@RestController
public class TestController {

    @GetMapping("/test")
    public ResponseEntity<Test> example (@RequestBody Test test){
        return new ResponseEntity<>(test, HttpStatus.OK);
    }
}

public class Test {
    public String test;

    public Test(String test) {
        this.test = test;
    }

    public String getTest() {
        return test;
    }

    public void setTest(String test) {
        this.test = test;
    }
}