The utility of Flink applications is unparalleled such as with a stackTrace hasher example to collect the top exceptions encountered from log archives:
private static class ExtractStackTraceHasher implements FlatMapFunction<String, String>{
                @Override
                public void flatMap(String value, Collector< String> out) throws Exception {
StringTokenizer tokenizer = new StringTokenizer(value);
While (tokenizer.hasMoreTokens()) {
String word = tokenizer.nextToken();
If (word.contains(“Exception:”) {
int start = value.indexOf(word); // word has unique timestamp
int end = value.indexOf(word.substring(8), start+8);
if (end != -1 && start != -1 && end > start) {
String exceptionString = value.substring(start+11, end); // skip the timestamp
Throwable error = Throwable.parse(exceptionString);
var stackHasher = new net.logstash.logback.stacktrace.StackHasher();
out.collect(stackHasher.hexHash(error));
}
}
}
                }
        }

final StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
For (string path: pathsInExtractedLogArchive(archiveLocation)) {
env.readTextFile(path)
            .flatMap(new ExtractStackTraceHasher ())
            .keyBy(0)
            .sum(1)
            .print();
}