springboot-demo/src/main/java/com/example/demo/security/LearningJwtUtil.java

package com.example.demo.security;

import io.jsonwebtoken.Claims;
import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.security.Keys;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

import javax.crypto.SecretKey;
import java.nio.charset.StandardCharsets;
import java.util.Date;
import java.util.Map;

@Component
public class LearningJwtUtil {

    @Value("${learning.auth.jwt.secret}")
    private String secret;

    @Value("${learning.auth.jwt.expiration:86400000}")
    private long expiration;

    private SecretKey key() {
        return Keys.hmacShaKeyFor(secret.getBytes(StandardCharsets.UTF_8));
    }

    public String generateToken(String username) {
        Date now = new Date();
        return Jwts.builder()
                .claims(Map.of("username", username))
                .subject(username)
                .issuedAt(now)
                .expiration(new Date(now.getTime() + expiration))
                .signWith(key(), Jwts.SIG.HS256)
                .compact();
    }

    public boolean validate(String token) {
        try {
            parse(token);
            return true;
        } catch (Exception e) {
            return false;
        }
    }

    public String username(String token) {
        return parse(token).getSubject();
    }

    public Map<String, Object> claims(String token) {
        return Map.copyOf(parse(token));
    }

    private Claims parse(String token) {
        return Jwts.parser().verifyWith(key()).build().parseSignedClaims(token).getPayload();
    }
}