Use of java.lang.Class.getResources

Question

I've seen some posts on using java.lang.Class.getResources() and java.lang.Class.getResourcesAsStream() on SO today. Somehow, I still have confusion.

I have a Jar file that contains this structure (resources/test.xml)

This jar file is on the classpath of my application, and when I call below piece of code, it returns null, i.e. value of mappingURL is null.

 URL mappingURL = this.getClass().getResource("/resources/test.xml");

However when I store the XML file in exploded format on the classpath i.e. by creating a directory "resources" and storing mapping.xml inside, it works.

I'm using this URL for reading the content of the "test.xml" file later.

Does that mean, getResources() is not the appropriate method for reading the files from inside a Jar? I didn't understand why mappingURL is null when file (test.xml) is present in the Jar file?

Community · Accepted Answer · 2020-06-20 09:12:55Z

3

The getResource() method will return null if it cannot find the resource. You are prefixing the resource with a / which means that it is trying to look in the folder. You should be able to remove the leading / and achieve your intended result.

Here is the getResource() method description from the documentation:

Finds the resource with the given name. A resource is some data (images, audio, text, etc) that can be accessed by class code in a way that is independent of the location of the code.

The name of a resource is a '/'-separated path name that identifies the resource.

This method will first search the parent class loader for the resource; if the parent is null the path of the class loader built-in to the virtual machine is searched. That failing, this method will invoke findResource(String) to find the resource.

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered Nov 22, 2011 at 4:45

Deco

3,32120 silver badges25 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Vicky Over a year ago

prefixing with "/" should look for the file in classpath. I somewhere read that If I do not prefix with "/" it looks for the file inside the same folder from which class belong. So if your file that you're trying to look for is somewhere else and not in the same package hierarchy of your calling class, you shd use "/" as prefix. Is this correct?

Deco Over a year ago

If you do not prefix with "/" then it will look inside the package to which the class belongs. If you want to look in the /resources/xmlfiles folder you would do getResource('/resources/xmlfiles/myXmlFile.xml');

Thilo · Accepted Answer · 2011-11-22 04:45:44Z

1

this.getClass().getResource("/resources/test.xml");

That should work, provided that the class file you are starting with is also in the same JAR file.

answered Nov 22, 2011 at 4:45

Thilo

264k107 gold badges527 silver badges674 bronze badges

2 Comments

Vicky Over a year ago

So, scope of getResources() is just the jar from which its called?

Thilo Over a year ago

Not exactly. It uses the same classloader as the class, so it includes that jar, and any parent classloaders (but not completely unrelated jars).

Jonathan Schneider · Accepted Answer · 2011-11-22 04:56:13Z

0

Does that mean, getResources() is not the appropriate method for reading the files from inside a Jar?

This is correct. If your resource will be bundled in a jar, you always want to use getResourceAsStream().

A single line later and you can start reading the file:

BufferedReader reader = new BufferReader(InputStreamReader(getResourceAsStream("/test.xml")));

reader.readLine();
//...

answered Nov 22, 2011 at 4:56

Jonathan Schneider

27.9k13 gold badges79 silver badges101 bronze badges

Collectives™ on Stack Overflow

Use of java.lang.Class.getResources

3 Answers 3

2 Comments

2 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related