使用String.split（）一个接一个地添加2个分隔符时如何添加空字符串

Question

I'm quite new to regex and I have to split EDI files for a loader I'm developing. If you are not familiar with it, here is an example of 2 segments (modified to explain all so it's not a real example):

APD+EM2:0:16?'30::6+++++++DA'APD+EM2:0:1630::6+++++++DA'

End of lines are marked with ' and I ignore if there's an escaping char which is the question mark - ?' is to ignore for example for the end of a line. \+ and : are the main delimiters (when data are composite like an address).

The split for the segments works fine, but I have issues with the other delimiters. I would like to have a String[] with all the elements, even if they are empty, because I need to process it after (insert in DB). With the example above, I would like to have a tab like this:

APD+EM2:0:16?'30::6+++++++DA

would transform into:

{"APD","EM2","0","16?'30","","6","","","","","","","DA"}

Currently with my code, I get a tab like this:

{"APD","EM2","0","16?'30","6","DA"}

Can I please have some help with my regex? Making it match ++ and :: is beyond my skills for now. I need to remove the escaping characters as well, but I'll work on that on my own.

BTW, I need to process a lot of data - 300gb of raw text - so if what I do is bad performance-wise, don't hesitate to tell me - like per example split with both + and : at the same time.

The EDIFACT format is not something discussed a lot around here, and the few examples I found were not working for me.

Current code:

private final String DATA_ELEMENT_DELIMITER = "(?<!\\?)\\+";
private final String DATA_COMPOSITE_ELEMENT_DELIMITER = "(?<!\\?):";

private String[] split (String segments){       
    return Stream.of(segments)
            .flatMap(Pattern.compile(DATA_ELEMENT_DELIMITER)::splitAsStream)
            .flatMap(Pattern.compile(DATA_COMPOSITE_ELEMENT_DELIMITER)::splitAsStream)
            .toArray(String[]::new);
}

---

EDIT: The code I'm running - BTW, I'm running on Java 8, not sure it makes a difference though:

import java.util.Arrays;
import java.util.regex.Pattern;
import java.util.stream.Stream;
public class Split {

    public static void main(String[] args) {
        Split s = new Split();
        System.out.println(
                Arrays.toString(
                    s.split("APD+EM2:0:16?'30::6+++++++DA'")
                )
            );
    }
    
    
    private static final Pattern DATA_ELEMENT_DELIMITER = Pattern.compile("(?<!\\?)\\+");
    private static final Pattern DATA_COMPOSITE_ELEMENT_DELIMITER = Pattern.compile("(?<!\\?):");
    
    private String[] split (String segments){       
        return Stream.of(segments)
                .flatMap(DATA_ELEMENT_DELIMITER::splitAsStream)
                .flatMap(DATA_COMPOSITE_ELEMENT_DELIMITER::splitAsStream)
                .toArray(String[]::new);
    }
}

Here is the output i get:

[APD, EM2, 0, 16?'30, , 6, DA']

---

EDIT EDIT

After trying to run this code in an online Java 11 compiler, the output is correct, but not on Java 8.

Answer 1

My first note is that for improved performance, you definitely want to compile the Pattern s once and reuse the instance:

private static final Pattern DATA_ELEMENT_DELIMITER = Pattern.compile("(?<!\\?)\\+");
private static final Pattern DATA_COMPOSITE_ELEMENT_DELIMITER = Pattern.compile("(?<!\\?):");
// ...
.flatMap(DATA_ELEMENT_DELIMITER::splitAsStream)
.flatMap(DATA_COMPOSITE_ELEMENT_DELIMITER::splitAsStream)

---

Second, as @user15244370 mentioned, running your code does produce the output you are looking for. I ran it like this:

System.out.println(
    Arrays.toString(
        split("APD+EM2:0:16?'30::6+++++++DA'APD+EM2:0:1630::6+++++++DA'")
    )
);

and got the output:

[APD, EM2, 0, 16?'30, , 6, , , , , , , DA'APD, EM2, 0, 1630, , 6, , , , , , , DA']

---

Assuming there is some difference between what you have posted and what you are actually running, the documentation for splitAsStream mentions:

Trailing empty strings will be discarded and not encountered in the stream.

---

Are you doing any additional processing after the call to split ? And how are you printing the array? Is it possible that the method you are using to print the string[] may be removing empty strings? As far as I can tell, your implementation should function as you intend.