1.关于request.getRealPath
问题：
String filename=request.getRealPath(filename)
-------------------
信息：
warning: [deprecation] getRealPath(java.lang.String) in javax.servlet.ServletRequest has been deprecated
解决：
这个getRealPath方法已经不建议使用了
参看request.getRealPath的java doc:
Deprecated. As of Version 2.1 of the Java Servlet API, use ServletContext.getRealPath(java.lang.String) instead.
而在servlet中使用getServletContext.getRealPath()这个方法受到war 和non-war的影响，以及不同app server实现的影响，运气好的话，你常常会得到null，嘿嘿，比如你在weblogic上部署war文件，又调用这个方法..
推荐ServletContext.getResourceAsStream
2.关于serveletContext.getRealPath返回NULL和不同的app server返回不同的结果
问题：
有几个配置文本配置文件（是一些报表的模板),放在WEB-INF下面的config目录下，程序中是这样得到这个config的实际路径的:
先用 serveletContext.getRealPath得到根路径，tomcat中比如是
c:\tomcat\webapp\test
然后我加上 "/WEB-INF/config/aa.config"，这样得到文件的path然后进行读入，应用在tomcat上跑是ok的，后来将war放到weblogic上，出错，原因是：
在weblogic上用getRealPath得到的是像
myserver\stage\_appsdir_test_war\test.war!\WEB-INF\config....
这样的路径，于是一直报FileNotFoundException
解决：
serveletContext.getRealPath
这个方法在不同的服务器上所获得的实现是不一样的， 建议是通过classloader来获得你配置的资源文件
context.getRealPath("/")可能返回了null,你可以输入来看看,
对一个打包的应用来说，是没有RealPath的概念的，调用getRealPath只会简单地返回null。其实，也很
好理解，一个文件被打包入了.war文件，就不存在目录结构了（虽然包中仍然存在目录结构，但这不等同于文件系统中的目录结构）。所以，对war包中的资源是无法得到RealPath的。这样也就无从通过文件IO进行读取了。
那么，如何读取war包中的资源呢？答案是使用：
ServletContext.getResourceAsStream("/WEB-INF/config/aa.config")方法。
原则：基本上就是尽量使用j2ee规范中的各层次classloader来获取资源，而不是试图去找文件的绝对路
径
方法：调用this.getClass().getClassLoader().getResource("/").getPath(); 获取到classes目录的全路径
使用：在得到classes目录的全路径后再根据字符串的截取与拼装达到你的要求即可。
绝对不要使用ServletContext的getRealPath方法获取Web应用的路径！应该使用ServletContext的getResource()方法，直接使用相对于Web应用根目录的相对路径来获取资源。
ServletContext接口中定位资源的方法
getResource
java.net.URL
getResource(java.lang.String path)
throws java.net.MalformedURLException
Returns a URL to the resource that is mapped to a specified path. The path must begin with a "/" and is interpreted as relative to the current context root.
This method allows the servlet container to make a resource available to servlets from any source. Resources can be located on a local or remote file system, in a database, or in a .war file.
The servlet container must implement the URL handlers and URLConnection objects that are necessary to access the resource.
This method returns null if no resource is mapped to the pathname.
Some containers may allow writing to the URL returned by this method using the methods of the URL class.
The resource content is returned directly, so be aware that requesting a .jsp page returns the JSP source code. Use a RequestDispatcher instead to include results of an execution.
This method has a different purpose than java.lang.Class.getResource, which looks up resources based on a class loader. This method does not use class loaders.
Parameters:
path - a String specifying the path to the resource
Returns:
the resource located at the named path, or null if there is no resource at that path
Throws:
java.net.MalformedURLException - if the pathname is not given in the correct form
getResourceAsStream
java.io.InputStream
getResourceAsStream(java.lang.String path)
Returns the resource located at the named path as an InputStream object.
The data in the InputStream can be of any type or length. The path must be specified according to the rules given in getResource. This method returns null if no resource exists at the specified path.
Meta-information such as content length and content type that is available via getResource method is lost when using this method.
The servlet container must implement the URL handlers and URLConnection objects necessary to access the resource.
This method is different from java.lang.Class.getResourceAsStream, which uses a class loader. This method allows servlet containers to make a resource available to a servlet from any location, without using a class loader.
Parameters:
path - a String specifying the path to the resource
Returns:
the InputStream returned to the servlet, or null if no resource exists at the specified path
getRealPath
java.lang.String
getRealPath(java.lang.String path)
Returns a String containing the real path for a given virtual path. For example, the path "/index.html" returns the absolute file path on the server's filesystem would be served by a request for "http://host/contextPath/index.html", where contextPath is the context path of this ServletContext..
The real path returned will be in a form appropriate to the computer and operating system on which the servlet container is running, including the proper path separators. This method returns null if the servlet container cannot translate the virtual path to a real path for any reason (such as when the content is being made available from a .war archive).
Parameters:
path - a String specifying a virtual path
Returns:
a String specifying the real path, or null if the translation cannot be performed
说明
可以看到，ServletContext接口中的getResource()等方法，可以找到任何从应用程序的根目录开始的资源。包括在.war包这样的压缩文件中。参数必须以/开头。
而我们常用的getRealPath(“/”)方法，在.war包发布时，就会失效。会返回null。
因此，我们应该避免使用getRealPath(“/”)这样的方法来获取应用程序的绝对路径。