Spring Boot与React项目出现MissingPathVariableException问题求助

错误org.springframework.web.bind.MissingPathVariableException: Required URI template variable 'userId' for method parameter type Long is not present的核心原因是：后端接口的路径变量名与@PathVariable注解绑定的参数名不匹配。

具体细节：

• @GetMapping定义的路径是/expense/{id}，路径变量名为id
• 方法参数上的@PathVariable Long userId未指定对应路径变量名，Spring默认会寻找名为userId的路径变量，两者不匹配导致异常

两种修改方式任选其一即可：

方式一：指定@PathVariable对应路径变量名 #

修改后端ExpenseController的getExpense方法，在@PathVariable注解中明确绑定路径变量id：

@CrossOrigin(origins = "http://localhost:3000", maxAge = 3600)
@RestController
@RequestMapping("/api/test")
public class ExpenseController {
    @Autowired
    ExpenseRepository expenseRepository;
    @GetMapping("/expense/{id}")
    public ResponseEntity<?> getExpense(@PathVariable("id") Long userId){
        Optional<Expense> expense = expenseRepository.findByUserId(userId);
        return expense.map(response -> ResponseEntity.ok().body(response))
                .orElse(new ResponseEntity<>(HttpStatus.NOT_FOUND));
    }
}

方式二：统一路径变量名与参数名 #

将路径中的变量名改为userId，与参数名保持一致，无需额外指定注解参数：

@CrossOrigin(origins = "http://localhost:3000", maxAge = 3600)
@RestController
@RequestMapping("/api/test")
public class ExpenseController {
    @Autowired
    ExpenseRepository expenseRepository;
    @GetMapping("/expense/{userId}")
    public ResponseEntity<?> getExpense(@PathVariable Long userId){
        Optional<Expense> expense = expenseRepository.findByUserId(userId);
        return expense.map(response -> ResponseEntity.ok().body(response))
                .orElse(new ResponseEntity<>(HttpStatus.NOT_FOUND));
    }
}

你的前端axios请求代码逻辑正确，拼接后的URL格式为http://localhost:8080/api/test/expense/{userId}，上述两种修改方式都能与前端请求匹配。

内容的提问来源于stack exchange，提问作者Mohammed Faraz