JGROUPS源码分析之一：协议栈的创建（二）

/**

     * Returns an XmlConfigurator based on the provided properties string (if

     * possible).

     *

     * @param properties a string representing a system resource containing a

     *                   JGroups XML configuration, a string representing a URL

     *                   pointing to a JGroups ML configuration, or a string

     *                   representing a file name that contains a JGroups XML

     *                   configuration.

     *

     * @return an XmlConfigurator instance based on the provided properties

     *         string; <code>null</code> if the provided properties string does

     *         not point to an XML configuration.

     *

     * @throws IOException  if the provided properties string appears to be a

     *                      valid URL but is unreachable, or if the JGroups XML

     *                      configuration pointed to by the URL can not be

     *                      parsed.

     */

static XmlConfigurator getXmlConfigurator(String properties) throws IOException {

        XmlConfigurator returnValue=null;

        InputStream configStream=getConfigStream(properties);

 

        if (configStream != null) {

            checkJAXPAvailability();

            returnValue=XmlConfigurator.getInstance(configStream);

        }

 

        return returnValue;

    }

参数properties为JCHANNEL构造函数传过来，一般为udp.xml.

getConfigStream返回一个配置输入流，

XmlConfigurator.getInstance(configStream)，解析流并构造一个XmlConfigurator 的实例。
输入流调用过程：

public static InputStream getConfigStream(String properties) throws IOException {

        InputStream configStream = null;

        if (propertiesOverride != null)

            return getConfigStream(propertiesOverride);

 

        // Check to see if the properties string is the name of a file.

        try {

            configStream=new FileInputStream(properties);

        }

        catch(FileNotFoundException fnfe) {

            // the properties string is likely not a file

        }

        catch(AccessControlException access_ex) {

            // fixes http://jira.jboss.com/jira/browse/JGRP-94

        }

 

        // Check to see if the properties string is a URL.

        if(configStream == null) {

            try {

                configStream=new URL(properties).openStream();

            }

            catch (MalformedURLException mre) {

                // the properties string is not a URL

            }

        }

        // Commented so the caller is notified of this condition, but left in

        // the code for documentation purposes.

        //

        // catch (IOException ioe) {

            // the specified URL string was not reachable

        // }

 

        // Check to see if the properties string is the name of a resource,

        // e.g. udp.xml.

        if(configStream == null && properties.endsWith("xml")) {

            configStream=Util.getResourceAsStream(properties, ConfiguratorFactory.class);

        }

        return configStream;

    }

XmlConfigurator对象构造过程如下：

public static XmlConfigurator getInstance(InputStream stream) throws java.io.IOException {

        return parse(stream);

    }

解析流调用过程如下，参数stream为XML配置内容

protected static XmlConfigurator parse(InputStream stream) throws java.io.IOException {

        /**

         * CAUTION: crappy code ahead ! I (bela) am not an XML expert, so the code below is pretty amateurish...

         * But it seems to work, and it is executed only on startup, so no perf loss on the critical path.

         * If somebody<span style