Unsafe usage of `getResource`JAVA-E0029

Usage of getResource may be unsafe if this class is extended.

Calling this.getClass().getResource(...) with a non-absolute path could have unexpected results if this class is extended by a class in another package. Resources defined in one package may not be available in another. In addition, there is a possibility of different packages having different resources under the same name, which may lead to unexpected bugs from accessing the wrong resource.

Bad Practice

getClass().getResource("someResource");

Consider how getClass works. getClass effectively returns the final runtime type of an object:

Number n1 = new Float(3.2f);
n1.getClass(); // Float.class

n1 = new Integer(3);
n1.getClass(); // Integer.class

Note that it returns the referenced object's type, not the reference's type. Now consider the case of two maven modules both of which declare classes under different packages within the same group:

Project
+- Project-subproject1
|  +- src/main/java      - com.example.project.subproject1.Class1
|  \- src/main/resources - com/example/project/subproject1/a.png
\- Project-subproject2
   +- src/main/java      - com.example.project.subproject2.Class2

Within Class1.java:

// ...

getClass().getResource("a.png");

// ...

If Class2 inherits from Class1, the getClass call would return Class2.class, not Class1.class. Project-subproject1 defines a resource a.png within its resource directory, which is accessible with a relative path from Class1.getClass().getResource(...). If the same code runs in Class2's context, an IOException may occur because the resource is not declared relative to Class2. Unless the resources are referred to with absolute paths like /com/example/subproject1/a.png, each class can only access the resource declared under its own respective package.

Such code is likely to break in production (if it hasn't already broken in testing).

Recommended

Access the resource through the static class object, or using an absolute path instead:

Class1.class.getResourceAsStream("a.png");

// OR:

getClass().getResource("/com/example/subProject1/a.png");

References

• Spotbugs - UI_INHERITANCE_UNSAFE_GETRESOURCE