Java - 使用多正则表达式从字符串中提取 JSON 值

Question

I am trying to use this multi regex java library to extract JSON field value from a string.

My JSON look like this:

{
  "field1": "something",
  "field2": 13
  "field3": "some"
}

I have created a regex pattern to fit each field, and it is working with Java Regex Pattern by simply doing something like this for each pattern:

Matcher matcher = patternToSearch.matcher(receiveData);
        if (matcher.find()) {
            return matcher.group(1);
        }

I decided to try and improve the code and use multi regex so instead of scanning the string 3 times, it will scan it only one time and extract all needed values.

So I came up with something like this:

String[] patterns = new String[]{
                    "\"field1\":\\s*\"(.*?)\"",
                    "\"field2\":\\s*(\\d+)(\\.\\d)?",
                    "\"field3\":\\s*\"(.*?)\"",
            };
            this.matcher = MultiPattern.of(patterns).matcher();

the matcher has only one method - match - used like this:

int[] match = this.matcher.match(jsonStringToScan);

so I ended up with a list of integers, but I have no idea how to get the json values from these strings and how those integers are helping me. The multi regex matcher does not support the group method I used before to get the value.

Any idea of how I can extract multiple json values from string using multi regex? (Scanning string only once)

Answer 1

As mentioned on github page from your link match returnes indexes of patterns matched. Another point from this page:

The library does not handle groups.

Consider matching key as group too. Look at this simple example:

    final Pattern p = Pattern.compile("\"(field.)\":((?:\".*?\")|(?:\\d+(?:\\.\\d+)?))");
    final Matcher m = p.matcher("{\"field3\":\"hi\",\"field2\":100.0,\"field1\":\"hi\"}");
    while (m.find()) {
        for (int i = 1; i <= m.groupCount(); i++) {
            System.out.print(m.group(i) + " ");
        }
        System.out.println();
    }

It prints:

field3 "hi" 
field2 100.0 
field1 "hi" 

If you want to avoid quotes in value group, you need more complicated logic. I've stopped at:

        final Pattern p = Pattern.compile("\"(field.)\":(?:(?:\"(.*?(?=\"))\")|(\\d+(?:\\.\\d+)?))");

resulting in

field3 hi null 
field2 null 100.0 
field1 hi null