How to split long strings in IntelliJ IDEA automatically?

You can use auto-formatting by running the Reformat code function
(CTRL+ALT+L) after few changes in Code Style settings.

(alternatively Reformat code, ⌥+⌘+L on MacOS),

• Press CTRL+ALT+S to open Settings window (or Preferences, ⌘+, on MacOS)
• Go to Code Style menu, and choose Java submenu
• Go to Wrapping and Braces tab
• Make sure to uncheck Line Breaks option and check Ensure right margin is not exceeded option
• Press OK to accept changes you’ve made

Now when using auto-formatting (CTRL+ALT+L / MacOS ⌥+⌘+L) long strings exceeding line character limit will be automatically cut into multiple lines.