getResourceAsStream vs FileInputStream

Question

I was trying to load a file in a webapp  and I was getting a FileNotFound exception when I used FileInputStream  However  using the same path  I was able to load the file when I did getResourceAsStream     What is the difference between the two methods  and why does one work while the other doesn t

User · Answer

I am here by separating both the usages by marking them as File Read(java.io) and Resource Read(ClassLoader.getResourceAsStream()).

File Read - 1. Works on local file system. 2. Tries to locate the file requested from current JVM launched directory as root 3. Ideally good when using files for processing in a pre-determined location like,/dev/files or C:\Data.

Resource Read - 1. Works on class path 2. Tries to locate the file/resource in current or parent classloader classpath. 3. Ideally good when trying to load files from packaged files like war or jar.

User · Answer

The java io File and consorts acts on the local disk file system  The root cause of your problem is that relative paths in java io are dependent on the current working directory  I e  the directory from which the JVM  in your case  the webserver s one  is started  This may for example be C  Tomcat bin or something entirely different  but thus not C  Tomcat webapps contextname or whatever you d expect it to be  In a normal Eclipse project  that would be C  Eclipse workspace projectname  You can learn about the current working directory the following way  System out println new File  quot   quot   getAbsolutePath      However  the working directory is in no way programmatically controllable  You should really prefer using absolute paths in the File API instead of relative paths  E g  C  full path to file ext  You don t want to hardcode or guess the absolute path in Java  web applications  That s only portability trouble  i e  it runs in system X  but not in system Y   The normal practice is to place those kind of resources in the classpath  or to add its full path to the classpath  in an IDE like Eclipse that s the src folder and the  quot build path quot  respectively   This way you can grab them with help of the ClassLoader by  ClassLoader getResource   or ClassLoader getResourceAsStream    It is able to locate files relative to the  quot root quot  of the classpath  as you by coincidence figured out  In webapplications  or any other application which uses multiple classloaders  it s recommend to use the ClassLoader as returned by Thread currentThread   getContextClassLoader   for this so you can look  quot outside quot  the webapp context as well  Another alternative in webapps is the ServletContext getResource   and its counterpart ServletContext getResourceAsStream    It is able to access files located in the public web folder of the webapp project  including the  WEB-INF folder  The ServletContext is available in servlets by the inherited getServletContext   method  you can call it as-is  See also   Where to place and how to read configuration resource files in servlet based application  What does servletcontext getRealPath  quot   quot   mean and when should I use it Recommended way to save uploaded files in a servlet application How to save generated file temporarily in servlet based web application

User · Answer

FileInputStream will load a the file path you pass to the constructor as relative from the working directory of the Java process  Usually in a web container  this is something like the bin folder   getResourceAsStream   will load a file path relative from your application s classpath

User · Answer

classname getResourceAsStream   loads a file via the classloader of classname  If the class came from a jar file  that is where the resource will be loaded from   FileInputStream is used to read a file from the filesystem

User · Answer

getResourceAsStream is the right way to do it for web apps  as you already learned    The reason is that reading from the file system cannot work if you package your web app in a WAR   This is the proper way to package a web app   It s portable that way  because you aren t dependent on an absolute file path or the location where your app server is installed

User · Answer

The FileInputStream class works directly with the underlying file system  If the file in question is not physically present there  it will fail to open it  The getResourceAsStream   method works differently  It tries to locate and load the resource using the ClassLoader of the class it is called on  This enables it to find  for example  resources embedded into jar files

[java] getResourceAsStream() vs FileInputStream

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