什么是JWT？

1.引入依赖
<dependencies>
    <!-- JWT-->
    <dependency>
        <groupId>io.jsonwebtoken</groupId>
        <artifactId>jjwt</artifactId>
    </dependency>
</dependencies>

2.创建JWT工具类

import io.jsonwebtoken.Claims;
import io.jsonwebtoken.Jws;
import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;
import org.springframework.util.StringUtils;

import javax.servlet.http.HttpServletRequest;
import java.util.Date;

/**
 * @author
 */
public class JwtUtils {

    public static final long EXPIRE = 1000 * 60 * 60 * 24;//token过期的时间
    public static final String APP_SECRET = "ukc8BDbRigUDaY6pZFfWus2jZWLPHO";//密钥

    /**
     * 生成token字符串的方法
     */
    public static String getJwtToken(String id, String nickname) {

        String JwtToken = Jwts.builder()
                .setHeaderParam("typ", "JWT")
                .setHeaderParam("alg", "HS256")//这两个是头信息，默认就好

                .setSubject("guli-user")//名字随意取
                .setIssuedAt(new Date())
                .setExpiration(new Date(System.currentTimeMillis() + EXPIRE))//设置过期时间

                .claim("id", id)//设置token的主体部分，存储用户信息
                .claim("nickname", nickname)

                .signWith(SignatureAlgorithm.HS256, APP_SECRET)//签名哈希。默认就好
                .compact();

        return JwtToken;
    }

    /**
     * 判断token是否存在与有效
     *
     * @param jwtToken
     * @return
     */
    public static boolean checkToken(String jwtToken) {
        if (StringUtils.isEmpty(jwtToken)) return false;
        try {
            Jwts.parser().setSigningKey(APP_SECRET).parseClaimsJws(jwtToken);
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
        return true;
    }

    /**
     * 判断token是否存在与有效
     *
     * @param request
     * @return
     */
    public static boolean checkToken(HttpServletRequest request) {
        try {
            String jwtToken = request.getHeader("token");
            if (StringUtils.isEmpty(jwtToken)) return false;
            Jwts.parser().setSigningKey(APP_SECRET).parseClaimsJws(jwtToken);
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
        return true;
    }

    /**
     * 根据token获取会员id
     *
     * @param request
     * @return
     */
    public static String getMemberIdByJwtToken(HttpServletRequest request) {
        String jwtToken = request.getHeader("token");
        if (StringUtils.isEmpty(jwtToken)) return "";
        Jws<Claims> claimsJws = Jwts.parser().setSigningKey(APP_SECRET).parseClaimsJws(jwtToken);
        Claims claims = claimsJws.getBody();
        return (String) claims.get("id");
    }
}