常见状态码

    SWITCH_PROTOCOL(101, "Switching Protocols"),

    OK(200, "OK"),
    CREATED(201, "Created"),
    ACCEPTED(202, "Accepted"),
    NO_CONTENT(204, "No Content"),
    PARTIAL_CONTENT(206, "Partial Content"),
    MULTI_STATUS(207, "Multi-Status"),

    REDIRECT(301, "Moved Permanently"),
    /**
     * Many user agents mishandle 302 in ways that violate the RFC1945
     * spec (i.e., redirect a POST to a GET). 303 and 307 were added in
     * RFC2616 to address this. You should prefer 303 and 307 unless the
     * calling user agent does not support 303 and 307 functionality
     */
    @Deprecated
    FOUND(302, "Found"),
    REDIRECT_SEE_OTHER(303, "See Other"),
    NOT_MODIFIED(304, "Not Modified"),
    TEMPORARY_REDIRECT(307, "Temporary Redirect"),

    BAD_REQUEST(400, "Bad Request"),
    UNAUTHORIZED(401, "Unauthorized"),
    FORBIDDEN(403, "Forbidden"),
    NOT_FOUND(404, "Not Found"),
    METHOD_NOT_ALLOWED(405, "Method Not Allowed"),
    NOT_ACCEPTABLE(406, "Not Acceptable"),
    REQUEST_TIMEOUT(408, "Request Timeout"),
    CONFLICT(409, "Conflict"),
    GONE(410, "Gone"),
    LENGTH_REQUIRED(411, "Length Required"),
    PRECONDITION_FAILED(412, "Precondition Failed"),
    PAYLOAD_TOO_LARGE(413, "Payload Too Large"),
    UNSUPPORTED_MEDIA_TYPE(415, "Unsupported Media Type"),
    RANGE_NOT_SATISFIABLE(416, "Requested Range Not Satisfiable"),
    EXPECTATION_FAILED(417, "Expectation Failed"),
    TOO_MANY_REQUESTS(429, "Too Many Requests"),

    INTERNAL_ERROR(500, "Internal Server Error"),
    NOT_IMPLEMENTED(501, "Not Implemented"),
    SERVICE_UNAVAILABLE(503, "Service Unavailable"),
    UNSUPPORTED_HTTP_VERSION(505, "HTTP Version Not Supported");

500：服务器内部出现错误
501：服务器无法识别请求方法
503：（服务不可用） 服务器目前无法使用（由于超载或停机维护）。通常，这只是暂时状态。
505： （HTTP 版本不受支持） 服务器不支持请求中所用的 HTTP 协议版本。
400: 服务器不懂客户端的请求
401：请求要求用户的身份认证（客户端：我要一瓶可乐，并打85折，服务器：有会员卡？有就打折）
403：服务器理解客户端的请求，但是拒绝执行此请求（客户端：把你的钱都给我，服务器：对不起，拒绝服务）
404：服务器无法根据客户端的请求找到资源（网页）（客户端：请给我一瓶香飘飘奶茶，服务器：我们这里没有优乐美奶茶）
405：客户端请求的方法被禁止。（客户端：我用微信支付，服务端：对不起，我们不支持手机支付，只能现金）
502：作为网关或者代理工作的服务器尝试执行请求时，从上游服务器接收到无效的响应。
504：作为网关或者代理工作的服务器尝试执行请求时，未能及时从上游服务器（URI标识出的服务器，例如HTTP、FTP、LDAP）或者辅助服务器（例如DNS）收到响应。