API Rest completa

package com.trifulcas.SpringBootAPI.controller;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.DeleteMapping;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.PutMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.trifulcas.SpringBootAPI.model.Category;
import com.trifulcas.SpringBootAPI.repository.CategoryRepository;

@RestController
@RequestMapping("/category")
public class CategoryController {

	@Autowired
	CategoryRepository categoryRepository;

	@GetMapping("")
	public List<Category> getAll() {
		try {
			return categoryRepository.findAll();
		} catch (Exception ex) {
			System.out.println(ex.getMessage());
			return null;
		}
	}

	// Poner los valores en la URL, no parámetros nombrados
	@GetMapping("/{id}")
	public Category getById(@PathVariable int id) {
		System.out.println(id);

		try {
			return categoryRepository.findById(id).orElse(null);
		} catch (Exception ex) {
			System.out.println(ex.getMessage());
			return null;
		}
	}

	@PostMapping("")
	public Category add(@RequestBody Category cat) {
		System.out.println(cat);
		try {
			if (cat.getCategoryId() == 0 && cat.getName() != null) {
				return categoryRepository.save(cat);
			} else {
				return null;
			}
		} catch (Exception ex) {
			System.out.println(ex.getMessage());
			return null;
		}
	}

	@PutMapping("/{id}")
	public Category put(@RequestBody Category cat, @PathVariable int id) {
		System.out.println(cat);
		System.out.println(id);
		try {
			if (cat.getCategoryId() == id) {
				return categoryRepository.save(cat);
			} else {
				return null;
			}

		} catch (Exception ex) {
			System.out.println(ex.getMessage());
			return null;
		}
	}

	@DeleteMapping("/{id}")
	public int delete(@PathVariable int id) {
		try {
			System.out.println(id);
			categoryRepository.deleteById(id);
			return id;
		} catch (Exception ex) {
			System.out.println(ex.getMessage());
			return 0;
		}
	}
}