StringUtils.substringAfterLast()和StringUtils.substringAfter()的区别

package org.apache.commons.lang3;

pom.xml中maven的依赖包

        org.apache.commons
        commons-lang3
        3.4
   

1. substringAfter()源码解读

   /**
     *

Gets the substring after the first occurrence of a separator.
     * The separator is not returned.

     *
     *

A {@code null} string input will return {@code null}.
     * An empty ("") string input will return the empty string.
     * A {@code null} separator will return the empty string if the
     * input string is not {@code null}.

     *
     *

If nothing is found, the empty string is returned.

     *
     *

      * StringUtils.substringAfter(null, *)      = null
      * StringUtils.substringAfter("", *)        = ""
      * StringUtils.substringAfter(*, null)      = ""
      * StringUtils.substringAfter("abc", "a")   = "bc"
      * StringUtils.substringAfter("abcba", "b") = "cba"
      * StringUtils.substringAfter("abc", "c")   = ""
      * StringUtils.substringAfter("abc", "d")   = ""
      * StringUtils.substringAfter("abc", "")    = "abc"
      * 

     *
     * @param str  the String to get a substring from, may be null
     * @param separator  the String to search for, may be null
     * @return the substring after the first occurrence of the separator,
     *  {@code null} if null String input
     * @since 2.0
     */
    public static String substringAfter(final String str, final String separator) {
        if (isEmpty(str)) {
            return str;
        }
        if (separator == null) {
            return EMPTY;
        }
        final int pos = str.indexOf(separator);//indexOf() 方法可返回某个指定的字符串值在字符串中首次出现的位置。
        if (pos == INDEX_NOT_FOUND) {
            return EMPTY;
        }
        return str.substring(pos + separator.length());
    }

2.substringAfterLast()源码解读

    /**
     *

Gets the substring after the last occurrence of a separator.
     * The separator is not returned.

     *
     *

A {@code null} string input will return {@code null}.
     * An empty ("") string input will return the empty string.
     * An empty or {@code null} separator will return the empty string if
     * the input string is not {@code null}.

     *
     *

If nothing is found, the empty string is returned.

     *
     *

      * StringUtils.substringAfterLast(null, *)      = null
      * StringUtils.substringAfterLast("", *)        = ""
      * StringUtils.substringAfterLast(*, "")        = ""
      * StringUtils.substringAfterLast(*, null)      = ""
      * StringUtils.substringAfterLast("abc", "a")   = "bc"
      * StringUtils.substringAfterLast("abcba", "b") = "a"
      * StringUtils.substringAfterLast("abc", "c")   = ""
      * StringUtils.substringAfterLast("a", "a")     = ""
      * StringUtils.substringAfterLast("a", "z")     = ""
      * 

     *
     * @param str  the String to get a substring from, may be null
     * @param separator  the String to search for, may be null
     * @return the substring after the last occurrence of the separator,
     *  {@code null} if null String input
     * @since 2.0
     */
    public static String substringAfterLast(final String str, final String separator) {
        if (isEmpty(str)) {
            return str;
        }
        if (isEmpty(separator)) {
            return EMPTY;
        }
        final int pos = str.lastIndexOf(separator);//返回指定字符在此字符串中最后一次出现处的索引，如果此字符串中没有这样的字符，则返回 -1。
        if (pos == INDEX_NOT_FOUND || pos == str.length() - separator.length()) {
            return EMPTY;
        }
        return str.substring(pos + separator.length());
    }

 

总结： 阅读源码进行对比，源码中有注解的部分给与case学习。源码没有你想象中的难读懂。

substringAfter()方法取str内，首次出现分隔符separator后的字符串。 

substringAfterLast()方法取str内，最后一个分隔符separator后的字符串。