Migrate Java 9+ `@Deprecated` to Java 8 Deprecated annotations

DeprecationAnnotationMigrator.java

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.util.Iterator;
import java.util.List;

public class DeprecationAnnotationMigrator {
    public static void main(String[] args) throws IOException {
        migrate(Paths.get("").toAbsolutePath());
    }

    private static void migrate(Path p) throws IOException {
        Iterator<Path> children = Files.list(p).iterator();
        while (children.hasNext()) {
            Path child = children.next();
            //System.out.println(child);
            if (Files.isDirectory(child)) {
                migrate(child);
                continue;
            }
            if (child.getFileName().toString().endsWith(".java")) {
                migrateFile(child);
            }
        }
    }

    private static void migrateFile(Path child) throws IOException {
        List<String> lines = Files.readAllLines(child);
        boolean modified = false;
        loop0:
        for (int i = 0; i < lines.size(); i++) {
            String line = lines.get(i);
            int atSign = line.indexOf('@');
            if (atSign == -1) {
                continue;
            }
            for (int j = 0; j < atSign; j++) {
                if (!Character.isWhitespace(line.codePointAt(j))) {
                    continue loop0;
                }
            }
            if (!line.regionMatches(atSign + 1, "Deprecated(", 0, 11) || line.codePointBefore(line.length()) != ')') {
                continue;
            }
            int firstEq = line.indexOf('=', atSign + 12);
            if (firstEq == -1) {
                continue;
            }
            int separator = line.indexOf(',');
            String since = null;
            String forRemoval = null;
            if (separator == -1) {
                String key = line.substring(atSign + 12, firstEq).trim();
                String value = line.substring(firstEq + 1, line.length() - 1).trim();
                if (key.equals("since")) {
                    since = value;
                } else if (key.equals("forRemoval")) {
                    forRemoval = value;
                } else {
                    throw new IllegalStateException("Unknown key: " + key);
                }
            } else {
                int lastEq = line.lastIndexOf('=');
                String key = line.substring(atSign + 12, firstEq).trim();
                String value = line.substring(firstEq + 1, separator).trim();
                if (key.equals("since")) {
                    since = value;
                } else if (key.equals("forRemoval")) {
                    forRemoval = value;
                } else {
                    throw new IllegalStateException("Unknown key: " + key);
                }
                key = line.substring(separator + 1, lastEq).trim();
                value = line.substring(lastEq + 1, line.length() - 1).trim();
                if (key.equals("since")) {
                    since = value;
                } else if (key.equals("forRemoval")) {
                    forRemoval = value;
                } else {
                    throw new IllegalStateException("Unknown key: " + key);
                }
            }

            modified = true;
            String indent = line.substring(0, atSign + 1);
            lines.set(i, indent + "Deprecated");
            if (since != null) {
                lines.add(i, indent + "DeprecatedSince(" + since + ")");
            }
            if ("true".equals(forRemoval)) {
                lines.add(i, indent + "ScheduledForRemoval(inVersion = \"3.0.0\")");
            }
        }
        if (modified) {
            Files.write(child, lines, StandardOpenOption.TRUNCATE_EXISTING, StandardOpenOption.CREATE);
        }
    }
}