Accessing Environment And System Variables On Windows 7

This is a reminder describing how to access environment and system (including path) variables under Window 7:

1. Open Windows Explorer.
2. On the left part of the screen, select the Computer icon.
3. Right-click this icon and select properties.
4. A window will open, select Advanced System Settings.
5. A System Properties windows will open.
6. At the bottom, click Environment Variables.

Understanding Absolute and Relative Path with getResourceAsStream()

Not making the difference between absolute and relative paths when loading resources in Java is a common source of errors leading to NullPointerException (NPE).

Assuming the following structure and content in a maven project:

My Project
  |-src
    |-main
      |-java

      | |-SomePackage
      |   |-SomeClass.java
      |-resources
        |-Root.txt

        |-SomePackage
          |-MyData.txt
          |-SomePackage2
            |-MySubData.txt

Content will be re-organized as following in the .jar:

  |-Root.txt

  |-SomePackage
    |-SomeClass.java
    |-MyData.txt
    |-SomePackage2
      |-MySubData.txt

The following indicates what works and what does not work to retrieve resource data:

InputStream IS;

IS = SomeClass.class.getResourceAsStream(
    "Root.txt"); // Not OK

IS = SomeClass.class.getResourceAsStream(
    "/Root.txt"); // OK

IS = SomeClass.class.getResourceAsStream(
    "/MyData.txt"); // Not OK

IS = SomeClass.class.getResourceAsStream(
    "MyData.txt"); // OK

IS = SomeClass.class.getResourceAsStream(
    "/SomePackage/MyData.txt"); // OK

IS = SomeClass.class.getResourceAsStream(
    "SomePackage/MyData.txt"); // Not OK

IS = SomeClass.class.getResourceAsStream(
    "MySubData.txt"); // Not OK

IS = SomeClass.class.getResourceAsStream(
    "SomePackage/SomePackage2/MySubData.txt"); // OK

IS = SomeClass.class.getResourceAsStream(
    "/SomePackage/SomePackage2/MySubData.txt"); // Not OK

IS = SomeClass.class.getResourceAsStream(
    "/SomePackage2/MySubData.txt"); // Not OK

IS = SomeClass.class.getResourceAsStream(
    "SomePackage2/MySubData.txt"); // OK

getResourceAsStream() operates relative to the package corresponding to the called Class instance.