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爱聊网站,wordpress主题 her,网页版word在线编辑,广东网站建设熊掌号java#xff1a;java.util.StringTokenizer实现字符串切割 1 前言 java.util工具包提供了字符串切割的工具类StringTokenizer#xff0c;Spring等常见框架的字符串工具类#xff08;如Spring的StringUtils#xff09;#xff0c;常见此类使用。 例如Spring的StringUtil…javajava.util.StringTokenizer实现字符串切割 1 前言 java.util工具包提供了字符串切割的工具类StringTokenizerSpring等常见框架的字符串工具类如Spring的StringUtils常见此类使用。 例如Spring的StringUtils下的方法 public static String[] tokenizeToStringArray(Nullable String str, String delimiters, boolean trimTokens, boolean ignoreEmptyTokens) {if (str null) {return EMPTY_STRING_ARRAY;}StringTokenizer st new StringTokenizer(str, delimiters);ListString tokens new ArrayList();while (st.hasMoreTokens()) {String token st.nextToken();if (trimTokens) {token token.trim();}if (!ignoreEmptyTokens || token.length() 0) {tokens.add(token);}}return toStringArray(tokens); }又如定时任务框架Quartz中cron表达式类CronExpression其中的buildExpression方法是为了处理cron表达式的cron表达式有7个子表达式空格隔开cron表达式字符串的切割也使用到了StringTokenizer类方法如下 protected void buildExpression(String expression) throws ParseException {this.expressionParsed true;try {if (this.seconds null) {this.seconds new TreeSet();}if (this.minutes null) {this.minutes new TreeSet();}if (this.hours null) {this.hours new TreeSet();}if (this.daysOfMonth null) {this.daysOfMonth new TreeSet();}if (this.months null) {this.months new TreeSet();}if (this.daysOfWeek null) {this.daysOfWeek new TreeSet();}if (this.years null) {this.years new TreeSet();}int exprOn 0;for(StringTokenizer exprsTok new StringTokenizer(expression, \t, false); exprsTok.hasMoreTokens() exprOn 6; exprOn) {String expr exprsTok.nextToken().trim();if (exprOn 3 expr.indexOf(76) ! -1 expr.length() 1 expr.contains(,)) {throw new ParseException(Support for specifying L and LW with other days of the month is not implemented, -1);}if (exprOn 5 expr.indexOf(76) ! -1 expr.length() 1 expr.contains(,)) {throw new ParseException(Support for specifying L with other days of the week is not implemented, -1);}if (exprOn 5 expr.indexOf(35) ! -1 expr.indexOf(35, expr.indexOf(35) 1) ! -1) {throw new ParseException(Support for specifying multiple \nth\ days is not implemented., -1);}StringTokenizer vTok new StringTokenizer(expr, ,);while(vTok.hasMoreTokens()) {String v vTok.nextToken();this.storeExpressionVals(0, v, exprOn);}}if (exprOn 5) {throw new ParseException(Unexpected end of expression., expression.length());} else {if (exprOn 6) {this.storeExpressionVals(0, , 6);}TreeSetInteger dow this.getSet(5);TreeSetInteger dom this.getSet(3);boolean dayOfMSpec !dom.contains(NO_SPEC);boolean dayOfWSpec !dow.contains(NO_SPEC);if ((!dayOfMSpec || dayOfWSpec) (!dayOfWSpec || dayOfMSpec)) {throw new ParseException(Support for specifying both a day-of-week AND a day-of-month parameter is not implemented., 0);}}} catch (ParseException var8) {throw var8;} catch (Exception var9) {throw new ParseException(Illegal cron expression format ( var9.toString() ), 0);} }2 使用 import com.google.common.collect.Lists;import java.util.List; import java.util.StringTokenizer;/** author xiaoxu* date 2023-10-18* spring_boot:com.xiaoxu.boot.tokenizer.TestStringTokenizer*/ public class TestStringTokenizer {public static void main(String[] args) {print(你 好 吗\t我是 \t你的\t 朋友 \t, \t, false);}public static void print(String str, String delimiter, boolean isReturnDelims) {System.out.println(切割字符串【 str 】 分隔符【 delimiter 】。);ListString strs Lists.newArrayList();String s;boolean x;for (StringTokenizer strToken new StringTokenizer(str, delimiter, false); strToken.hasMoreTokens(); x (s ! null strs.add(s))) {s strToken.nextToken();System.out.println(切割【 s 】);if(s.equals(吗))s null;}System.out.println(字符串数组 strs);}}执行结果 切割字符串【你 好 吗 我是 你的 朋友 】分隔符【 】。 切割【你】 切割【好】 切割【吗】 切割【我是】 切割【你的】 切割【朋友】 字符串数组[你, 好, 我是, 你的, 朋友]源码片段分析 public StringTokenizer(String str, String delim, boolean returnDelims) {currentPosition 0;newPosition -1;delimsChanged false;this.str str;maxPosition str.length();delimiters delim;retDelims returnDelims;setMaxDelimCodePoint(); }private void setMaxDelimCodePoint() {if (delimiters null) {maxDelimCodePoint 0;return;}int m 0;int c;int count 0;for (int i 0; i delimiters.length(); i Character.charCount©) {c delimiters.charAt(i);if (c Character.MIN_HIGH_SURROGATE c Character.MAX_LOW_SURROGATE) {c delimiters.codePointAt(i);hasSurrogates true;}if (m c)m c;count;}maxDelimCodePoint m;if (hasSurrogates) {delimiterCodePoints new int[count];for (int i 0, j 0; i count; i, j Character.charCount©) {c delimiters.codePointAt(j);delimiterCodePoints[i] c;}} }调用setMaxDelimCodePoint()方法源码可知切割时设置int maxDelimCodePoint是为了优化分隔符的检测取的是分隔字符串中char的ASCII码值最大的字符的ASCII值存入maxDelimCodePoint中。在方法int scanToken(int startPos)中若满足条件(c maxDelimCodePoint) (delimiters.indexOf© 0)意即该字符的ASCII码值小于等于最大的maxDelimCodePoint那么这个字符可能存在于分隔字符串中再检测delimiters分隔字符串中是否包含该字符反之若ASCII码值大于分隔字符串中最大的maxDelimCodePoint也就是说该字符一定不存在于分隔字符串里直接跳过delimiters.indexOf的检测也就达到了优化分隔符检测的效果了。 private int scanToken(int startPos) {int position startPos;while (position maxPosition) {if (!hasSurrogates) {char c str.charAt(position);if ((c maxDelimCodePoint) (delimiters.indexOf© 0))break;position;} else {int c str.codePointAt(position);if ((c maxDelimCodePoint) isDelimiter©)break;position Character.charCount©;}}if (retDelims (startPos position)) {if (!hasSurrogates) {char c str.charAt(position);if ((c maxDelimCodePoint) (delimiters.indexOf© 0))position;} else {int c str.codePointAt(position);if ((c maxDelimCodePoint) isDelimiter©)position Character.charCount©;}}return position; }scanToken方法即跳过分隔字符串只要某此循环时该字符包含在分隔字符串里那么position不再自增以此时的position值作为实际切割获取字符串的末索引 因为subString方法是左闭右开的该值是实际获取字符串的末索引值1所以可以截取到完整的不包含分隔符的字符串片段。 skipDelimiters方法类似即过滤连续包含于分隔字符串中的字符获取实际需要切割获取的字符串的开始索引值。 private int skipDelimiters(int startPos) {if (delimiters null)throw new NullPointerException();int position startPos;while (!retDelims position maxPosition) {if (!hasSurrogates) {char c str.charAt(position);if ((c maxDelimCodePoint) || (delimiters.indexOf© 0))break;position;} else {int c str.codePointAt(position);if ((c maxDelimCodePoint) || !isDelimiter©) {break;}position Character.charCount©;}}return position; }上述分析可知只要待切割字符串中的字符在分隔字符串中出现那么就会做一次切割也就是不论分隔字符串中的每个char或字符串片段的顺序只要连续包含在分隔字符串里就切割。 演示如下注意countTokens()方法不要在循环中和nextToken()一同使用 public static void print2(String str, String delimiter, boolean isReturnDelims) {StringTokenizer strTokenizer new StringTokenizer(str, delimiter);System.out.println(总数目: strTokenizer.countTokens());int count;String[] strs new String[count strTokenizer.countTokens()];// 注意不要在循环里写 int i 0; i strTokenizer.countTokens();// 因为 countTokens方法需要使用currentPosition而每次执行nextToken方法时currentPosition会一直往下偏移计算// 会导致循环中 i strTokenizer.countTokens();发生改变这里应该是常量总数目for (int i 0; i count; i) {String s strTokenizer.nextToken();strs[i] s;}System.out.println(Arrays.toString(strs)); }countTokens源码如下 public int countTokens() {int count 0;int currpos currentPosition;while (currpos maxPosition) {currpos skipDelimiters(currpos);if (currpos maxPosition)break;currpos scanToken(currpos);count;}return count; }执行 print2(1a2b3c4ca5bc6ba7abc8acbbaba9, abc, false);结果如下所示 总数目:9 [1, 2, 3, 4, 5, 6, 7, 8, 9]