How to retrieve JSON array values from a string with regex in Java

Question

I need to get values from a string with a JSON array using regex String example:

[INFO][2022-11-11] Response body : 
{
   "values":[
      "abc123",
      "def456",
      "xyz789"
   ]
}

So I want to get the values: abc123, def456, xyz789

Please note I'm working with a string (actually it's a log output) so I'm not sure if I can use any libraries for JSON parsing

I'm trying to use the following regex, but getting only the last array value xyz789:

"values"\s*:\s*\[(\s*"(\w+)"\s*,?)*]

My solution in Java

String pattern = "\"values\"\\s*:\\s*\\[(\\s*\"(\\w+)\"\\s*,?)*]" ;

Matcher matcher = Pattern.compile(pattern).matcher(source());
while (matcher.find()) {
    System.out.println("matcher.group() = " + matcher.group());
    System.out.println("matcher.group(1) = " + matcher.group(1));
    System.out.println("matcher.group(1) = " + matcher.group(2)); //xyz789
}

private static String source() {
    String s = "{\"values\": [\n"
            + "        \"abc123\",        \"def456\",      "
            + "          \"xyz789\" ]\n"
            + "    }";

    return s;
}

Your solution should be based on a JSON Framework like Jackson or JAX-RS. — Christoph Dahlen
– Christoph Dahlen, Commented Nov 10, 2022 at 17:11

Alexander Ivanchenko · Accepted Answer · 2022-11-10 19:02:22Z

1

Example with Jackson

It can be done almost effortlessly if you would use a library for parsing JSON, like Jackson, Gson, etc., instead of trying to reinvent the wheel.

Here's an example of how it can be done using Jackson.

Assume you have the following POJO:

public class MyPojo {
    private List<String> values;
    
    // getters, setters
}

That's all you need to deserialize the incoming JSON:

String jsonStr = // incoming JSON

ObjectMapper mapper = new JsonMapper();
        
MyPojo pojo = mapper.readValue(jsonStr, MyPojo.class);
System.out.println(pojo.getValues());

Output:

[abc123, def456, xyz789]

More over, if you would use platforms like Spring, or Jakarta EE conversion of requests and responses would be done automatically for you.

If the data is dynamic and introducing a POJO doesn't make much sense, then you can parse it as a Tree, and work with Nodes of that Tree:

String jsonStr = // incoming JSON
        
ObjectMapper mapper = new JsonMapper();
JsonNode node = mapper.readTree(jsonStr).get("values");
List<String> values = mapper.readerFor(new TypeReference<List<String>>() {}).readValue(node);

values.forEach(System.out::println);

Output:

abc123
def456
xyz789

Parsing Manually

If you want to do it manually at all costs, here is a way to extract these values by capturing the JSON-array and splitting it:

String jsonStr = // incoming JSON
        
Pattern pattern1 = Pattern.compile("\"values\"\\s*:\\s*\\[(.+)]");
Matcher matcher = pattern1.matcher(jsonStr);
        
List<String> values = List.of();
        
if (matcher.find()) {
    values = Arrays.stream(matcher.group(1).split(","))
        .map(s -> s.replaceAll("\"", "").strip())
        .toList();
}
        
values.forEach(System.out::println);

Output:

abc123
def456
xyz789

edited Nov 10, 2022 at 19:02

answered Nov 10, 2022 at 18:47

Alexander Ivanchenko

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2 Comments

dykovo Over a year ago

Thanks a lot! Finally, I've used this pattern to extract an array entry: \"values\"\s*:\s*\[([\s\n\"\w\,]*)\]

Alexander Ivanchenko Over a year ago

@dykovo You are welcome, by the way a closing square bracket ] doesn't need to be escaped, it required only for opening bracket \[.

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Example with Jackson

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