MqttConnectReturnCode枚举值

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1、MqttConnectReturnCode类

/*
 * Copyright 2014 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

package io.netty.handler.codec.mqtt;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

/**
 * Return Code of {@link MqttConnAckMessage}
 */
public enum MqttConnectReturnCode {
    CONNECTION_ACCEPTED((byte) 0x00),
    CONNECTION_REFUSED_UNACCEPTABLE_PROTOCOL_VERSION((byte) 0X01),
    CONNECTION_REFUSED_IDENTIFIER_REJECTED((byte) 0x02),
    CONNECTION_REFUSED_SERVER_UNAVAILABLE((byte) 0x03),
    CONNECTION_REFUSED_BAD_USER_NAME_OR_PASSWORD((byte) 0x04),
    CONNECTION_REFUSED_NOT_AUTHORIZED((byte) 0x05);
    private static final Map<Byte, MqttConnectReturnCode> VALUE_TO_CODE_MAP;
    static {
        final Map<Byte, MqttConnectReturnCode> valueMap = new HashMap<Byte, MqttConnectReturnCode>();
        for (MqttConnectReturnCode code: values()) {
            valueMap.put(code.byteValue, code);
        }
        VALUE_TO_CODE_MAP = Collections.unmodifiableMap(valueMap);
    }

    private final byte byteValue;

    MqttConnectReturnCode(byte byteValue) {
        this.byteValue = byteValue;
    }

    public byte byteValue() {
        return byteValue;
    }

    public static MqttConnectReturnCode valueOf(byte b) {
        if (VALUE_TO_CODE_MAP.containsKey(b)) {
            return VALUE_TO_CODE_MAP.get(b);
        }
        throw new IllegalArgumentException("unknown connect return code: " + (b & 0xFF));
    }
}

2、返回值具体含义

返回值	16进制	含义
0	0x00	Connection Accepted   正常连接
1	0x01	Connection Refused: unacceptable protocol version   协议版本不被接受
2	0x02	Connection Refused: identifier rejected   连接拒绝
3	0x03	Connection Refused: server unavailable   服务不可用
4	0x04	Connection Refused: bad user name or password    账号密码错误
5	0x05	Connection Refused: not authorized    权限不足
6-255		Reserved for future use

只有0-5目前被使用到，其他值有待日后使用。一般返回值为0x00，表示连接建立。非法的请求，需要返回相应的数值。