Using Regular Expressions to Extract a Value in Java

Using Regular Expressions to Extract a Value in Java

Full example:

private static final Pattern p = Pattern.compile("^([a-zA-Z]+)([0-9]+)(.*)");
public static void main(String[] args) {
    // create matcher for pattern p and given string
    Matcher m = p.matcher("Testing123Testing");

    // if an occurrence if a pattern was found in a given string...
    if (m.find()) {
        // ...then you can use group() methods.
        System.out.println(m.group(0)); // whole matched expression
        System.out.println(m.group(1)); // first expression from round brackets (Testing)
        System.out.println(m.group(2)); // second one (123)
        System.out.println(m.group(3)); // third one (Testing)
    }
}

Since you're looking for the first number, you can use such regexp:

^\D+(\d+).*

and m.group(1) will return you the first number. Note that signed numbers can contain a minus sign:

^\D+(-?\d+).*

How to Extract a Value from string Using Regular Expressions

Use String.split instead of regex:

String[] split = input.split(',');
String pos16 = split[15];

In case you do want to use regex, match using this and get groups 1 and 2:

Matcher m = Pattern.compile("(?:[^,]*,){15}([^,]*),([^,]*)").matcher(input);
m.find();
String pos16 = m.group(1);

Using Regular Expressions to Extract specific Values in Java

You can use regex groups:

Pattern pattern = Pattern.compile("for user (\\w+)");
Matcher matcher = pattern.matcher(s);
if (matcher.find()) {
    System.out.println(matcher.group(1));
}

The pair of parenthesis ( and ) forms a group that can be obtained by the matcher using group method (as it's the first parenthesis, it's group 1).

\w means a "word character" (letters, numbers and _) and + means "one or more ocurrences". So \w+ means basically "a word" (assuming your username has only these characters). PS: note that I had to escape \, so the resulting expression is \\w+.

The ouput of this code is:

username

---

If you want to match all the values (websiteName, userAgentNameWithSpaces and so on), you could do the following:

Pattern pattern = Pattern.compile("Rendering content from (.*) using user agent (.*) ; for user (.*) ; at time (.*)");
Matcher matcher = pattern.matcher(s);
if (matcher.find()) {
    System.out.println(matcher.group(1));
    System.out.println(matcher.group(2));
    System.out.println(matcher.group(3));
    System.out.println(matcher.group(4));
}

The output will be:

websiteNAme
userAgentNameWithSpaces
username
someTime

Note that if userAgentNameWithSpaces contains spaces, \w+ won't work (because \w doesn't match spaces), so .* will work in this case.

---

But you can also use [\w ]+ - the brackes [] means "any of the characters inside me", so [\w ] means "a word character, or a space" (note that there's a space between w and ]. So the code would be (testing with a username with spaces):

String s = "Rendering content from websiteNAme using user agent userAgent Name WithSpaces ; for user username ; at time someTime";
Pattern pattern = Pattern.compile("Rendering content from (.*) using user agent ([\\w ]+) ; for user (.*) ; at time (.*)");
Matcher matcher = pattern.matcher(s);
if (matcher.find()) {
    System.out.println(matcher.group(1));
    System.out.println(matcher.group(2));
    System.out.println(matcher.group(3));
    System.out.println(matcher.group(4));
}

And the output will be:

websiteNAme
userAgent Name WithSpaces
username
someTime

---

Note: you can test if the groups were matched before calling matcher.group(n). The method matcher.groupCount() returns how many groups were matched (because if you call matcher.group(n) and group n is not available, you'll get an IndexOutOfBoundsException)

How to extract a substring using regex

Assuming you want the part between single quotes, use this regular expression with a Matcher:

"'(.*?)'"

Example:

String mydata = "some string with 'the data i want' inside";
Pattern pattern = Pattern.compile("'(.*?)'");
Matcher matcher = pattern.matcher(mydata);
if (matcher.find())
{
    System.out.println(matcher.group(1));
}

Result:

the data i want

Using Java regex : extract a portion of text from another String

Assuming that you are certain you can isolate your input text to the starting string in your question, you might be able to use a regex String#replaceAll one-liner approach:

String input = "<%= @my_secrets['/abc/PQ-XYZ/1234/'] %>";
if (input.matches("<%= @my_secrets\\['.*'\\] %>")) {
    String output = input.replaceAll(".*'(.*?)'.*", "$1");
    System.out.println(output);  // /abc/PQ-XYZ/1234/
}
else {
    System.out.println("input does not match required format");
}

How to extract parameter and values from a string using regex

You can use the following :

String str = "((created_date{[1976-03-06T23:59:59.999Z TO *]}|1))";
String patt = "\\(\\(([^{]+)\\{\\[([^ ]+) TO ([^]]+)]}\\|([01])\\)\\)";
Pattern p = Pattern.compile(patt);
Matcher m = p.matcher(str);
if (m.matches()) {
    System.out.println(m.group(1));
    System.out.println(m.group(2));
    System.out.println(m.group(3));
    System.out.println(m.group(4));
}

Try it here !

Note that you need to invoke a Matcher's find(), matches() or more rarely lookingAt() before you can use most of its other methods, including the toMatchResult() you were trying to use.

---

Related Topics