正确的正则表达式

Question

I'm using Java Regex to read String of the type

"{\n  'Step 1.supply.vendor1.quantity':\"80"\,\n
      'Step 2.supply.vendor2.quantity':\"120"\,\n
      'Step 3.supply.vendor3.quantity':\"480"\,\n
      'Step 4.supply.vendor4.quantity':\"60"\,\n}"

I have to detect strings of type

'Step 2.supply.vendor2.quantity':\"120"\,\n.

I'm trying to use pattern and matcher of regex but I'm not able to figure out the correct regular expression for lines like

 <Beginning of Line><whitespace><whitespace><'Step><whitespace><Number><.><Any number & any type of characters><,\n><EOL>.

The <Beginning of Line> and <EOL> I have used for clarification purpose.

I have tried several patterns

String regex = "(\\n\\s{2})'Step\\s\\d.*,\n";
String regex = "\\s\\s'Step\\s\\d.*,\n";

I always get IllegalStateException : No match found .

I'm not able to find proper material to read on Java Regex with good examples. Any help would be really great. Thanks.

Answer 1

As the others said in the comments, you should really use a JSON Parser.

But if you want to see how it could work with a regex, here is how you can do it :

• Take an example of a line you want to capture : Step 1.supply.vendor1.quantity':"80"
• Replace digits with \\\\d* ( \\\\d matches any digit)
• Replace dots with \\\\. (dots need to be escaped)
• Add some parenthesis around the parts that you want to capture

Here is the resulting regex : "Step (\\\\d*)\\\\.supply\\\\.vendor(\\\\d*)\\\\.quantity':\\"(\\\\d*)\\""

Now, use a Regex and a Matcher :

String input = "{\n  'Step 1.supply.vendor1.quantity':\"80\"\\,\n";
Pattern pattern = Pattern.compile("Step (\\d*)\\.supply\\.vendor(\\d*)\\.quantity':\"(\\d*)\"");
Matcher matcher = pattern.matcher(input);
while(matcher.find()) {
  System.out.println(matcher.group(1));
  System.out.println(matcher.group(2));
  System.out.println(matcher.group(3));
}

Output :

1 //(corresponds to "Step (\\d*)")
1 //(corresponds to "vendor(\\d*)")
80 //(corresponds to "quantity':\"(\\d*)")