Java :: Parsing a multiline text with regular expressions

Question

I want to parse a multiline text, so I wrote something like this:

String text = "[timestamp1] INFO - Message1 \r\n"
            + "[timestamp2] ERROR - Message2 \r\n"
            + "[timestamp3] INFO - Message3 \r\n"
            + "Message3_details1......... \r\n"
            + "Message3_details2 ......... \r\n";
String regex = "\\[(.*)\\] (.*) - (.*)";
Pattern p = Pattern.compile(regex, Pattern.DOTALL);
Matcher m = p.matcher(text);
while (m.find()) {
    System.out.println("G1: " + m.group(1));
    System.out.println("G2: " + m.group(2));
    System.out.println("G3: " + m.group(3));
    System.out.println();
}

What I want to get is this:

G1: timestamp1
G2: INFO
G3: message1

G1: timestamp2
G2: ERROR
G3: message2

G1: timestamp3
G2: INFO
G3: message3
    message_details1....
    message_details2...

But what I get is like this:

G1: timestamp1] INFO - Message1
    [timestamp2] ERROR - Message2
    [timestamp3
G2: INFO
G3: Message3
    Message3_details1........
    Message3_details2........

I'm not able to solve that even with Google's help.

Rohit Jain · Accepted Answer · 2013-10-07 10:45:53Z

4

You have used greedy quantifier in your regex. So, .* in [(.*)] will consume everything till the last found ]. You need to use reluctant quantifier. Add a ? after .*.

Also, for the last .*, you need to use a look-ahead, to make it stop before the next [.

The following code would work:

String text = "[timestamp1] INFO - Message1 \r\n"
            + "[timestamp2] ERROR - Message2 \r\n"
            + "[timestamp3] INFO - Message3 \r\n"
            + "Message3_details1......... \r\n"
            + "Message3_details2 ......... \r\n";

String regex = "\\[(.*?)\\] (.*?) - (.*?)(?=\\[|$)";

Pattern p = Pattern.compile(regex, Pattern.DOTALL);
Matcher m = p.matcher(text);
while (m.find()) {
    System.out.println("G1: " + m.group(1));
    System.out.println("G2: " + m.group(2));
    System.out.println("G3: " + m.group(3));
    System.out.println();
}

The last part of the regex - (.*?)(?=\\[|$) matches everything till the [ in the next line, or till the end ($). $ is required for the last two lines to be captured in group 3 of the last match.

Output:

G1: timestamp1
G2: INFO
G3: Message1 


G1: timestamp2
G2: ERROR
G3: Message2 


G1: timestamp3
G2: INFO
G3: Message3 
Message3_details1......... 
Message3_details2 .........

edited Oct 7, 2013 at 10:45

answered Oct 7, 2013 at 10:39

Rohit Jain

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2 Comments

yataodev Over a year ago

Thanks a lot. But what if Message3_datails contains a text in square brackets? It will stop on it.

Rohit Jain Over a year ago

@yataodev Yeah it will stop there. In that case, you would have to modify the look-ahead a little bit.

Evgeniy Dorofeev · Accepted Answer · 2013-10-07 10:52:51Z

0

try "\\[(.*?)\\] (.*?) - (.*?) \\r\\n"

answered Oct 7, 2013 at 10:52

Evgeniy Dorofeev

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