将Java字符串从所有大写字母（用下划线分隔的单词）转换为CamelCase（无单词分隔符）的最简单方法是什么？

标题基本概括了所有内容。我可以用Java将字符串从格式转换"THIS_IS_AN_EXAMPLE_STRING"为“ ThisIsAnExampleString” 的最简单/最优雅的方法是什么？我认为必须至少有一种使用String.replaceAll()正则表达式的方法。

我最初的想法是：在字符串前加一个下划线（_），将整个字符串转换为小写，然后使用replaceAll转换后跟下划线及其大写版本的每个字符。

另一个选择是使用Google Guava的 com.google.common.base.CaseFormat

乔治·霍金斯对此用法示例发表了评论：

CaseFormat.UPPER_UNDERSCORE.to(CaseFormat.UPPER_CAMEL, "THIS_IS_AN_EXAMPLE_STRING");

看看Apache Commons lang中的WordUtils库：

具体来说，capitalizeFully（String str，char [] delimiters）方法应该可以完成以下工作：

String blah = "LORD_OF_THE_RINGS";
assertEquals("LordOfTheRings", WordUtils.capitalizeFully(blah, new char[]{'_'}).replaceAll("_", ""));

绿色吧！

static String toCamelCase(String s){
   String[] parts = s.split("_");
   String camelCaseString = "";
   for (String part : parts){
      camelCaseString = camelCaseString + toProperCase(part);
   }
   return camelCaseString;
}

static String toProperCase(String s) {
    return s.substring(0, 1).toUpperCase() +
               s.substring(1).toLowerCase();
}

注意：您需要添加参数验证。

使用Apache Commons Lang3 lib非常容易。

import org.apache.commons.lang3.StringUtils;
import org.apache.commons.lang3.text.WordUtils;

public String getName(String text) {
  return StringUtils.remove(WordUtils.capitalizeFully(text, '_'), "_");
}

例：

getName("SOME_CONSTANT");

给出：

"SomeConstant"

public static void main(String[] args) {
    String start = "THIS_IS_A_TEST";
    StringBuffer sb = new StringBuffer();
    for (String s : start.split("_")) {
        sb.append(Character.toUpperCase(s.charAt(0)));
        if (s.length() > 1) {
            sb.append(s.substring(1, s.length()).toLowerCase());
        }
    }
    System.out.println(sb);
}

以下代码片段可能会有所帮助：

String input = "ABC_DEF";
StringBuilder sb = new StringBuilder();
for( String oneString : input.toLowerCase().split("_") )
{
    sb.append( oneString.substring(0,1).toUpperCase() );
    sb.append( oneString.substring(1) );
}

// sb now holds your desired String

使用Streams的Java 1.8示例

String text = "THIS_IS_SOME_TEXT";

String bactrianCamel = Stream.of(text.split("[^a-zA-Z0-9]"))
        .map(v -> v.substring(0, 1).toUpperCase() + v.substring(1).toLowerCase())
        .collect(Collectors.joining());
String dromedaryCamel = bactrianCamel.toLowerCase().substring(0, 1) + bactrianCamel.substring(1); 

System.out.printf("%s is now %s%n", text, dromedaryCamel); 

THIS_IS_SOME_TEXT现在是thisIsSomeText

不能确定，但​​是我认为通过逐个字符地进行处理，我可以使用更少的内存并获得可靠的性能。我在做类似的事情，但是在后台线程中处于循环中，所以我现在尝试这样做。我有一些String.split的经验，它比预期的要贵。我正在Android上工作，希望GC打ic比使用CPU更为重要。

  public static String toCamelCase(String value) {
    StringBuilder sb = new StringBuilder();

    final char delimChar = '_';
    boolean lower = false;
    for (int charInd = 0; charInd < value.length(); ++charInd) {
      final char valueChar = value.charAt(charInd);
      if (valueChar == delimChar) {
        lower = false;
      } else if (lower) {
        sb.append(Character.toLowerCase(valueChar));
      } else {
        sb.append(Character.toUpperCase(valueChar));
        lower = true;
      }
    }

    return sb.toString();
  }

一个暗示String.split昂贵的提示是它的输入是一个正则表达式（不是String.indexOf之类的字符），它返回一个数组（而不是迭代器，因为循环一次只使用一件事）。再加上诸如“ AB_AB_AB_AB_AB_AB ...”之类的示例，将破坏任何批量复制的效率，并且对于长字符串，使用的内存要比输入字符串多一个数量级。

循环遍历字符没有规范的情况。因此，对我而言，不需要的正则表达式和数组的开销通常似乎不太理想（然后放弃了可能的批量复制效率）。有兴趣听取意见/更正，谢谢。

public String withChars(String inputa) {
    String input = inputa.toLowerCase();
    StringBuilder sb = new StringBuilder();
    final char delim = '_';
    char value;
    boolean capitalize = false;
    for (int i=0; i<input.length(); ++i) {
        value = input.charAt(i);
        if (value == delim) {
            capitalize = true;
        }
        else if (capitalize) {
            sb.append(Character.toUpperCase(value));
            capitalize = false;
        }
        else {
            sb.append(value);
        }
    }

    return sb.toString();
}

public String withRegex(String inputa) {
    String input = inputa.toLowerCase();
    String[] parts = input.split("_");
    StringBuilder sb = new StringBuilder();
    sb.append(parts[0]);
    for (int i=1; i<parts.length; ++i) {
        sb.append(parts[i].substring(0,1).toUpperCase());
        sb.append(parts[i].substring(1));
    }

    return sb.toString();
}

时间：以毫秒为单位。

Iterations = 1000
WithChars: start = 1379685214671 end = 1379685214683 diff = 12
WithRegex: start = 1379685214683 end = 1379685214712 diff = 29

Iterations = 1000
WithChars: start = 1379685217033 end = 1379685217045 diff = 12
WithRegex: start = 1379685217045 end = 1379685217077 diff = 32

Iterations = 1000
WithChars: start = 1379685218643 end = 1379685218654 diff = 11
WithRegex: start = 1379685218655 end = 1379685218684 diff = 29

Iterations = 1000000
WithChars: start = 1379685232767 end = 1379685232968 diff = 201
WithRegex: start = 1379685232968 end = 1379685233649 diff = 681

Iterations = 1000000
WithChars: start = 1379685237220 end = 1379685237419 diff = 199
WithRegex: start = 1379685237419 end = 1379685238088 diff = 669

Iterations = 1000000
WithChars: start = 1379685239690 end = 1379685239889 diff = 199
WithRegex: start = 1379685239890 end = 1379685240585 diff = 695

Iterations = 1000000000
WithChars: start = 1379685267523 end = 1379685397604 diff = 130081
WithRegex: start = 1379685397605 end = 1379685850582 diff = 452977

您可以使用org.modeshape.common.text.Inflector。

特别：

String camelCase(String lowerCaseAndUnderscoredWord,
    boolean uppercaseFirstLetter, char... delimiterChars) 

默认情况下，此方法将字符串转换为UpperCamelCase。

Maven工件是：org.modeshape：modeshape-common：2.3.0.Final

在JBoss存储库上： https //repository.jboss.org/nexus/content/repositories/releases

这是JAR文件：https : //repository.jboss.org/nexus/content/repositories/releases/org/modeshape/modeshape-common/2.3.0.Final/modeshape-common-2.3.0.Final.jar

您也可以尝试以下方法：

 public static String convertToNameCase(String s)
    {
        if (s != null)
        {
            StringBuilder b = new StringBuilder();
            String[] split = s.split(" ");
            for (String srt : split)
            {
                if (srt.length() > 0)
                {
                    b.append(srt.substring(0, 1).toUpperCase()).append(srt.substring(1).toLowerCase()).append(" ");
                }
            }
            return b.toString().trim();
        }
        return s;
    }

protected String toCamelCase(String input) {
    if (input == null) {
        return null;
    }

    if (input.length() == 0) {
        return "";
    }

    // lowercase the first character
    String camelCaseStr = input.substring(0, 1).toLowerCase();

    if (input.length() > 1) {
        boolean isStartOfWord = false;

        for (int i = 1; i < input.length(); i++) {
            char currChar = input.charAt(i);
            if (currChar == '_') {
                // new word. ignore underscore
                isStartOfWord = true;
            } else if (Character.isUpperCase(currChar)) {
                // capital letter. if start of word, keep it
                if (isStartOfWord) {
                    camelCaseStr += currChar;
                } else {
                    camelCaseStr += Character.toLowerCase(currChar);
                }
                isStartOfWord = false;
            } else {
                camelCaseStr += currChar;
                isStartOfWord = false;
            }
        }
    }

    return camelCaseStr;
}

public String CamelCase(String str)
{
    String CamelCase="";
    String parts[] = str.split("_");
    for(String part:parts)
    {
        String as=part.toLowerCase();
        int a=as.length();
        CamelCase = CamelCase + as.substring(0, 1).toUpperCase()+ as.substring(1,a);    
    }
    return CamelCase;
}

这是转换为CamelCase的最简单程序。希望对您有帮助。

它将转换Enum Constant成骆驼套。这将对正在寻求这种功能性的任何人有所帮助。

public enum TRANSLATE_LANGUAGES {
        ARABIC("ar"), BULGARIAN("bg"), CATALAN("ca"), CHINESE_SIMPLIFIED("zh-CN"), CHINESE_TRADITIONAL("zh-TW"), CZECH("cs"), DANISH("da"), DUTCH("nl"), ENGLISH("en"), ESTONIAN("et"), FINNISH("fi"), FRENCH(
                "fr"), GERMAN("de"), GREEK("el"), HAITIAN_CREOLE("ht"), HEBREW("he"), HINDI("hi"), HMONG_DAW("mww"), HUNGARIAN("hu"), INDONESIAN("id"), ITALIAN("it"), JAPANESE("ja"), KOREAN("ko"), LATVIAN(
                "lv"), LITHUANIAN("lt"), MALAY("ms"), NORWEGIAN("no"), PERSIAN("fa"), POLISH("pl"), PORTUGUESE("pt"), ROMANIAN("ro"), RUSSIAN("ru"), SLOVAK("sk"), SLOVENIAN("sl"), SPANISH("es"), SWEDISH(
                "sv"), THAI("th"), TURKISH("tr"), UKRAINIAN("uk"), URDU("ur"), VIETNAMESE("vi");

        private String code;

        TRANSLATE_LANGUAGES(String language) {
            this.code = language;
        }

        public String langCode() {
            return this.code;
        }

        public String toCamelCase(TRANSLATE_LANGUAGES lang) {
            String toString = lang.toString();
            if (toString.contains("_")) {
                String st = toUpperLowerCase(toString.split("_"));
            }

            return "";
        }

        private String toUpperLowerCase(String[] tempString) {
            StringBuilder builder = new StringBuilder();

            for (String temp : tempString) {

                String char1 = temp.substring(0, 1);
                String restString = temp.substring(1, temp.length()).toLowerCase();
                builder.append(char1).append(restString).append(" ");

            }

            return builder.toString();
        }
    }

对此的另一解决方案如下。

public static String toCamelCase(String str, String... separators) {
    String separatorsRegex = "\\".concat(org.apache.commons.lang3.StringUtils.join(separators, "|\\"));
    List splits = Arrays.asList(str.toLowerCase().split(separatorsRegex));
    String capitalizedString = (String)splits.stream().map(WordUtils::capitalize).reduce("", String::concat);
    return capitalizedString.substring(0, 1).toLowerCase() + capitalizedString.substring(1);
}

public static final String  UPPER_CAMEL = "initUp";
public static final String  LOWER_CAMEL = "initLow";

public String toCamel(String src, String separator, String format) {
    StringBuilder builder = new StringBuilder(src.toLowerCase());
    int len = builder.length();

    for (int idx = builder.indexOf(separator); idx > 0 && idx < len; idx = builder.indexOf(separator, idx)) {
        builder = builder.replace(idx, idx + 2, (String.valueOf(builder.charAt(idx + 1)).toUpperCase()));
    }

    switch (format) {
    case LOWER_CAMEL:
        builder.setCharAt(0, Character.toLowerCase(builder.charAt(0)));
        break;
    default:
        builder.setCharAt(0, Character.toUpperCase(builder.charAt(0)));
        break;
    }

    return builder.toString();

}

调用为

toCamel("THIS_IS_AN_EXAMPLE_STRING", "_", UPPER_CAMEL)

执行时间：14 ms

一个简单的片段：

 public static String camelCase(String in) {
    if (in == null || in.length() < 1) { return ""; } //validate in
    String out = "";
    for (String part : in.toLowerCase().split("_")) {
        if (part.length() < 1) { //validate length
            continue;
        }
        out += part.substring(0, 1).toUpperCase();
        if (part.length() > 1) { //validate length
            out += part.substring(1);
        }
    }
    return out;
}

Java 8用于多个字符串：

import com.google.common.base.CaseFormat;



String camelStrings = "YOUR_UPPER, YOUR_TURN, ALT_TAB";

List<String> camelList = Arrays.asList(camelStrings.split(","));
camelList.stream().forEach(i -> System.out.println(CaseFormat.UPPER_UNDERSCORE.to(CaseFormat.UPPER_CAMEL, i) + ", "));

    protected String toCamelCase(CaseFormat caseFormat, String... words){
        if (words.length  == 0){
          throw new IllegalArgumentException("Word list is empty!");
        }

        String firstWord = words[0];
        String [] restOfWords = Arrays.copyOfRange(words, 1, words.length);

        StringBuffer buffer = new StringBuffer();
        buffer.append(firstWord);
        Arrays.asList(restOfWords).stream().forEach(w->buffer.append("_"+ w.toUpperCase()));

        return CaseFormat.UPPER_UNDERSCORE.to(caseFormat, buffer.toString());

    }