Develop Reference

How to extract a substring from a sentence until a delimeter

Hi I have some string like this:
location/city/home-a-berlin?/someNewAdress
I want to extract word berlin which placed between "-a-" and "?". How can i do that with regex in java?
I can do it by using string API but kinda stuck with regex.
String cityName = url.substring(url.lastIndexOf("-a-")+3, url.indexOf('?')) //berlin

You can use a capture group with a negated character class.
-a-([^\?]+)\?
Regex demo | Java demo
In Java:
String regex = "-a-([^\\?]+)\\?";
String string = "location/city/home-a-berlin?/someNewAdress\n";
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(string);
if (matcher.find()) {
System.out.println(matcher.group(1));
}
Output
berlin

Or
s = s.replaceAll(".*-(.*?)\\?.*", "$1");

Alternative regex:
"-a-(.+?)\\?"
Regex in testbench and context:
public static void main(String[] args) {
String input1 = "location/city/home-a-berlin?/someNewAdress";
List<String> inputs = Arrays.asList(input1);
Pattern pattern = Pattern.compile("-a-(.+?)\\?");
List<String> results = inputs.stream().map(s -> pattern.matcher(s))
.filter(Matcher::find).map(m -> m.group(1)).collect(Collectors.toList());
//Output:
results.forEach(System.out::println);
}
Output:
berlin
Summary of regular-expression constructs:
https://docs.oracle.com/javase/10/docs/api/java/util/regex/Pattern.html

Regex to split the first from a "/token1/token2/token3"

I'm pretty rusty with regex, but I have the requirement to extract the first token of the following string:
Input: /token1/token2/token3
Required output: /token1
I have tried:
List<String> connectorPath = Splitter.on("^[/\\w+]+")
.trimResults()
.splitToList(actionPath);
Doesn't work for me, any ideas?

Instead of split, you can match
^/\\w+
Or if the string has 3 parts, use a capture group for the first part.
^(/\\w+)/\\w+/\\w+$
Java example
Pattern pattern = Pattern.compile("^/\\w+");
Matcher matcher = pattern.matcher("/token1/token2/token3");
if (matcher.find()) {
System.out.println(matcher.group(0));
}
Output
/token1

You can split on the / that is not at the string start using the (?!^)/ regex:
String[] res = "/token1/token2/token3".split("(?!^)/");
System.out.println(res[0]); // => /token1
See the Java code demo and the regex demo.
(?!^) - a negative lookahead that matches a location not at the start of string
/ - a / char.
Using Guava:
Splitter splitter = Splitter.onPattern("(?!^)/").trimResults();
Iterable<String> iterable = splitter.split(actionPath);
String first = Iterables.getFirst(iterable, "");

You are over-complicating it.
Try the following regular expression: ^(\/\w+)(.+)$
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class PathSplitter {
public static void main(String args[]) {
String input = "/token1/token2/token3";
Pattern pattern = Pattern.compile("^(\\/\\w+)(.+)$");
Matcher matcher = pattern.matcher(input);
if (matcher.find()) {
System.out.println(matcher.group(1)); // /token1
System.out.println(matcher.group(2)); // /token2/token3
} else {
System.out.println("NO MATCH");
}
}
}

How to write regEx to get value .4318. from String app.abc.4318.20161017223456.log.gz in Java

I am using below pattern to get four digit number from below string.
Required output is .4318.
public static void main(String args[]) {
String path = "app.xyz.4318.20161017223456.log.gz";
Pattern p = Pattern.compile("(\\d{4})");
Matcher m = p.matcher(path);
if (m.find()) {
System.out.println(m.group(1));
}
}
Output: 4318 but, I need output like .4318.
Please suggest any pattern to get the output as .4318.

Pattern p=Pattern.compile("(\\.\\d{4})");
"\." is an escaped period.

How to preserve delimeters while using String.split() in Java?

String TextValue = "hello{MyVar} Discover {MyVar2} {MyVar3}";
String[] splitString = TextValue.split("\\{*\\}");
What I'm getting output is [{MyVar, {MyVar2, {MyVar3] in splitString
But my requirement is to preserve those delimiters {} i.e. [{MyVar}, {MyVar2}, {MyVar3}].
Required a way to match above output.

Use something like so:
Pattern p = Pattern.compile("(\\{\\w+\\})");
String str = ...
Matcher m = p.matcher(str);
while(m.find())
System.out.println(m.group(1));
Note, the code above is untested but that will look for words within curly brackets and place them in a group. It will then go over the string and output any string which matches the expression above.
An example of the regular expression is available here.

Thanks kelvin & npinti.
import java.util.regex.Pattern;
import java.util.regex.Matcher;
public class CreateMatcherExample {
public static void main(String[] args) {
String TextValue = "hello{MyVar} Discover {My_Var2} {My_Var3}";
String patternString = "\\{\\w+\\}";
Pattern pattern = Pattern.compile(patternString);
Matcher matcher = pattern.matcher(TextValue);
while(matcher.find()) {
System.out.println(matcher.group());
}
}
}

Extracting Number from URL in Java via Regex

Take URL http://www.abc.com/alpha/beta/33445566778899/gamma/delta
i need to return the number 33445566778899 (with forward slashes removed, number is of variable length but between 10 & 20 digits)
Simple enough (or so i thought) except everything I've tried doesn't seem to work but why?
Pattern pattern = Pattern.compile("\\/([0-9])\\d{10,20}\\/");
Matcher matcher = pattern.matcher(fullUrl);
if (matcher.find()) {
return matcher.group(1);
}

Try this one-liner:
String number = url.replaceAll(".*/(\\d{10,20})/.*", "$1");

This regex works -
"\\/(\\d{10,20})\\/"
Testing it-
String fullUrl = "http://www.abc.com/alpha/beta/33445566778899/gamma/delta";
Pattern pattern = Pattern.compile("\\/(\\d{10,20})\\/");
Matcher matcher = pattern.matcher(fullUrl);
if (matcher.find()) {
System.out.println(matcher.group(1));
}
OUTPUT - 33445566778899

Try,
String url = "http://www.abc.com/alpha/beta/33445566778899/gamma/delta";
String digitStr = null;
for(String str : url.split("/")){
System.out.println(str);
if(str.matches("[0-9]{10,20}")){
digitStr = str;
break;
}
}
System.out.println(digitStr);
Output:
33445566778899

Instead of saying it "doesn't seem to work", you should have given use what it was returning. Testing it confirmed what I thought: your code would return 3 for this input.
This is simply because your regexp as written will capture a digit following a / and followed by 10 to 20 digits themselves followed by a /.
The regex you want is "/(\\d{10,20})/" (you don't need to escape the /). Below you'll find the code I tested this with.
public static void main(String[] args) {
String src = "http://www.abc.com/alpha/beta/33445566778899/gamma/delta";
Pattern pattern = Pattern.compile("/(\\d{10,20})/");
Matcher matcher = pattern.matcher(src);
if (matcher.find()) {
System.out.println(matcher.group(1));
}
}