Troubleshooting and Fixing JWT Issues in Java 25 with Spring Boot and JJWT 0.12.x

As Java continues to evolve, upgrading to Java 25 while using the latest Spring Boot and JJWT (Java JSON Web Token) library can introduce compatibility issues. This article explores how we debugged and resolved critical issues related to JWT authentication.

Understanding the Issues

After upgrading to Java 25 and using JJWT 0.12.x, we encountered multiple issues in our JWT authentication setup:

1. Method parserBuilder() Not Found:
   • The Jwts.parserBuilder() method is removed in JJWT 0.12.x.
   • Jwts.parser() must be used instead.
2. Incorrect Key Type for verifyWith():
   • JJWT 0.12.x requires a SecretKey, but we were using a Key.
   • The error message: The method verifyWith(SecretKey) in the type JwtParserBuilder is not applicable for the arguments (Key)
3. Deprecated or Removed Methods:
   • parseClaimsJws() is replaced by parseSignedClaims().
   • Using signWith(SignatureAlgorithm.HS256, key) is no longer recommended.

Step-by-Step Debugging & Fixes

1. Replacing parserBuilder()

Problem:

private Claims parseClaims(String token) {
    return Jwts.parserBuilder()
            .setSigningKey(signingKey)
            .build()
            .parseClaimsJws(token)
            .getBody();
}

Fix:

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

2. Fixing verifyWith() Key Type Issue

Problem:

• We were passing a Key, but JJWT now requires a SecretKey.

Fix:

import javax.crypto.SecretKey;

private SecretKey signingKey;

@Value("${jwt.secret-key}")
public void setSecretKey(String secretKey) {
    byte[] keyBytes = Base64.getDecoder().decode(secretKey);
    if (keyBytes.length < 32) {
        throw new IllegalArgumentException("Secret key must be at least 256 bits (32 bytes)");
    }
    this.signingKey = Keys.hmacShaKeyFor(keyBytes);
}

3. Using parseSignedClaims() Instead of parseClaimsJws()

Problem:

• parseClaimsJws() does not work anymore.

Fix:

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

4. Secure Token Generation

Fix:

public String generateToken(UserDetails userDetails) {
    Map<String, Object> claims = new HashMap<>();
    return Jwts.builder()
            .claims(claims)
            .subject(userDetails.getUsername())
            .issuedAt(new Date())
            .expiration(new Date(System.currentTimeMillis() + expirationTime))
            .signWith(signingKey)
            .compact();
}

Best Practices for JWT Implementation

• Use at least a 256-bit secret key.
• Always validate tokens securely using verifyWith(signingKey).
• Keep secrets safe (use environment variables or secure vaults).
• Use JJWT’s latest parsing methods to prevent security vulnerabilities.

Conclusion

By troubleshooting and applying these fixes, we ensured that our JWT-based authentication system is compatible with Java 25, Spring Boot latest version, and JJWT 0.12.x. The key takeaways include adapting to API changes, ensuring proper key usage, and following secure coding practices for JWT handling.

By following these steps, you can avoid common pitfalls and maintain a robust authentication mechanism in your Java 25 Spring Boot applications.