解决Opentaps/OFBiz在Eclipse启动时"Could not load VFS configuration"的问题

在命令行使用./startofbiz.sh启动Opentaps正常, 而在Eclipse中启动时出现异常,异常信息如下:

org.ofbiz.base.start.StartupException: Cannot start()
org.ofbiz.commons.vfs.CommonsVfsContainer (Initializing
StandardFileSystemManager (Could not load VFS configuration from
"file:/home/engineers/workspaces/ws-opentaps-tpg/opentaps/bin/META-INF/vfs-providers.xml ".))
at org.ofbiz.base.container.ContainerLoader.start(ContainerLoader.java:104)
at org.ofbiz.base.start.Start.startStartLoaders(Start.java:264)
at org.ofbiz.base.start.Start.startServer(Start.java:313)
at org.ofbiz.base.start.Start.start(Start.java:317)
at org.ofbiz.base.start.Start.main(Start.java:400)
org.ofbiz.base.container.ContainerException: Initializing
StandardFileSystemManager (Could not load VFS configuration from
"file:/home/engineers/workspaces/ws-opentaps-tpg/opentaps/bin/META-INF/vfs-providers.xml ".)
at
org.ofbiz.commons.vfs.CommonsVfsContainer.start(CommonsVfsContainer.java:51)
at org.ofbiz.base.container.ContainerLoader.start(ContainerLoader.java:102)
at org.ofbiz.base.start.Start.startStartLoaders(Start.java:264)
at org.ofbiz.base.start.Start.startServer(Start.java:313)
at org.ofbiz.base.start.Start.start(Start.java:317)
at org.ofbiz.base.start.Start.main(Start.java:400)
Caused by: org.apache.commons.vfs.FileSystemException: Could not load VFS
configuration from "file:/home/engineers/workspaces/ws-opentaps-tpg/opentaps/bin/META-INF
/vfs-providers.xml ".
at
org.apache.commons.vfs.impl.StandardFileSystemManager.configure(StandardFileSystemManager.java:199)
at
org.apache.commons.vfs.impl.StandardFileSystemManager.configurePlugins(StandardFileSystemManager.java:156)
at
org.apache.commons.vfs.impl.StandardFileSystemManager.init(StandardFileSystemManager.java:129)
at
org.webslinger.commons.vfs.VFSUtil.createStandardFileSystemManager(VFSUtil.java:351)
at
org.webslinger.commons.vfs.VFSUtil.createStandardFileSystemManager(VFSUtil.java:345)
at
org.ofbiz.commons.vfs.CommonsVfsContainer.start(CommonsVfsContainer.java:45)
... 5 more
Caused by: org.apache.commons.vfs.FileSystemException: Multiple providers
registered for URL scheme "ofbiz-home".
at
org.apache.commons.vfs.impl.DefaultFileSystemManager.addProvider(DefaultFileSystemManager.java:174)
at
org.apache.commons.vfs.impl.StandardFileSystemManager.addProvider(StandardFileSystemManager.java:362)
at
org.apache.commons.vfs.impl.StandardFileSystemManager.configure(StandardFileSystemManager.java:262)
at
org.apache.commons.vfs.impl.StandardFileSystemManager.configure(StandardFileSystemManager.java:195)
... 10 more

网络上(包括Opentaps论坛与OFBiz Mailing Lists)所提供的解决方案是在Opentaps中禁用vfs和webslinger,即把\framework\base\config\ofbiz-containers.xml中以下两行注释掉:

<container name="commons-vfs-container" class="org.ofbiz.commons.vfs.CommonsVfsContainer"/>
<container name="webslinger-container" class="org.ofbiz.webslinger.WebslingerContainer"/>

这种解决方案能够使Opentaps启动成功,但是实际上在Opentaps真正需要使用到vfs与webslinger就显得非常无能为力.

根据异常信息分析,原因有可能是重复加载了vfs-providers.xml(定义URL scheme为ofbiz-home的Provider).经过调试证实了笔者的猜测,在实例化org.apache.commons.vfs.impl.StandardFileSystemManager后,会调用其init方法来初始化,在init方法中调用了configurePlugins方法,以下为configurePlugins方法的代码:

	protected void configurePlugins() throws FileSystemException
	 {
		ClassLoader cl = findClassLoader();

		Enumeration enumResources = null;
		try
		{
			enumResources = cl.getResources(PLUGIN_CONFIG_RESOURCE);
		}
		catch (IOException e)
		{
			throw new FileSystemException(e);
		}

		while (enumResources.hasMoreElements())
		{
			URL url = (URL) enumResources.nextElement();
			configure(url);
		}
	}

在此段代码设置断点,发现%OPENTAPS_HOME%/bin/META-INF/vfs-providers.xml被加载了两次,同时抛出了异常,这正是问题所在.那么vfs-providers.xml为什么会被加载两次,请看以下代码:

protected void configurePlugins() throws FileSystemException
{
...
enumResources = cl.getResources(PLUGIN_CONFIG_RESOURCE);
...
}

java.lang.ClassLoader :

    public Enumeration<URL> getResources(String name) throws IOException {
	Enumeration[] tmp = new Enumeration[2];
	if (parent != null) {
	    tmp[0] = parent.getResources(name);
	} else {
	    tmp[0] = getBootstrapResources(name);
	}
	tmp[1] = findResources(name);

	return new CompoundEnumeration(tmp);
    }

推断出vfs-providers.xml在Parent ClassLoader中被加载后,又被Current ClassCloader加载.从ClassLoder方面再深入的分析就太费时间精力了,毕竟只是在Eclipse才有这个问题.有更快速方便的方法,就是修改StandardFileSystemManager.

在Opentaps根目录新建目录debug-in-eclipse-hack/src,在Eclipse中设置为源代码目录,把StandardFileSystemManager根据包路径拷贝进去,修改configurePlugins方法,代码如下.

    protected void configurePlugins() throws FileSystemException
    {
		ClassLoader cl = findClassLoader();

		Enumeration enumResources = null;
		try
		{
			enumResources = cl.getResources(PLUGIN_CONFIG_RESOURCE);
		}
		catch (IOException e)
		{
			throw new FileSystemException(e);
		}
		
		Set set = new HashSet();
		
		while (enumResources.hasMoreElements())
		{
			URL url = (URL) enumResources.nextElement();
			if (!set.contains(url.toString())){
				set.add(url.toString());
			}
		}
		
		Iterator itr = set.iterator();
		while (itr.hasNext()){
			String url = (String)itr.next();
			try {
				configure(new URL(url));
			} catch (MalformedURLException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}

Opentaps启动时新的StandardFileSystemManager类会被加载.
修改的代码会把重复的vfs-providers.xml去掉,从而解决问题.

好了,现在重新在Eclipse中启动Opentaps.如果还出现同样的问题,则把framework/webslinger/build/lib/ofbiz-webslinger.jar删除就可解决问题.