Java regex using pattern matcher not returning correctly?

Question

I have to get index value from the following string:

Home.number[12].parent.

I want to get back value of 12.

Here is what I tried:

//escape . / [ ]
 private static final String pattern = "Home\\.number\\[([0-9]*)\\]*";
 private static final Pattern addressPattern = Pattern.compile(pattern);

   private static int getIndex(String input, Pattern pattern){

        Matcher m = pattern.matcher(input);
        if (m.matches()){
        return Integer.valueOf(m.group(2));
        }
        return -1;
    }

    public static void main(String[] args){

    System.out.println(getIndex("Home.number[123].parent", addressPattern);
    System.out.println(getIndex("Home.number[456].child", addressPattern);   
}

I get back -1 for both, meaning no match is found.

Using the debugger, I found that m.matches() is returning false. I am unable to figure out why.

P.S: I also tried using Pattern.quote("Home.number[([0-9]*])*") and StringUtils.EscapeJava("Home.number[([0-9]*)]*"). Both are not returning any matching results.

Elliott Frisch · Accepted Answer · 2015-07-09 00:06:16Z

3

Your Pattern should look something like

private static final String pattern = "Home\\.number\\[(\\d+)\\]\\..*";
private static final Pattern addressPattern = Pattern.compile(pattern);

And your matcher only has 1 group.

private static int getIndex(String input, Pattern pattern) {
    Matcher m = pattern.matcher(input);
    if (m.matches()) {
        return Integer.parseInt(m.group(1));
    }
    return -1;
}

And you need to close the second paren in your calls in main. Something like

public static void main(String[] args) {
    System.out.println(getIndex("Home.number[123].parent", addressPattern));
    System.out.println(getIndex("Home.number[456].child", addressPattern));
}

When I make those changes I get the expected

123
456

edited Jul 9, 2015 at 0:06

answered Jul 8, 2015 at 23:45

Elliott Frisch

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4 Comments

brain storm Over a year ago

is there no need to escape the dot in "Home.number"?

MT0 Over a year ago

Escaping the dot does work - if you don't escape it then you can match HomeXnumber[123].cousin

brain storm Over a year ago

what you suggested worked fine. I had two issues. one is espacing the dot and missing dot in the end for "].*". Thanks a ton

MT0 Over a year ago

You want the last dot to be unescaped (since it needs to match the rest of the string) but the first one needs to be escaped (since you want to match a full stop not any character). Either Home\\.number\\[(\\d+)\\].* or Home\\.number\\[(\\d+)\\]\\..* will match.

MT0 · Accepted Answer · 2015-07-09 00:04:06Z

1

Change the pattern from: "Home\\.number\\[([0-9]*)\\]*" to "Home\\.number\\[([0-9]+)\\].*" (adding the dot before the last *)
Change the group to #1: return Integer.valueOf(m.group(1));
Add closing brackets to the System.out.println() calls.

Like this:

private static final String pattern = "Home\\.number\\[([0-9]*)\\].*";
private static final Pattern addressPattern = Pattern.compile(pattern);

private static int getIndex(String input, Pattern pattern){
  Matcher m = pattern.matcher(input);
  if (m.matches()){
    return Integer.valueOf(m.group(1));
  }
  return -1;
}

public static void main( String[] args ){
  System.out.println(getIndex("Home.number[123].parent", addressPattern));
  System.out.println(getIndex("Home.number[456].child", addressPattern));   
}

edited Jul 9, 2015 at 0:04

answered Jul 8, 2015 at 23:45

MT0

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2 Comments

brain storm Over a year ago

i am passing as method parameter. so it is fine

user4910279 Over a year ago

This code fails in case of Home.number[].parent. [0-9]* -> [0-9]+ or \\d+

Bohemian · Accepted Answer · 2015-07-09 00:25:21Z

1

If you remove everything except what between the square brackets, you can do it in one line:

private static int getIndex(String input) {
    return input.matches(".*\\[\\d+].*") ? -1 : Integer.parseInt(input.replaceAll(".*\\[|].*", ""));
}

edited Jul 9, 2015 at 0:25

answered Jul 8, 2015 at 23:59

Bohemian♦

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1 Comment

Bohemian Over a year ago

@MTO hmmm. good point. I've replace changed the regex to leave only what's between the brackets, and I'm also checking there are only numbers between brackets.

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