HttpHeaders::setAcceptLanguageAsLocales 使标题小写答案

【问题标题】：HttpHeaders::setAcceptLanguageAsLocales makes header lowercaseHttpHeaders::setAcceptLanguageAsLocales 使标题小写
【发布时间】：2022-01-10 12:39:45
【问题描述】：

当我使用 setAcceptLanguageAsLocales 时，标题内容都是小写的

HttpHeaders headers = new HttpHeaders();
headers.setAcceptLanguageAsLocales(List.of(Locale.US, Locale.GERMANY));

结果：

Accept-Language: en-us, de-de

为什么要转成小写？我希望：

Accept-Language: en-US, de-DE

【问题讨论】：

标签： java spring-boot http-headers locale

【解决方案1】：

这就是 Spring Framework 代码的结果。如果你查看HttpHeaderscode，你会发现setAcceptLanguageAsLocales方法的实现如下：

public void setAcceptLanguageAsLocales(List<Locale> locales) {
  setAcceptLanguage(locales.stream()
      .map(locale -> new Locale.LanguageRange(locale.toLanguageTag()))
      .collect(Collectors.toList()));
}

重要的部分是转换为Locale.LanguageRange 对象。如果你查看它的代码，你会发现它的LanguageRange(String range, double weight)构造函数是这样实现的：

public LanguageRange(String range, double weight) {
    if (range == null) {
        throw new NullPointerException();
    }
    if (weight < MIN_WEIGHT || weight > MAX_WEIGHT) {
        throw new IllegalArgumentException("weight=" + weight);
    }

    range = range.toLowerCase(Locale.ROOT);

    // Do syntax check.
    boolean isIllFormed = false;
    String[] subtags = range.split("-");
    if (isSubtagIllFormed(subtags[0], true)
        || range.endsWith("-")) {
        isIllFormed = true;
    } else {
        for (int i = 1; i < subtags.length; i++) {
            if (isSubtagIllFormed(subtags[i], false)) {
                isIllFormed = true;
                break;
            }
        }
    }
    if (isIllFormed) {
        throw new IllegalArgumentException("range=" + range);
    }

    this.range = range;
    this.weight = weight;
}

重要的部分是range = range.toLowerCase(Locale.ROOT); 行，它实际上将提供的locale.toLanguageTag() 中的所有内容转换为小写，因此您观察到了结果。下面的代码模仿 Spring Framework 代码，并将显示结果：

public class Main {
    public static void main(String[] args) {
        List<Locale> locales = List.of(Locale.US, Locale.GERMANY);
        System.out.println("::::: Original Locales :::::");
        System.out.println(locales);

        System.out.println("::::: Language Tags :::::");
        List<Locale.LanguageRange> languages = locales.stream()
                .map(locale -> {
                    String languageTag = locale.toLanguageTag();
                    System.out.println(languageTag);

                    return new Locale.LanguageRange(languageTag);
                })
                .collect(Collectors.toList());
        System.out.println("::::: Locales Language Rages :::::");
        System.out.println(languages);
    }
}

【讨论】：