在开发过程中我们通常会用开源库来实现JWT相关功能（不知道JWT的点这里），本篇文章会用JJWT来作示范
首先在pom.xml中引入依赖

<dependency>
            <groupId>io.jsonwebtoken</groupId>
            <artifactId>jjwt</artifactId>
            <version>0.7.0</version>
        </dependency>

创建

创建JWT之前首先要创建一个base64需要的key

import io.jsonwebtoken.*;
import org.apache.tomcat.util.codec.binary.Base64;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
...
String stringKey ="lwlsecret";
        byte[] encodedKey = Base64.decodeBase64(stringKey);
        SecretKey key = new SecretKeySpec(encodedKey, 0, encodedKey.length, "AES");

然后根据这个secret创建jwt

//设置算法为HS256
SignatureAlgorithm signatureAlgorithm = SignatureAlgorithm.HS256;
        Date now = new Date(System.currentTimeMillis());
        JwtBuilder builder = Jwts.builder()
                .setHeaderParam("typ", "JWT")    //设置header
                .setHeaderParam("alg", "HS256")
                .setIssuedAt(now)     //设置iat
                .claim("name", "liuwillow")   //设置payload的键值对
                .claim("level", "100")
                .setIssuer("lwl")
                .signWith(signatureAlgorithm, key);    //签名，需要算法和key
        String jwt = builder.compact();
        System.out.println("生成的jwt:" + jwt);

即可输出得到的jwt字符串

验证

//获取claims
    Claims claims = Jwts.parser()
                .setSigningKey(key)     //此处的key要与之前创建的key一致
                .parseClaimsJws(jwt)
                .getBody();
//获取name和level
    String name = (String) claims.get("name");
    String level = (String) claims.get("level");
    System.out.println("name:" + name + " level:" + level);