this is a maven project , and have one image in resources directory :
├─ src
├─ main
├─ java
└─ resources
└─imgs
└─logo.png
Code:
public class Test {
public static void main(String[] args) {
InputStream stream = Test.class.getClassLoader().getResourceAsStream("/imgs/logo.png");
InputStream stream1 = Test.class.getClassLoader().getResourceAsStream("imgs/logo.png");
System.out.println(stream == null ? "stream is null!" : "stream is not null!");
System.out.println(stream1 == null ? "stream1 is null!" : "stream1 is not null!");
}
}
when I add module-info.java
to project, will print:
stream is null!
stream1 is null!
but when I remove module-info.java
from project, will print:
stream is null!
stream1 is not null!
why? and how to use ClassLoader
to load resources in modular java project?
Resources should be loaded over the Test.class
, not its ClassLoader. By loading the resource over the class, you establish a context (JAR, module, dependencies) for where the resource is located.
For resources in the same package , use a relative path:
Test.class.getResource("logo.png")
If the qualified name of Test is org.foo.Test
, it would lookup the resource in org/foo/logo.png
in the JAR (or in the resources folder, before building the JAR).
For resources in the same module , use an absolute path, starting with a slash:
Test.class.getResource("/logo.png")
^ this is what you want to use most of the time.
There's no need to go over the classloader . I see this often when developers are unaware of how to properly address a resource, and load the resource with a relative path but over the classloader , which works most of the time but not very well with modular projects/classloaders such as Java9 and OSGI.
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