Matching specific YAML format patterns with Java regular expressions

01 Oct 2023

YAML

YAML (YAML Ain’t Markup Language) is a popular human-readable data serialization format. It is often used for configuration files and data interchange between programming languages. In this blog post, we will explore how to match specific patterns in YAML using Java regular expressions.

Regular expressions (regex) are a powerful tool for pattern matching in strings. Java provides the java.util.regex package, which includes classes and methods to work with regular expressions.

Finding key-value pairs in YAML

YAML data consists of key-value pairs, where the key and value are separated by a colon (:). To find and extract key-value pairs from a YAML string, we can use the following regular expression pattern:

String yamlData = "your YAML data here";
String pattern = "\\b(\\w+):(.*?)(?=\\w+:|\\Z)";
Pattern regexPattern = Pattern.compile(pattern, Pattern.DOTALL);
Matcher matcher = regexPattern.matcher(yamlData);

while (matcher.find()) {
    String key = matcher.group(1).trim();
    String value = matcher.group(2).trim();

    // Process the key-value pair
    // ...
}

Explanation of the regex pattern:

\\b(\\w+) matches a word character (alphanumeric or underscore) as the key
: matches the colon separator
(.*?) matches any characters (the value) lazily until the next key or the end of the document
(?=\\w+:|\\Z) is a positive lookahead assertion to ensure the match stops at the next key or the end of the document

Extracting YAML sequences

YAML supports sequences, which are represented as a list of items enclosed in square brackets ([]). To extract the items from a YAML sequence, we can use the following regular expression pattern:

String yamlData = "your YAML data here";
String pattern = "\\[(.*?)\\]";
Pattern regexPattern = Pattern.compile(pattern, Pattern.DOTALL);
Matcher matcher = regexPattern.matcher(yamlData);

while (matcher.find()) {
    String sequenceItems = matcher.group(1).trim();
    
    // Process each item in the sequence
    String[] items = sequenceItems.split(",");
    for (String item : items) {
        // Process the item
        // ...
    }
}

Explanation of the regex pattern:

\\[ matches the opening square bracket
(.*?) matches any characters (the items) lazily until the closing square bracket
\\] matches the closing square bracket

Conclusion

Java regular expressions provide a powerful way to match specific patterns in YAML data. In this blog post, we explored how to extract key-value pairs and sequences from a YAML string using regex patterns.

Regular expressions can be complex and error-prone, so it’s important to test and verify the patterns with different YAML inputs. Additionally, for complex YAML parsing, consider using a YAML library like SnakeYAML or Jackson YAML.

#Java #YAML #RegularExpressions