始于之前的阿里面试，根据面试官的提示，重写了三遍方法才写对，教条？不过我对此有另外的看法。
如下代码，三种不同的截取方式，前面两种都比面试官所说的方法快，美国服务器，速度并且不在同一个量级。
而以字节操作又比以字符操作略慢，其原因在于以字节操作的最后要求new String，从源码可知其会导致重新按字符集编码。
可知，快速的操作字符串，根本的手段是以JAVA字符(char)形式进行操作，香港虚拟主机，其次是字节形式，在字节与字符串之间互操作是性能最差的方式。
import java.io.UnsupportedEncodingException;import java.util.Random;public class Example {/**** <pre>* 以字符字节的形式操作字节截取。* </pre>** @param src* @param length* @param charset* @return* @throws UnsupportedEncodingExceptionString subStringInChars(String src, int length, String charset) throws UnsupportedEncodingException {int srcLength = src.length();int i = 0;int len = 0;int rollback = 0;while (true) {if (len >= length || length>=srcLength) {break;}if (src.charAt(i) < 256) {rollback=0;len += 1;} else {rollback=1;len += 2;}i+=1;}if (len!=length){i-=rollback;}return src.substring(0, i);}/**** <pre>* 逐字节截取字符。* </pre>** @param src* @param length* @param charset* @return* @throws UnsupportedEncodingExceptionString subStringInBytes(String src, int length, String charset) throws UnsupportedEncodingException {if (charset == null) {charset = “GBK”;}int firstStartScope = 129 – 1;int firstEndScope = 254 + 1;int secondStartScope = 64 – 1;int secondEndScope = 254 + 1;byte[] bytes = src.getBytes(charset);int i = 0;while (i < bytes.length) {int b1 = bytes[i] & 0xFF;int b2 = bytes[i+1] & 0xFF;if (b1 > firstStartScope && b1 < firstEndScope && b2 > secondStartScope && b2 < secondEndScope) {if (i+1==length){i=length-1;break;}else if (i+1>length){i=length;break;}i+=2;}else{i+=1;if (i==length){break;}}}return new String(bytes, 0, i, charset);}/**** <pre>* 面试官认可的操作方法* </pre>** @param str* @param subSLength* @param charset* @return* @throws UnsupportedEncodingExceptionString subStringInStrings(String str, int subSLength, String charset) throws UnsupportedEncodingException {if (charset == null) {charset = “GBK”;}if (str == null) {return “”;} else {strLength = str.length();String subStr = str.substring(0, strLength < subSLength ? strLength : subSLength);subStrByetsL = subStr.getBytes(charset).length;(subStrByetsL > tempSubLength) {int subSLengthTemp = –subSLength;subStr = str.substring(0, subSLengthTemp > strLength ? strLength : subSLengthTemp);subStrByetsL = subStr.getBytes(charset).length;//subStrByetsL = subStr.getBytes().length;}return subStr;}}private static Random random = new Random();public static String getRandomString(int randomLength) {String base = “abcdefghijklmnopqrstuvwxyz0123456789”;int strLength = random.nextInt(randomLength);while (strLength < randomLength / 2) {strLength = random.nextInt(randomLength);}char[] chars = new char[strLength];for (int i = 0; i < chars.length; i++) {char c = (char) (0x4e00 + (int) (Math.random() * (0x9fa5 – 0x4e00 + 1)));if (random.nextInt(3) > 0) {c = base.charAt(random.nextInt(base.length()));}chars[i] = c;}return new String(chars);}main(String[] args) throws UnsupportedEncodingException {long start = System.currentTimeMillis();long s1 = 0;long s2 = 0;long s3 = 0;Random random = new Random();int randomLength = 10000;for (int i = 0; i < 100; i++) {String str = getRandomString(randomLength);//String str = “我ABC汗”;(str.length() == 0) {continue;}int randomLeng = random.nextInt(str.length());//int randomLeng = 6;//subStringInBytes(str, randomLeng, null);start = System.currentTimeMillis();String str1 = subStringInBytes(str, randomLeng, null);//System.out.println(str1);s1 += (System.currentTimeMillis() – start);start = System.currentTimeMillis();String str2 = subStringInStrings(str, randomLeng, null);//System.out.println(str2);s2 += (System.currentTimeMillis() – start);start = System.currentTimeMillis();String str3 = subStringInChars(str, randomLeng, null);//System.out.println(str3);s3 += (System.currentTimeMillis() – start);if (!str1.equals(str2) || !str2.equals(str3) || !str1.equals(str3)) {System.out.println(i);System.out.println(str);System.out.println(randomLeng);System.out.println(str1);System.out.println(str2);System.out.println(str3);break;}}System.out.println(“字节截取:”+s1);System.out.println(“字符串截取:”+s2);System.out.println(“字符截取:”+s3);}}，香港虚拟主机没有什么可留恋，只有抑制不住的梦想，
