URI is not registered (Settings | Languages & Frameworks | Schemas and DTDs) in applicationContext.xml
You can easy solve it by: Fetch external resource.
Click the light(your is red) -> Fetch external resource.
I'm assuming this is in IntelliJ IDEA or some other JetBrains tool. If you place the cursor over the URL (or select it), you should see a red bulb on the left border of the window. That red bulb, when clicked, will give you some options to correct any errors. One of the options should be to download the DTD (Fetch external resource). Do that and the error should go away.