Dom4j中XPath遇到名字空间的问题（引用）

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第一种情况是遇到默认名字空间的情况，示例文档如下：
        <?xml version="1.0" encoding="utf-8"?>
        <root xmlns="http://www.example.com" xmlns:ns1="http://www.example.com">
                <book>
                        <author>tom</author>
                        <exauthor>
                                <author>robin</author>
                                <author>mike</author>
                        </exauthor>
                        <price>75</price>
                </book>
        </root>

第二种情况是遇到使用显式名字空间的情况，示例文档如下：
        <?xml version="1.0" encoding="utf-8"?>
        <ns1:root xmlns="http://www.example.com" xmlns:ns1="http://www.example.com">
                <ns1:book>
                        <ns1:author>tom</ns1:author>
                        <ns1:exauthor>
                                <ns1:author>robin</ns1:author>
                                <ns1:author>mike</ns1:author>
                        </ns1:exauthor>
                        <ns1:price>75</ns1:price>
                </ns1:book>
        </ns1:root>

总的来说，大概有两种方式可以达到目的，每种方式里又可分为默认名字空间和显式名字空间区别开来，具体代码如下：
        public void testXPathWithNs(){
                try {
                        SAXReader sr = new SAXReader();
                        Document doc = sr.read(new FileInputStream(filename));
                        //使用XPath的内置函数，支持显式名字空间的两种不同方式
                        List res = doc.selectNodes("//*[name()='ns1:author']");
                        List res = doc.selectNodes("//*[local-name()='author']");

                        //使用XPath内置函数，支持默认名字空间的方式
                        List res = doc.selectNodes("//*[name()='author']");
                        //使用Dom4j的XPath类的方法支持显式名字空间的方式
                        //此方式就测试结果来说暂不支持默认名字空间的访问
                        Map ns = new HashMap();
                        ns.put("ns1", "http://www.example.com");
                        //加入默认名字空间到Map中
                        //ns.put("", "http://www.example.com");
                        XPath xpath = doc.createXPath("//ns1:author");
                        //不能够正确访问，会返回NULL值
                        //XPath xpath = doc.createXPath("//author");
                        xpath.setNamespaceURIs(ns);
                        List res = xpath.selectNodes(doc);
                        System.out.println("Size: "+res.size());
                        if(res.size() != 0){
                                for(int i = 0; i < res.size(); i++){
                                        Element tmp = (Element)res.get(i);
                                        System.out.println("element["+i+"] name: "+tmp.getName());
                                        System.out.println("element["+i+"] parent name: "+
                                                                tmp.getParent().getName());
                                }
                        }
                } catch (DocumentException e) {
                        e.printStackTrace();
                } catch (FileNotFoundException e) {
                        e.printStackTrace();
                }
        }