        int len = s.length();
        for (int i = 0; i < len; i++) {
            char c = s.charAt(i);
            switch (c) {
            default:
                sb.append(c);
                break;
            case '<':
                sb.append("&lt;");
                break;
            case '>':
                sb.append("&gt;");
                break;
            case '&':
                sb.append("&amp;");
                break;
            case '"':
                sb.append("&quot;");
                break;
            case '\'':
                sb.append("&apos;");
                break;            }        }
        return sb.toString();
    }}