get username from jwt token request spring boot

1. Create a class to represent the JwtTokenUtil:

import io.jsonwebtoken.Claims;
import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.security.core.userdetails.UserDetails;
import org.springframework.stereotype.Component;

import java.io.Serializable;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;
import java.util.function.Function;

@Component
public class JwtTokenUtil implements Serializable {

    public static final long JWT_TOKEN_VALIDITY = 5  60  60;

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

    public String getUsernameFromToken(String token) {
        return getClaimFromToken(token, Claims::getSubject);
    }

    public Date getExpirationDateFromToken(String token) {
        return getClaimFromToken(token, Claims::getExpiration);
    }

    public <T> T getClaimFromToken(String token, Function<Claims, T> claimsResolver) {
        final Claims claims = getAllClaimsFromToken(token);
        return claimsResolver.apply(claims);
    }

    private Claims getAllClaimsFromToken(String token) {
        return Jwts.parser().setSigningKey(secret).parseClaimsJws(token).getBody();
    }

    private Boolean isTokenExpired(String token) {
        final Date expiration = getExpirationDateFromToken(token);
        return expiration.before(new Date());
    }

    public String generateToken(UserDetails userDetails) {
        Map<String, Object> claims = new HashMap<>();
        return doGenerateToken(claims, userDetails.getUsername());
    }

    private String doGenerateToken(Map<String, Object> claims, String subject) {
        return Jwts.builder()
                .setClaims(claims)
                .setSubject(subject)
                .setIssuedAt(new Date(System.currentTimeMillis()))
                .setExpiration(new Date(System.currentTimeMillis() + JWT_TOKEN_VALIDITY * 1000))
                .signWith(SignatureAlgorithm.HS512, secret)
                .compact();
    }

    public Boolean validateToken(String token, UserDetails userDetails) {
        final String username = getUsernameFromToken(token);
        return (username.equals(userDetails.getUsername()) && !isTokenExpired(token));
    }
}

1. Add the following property to your application.properties or application.yml file:

jwt.secret=yourSecretKey

Replace "yourSecretKey" with your desired secret key.

1. In your controller or service, inject the JwtTokenUtil and use it to extract the username from the JWT token:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.security.core.userdetails.UserDetails;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestHeader;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class YourController {

    @Autowired
    private JwtTokenUtil jwtTokenUtil;

    @GetMapping("/getUsername")
    public String getUsernameFromToken(@RequestHeader("Authorization") String token) {
        token = token.substring(7); // Remove "Bearer " prefix
        String username = jwtTokenUtil.getUsernameFromToken(token);
        return "Username: " + username;
    }
}

Make sure to handle the case where the Authorization header does not exist or is malformed in a production environment.