前言

在项目中实战学习并记录可用的工具类

1. 概念

Java标准库（java.lang包）并没有提供名为StringHelper的类。通常，类似的字符串处理工具类并不是Java标准库的一部分，而是由程序员自行编写或者使用第三方库提供的工具类。

2. 功能示例

功能	作用	示例
join(Object[] array, String separator)	将数组中的元素用指定的分隔符连接成一个字符串。	join(new String[]{“a”, “b”, “c”}, “-”) 返回 “a-b-c”。
join(Iterable<?> iterable, String separator)	将可迭代对象中的元素用指定的分隔符连接成一个字符串。	join(Arrays.asList(“a”, “b”, “c”), “-”) 返回 “a-b-c”。
decapitalize(String string)	将字符串的首字母转换为小写，除非字符串以多个大写字母开头	示例： decapitalize(“Hello”) 返回 “hello”。
isNullOrEmptyString(String value)	检查字符串是否为null或仅包含空格	isNullOrEmptyString(" ") 返回 true。
toShortString(Member member)	创建成员对象的紧凑字符串表示形式，用于调试或toString()方法。	toShortString(someMethod) 返回方法的紧凑字符串表示。
toShortString(Type type)	创建类型对象的紧凑字符串表示形式，用于调试或toString()方法	toShortString(String.class) 返回 “java.lang.String”。

其他辅助方法：包括一些私有辅助方法，如startsWithSeveralUpperCaseLetters等。

实际上是一个自定义的StringHelper工具类，包含了一系列用于字符串操作的静态方法。

3. Demo示例

以下是该类中主要方法的作用和功能：

public class StringHelper {private static final Pattern DOT = Pattern.compile( "\\." );private StringHelper() {}/*** Joins the elements of the given array to a string, separated by the given separator string.** @param array the array to join* @param separator the separator string** @return a string made up of the string representations of the given array's members, separated by the given separator*         string*/public static String join(Object[] array, String separator) {return array != null ? join( Arrays.asList( array ), separator ) : null;}/*** Joins the elements of the given iterable to a string, separated by the given separator string.** @param iterable the iterable to join* @param separator the separator string** @return a string made up of the string representations of the given iterable members, separated by the given separator*         string*/public static String join(Iterable<?> iterable, String separator) {if ( iterable == null ) {return null;}StringBuilder sb = new StringBuilder();boolean isFirst = true;for ( Object object : iterable ) {if ( !isFirst ) {sb.append( separator );}else {isFirst = false;}sb.append( object );}return sb.toString();}/*** Returns the given string, with its first letter changed to lower-case unless the string starts with more than* one upper-case letter, in which case the string will be returned unaltered.* <p>* Provided to avoid a dependency on the {@link java.beans.Introspector} API which is not available on the Android* platform (HV-779).** @param string the string to decapitalize** @return the given string, decapitalized. {@code null} is returned if {@code null} is passed as input; An empty*         string is returned if an empty string is passed as input** @see java.beans.Introspector#decapitalize(String)*/public static String decapitalize(String string) {if ( string == null || string.isEmpty() || startsWithSeveralUpperCaseLetters( string ) ) {return string;}else {return string.substring( 0, 1 ).toLowerCase( Locale.ROOT ) + string.substring( 1 );}}/*** Indicates if the string is null or is empty ie only contains whitespaces.** @param value the string considered* @return true if the string is null or only contains whitespaces*/public static boolean isNullOrEmptyString(String value) {return value == null || value.trim().isEmpty();}/*** Creates a compact string representation of the given member, useful for debugging or toString() methods. Package* names are shortened, e.g. "org.hibernate.validator.internal.engine" becomes "o.h.v.i.e". Not to be used for* user-visible log messages.*/public static String toShortString(Member member) {if ( member instanceof Field ) {return toShortString( (Field) member );}else if ( member instanceof Method ) {return toShortString( (Method) member );}else {return member.toString();}}private static String toShortString(Field field) {return toShortString( field.getGenericType() ) + " " + toShortString( field.getDeclaringClass() ) + "#" + field.getName();}private static String toShortString(Method method) {return toShortString( method.getGenericReturnType() ) + " " +method.getName() +Arrays.stream( method.getGenericParameterTypes() ).map( StringHelper::toShortString ).collect( Collectors.joining( ", ", "(", ")" ) );}/*** Creates a compact string representation of the given type, useful for debugging or toString() methods. Package* names are shortened, e.g. "org.hibernate.validator.internal.engine" becomes "o.h.v.i.e". Not to be used for* user-visible log messages.*/public static String toShortString(Type type) {if ( type instanceof Class ) {return toShortString( (Class<?>) type );}else if ( type instanceof ParameterizedType ) {return toShortString( (ParameterizedType) type );}else {return type.toString();}}private static String toShortString(Class<?> type) {if ( type.isArray() ) {return toShortString( type.getComponentType() ) + "[]";}else if ( type.getEnclosingClass() != null ) {return toShortString( type.getEnclosingClass() ) + "$" + type.getSimpleName();}else if ( type.getPackage() == null ) {return type.getName();}return toShortString( type.getPackage() ) + "." + type.getSimpleName();}private static String toShortString(ParameterizedType parameterizedType) {Class<?> rawType = ReflectionHelper.getClassFromType( parameterizedType );if ( rawType.getPackage() == null ) {return parameterizedType.toString();}String typeArgumentsString = Arrays.stream( parameterizedType.getActualTypeArguments() ).map( t -> toShortString( t ) ).collect( Collectors.joining( ", ", "<", ">" ) );return toShortString( rawType ) + typeArgumentsString;}private static String toShortString(Package pakkage) {String[] packageParts = DOT.split( pakkage.getName() );return Arrays.stream( packageParts ).map( n -> n.substring( 0, 1 ) ).collect( Collectors.joining( "." ) );}private static boolean startsWithSeveralUpperCaseLetters(String string) {return string.length() > 1 &&Character.isUpperCase( string.charAt( 0 ) ) &&Character.isUpperCase( string.charAt( 1 ) );}}