如何恢复用Java中的正则表达式拆分的字符串

Question

We know that String.split(String regex) returns a String[] . So, how can we recover a string by using the returned String[] and the regex (or needs more inputs)?

1. It seems like if the regex is a constant, say \\t , we can recover the original string by appending the joint of each member of the String[] and the constant sequentially. However, what if the regex is sth. like [AB]+ ?

2. If there is a all-around way(function) that can handle the above both cases ?

Answer 1

There is no method present in JDK which can do this, but you can use the Apache Commons Langs StringUtls class , it will work

import org.apache.commons.lang3.StringUtils;

/**
 *
 * @author Himanshu Mishra
 */
public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {

        String orignalStr = "AB:#:CD:#:EF";
        String[] orignalSplit = orignalStr.split(":#:");


        // Join all Strings in the Array into a Single String, separated by :#:

        System.out.println("Join Strings using separator " + StringUtils.join(orignalSplit, ":#:"));
    }
}

Answer 2

You can't, unless the regex is a literal, and even then it's not 100% reliable.

The reason is the matched separators are discarded, so a non-literal regex, for example

 \s+ (any number if whitespace characters)

can not be reconstructed, because we don't know how many, and what type of, whitespace characters originally existed.

If the regex is a literal, you can simply rebuild the string by inserting the literal between the elements split, but not that trailing blanks as ignored, both of these inputs:

a,b,c
a,b,c,,,,,

when split with "," both yield the same result of [a, b, c] , so even with a literal regex you can't confidently recreate the original input.