为什么 Spring/java 不支持 Optional 和 @PathVariable 组合？

Question

我想制作一个 api 可以接受两个 Path 变量，其中一个可以是可选的。在这个 article 他们说我们可以通过使用 Optional 来实现这一点，但这不起作用。

这是我的控制器

@GetMapping("/users/{dateDu}/{dateAu}")
    public ResponseEntity<List<User>> getAllUsersByDate(
        @PathVariable LocalDate dateDu,
        @PathVariable(required = false) Optional<LocalDate> dateAu,
        @org.springdoc.api.annotations.ParameterObject Pageable pageable
    ) {
        if(dateAu.isEmpty()){
            dateAu = Optional.of(LocalDate.now()); 
        }
        Page<User> page = userRepository.getUsersByDate(dateDu, dateAu.get(), pageable);
        HttpHeaders headers = PaginationUtil.generatePaginationHttpHeaders(ServletUriComponentsBuilder.fromCurrentRequest(), page);
        return ResponseEntity.ok().headers(headers).body(page.getContent());
    }

在这张大摇大摆的图片中，即使第二个参数有 Optional

，这两个参数也是必需的

自从我使用 JHipster 生成我的 spring 启动应用程序后，当我没有给出 Optional 参数的值时在邮递员上。我收到这个错误

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如果有人能帮助我理解为什么会这样，我将不胜感激and/or我该如何解决它。提前谢谢你。

Answer 1

也许尝试将 2 条路径添加到 @GetMapping？

@GetMapping("/users/{dateDu}", "/users/{dateDu}/{dateAu}")

Answer 2

这是一道复合题。我在你的问题中发现了一些问题。

首先，您应该将路径更改为

@GetMapping(value = {"/users/{dateDu}", "/users/{dateDu}/{dateAu}"})

否则，如果您不在请求中提供 dateAu，您将收到 404 错误。

其次，您应该在参数中添加 @DateTimeFormat(iso = DateTimeFormat.ISO.DATE) 以告知 Spring 如何将 String 转换为 LocalDate。否则你会得到一个 Bad Request 错误信息。

Failed to convert value of type 'java.lang.String' to required type 'java.time.LocalDate'

你没有注意到这个问题，我猜是因为 Swagger 已经为你处理好了。

我尝试修复您的代码：

@GetMapping(value = {"/users/{dateDu}", "/users/{dateDu}/{dateAu}"})
public ResponseEntity<List<User>> getAllUsersByDate(
    @PathVariable @DateTimeFormat(iso = DateTimeFormat.ISO.DATE) LocalDate dateDu,
    @PathVariable(required = false) @DateTimeFormat(iso = DateTimeFormat.ISO.DATE) Optional<LocalDate> dateAu,
    @org.springdoc.api.annotations.ParameterObject Pageable pageable) {
    if (dateAu.isEmpty()) {
        dateAu = Optional.of(LocalDate.now()); 
    }
    Page<User> page = userRepository.getUsersByDate(dateDu, dateAu.get(), pageable);
    HttpHeaders headers = PaginationUtil
        .generatePaginationHttpHeaders(ServletUriComponentsBuilder.fromCurrentRequest(), page);
    return ResponseEntity.ok().headers(headers).body(page.getContent());
}

我觉得用postman测试应该可以吧

第三，根据，所有 @PathVariable 必须在 Swagger 中被要求 。这意味着您的问题与 Java 中 @PathVariable 和 Optional 的组合无关。这是 Swagger 的 spec/limitation。因此，如果你真的想使用 Swagger 来测试你的 API，你有 2 个选择：

如@tucuxi 所说，将其拆分为 2 个端点。
改为使用 QueryString 样式。

最后，您似乎不需要 Optional。 Optional 被设计为在大多数情况下用作 return 类型。但这是一个有争议的设计问题。所以，如果你真的想使用 Optional，你可以遵循 this excellent article

描述的最佳实践

Answer 3

不确定这是否能解决您的问题，但您应该删除参数注释中的 false 标志： @PathVariable Optional<LocalDate> dateAu 并添加两条路径：@GetMapping(value = {"/users/{dateDu}", "/users/{dateDu}/{dateAu}"}).

为什么 Spring/java 不支持 Optional 和 @PathVariable 组合？

Why Optional and @PathVariable combination is not supported by Spring/java?

java

spring

swagger

spring-boot