public static Integer getTomcatPortFromConfigXml(File serverXml) {
    Integer port;
    try {
       DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
       domFactory.setNamespaceAware(true); // never forget this!
       DocumentBuilder builder = domFactory.newDocumentBuilder();
       Document doc = builder.parse(serverXml);
       XPathFactory factory = XPathFactory.newInstance();
       XPath xpath = factory.newXPath();
       XPathExpression expr = xpath.compile
         ("/Server/Service[@name='Catalina']/Connector[count(@scheme)=0]/@port[1]");
       String result = (String) expr.evaluate(doc, XPathConstants.STRING);
       port =  result != null && result.length() > 0 ? Integer.valueOf(result) : null;
    } catch (Exception e) {
      port = null;
    }
    return port;
 }

另外：System.getProperty()中的字符串參數如下：

System.getProperty()參數大全
# java.version                                Java Runtime Environment version
# java.vendor                                Java Runtime Environment vendor
# java.vendor.url                           Java vendor URL
# java.home                                Java installation directory
# java.vm.specification.version   Java Virtual Machine specification version
# java.vm.specification.vendor    Java Virtual Machine specification vendor
# java.vm.specification.name      Java Virtual Machine specification name
# java.vm.version                        Java Virtual Machine implementation version
# java.vm.vendor                        Java Virtual Machine implementation vendor
# java.vm.name                        Java Virtual Machine implementation name
# java.specification.version        Java Runtime Environment specification version
# java.specification.vendor         Java Runtime Environment specification vendor
# java.specification.name           Java Runtime Environment specification name
# java.class.version                    Java class format version number
# java.class.path                      Java class path
# java.library.path                 List of paths to search when loading libraries
# java.io.tmpdir                       Default temp file path
# java.compiler                       Name of JIT compiler to use
# java.ext.dirs                       Path of extension directory or directories
# os.name                              Operating system name
# os.arch                                  Operating system architecture
# os.version                       Operating system version
# file.separator                         File separator ("/" on UNIX)
# path.separator                  Path separator (":" on UNIX)
# line.separator                       Line separator ("/n" on UNIX)
# user.name                        User's account name
# user.home                              User's home directory
# user.dir                               User's current working directory

# 對于getCanonicalPath()函數，“."就表示當前的文件夾，而”..“則表示當前文件夾的上一級文件夾
# 對于getAbsolutePath()函數，則不管”.”、“..”，返回當前的路徑加上你在new File()時設定的路徑
# 至于getPath()函數，得到的只是你在new File()時設定的路徑

比如當前的路徑為 C:/test ：
File directory = new File("abc");
directory.getCanonicalPath(); //得到的是C:/test/abc
directory.getAbsolutePath();    //得到的是C:/test/abc
direcotry.getPath();                    //得到的是abc

File directory = new File(".");
directory.getCanonicalPath(); //得到的是C:/test
directory.getAbsolutePath();    //得到的是C:/test/.
direcotry.getPath();                    //得到的是.

File directory = new File("..");
directory.getCanonicalPath(); //得到的是C:/
directory.getAbsolutePath();    //得到的是C:/test/..
direcotry.getPath();                    //得到的是..