Java - Relative path of a file in a java web application

Question

I want to read a file from a java web application  I don t want to give the absolute path of the file  I just want to put the file in some directory of my web application   Or  It can be placed along with  war file  packaged web application    What relative path to give for the file  I tried   filename csv but it didn t work           Updated          I will deliver a WAR file  packaged web application  to my client  This web application will read a file  lets say SuppliedFile csv  which will be copied to the server by the client  So I need a mechanism  that will work irrespective of whether the application server will unpak the WAR or not  so that web application can read that file   Note  I am not using the SuppliedFile csv in a servlet    I am using it in a plain Java class

User · Answer

Many popular Java webapps  including Jenkins and Nexus  use this mechanism    Optionally  check a servlet context-param   init-param  This allows configuring multiple webapp instances per servlet container  using context xml which can be done by modifying the WAR or by changing server settings  in case of Tomcat   Check an environment variable  using System getenv   if it is set  then use that folder as your application data folder  e g  Jenkins uses JENKINS HOME and Nexus uses PLEXUS NEXUS WORK  This allows flexible configuration without any changes to WAR  Otherwise  use a subfolder inside user s home folder  e g   HOME  yourapp  In Java code this will be   final File appFolder   new File System getProperty  user home      yourapp

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there is another way  if you are using a container like Tomcat    String textPath    http   localhost 8080 NameOfWebapp resources images file txt

User · Answer

The alternative would be to use ServletContext getResource   which returns a URI  This URI    may be a  file   URL  but there s no guarantee for that    You don t need it to be a file     URL   You just need it to be a URL that your JVM can read--and it will be

User · Answer

If you have a path for that file in the web server  you can get the real path in the server s file system using ServletContext getRealPath    Note that it is not guaranteed to work in every container  as a container is not required to unpack the WAR file and store the content in the file system - most do though   And I guess it won t work with files in  WEB-INF  as they don t have a virtual path   The alternative would be to use ServletContext getResource   which returns a URI  This URI may be a  file   URL  but there s no guarantee for that

User · Answer

Do you really need to load it from a file  If you place it along your classes  in WEB-INF classes  you can get an InputStream to it using the class loader   InputStream csv       SomeClassInTheSamePackage class getResourceAsStream  filename csv

User · Answer

You may be able to simply access a pre-arranged file path on the system  This is preferable since files added to the webapp directory might be lost or the webapp may not be unpacked depending on system configuration   In our server  we define a system property set in the App Server s JVM which points to the  home directory  for our app s external data  Of course this requires modification of the App Server s configuration  -DAPP HOME     added to JVM OPTS at startup   we do it mainly to ease testing of code run outside the context of an App Server    You could just as easily retrieve a path from the servlet config    lt web-app gt   lt context-param gt       lt param-name gt MyAppHome lt  param-name gt       lt param-value gt  usr share myapp lt  param-value gt   lt  context-param gt       lt  web-app gt    Then retrieve this path and use it as the base path to read the file supplied by the client   public class MyAppConfig implements ServletContextListener           NOTE  static references are not a great idea  shown here for simplicity     static File appHome      static File customerDataFile       public void contextInitialized ServletContextEvent e             appHome   new File e getServletContext   getInitParameter  MyAppHome             File customerDataFile   new File appHome   SuppliedFile csv             class DataProcessor       public void processData             File dataFile   MyAppConfig customerDataFile                           As I mentioned the most likely problem you ll encounter is security restrictions  Nothing guarantees webapps can ready any files above their webapp root  But there are generally simple methods for granting exceptions for specific paths to specific webapps   Regardless of the code in which you then need to access this file  since you are running within a web application you are guaranteed this is initialized first  and can stash it s value somewhere convenient for the rest of your code to refer to  as in my example or better yet  just simply pass the path as a paramete to the code which needs it

[java] Java - Relative path of a file in a java web application

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