Journaling is very powerful.
But along the same note, most of this is about processing. The reason the thoughts gets stuck and become obsessions is for lack of process. But there are actually many ways, similar to writing.
One of my favorite stories was Alanis Morissette. She was angry for valid reasons, but admitted that over time lost the ability to write music for a while because she wasn't angry anymore. She literally sang the anger right out of herself.
But I have heard that dance, yoga, drumming, playing piano, singing, walking, and running all have similar benefits.
There are very specific techniques that people have developed over the years involving writing that are pretty cool One such method is the 12 steps, doing character defects, and wrongs against others, etc. Even if you don't show them to other people, just writing them down has a great benefit.
But using the body in a physical way to process mental issue has a very powerful affect. Like typing, writing with your pen, writing in the sand, or carving it in a tree or park table top (never done that.)
The important part is using the body in a physical way while working out your problems. Just thinking about them often just turns into obsession without resolution.