Commons Lang、StringUtils.substringBeforeLast()

まんま

import org.apache.commons.lang.StringUtils;

public class C2008113000 {
    public static void main(String[] args) {
        System.out.println(StringUtils.substringBeforeLast(null, "z"));
        System.out.println(StringUtils.substringBeforeLast("", "z"));
        System.out.println(StringUtils.substringBeforeLast("abcba", "b"));
        System.out.println(StringUtils.substringBeforeLast("abc", "c"));
        System.out.println(StringUtils.substringBeforeLast("a", "a"));
        System.out.println(StringUtils.substringBeforeLast("a", "z"));
        System.out.println(StringUtils.substringBeforeLast("a", null));
        System.out.println(StringUtils.substringBeforeLast("a", ""));
    }
}

で、

null

abc
ab

a
a
a