什么是 JWT -- JSON WEB TOKEN

import java.io.Serializable;
import java.util.Date;
import java.util.Map;
import org.springframework.stereotype.Component;

import io.jsonwebtoken.Claims;
import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;

@Component
public class JwtTokenService implements Serializable {

private static final long serialVersionUID = -3301605591108950415L;

private static final String CLAIM_KEY_CREATED = "created";

private String secret="absd";

private Long expiration=7200L;

/**
* 获取创建token时间
* @param token
* @return
*/
public Date getCreatedDateFromToken(String token) {
Date created;
try {
final Claims claims = getClaimsFromToken(token);
created = new Date((Long) claims.get(CLAIM_KEY_CREATED));
} catch (Exception e) {
created = null;
}
return created;
}

/**
* 获取过期时间
* @param token
* @return
*/
public Date getExpirationDateFromToken(String token) {
Date expiration;
try {
final Claims claims = getClaimsFromToken(token);
expiration = claims.getExpiration();
} catch (Exception e) {
expiration = null;
}
return expiration;
}

/**
* 判断是否过期
* @param token
* @return
*/
private Boolean isTokenExpired(String token) {
final Date expiration = getExpirationDateFromToken(token);
return expiration.before(new Date());
}

/**
* 获取jwt中的body部分
* @param token
* @return
*/
public Claims getClaimsFromToken(String token) {
Claims claims;
try {
claims = Jwts.parser()
.setSigningKey(secret)
.parseClaimsJws(token)
.getBody();
} catch (Exception e) {
claims = null;
// throw e;

}
return claims;
}

public String getSubject(String token){
try {
return   getClaimsFromToken(token).getSubject();
}catch (Exception e){

}
return null;

}

/**
* 生成过期时间
* @return
*/
private Date generateExpirationDate() {
return new Date(System.currentTimeMillis() + expiration * 1000);
}

/**
*  生成token
* @param claims
* @return
*/
public String generateToken(Map<String, Object> claims, String subject) {
return Jwts.builder()
.setClaims(claims)
.setSubject(subject)
.setExpiration(generateExpirationDate())
.signWith(SignatureAlgorithm.HS512, secret)
.compact();
}

public String generateToken( String subject) {
return Jwts.builder()
.setSubject(subject)
.setExpiration(generateExpirationDate())
.signWith(SignatureAlgorithm.HS512, secret)
.compact();
}

public String refreshToken(String token) {
String refreshedToken;
try {
final Claims claims = getClaimsFromToken(token);
claims.put(CLAIM_KEY_CREATED, new Date());
refreshedToken = generateToken(claims,claims.getSubject());
} catch (Exception e) {
refreshedToken = null;
}
return refreshedToken;
}

/**
* token是否过期
* @param token
* @return
*/
public Boolean validateToken(String token) {
Claims claims = getClaimsFromToken(token);
if(claims==null) return false;
return !isTokenExpired(token);
}

}