Pattern lookahead - java

Pattern p = Pattern.compile("(ma)|([a-zA-Z_]+)");
Matcher m = p.matcher("ma");
m.find();
System.out.println("1 " + m.group(1) + ""); //ma
System.out.println("2 " + m.group(2)); // null
Matcher m = p.matcher("mad");
m.find();
System.out.println("1 " + m.group(1) + ""); //ma
System.out.println("2 " + m.group(2)); // null
But I need that the string "mad" would be in the 2nd group.


I think what you are looking for is something like:
(ma(?!d))|([a-zA-Z_]+)
from "perldoc perlre":
"(?!pattern)"
A zero-width negative look-ahead assertion. For
example
"/foo(?!bar)/" matches any occurrence of "foo" that
isn't
followed by "bar".
the only thing I'm not sure about is whether Java supports this syntax, but I think it does.


If you use matches instead of find, it will try to match the entire string against that pattern, which it can only do by putting mad in the second group:
import java.util.regex.*;
public class Test {
public static void main(String[] args) {
Pattern p = Pattern.compile("(ma)|([a-zA-Z_]+)");
Matcher m = p.matcher("ma");
m.matches();
System.out.println("1 " + m.group(1)); // ma
System.out.println("2 " + m.group(2)); // null
m = p.matcher("mad");
m.matches();
System.out.println("1 " + m.group(1)); // null
System.out.println("2 " + m.group(2)); // mad
}
}

Related

Java matcher unable to finding last group

I'm trying regex after a long time. I'm not sure if the issue is with regex or the logic.
String test = "project/components/content;contentLabel|contentDec";
String regex = "(([A-Za-z0-9-/]*);([A-Za-z0-9]*))";
Map<Integer, String> matchingGroups = new HashMap<>();
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(test);
//System.out.println("Input: " + test + "\n");
//System.out.println("Regex: " + regex + "\n");
//System.out.println("Matcher Count: " + matcher.groupCount() + "\n");
if (matcher != null && matcher.find()) {
for (int i = 0; i < matcher.groupCount(); i++) {
System.out.println(i + " -> " + matcher.group(i) + "\n");
}
}
I was expecting the above to give me the output as below:
0 -> project/components/content;contentLabel|contentDec
1 -> project/components/content
2 -> contentLabel|contentDec
But when running the code the group extractions are off.
Any help would be really appreciated.
Thanks!

You have a few issues:
You're missing | in your second character class.
You have an unnecessary capture group around the whole regex.
When outputting the groups, you need to use <= matcher.groupCount() because matcher.group(0) is reserved for the whole match, so your capture groups are in group(1) and group(2).
This will work:
String test = "project/components/content;contentLabel|contentDec";
String regex = "([A-Za-z0-9-/]*);([A-Za-z0-9|]*)";
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(test);
if (matcher != null && matcher.find()) {
for (int i = 0; i <= matcher.groupCount(); i++) {
System.out.println(i + " -> " + matcher.group(i) + "\n");
}
}

Java Pattern to match String beginning and end?

I have an input that looks like this : 0; expires=2016-12-27T16:52:39
I am trying extract from this only the date, using Pattern and Matcher.
private String extractDateFromOutput(String result) {
Pattern p = Pattern.compile("(expires=)(.+?)(?=(::)|$)");
Matcher m = p.matcher(result);
while (m.find()) {
System.out.println("group 1: " + m.group(1));
System.out.println("group 2: " + m.group(2));
}
return result;
}
Why does this matcher find more than 1 group ? The output is as follows:
group 1: expires=
group 2: 2016-12-27T17:04:39
How can I get only group 2 out of this?
Thank you !

Because you have used more than one capturing group in your regex.
Pattern p = Pattern.compile("expires=(.+?)(?=::|$)");
Just remove the capturing group around
expires
::

private String extractDateFromOutput(String result) {
Pattern p = Pattern.compile("expires=(.+?)(?=::|$)");
Matcher m = p.matcher(result);
while (m.find()) {
System.out.println("group 1: " + m.group(1));
// no group 2, accessing will gives you an IndexOutOfBoundsException
//System.out.println("group 2: " + m.group(2));
}
return result;
}

Java Regex with underscore

Pattern r = Pattern.compile("(\\w+)\\s+(\\w+)\\s+(\\w+)\\s*");
Matcher m = r.matcher(line);
if (m.find()) {
System.out.println("Found: " + m.group(2));
} else {
System.out.println("Not found");
}
And when i use this:
HEY_YO NICE GUYHERE
It shows output: Not found.
How to get a string with underscore? (_)
Input:
HEY_YO NICE GUYHERE
And i want to output:
Found: HEY_YO

i think you are not passing "HEY_YO NICE GUYHERE" as input because for this input your code will produce "Found: NICE" as output.To get the output you want
replace
System.out.println("Found: " + m.group(2));
with
System.out.println("Found: " + m.group(1));

When using matcher.find() you can specify only what you want to capture :
public static void main(String[] args) {
String line = "HEY_YO NICE GUYHERE";
Pattern r = Pattern.compile("[a-zA-Z]+_[a-zA-Z]+");
Matcher m = r.matcher(line);
if (m.find()) {
System.out.println("Found: " + m.group(0));
} else {
System.out.println("Not found");
}
}
O/P :
Found: HEY_YO

writing a regular expression in java for a string present in between a line

My input string is:
subtype=forward,level=notice,vd=root,srcip=10.100.1.121,srcport=55844,srcintf=port1,dstip=173.193.156.43,dstport=80,dstintf=port16,sessionid=1224203695,status=close
subtype=forward,level=notice,vd=root,srcip=10.100.1.121,srcport=55844,srcintf=port1,dstip=173.193.156.43,dstport=80,dstintf=port16,sessionid=1224203695,status=open
This is the code I tried:
Pattern patt = Pattern.compile("(srcip=(?:\\d+\\.)+\\d+)(?:.*)?(dstip=(?:\\d+\\.)+\\d+)(?:.*)?(status=(?=.*close.*)(?:.*)?(dstport=(\\d+))");
BufferedReader r = new BufferedReader(new FileReader("ttext.txt"));
// For each line of input, try matching in it.
String line;
while ((line = r.readLine()) != null) {
// For each match in the line, extract and print it.
Matcher m = patt.matcher(line);
while (m.find()) {
// Simplest method:
System.out.print(" " + m.group(1) + " " );
System.out.print(" " + m.group(2) + " " );
System.out.print(" " + m.group(3) + " " );
System.out.println(" " + m.group(4));
The expected output was:
srcip=10.100.1.121 dstip=173.193.156.43 srcport=55844 status=close dstport=80
But this is the output I get:
srcip=10.100.1.121 dstip=173.193.156.43 dstip=173.193.156.43 dstport=80
srcip=10.100.1.121 dstip=173.193.156.43 dstip=173.193.156.43 dstport=80
Any suggestions?

The order of your capturing groups doesn't correspond to the order of the fields in the input. Here is a re-ordered version of your regex that catches the 5 groups you need:
String s = "subtype=forward,level=notice,vd=root,srcip=10.100.1.121,srcport=55844,srcintf=port1,dstip=173.193.156.43,dstport=80,dstintf=port16,sessionid=1224203695,status=close";
Pattern p = Pattern.compile("(srcip=(?:\\d+\\.)+\\d+)(?:.*)?(srcport=(?:\\d+))(?:.*)?(dstip=(?:\\d+\\.)+\\d+)(?:.*)?(dstport=(?:\\d+))(?:.*)?(status=(?:.*))");
Matcher m = p.matcher(s);
if (m.find()) {
System.out.println(m.group(1) + " " + m.group(3) + " " + m.group(2) + " " + m.group(5) + " " + m.group(4));
}
Note that I also fixed an unclosed group, and made one of the groups non capturing.

how to filter out some substrings with regex effectively?

i want to filter out srcport and dstport from the input string. here is the code i tried:
String input = "2014<>10.100.2.3<><189>date=2014-01-16,time=11:26:14,devname=B3909601569,devid=B3909601569,logid=000013,type=traffic,srcip=192.168.192.123,srcport=2072,srcintf=port2,dstip=10.180.1.105,dstport=3206,dstintf=port1,sessionid=121543,status=close,policyid=196,service=MYSQL,proto=6,duration=10,sentbyte=3910,rcvdbyte=175085,sentpkt=74,rcvdpkt=132";
Pattern p = Pattern.compile("(srcport=)(\\d+).[\\s]?(dstport=)(\\d+)");
Matcher m = p.matcher(input);
StringBuffer result=new StringBuffer();
while (m.find()) {
System.out.println("Srcport: " + m.group(2) + " & ");
System.out.println("Dstport: " + m.group(4));
}
System.out.println(result);
but its not showing any output. Is there a mistake in the regex
Pattern p = Pattern.compile("(srcport=)(\\d+).[\\s]?(dstport=)(\\d+)");
or the println lines
System.out.println("Srcport: " + m.group(2) + " & ");
System.out.println("Dstport: " + m.group(4));"
any suggestions will be highly appreciated.

See following changes to both the regex and the captured groups:
String input = "2014<>10.100.2.3<><189>date=2014-01-16,time=11:26:14,devname=B3909601569,devid=B3909601569,logid=000013,type=traffic,srcip=192.168.192.123,srcport=2072,srcintf=port2,dstip=10.180.1.105,dstport=3206,dstintf=port1,sessionid=121543,status=close,policyid=196,service=MYSQL,proto=6,duration=10,sentbyte=3910,rcvdbyte=175085,sentpkt=74,rcvdpkt=132";
Pattern p = Pattern.compile("srcport=(\\d+).*?dstport=(\\d+)"); // update regex
Matcher m = p.matcher(input);
StringBuffer result=new StringBuffer();
while (m.find()) {
System.out.println("Srcport: " + m.group(1)); //print groups 1 + 2
System.out.println("Dstport: " + m.group(2));
}
System.out.println(result);

You forgot to use or(|) in your regex
srcport=(\\d+)|dstport=(\\d+)
Your code would be
while (m.find())
{
if(m.group().startsWith("srcport"))
System.out.println("Srcport: " + m.group(1) + " & ");
else
System.out.println("Dstport: " + m.group(1));
}

Try this :
Pattern p = Pattern.compile("srcport=(\\d+)|dstport=(\\d+)");

Try the below code. I have run this in my system and it it working fine.
String input = "2014<>10.100.2.3<><189>date=2014-01-16,time=11:26:14,devname=B3909601569,devid=B3909601569,logid=000013,type=traffic,srcip=192.168.192.123,srcport=2072,srcintf=port2,dstip=10.180.1.105,dstport=3206,dstintf=port1,sessionid=121543,status=close,policyid=196,service=MYSQL,proto=6,duration=10,sentbyte=3910,rcvdbyte=175085,sentpkt=74,rcvdpkt=132";
Pattern p = Pattern.compile("(srcport=)(\\d+)((.*)?)(dstport=)(\\d+)(\\.)*");
Matcher m = p.matcher(input);
StringBuffer result=new StringBuffer();
while (m.find()) {
System.out.println(m.group());
System.out.println("Srcport: " + m.group(2) );
System.out.println("Dstport: " + m.group(6));
}

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