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Java Regex : Extract a specific pattern from a string "I_INSERT_TO_TOPIC_345674_123456_4.json"

I want to extract only "_123456_4" from this string using java Regex.
I_INSERT_TO_TOPIC_345674_123456_4.json
I have tried
Pattern.compile("(_([^_]*_[^_]))") and Pattern.compile("_" + "([^[0-9]]*)" + "_[0-9]") but these do not work.

If you want to get 2 group of digits just before .json then you can use regex group to find the required match. You can modify the pattern as per your requirement.
Pattern p = Pattern.compile("(_\\d+_\\d+)\\.json");
Matcher matcher = p.matcher(s);
if (matcher.find()) {
String group = matcher.group(1);
}

【\_[0-9]\*\_[0-9]\*(?=\\.)】
You can try to see if this works

Regex: how to extract a JSESSIONID cookie value from cookie string?

I might receive the following cookie string.
hello=world;JSESSIONID=sdsfsf;Path=/ei
I need to extract the value of JSESSIONID
I use the following pattern but it doesn't seem to work. However https://regex101.com shows it's correct.
Pattern PATTERN_JSESSIONID = Pattern.compile(".*JSESSIONID=(?<target>[^;\\n]*)");

You can reach your goal with a simpler approach using regex (^|;)JSESSIONID=(.*);. Here is the demo on Regex101 (you have forgotten to link the regular expression using the save button). Take a look on the following code. You have to extract the matched values using the class Matcher:
String cookie = "hello=world;JSESSIONID=sdsfsf;Path=/ei";
Pattern PATTERN_JSESSIONID = Pattern.compile("(^|;)JSESSIONID=(.*);");
Matcher m = PATTERN_JSESSIONID.matcher(cookie);
if (m.find()) {
System.out.println(m.group(0));
}
Output value:
sdsfsf
Of course the result depends on the all of possible variations of the input text. The snippet above will work in every case the value is between JSESSIONID and ; characters.

You can try below regex:
JSESSIONID=([^;]+)
regex explanation
String cookies = "hello=world;JSESSIONID=sdsfsf;Path=/ei;submit=true";
Pattern pat = Pattern.compile("\\bJSESSIONID=([^;]+)");
Matcher matcher = pat.matcher(cookies);
boolean found = matcher.find();
System.out.println("Sesssion ID: " + (found ? matcher.group(1): "not found"));
DEMO

You can even get what you aiming for with Splitting and Replacing the string aswell, below I am sharing which is working for me.
String s = "hello=world;JSESSIONID=sdsfsf;Path=/ei";
List<String> sarray = Arrays.asList(s.split(";"));
String filterStr = sarray.get(sarray.indexOf("JSESSIONID=sdsfsf"));
System.out.println(filterStr.replace("JSESSIONID=", ""));

Getting multiple matches via regex

I want to retrieve a strings from a global string via Matcher & Pattern using REGEX.
String str = "<strong>ABC</strong>123<strong>DEF</strong>"
Pattern pattern = Pattern.compile("<strong>(.*)</strong>");
Matcher matcher = pattern.matcher(str);
My problem is that the matcher gives me just one match that is inside the global tag strong:
ABC</strong>123<strong>DEF
My objective is to get 2 matches:
ABC
DEF
Thank you very match for you help.

You need a non greedy regex:
Pattern pattern = Pattern.compile("<strong>.*?</strong>");
Use ? to specify non greedy. This means it will match the first match it finds instead of the outer most match...
If you only want ABC and DEF then you can do something like this using lookaheads and lookbehinds:
String str = "<strong>ABC</strong>123<strong>DEF</strong>";
Pattern pattern = Pattern.compile("((?<=<strong>).*?(?=</strong>))");
Matcher matcher = pattern.matcher(str);
while(matcher.find())
{
System.out.println(matcher.group());
}
If you do a google search you should be able to find information on lookaheads and lookbehinds...

I recommend to use JSOUP to parse your HTML code instead of regex as
Document doc = Jsoup.parse("<strong>ABC</strong>123<strong>DEF</strong>");
// select your tag
Elements elements = doc.select("strong");
// get the iterator to traverse all elements
Iterator<Element> it = elements.iterator();
// loop through all elements and fetch their text
while (it.hasNext()) {
System.out.println(it.next().text());
}
Output :
ABC
DEF
or get Output as single string
Document doc = Jsoup.parse("<strong>ABC</strong>123<strong>DEF</strong>");
Elements elements = doc.select("strong");
System.out.println(elements.text());
Output:
ABC DEF
Download Jsoup and add it as a dependency

How to remove an id out of a path using a Java Regex?

I am trying to get rid of an "id" in URI paths and I can only use Java regex transformation.
The paths look like this:
/web/service/1223345/add
/web/service/1223345/delete
/web/service/v2/1223345/add
/web/service/1223345
/web/service/do
The id is always a series of numbers. In the example above it is "1223345".
I have tried a couple of regexes but none of them worked. Here are my tries:
(/\w.*)/?[0-9]*/(.*)
([^0-9]+){0,}
(/.*/)[0-9]*(/.*)
Thanks for your help

String input = "/web/service/1223345/add";
System.out.println(input.replaceAll("/\\d*/","/"));
Output:
/web/service/add

If you are after removing id, you could do the following:
String input = "/web/service/v2/1223345/add";
String removed = input.replaceAll("/\\d*/?", "/");
System.out.println(removed);
Note that arnoud's regex "/\d*/" will not work for e.g. /web/service/1223345.
Question mark at the end of the regex takes care of such cases: "/\d*/?"
If on the other hand you are after extracting id:
Pattern pattern = Pattern.compile(".*?/(\\d*?)(/.*)?$");
Matcher matcher = pattern.matcher(input);
if (matcher.find()) {
String id = matcher.group(1);
System.out.println(id);
}

How to extract word from string?

Suppose I have a string:
String message = "you should try http://google.com/";
Now, I want to send "http://google.com/" to a new
String url
What I want to do is:
check if a "word" in the string begins with "http://" and extract that word, where a word is
something that's surrounded by spaces (general english definition of word).
I have no idea how to extract the string, and the best I can do is use startsWith on the string. How to I use startsWith on a word, and extract the word?
Sorry if this is a little bit difficult to explain.
Thanks in advance!
EDIT: Also, what should I do to extract the word from the REGEX operation? And how should I handle it if there is more than 1 url in the string?

Use Pattern & Matcher classes.
String str = "blabla http://www.mywebsite.com blabla";
String regex = "((https?:\\/\\/)?(www.)?(([a-zA-Z0-9-]){2,}\\.){1,4}([a-zA-Z]){2,6}(\\/([a-zA-Z-_/.0-9#:+?%=&;,]*)?)?)";
Matcher m = Pattern.compile(regex).matcher(str);
if (m.find()) {
String url = m.group(); //value "http://www.mywebsite.com"
}
This regex will work for http://..., https://... and even www... URLs. Others regex can be easily found on the net.

You can try this:
String str = "blabla http://www.mywebsite.com blabla";
Matcher m = Pattern.compile("(http://.*)").matcher(str);
if (m.find()) {
String url = (new StringTokenizer(m.group(), " ")).nextToken();
}

The "correct" way to perform this task is to split the String by whitespace -- String#split("\s") -- and then pipe it to the URL constructor. If the string starts with your prefix and a MalformedURLException is thrown it is invalid. The URL class constructor is far better tested and more robust than any solution that you or I could come up with. So, use it, please and don't reinvent the wheel.

You can use Java Regex for this:
The following regex catches any string starting with http:// or https:// till the next whitespace character:
Pattern urlPattern = Pattern.compile("(http(s)?://[.^[\\S]]*)");
Matcher matcher = compile.matcher(myString);
if (matcher.find()) {
String url = matcher.group();
}