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Why matcher.find() for input parameter always return 'false'?

I have a strange situation which I find difficult to understand regarding regex matcher.
When I pass the next input parameter issueBody to the matcher, the matcher.find() always return false, while passing a hard-coded String with the same value as the issueBody - it works as expected.
The regex function:
private Map<String, String> extractCodeSnippet(Set<String> resolvedIssueCodeLines, String issueBody) {
String codeSnippetForCodeLinePattern = "\\(Line #%s\\).*\\W\\`{3}\\W+(.*)(?=\\W+\\`{3})";
Map<String, String> resolvedIssuesMap = new HashMap<>();
for (String currentResolvedIssue : resolvedIssueCodeLines) {
String currentCodeLinePattern = String.format(codeSnippetForCodeLinePattern, currentResolvedIssue);
Pattern pattern = Pattern.compile(currentCodeLinePattern, Pattern.MULTILINE);
Matcher matcher = pattern.matcher(issueBody);
while (matcher.find()) {
resolvedIssuesMap.put(currentResolvedIssue, matcher.group());
}
}
return resolvedIssuesMap;
}
The following always return false
Pattern pattern = Pattern.compile(currentCodeLinePattern, Pattern.MULTILINE);
Matcher matcher = pattern.matcher(issueBody);
While the following always return true
Pattern pattern = Pattern.compile(currentCodeLinePattern, Pattern.MULTILINE);
Matcher matcher = pattern.matcher("**SQL_Injection** issue exists # **VB_3845_112_lines/encode.frm** in branch **master**\n" +
"\n" +
"Severity: High\n" +
"\n" +
"CWE:89\n" +
"\n" +
"[Vulnerability details and guidance](https://cwe.mitre.org/data/definitions/89.html)\n" +
"\n" +
"[Internal Guidance](https://checkmarx.atlassian.net/wiki/spaces/AS/pages/79462432/Remediation+Guidance)\n" +
"\n" +
"[ppttx](http://WIN2K12-TEMP/bbcl/ViewerMain.aspx?planid=1010013&projectid=10005&pathid=1)\n" +
"\n" +
"Lines: 41 42 \n" +
"\n" +
"---\n" +
"[Code (Line #41):](null#L41)\n" +
"```\n" +
" user_name = txtUserName.Text\n" +
"```\n" +
"---\n" +
"[Code (Line #42):](null#L42)\n" +
"```\n" +
" password = txtPassword.Text\n" +
"```\n" +
"---\n");
My question is - why? what is the difference between the two statements?

TL;DR:
By using Pattern.UNIX_LINES, you tell Java regex engine to match with . any char but a newline, LF. Use
Pattern pattern = Pattern.compile(currentCodeLinePattern, Pattern.UNIX_LINES);
In your hard-coded string, you have only newlines, LF endings, while your issueBody most likely contains \r\n, CRLF endings. Your pattern only matches a single non-word char with \W (see \\W\\`{3} pattern part), but CRLF consists of two non-word chars. By default, . does not match line break chars, so it does not match neither \r, CR, nor \n, LF. The \(Line #%s\).*\W\`{3} fails right because of this:
\(Line #%s\) - matches (Line #<NUMBER>)
.* - matches 0 or more chars other than any line break char (up to CR or CRLF)
\W - matches a char other than a letter/digit/_ (so, only \r or \n)
\`{3} - 3 backticks - these are only matched if there was a \n ending, not \r\n (CRLF).
Again, by using Pattern.UNIX_LINES, you tell Java regex engine to match with . any char but a newline, LF.
BTW, Pattern.MULTILINE only makes ^ match at the start of each line, and $ to match at the end of each line, and since there are neither ^, nor $ in your pattern, you may safely discard this option.

Regex only matches once

I have the following regex that matches only once:
Matcher m = Pattern.compile("POLYGON\\s\\(\\((([0-9]*\\.[0-9]+)\\s([0-9]*\\.[0-9]+),?)+\\)\\)")
.matcher("POLYGON ((12.789754538957263 36.12443963532555,12.778550292768816 36.089875458584984,12.77760353347314 36.12427601168043))");
while (m.find()) {
System.out.println("-> " + m.group(2) + " - " + m.group(3));
}
But it only prints the first match:
-> 12.789754538957263 - 36.12443963532555
Why does it not match the other coordinates?
I want to print a new line for each pair of coordinates, e.g.
12.789754538957263 - 36.12443963532555
12.778550292768816 - 36.089875458584984
12.77760353347314 - 36.12427601168043

Your regex should look like this (\[0-9\]*\.\[0-9\]+)\s(\[0-9\]*\.\[0-9\]+)
String input = ...
Matcher m = Pattern.compile("([0-9]*\\.[0-9]+)\\s([0-9]*\\.[0-9]+)").matcher(input);
while (m.find()) {
System.out.println("-> " + m.group(1) + " - " + m.group(2));
}
Outputs
-> 12.789754538957263 - 36.12443963532555
-> 12.778550292768816 - 36.089875458584984
-> 12.77760353347314 - 36.12427601168043
If you want to make sure that the input should between POLYGON (( .. )) you can use replaceAll to extract that inputs :
12.789754538957263 36.12443963532555,12.778550292768816 36.089875458584984,12.77760353347314 36.12427601168043
Your code should be :
.matcher(input.replaceAll("POLYGON \\(\\((.*?)\\)\\)", "$1"));
Instead of :
.matcher(input);
Solution 2
After analysing your problem, I think you need just this :
Stream.of(input.replaceAll("POLYGON \\(\\((.*?)\\)\\)", "$1").split(","))
.forEach(System.out::println);

You could still check if your input begins with a certain string like the following.
I'd use the following regex to do the check : (\[\\d.\]+)\\s(\[\\d.\]+)
It searches for sequences of digits or points separated by a space.
String input = ...
if (input.startsWith("POLYGON")) {
Matcher m = Pattern.compile("([\\d.]+)\\s([\\d.]+)").matcher(input);
while (m.find()) {
System.out.println("-> " + m.group(1) + " - " + m.group(2));
}
}

Nested/Repeated Group in Regex

I have to parse a multi line string and retrieve the email addresses in a specific location.
And I have done it using the below code:
String input = "Content-Type: application/ms-tnef; name=\"winmail.dat\"\r\n"
+ "Content-Transfer-Encoding: binary\r\n" + "From: ABC aa DDD <aaaa.b#abc.com>\r\n"
+ "To: DDDDD dd <sssss.r#abc.com>\r\n" + "CC: Rrrrr rrede <sssss.rv#abc.com>, Dsssssf V R\r\n"
+ " <dsdsdsds.vr#abc.com>, Psssss A <pssss.a#abc.com>, Logistics\r\n"
+ " <LOGISTICS#abc.com>, Gssss Bsss P <gdfddd.p#abc.com>\r\n"
+ "Subject: RE: [MyApps] (PRO-34604) PR for Additional Monitor allocation [CITS\r\n"
+ " Ticket:258849]\r\n" + "Thread-Topic: [MyApps] (PRO-34604) PR for Additional Monitor allocation\r\n"
+ " [CITS Ticket:258849]\r\n" + "Thread-Index: AQHRXMJHE6KqCFxKBEieNqGhdNy7Pp8XHc0A\r\n"
+ "Date: Mon, 1 Feb 2016 17:56:17 +0530\r\n"
+ "Message-ID: <B7F84439E634A44AB586E3FF2EA0033A29E27E47#JETWINSRVRPS01.abc.com>\r\n"
+ "References: <JA.101.1453963700000#myapps.abc.com>\r\n"
+ " <JA.101.1453963700000.978.1454311765375#myapps.abc.com>\r\n"
+ "In-Reply-To: <JIRA.450101.1453963700000.978.1454311765375#myapps.abc.com>\r\n"
+ "Accept-Language: en-US\r\n" + "Content-Language: en-US\r\n" + "X-MS-Has-Attach:\r\n"
+ "X-MS-Exchange-Organization-SCL: -1\r\n"
+ "X-MS-TNEF-Correlator: <B7F84439E634A44AB586E3FF2EA0033A29E27E47#JETWINSRVRPS01.abc.com>\r\n"
+ "MIME-Version: 1.0\r\n" + "X-MS-Exchange-Organization-AuthSource: TURWINSRVRPS01.abc.com\r\n"
+ "X-MS-Exchange-Organization-AuthAs: Internal\r\n" + "X-MS-Exchange-Organization-AuthMechanism: 04\r\n"
+ "X-Originating-IP: [1.1.1.7]";
Pattern pattern = Pattern.compile("To:(.*<([^>]*)>).*Message-ID", Pattern.DOTALL);
Matcher matcher = pattern.matcher(input);
while (matcher.find()) {
Pattern innerPattern = Pattern.compile("<([^>]*)>");
Matcher innerMatcher = innerPattern.matcher(matcher.group(1));
while (innerMatcher.find()) {
System.out.println("-->:" + innerMatcher.group(1));
}
}
Here it works fine. I'm first grouping the part from To till the Message which is the required part. And then I have another grouping to extract the email ids.
Is there any better way to do this? Can we do it with one pattern matcher set?
Update:
This is the expected output:
-->:sssss.r#abc.com
-->:sssss.rv#abc.com
-->:dsdsdsds.vr#abc.com
-->:pssss.a#abc.com
-->:LOGISTICS#abc.com
-->:gdfddd.p#abc.com

Ideally, you could have used lookarounds:
(?<=To:.*)<([^>]+)>(?=.*Message-ID)
Visualization by Debuggex
Unfortunately, Java doesn't support variable length in lookbehinds. A workaround could be:
(?<=To:.{0,1000})<([^>]+)>(?=.*Message-ID)

I think you are looking for all the emails inside <...> that come after To: and before Message-ID. So, you may use a \G based regex for one pass:
Pattern pt = Pattern.compile("(?:\\bTo:|(?!^)\\G).*?<([^>]*)>(?=.*Message-ID)", Pattern.DOTALL);
Matcher m = pt.matcher(input);
while (m.find()) {
System.out.println(m.group(1));
}
See IDEONE demo and a regex demo
The regex matches:
(?:\\bTo:|(?!^)\\G) - a leading boundary, either To: as a whole word or the location after the previous successful match
.*? - any characters, any number of occurrences up to the first
<([^>]*)> - substring starting with < followed with zero or more characters other than > (Group 1) and followed with a closing >
(?=.*Message-ID) - a positive lookahead that makes sure there is Message-ID somewhere ahead of the current match.

Java how to setup regex for this string

So I'm trying to pull two strings via a matcher object from one string that is stored in my online databases.
Each string appears after s:64: and is in quotations
Example s:64:"stringhere"
I'm currently trying to get them as so but any regex that I've tried has failed,
Pattern p = Pattern.compile("I don't know what to put as the regex");
Matcher m = p.matcher(data);
So with that said, all I need is the regex that will return the two strings in the matcher so that m.group(1) is my first string and m.group(2) is my second string.

Try this regex:-
s:64:\"(.*?)\"
Code:
Pattern pattern = Pattern.compile("s:64:\"(.*?)\"");
Matcher matcher = pattern.matcher(YourStringVar);
// Check all occurance
int count = 0;
while (matcher.find() && count++ < 2) {
System.out.println("Group : " + matcher.group(1));
}
Here group(1) returns the each match.
OUTPUT:
Group : First Match
Group : Second Match
Refer LIVE DEMO

String data = "s:64:\"first string\" random stuff here s:64:\"second string\"";
Pattern p = Pattern.compile("s:64:\"([^\"]*)\".*s:64:\"([^\"]*)\"");
Matcher m = p.matcher(data);
if (m.find()) {
System.out.println("First string: '" + m.group(1) + "'");
System.out.println("Second string: '" + m.group(2) + "'");
}
prints:
First string: 'first string'
Second string: 'second string'

Regex you need should be compile("s:64:\"(.*?)\".*s:64:\"(.*?)\"")

How can I recognize the indefinite articles "a" or "an"?

My task is to devise a regular expression that will recognize the indefinite article in English – the word “a” or “an” i.e. to write a regular expression to identify the word a or the word an. I must test the expression by writing a test driver which reads a file containing approximately ten lines of text. Your program should count the occurrences of the words “a” and “an”. I shall not match the characters a and an in words such as than.
This is my code so far:
import java.io.IOException;
import java.util.Arrays;
import java.util.regex.Pattern;
import java.util.regex.Matcher;
public class RegexeFindText {
public static void main(String[] args) throws IOException {
// Input for matching the regexe pattern
String file_name = "Testing.txt";
ReadFile file = new ReadFile(file_name);
String[] aryLines = file.OpenFile();
String asString = Arrays.toString(aryLines);
// Regexe to be matched
String regexe = ""; //<<--this is where the problem lies
int i;
for ( i=0; i < aryLines.length; i++ ) {
System.out.println( aryLines[ i ] ) ;
}
// Step 1: Allocate a Pattern object to compile a regexe
Pattern pattern = Pattern.compile(regexe);
//Pattern pattern = Pattern.compile(regexe, Pattern.CASE_INSENSITIVE);
// case- insensitive matching
// Step 2: Allocate a Matcher object from the compiled regexe pattern,
// and provide the input to the Matcher
Matcher matcher = pattern.matcher(asString);
// Step 3: Perform the matching and process the matching result
// Use method find()
while (matcher.find()) { // find the next match
System.out.println("find() found the pattern \"" + matcher.group()
+ "\" starting at index " + matcher.start()
+ " and ending at index " + matcher.end());
}
// Use method matches()
if (matcher.matches()) {
System.out.println("matches() found the pattern \"" + matcher.group()
+ "\" starting at index " + matcher.start()
+ " and ending at index " + matcher.end());
} else {
System.out.println("matches() found nothing");
}
// Use method lookingAt()
if (matcher.lookingAt()) {
System.out.println("lookingAt() found the pattern \"" + matcher.group()
+ "\" starting at index " + matcher.start()
+ " and ending at index " + matcher.end());
} else {
System.out.println("lookingAt() found nothing");
}
}
}
What do I have to use to find those words within my text?

Here's the regex that will match "a" or "an":
String regex = "\\ban?\\b";
Let's break that regex down:
\b means word boundary (a single back slash is written as "\\" in java)
a is simply a literal "a"
n? means zero or one literal "n"