找不到返回类型的转换器

Question

虽然添加了各自的Json文件，但仍然没有转换错误

@ResponseBody
@RequestMapping(value="/web", method=RequestMethod.GET)

public ArrayList<Camera> getAllCameraInfo(){

    Camera c1= new Camera();
    c1.setCameraid("1122");

    Camera c2= new Camera();
    c2.setCameraid("1332");

    Camera c3= new Camera();
    c3.setCameraid("1000");

    ArrayList< Camera> al= new ArrayList<Camera>();
    al.add(c1);al.add(c2);al.add(c3);

    return al;


    }

jackson-core，注释，databind-2.9.4已添加