Spring MVC项目中出现空指针异常

Question

我正在创建一个包含教授字段的表单，这个字段是id（长）、nome（字符串）、username（字符串）、email（字符串）和curso_coord（curso），因为curso是一个类课程的引用变量。

我尝试了curso.get(0).getid()来解决这个问题，但这是不够的

@Controller
@RequestMapping(value = { "/professor" })
public class ProfessorController {
    @Autowired
    ProfessorRepository pr;
    CursoRepository c;

    @GetMapping(value = "")
    @ResponseBody
    public ModelAndView professorInicio() {
        ModelAndView form = new ModelAndView("/form");
        form.addObject("professor", new Professor());
        List<Curso> curso = c.findAll();
        curso.get(0).getId();
        form.addObject("curso", curso);
        return form;
    }

    @PostMapping(value = "")
    @ResponseBody
    public ModelAndView cadastraProfessor(@ModelAttribute ("professor") Professor professor){
        //Professor prof = new Professor();
        ModelAndView index = new ModelAndView("/index");
        professor.getUsername();
        professor.getEmail();
        professor.getNome();
        professor.getCursoCoord();
        pr.save(professor);

        return index;
    }

 ....
}

<form th:action="@{/professor}" th:object = "${professor}" method="POST">

            <div class = "form-group">
                <label for = "username">Username</label>
                <input type = "text" th:field = "*{username}" autofocus = "autofocus"/>
            </div>
            <div class = "form-group">
                    <label for = "nome">Nome</label>
                    <input type = "text" th:field = "*{nome}" autofocus = "autofocus"/>
            </div>
            <div class = "form-group">
                    <label for = "email">Email</label>
                    <input type = "hidden" name="email" value="">
                    <input type = "text" th:field = "*{email}" autofocus = "autofocus"/>
            </div>
            <div class = "form-group">
                <select th:field = "*{curso_coord}">
                    <option 
                    th:each = "c: ${cursos}"
                    th:value = "${c.id}">Cursos
                    </option>
                    <option value = -1> Não Coordenador
                    </option>
                </select>"
            </div>
            <button type = "submit" class = "btn btn-success ">Salvar</button>
        </form>

2019-10-04 15:37:00.700错误17580---[nio-8081-exec-1]C.P.P.Controller.ErrorController：Algum erro Ocorreu！

2019-10-04 15:37:00.702警告17580---[nio-8081-exec-1].M.M.A.ExceptionHandlerExceptionResolver：处理程序执行导致的已解决异常：java.lang.NullPointerException

Answer 1

您忘记将@autowired放在cursorepository c上

只需通过替换现有代码来修改代码：

@Autowired
CursoRepository c;