1.關於request.getRealPath
問題：
String filename=request.getRealPath(filename)
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信息：
warning: [deprecation] getRealPath(java.lang.String) in javax.servlet.ServletRequest has been deprecated
解決：
這個getRealPath方法已經不建議使用了
參看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()這個方法受到war 和non-war的影響，以及不同app server實現的影響，運氣好的話，你常常會得到null，嘿嘿，比如你在weblogic上部署war文件，又調用這個方法..
推薦ServletContext.getResourceAsStream
2.關於serveletContext.getRealPath返回NULL和不同的app server返回不同的結果
問題：
有幾個配置文本配置文件（是一些報表的模板),放在WEB-INF下面的config目錄下，程序中是這樣得到這個config的實際路徑的:
先用 serveletContext.getRealPath得到根路徑，tomcat中比如是
c:\tomcat\webapp\test
然後我加上 "/WEB-INF/config/aa.config"，這樣得到文件的path然後進行讀入，應用在tomcat上跑是ok的，後來將war放到weblogic上，出錯，原因是：
在weblogic上用getRealPath得到的是像
myserver\stage\_appsdir_test_war\test.war!\WEB-INF\config....
這樣的路徑，於是一直報FileNotFoundException
解決：
serveletContext.getRealPath
這個方法在不同的服務器上所獲得的實現是不一樣的， 建議是通過classloader來獲得你配置的資源文件
context.getRealPath("/")可能返回了null,你可以輸入來看看,
對一個打包的應用來說，是沒有RealPath的概念的，調用getRealPath只會簡單地返回null。其實，也很
好理解，一個文件被打包入了.war文件，就不存在目錄結構了（雖然包中仍然存在目錄結構，但這不等同於文件系統中的目錄結構）。所以，對war包中的資源是無法得到RealPath的。這樣也就無從通過文件IO進行讀取了。
那麼，如何讀取war包中的資源呢？答案是使用：
ServletContext.getResourceAsStream("/WEB-INF/config/aa.config")方法。
原則：基本上就是儘量使用j2ee規範中的各層次classloader來獲取資源，而不是試圖去找文件的絕對路
徑
方法：調用this.getClass().getClassLoader().getResource("/").getPath(); 獲取到classes目錄的全路徑
使用：在得到classes目錄的全路徑後再根據字符串的截取與拼裝達到你的要求即可。
絕對不要使用ServletContext的getRealPath方法獲取Web應用的路徑！應該使用ServletContext的getResource()方法，直接使用相對於Web應用根目錄的相對路徑來獲取資源。
ServletContext接口中定位資源的方法
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
說明
可以看到，ServletContext接口中的getResource()等方法，可以找到任何從應用程序的根目錄開始的資源。包括在.war包這樣的壓縮文件中。參數必須以/開頭。
而我們常用的getRealPath(“/”)方法，在.war包發佈時，就會失效。會返回null。
因此，我們應該避免使用getRealPath(“/”)這樣的方法來獲取應用程序的絕對路徑。
