Question

我想通过内部搜索实现此端点：

@PostMapping("terminals_risk_filter/change_order/{terminalId}")
    public ResponseEntity<?> updateFiltersPositions(@PathVariable Integer terminalId,
            @RequestBody List<ChangeOrderRiskFiltersDTO> newFiltersPositionsList) {

        List<RiskFilters> filterList = riskFilterService.findRiskFiltersByTerminalId(terminalId);

        for (int i = 0; i < newFiltersPositionsList.size(); i++) {
//          RiskFilters filter = filterList.findById(newFiltersPositionsList.get(i).getId());

            Optional<RiskFilters> filter_payload = filterList.stream().filter(f -> newFiltersPositionsList.get(i).getId() == f.getId()).findAny();
            RiskFilters filter = filter_payload.get();      

            filter.setPosition(newFiltersPositionsList.get(i).getPosition());
            riskFilterService.save(filter);
        }
        return ok().build();
    }

但是我收到错误消息Local variable i defined in an enclosing scope must be final or effectively final，能否请您给我一些建议，以解决此问题？例如，我可以跳过for周期并使用流到流吗？

Answer 1

能否请教我一些如何解决此问题的建议？

为什么会这样？您可以在这里阅读有关内容：Lambdas: local variables need final, instance variables don't

为解决您的问题而进行的最小更改：请勿使用i变量本身。创建它的副本并使其final。

final int iCopy = i;
Optional<RiskFilters> filter_payload = filterList.stream().filter(f -> newFiltersPositionsList.get(iCopy).getId() == f.getId()).findAny();

例如，我可以跳过for循环并使用流到流吗？

您可以尝试一下：

// replace the for-loop

// or just.... `newFiltersPositionsList.forEach(/* ... */)`
newFiltersPositionsList.stream().forEach(filterPosition -> {
    Optional<RiskFilters> filter_payload = filterList.stream()
            .filter(f -> filterPosition.getId() == f.getId())
            .findAny();
    RiskFilters filter = filter_payload.get();

    filter.setPosition(filterPosition.getPosition());
    riskFilterService.save(filter);
});

此外，您可以使用 for-each 代替 for循环：

for (ChangeOrderRiskFiltersDTO filterPosition : newFiltersPositionsList) {
    Optional<RiskFilters> filter_payload = filterList.stream()
           .filter(f -> filterPosition.getId() == f.getId())
           .findAny();
    RiskFilters filter = filter_payload.get();
    filter.setPosition(filterPosition.getPosition());
    riskFilterService.save(filter);
}

Answer 2

您也可以像下面一样进行操作。

final ChangeOrderRiskFiltersDTO dto = newFiltersPositionsList.get(i);
Optional<RiskFilters> filter_payload = filterList.stream().filter(f -> dto.getId() == f.getId()).findAny();
if(filter_payload.isPresent()){
  RiskFilters filter = filter_payload.get();
  //More operations
}

Answer 3

如果要避免添加i的最终副本的简单解决方案，则可以提取实际的“最终”信息：

final int id = newFiltersPositionsList.get(i).getId()

您的lambda可以变成：

f -> id == f.getId()

我在封闭范围内定义的局部变量必须是final或有效的final

3 个答案: