概述

CaseFormat用来转换各种不同的编程语言间的变量名命名格式, 主要用到的方法只有一个 CaseFormat.to(CaseFormat from, String s)

CaseFormat fromFormat = CaseFormat.LOWER_CAMEL;        CaseFormat toFormat = CaseFormat.UPPER_CAMEL;        String s = "lowerCamel";        System.out.println(fromFormat.to(toFormat, s));

输出

lowerCamel

LowerCamel

 

代码分析

package com.google.common.base;import com.google.common.annotations.GwtCompatible;/*** Utility class for converting between various ASCII case formats.* 转换ASCII字符串各种格式的工具类** @author Mike Bostock* @since 1.0*/@GwtCompatiblepublic enum CaseFormat {    /**     * Hyphenated variable naming convention, e.g., "lower-hyphen".     * 带连接符的变量名转换     */    LOWER_HYPHEN(CharMatcher.is('-'), "-"),    /**     * C++ variable naming convention, e.g., "lower_underscore".     * C++ 变量名转换     */    LOWER_UNDERSCORE(CharMatcher.is('_'), "_"),    /**     * Java variable naming convention, e.g., "lowerCamel".     * Java 变量名转换     */    LOWER_CAMEL(CharMatcher.inRange('A', 'Z'), ""),    /**     * Java and C++ class naming convention, e.g., "UpperCamel".     * Java 和 C++ 类名转换     */    UPPER_CAMEL(CharMatcher.inRange('A', 'Z'), ""),    /**     * Java and C++ constant naming convention, e.g., "UPPER_UNDERSCORE".     * Java 和 C++ 常量命名转换     */    UPPER_UNDERSCORE(CharMatcher.is('_'), "_");    private final CharMatcher wordBoundary;    private final String wordSeparator;    CaseFormat(CharMatcher wordBoundary, String wordSeparator) {        this.wordBoundary = wordBoundary;        this.wordSeparator = wordSeparator;    }    /**     * Converts the specified {
    @code String s} from this format to the specified {
    @code format}. A     * "best effort" approach is taken; if {
    @code s} does not conform to the assumed format, then the     * behavior of this method is undefined but we make a reasonable effort at converting anyway.     *     * 使用这个format将指定String s转为指定format.采取的是"尽力而为"的方法;假如s不符合设定的格式     * 那么这个方法的行为将会是不确定的,但我们会尽量做出合理的转换     *     * 实际上我们使用的只有这一个方法     */    public String to(CaseFormat format, String s) {        if (format == null) {            throw new NullPointerException();        }        if (s == null) {            throw new NullPointerException();        }        if (format == this) {            return s;        }        /* optimize cases where no camel conversion is required */        /* 没有驼峰转换的时候优化转换 */        switch (this) {            case LOWER_HYPHEN:                switch (format) {                    case LOWER_UNDERSCORE:                        return s.replace('-', '_');                    case UPPER_UNDERSCORE:                        return Ascii.toUpperCase(s.replace('-', '_'));                }                break;            case LOWER_UNDERSCORE:                switch (format) {                    case LOWER_HYPHEN:                        return s.replace('_', '-');                    case UPPER_UNDERSCORE:                        return Ascii.toUpperCase(s);                }                break;            case UPPER_UNDERSCORE:                switch (format) {                    case LOWER_HYPHEN:                        return Ascii.toLowerCase(s.replace('_', '-'));                    case LOWER_UNDERSCORE:                        return Ascii.toLowerCase(s);                }                break;        }        // otherwise, deal with camel conversion        // 处理驼峰转其他的转换        StringBuilder out = null;        int i = 0;        int j = -1;        // 将字符串按分隔符切分单词,转换每个单词        while ((j = wordBoundary.indexIn(s, ++j)) != -1) {            if (i == 0) {                // include some extra space for separators                // 为分隔符留出额外的空间                out = new StringBuilder(s.length() + 4 * wordSeparator.length());                // 第一个单词使用normalizeFirstWord处理                out.append(format.normalizeFirstWord(s.substring(i, j)));            } else {                // 后续单词用normalizeWord处理                out.append(format.normalizeWord(s.substring(i, j)));            }            out.append(format.wordSeparator);            // 当前坐标后移            i = j + wordSeparator.length();        }        if (i == 0) {            return format.normalizeFirstWord(s);        }        // 处理最后一个分隔符右边的字符串        out.append(format.normalizeWord(s.substring(i)));        return out.toString();    }    /**     * 将第一个单词普通化     * LOWER_CAMEL -> 全小写     * 其他 -> normalizeWord     */    private String normalizeFirstWord(String word) {        switch (this) {            case LOWER_CAMEL:                return Ascii.toLowerCase(word);            default:                return normalizeWord(word);        }    }    /**     * 将单词普通化     * LOWER_HYPHEN, LOWER_UNDERSCORE -> 全小写     * LOWER_CAMEL, UPPER_CAMEL -> 第一个字母大写其他字母小写     * UPPER_UNDERSCORE -> 全大写     */    private String normalizeWord(String word) {        switch (this) {            case LOWER_HYPHEN:                return Ascii.toLowerCase(word);            case LOWER_UNDERSCORE:                return Ascii.toLowerCase(word);            case LOWER_CAMEL:                return firstCharOnlyToUpper(word);            case UPPER_CAMEL:                return firstCharOnlyToUpper(word);            case UPPER_UNDERSCORE:                return Ascii.toUpperCase(word);        }        throw new RuntimeException("unknown case: " + this);    }    /**     * 将单词第一个字母变大写,其他变小写     */    private static String firstCharOnlyToUpper(String word) {        int length = word.length();        if (length == 0) {            return word;        }        return new StringBuilder(length)                .append(Ascii.toUpperCase(word.charAt(0)))                .append(Ascii.toLowerCase(word.substring(1)))                .toString();    }}