{"id":460,"date":"2015-09-08T14:59:58","date_gmt":"2015-09-08T14:59:58","guid":{"rendered":"98b297950041a42470269d56260243a1"},"modified":"2015-09-08T14:59:58","modified_gmt":"2015-09-08T14:59:58","slug":"","status":"publish","type":"post","link":"https:\/\/www.xiaobo.li\/notes\/archives\/460","title":{"rendered":"\u4e00.MQTT\u534f\u8bae\u7b14\u8bb0\u4e4b\u5934\u90e8\u4fe1\u606f"},"content":{"rendered":"

\u524d\u8a00<\/h2>\n

MQTT\uff08Message Queue Telemetry Transport\uff09,\u9065\u6d4b\u4f20\u8f93\u534f\u8bae\uff0c\u63d0\u4f9b\u8ba2\u9605\/\u53d1\u5e03\u6a21\u5f0f\uff0c\u66f4\u4e3a\u7b80\u7ea6\u3001\u8f7b\u91cf\uff0c\u6613\u4e8e\u4f7f\u7528\uff0c\u9488\u5bf9\u53d7\u9650\u73af\u5883\uff08\u5e26\u5bbd\u4f4e\u3001\u7f51\u7edc\u5ef6\u8fdf\u9ad8\u3001\u7f51\u7edc\u901a\u4fe1\u4e0d\u7a33\u5b9a\uff09\uff0c\u53ef\u4ee5\u7b80\u5355\u6982\u62ec\u4e3a\u7269\u8054\u7f51\u6253\u9020\uff0c\u5b98\u65b9\u603b\u7ed3\u7279\u70b9\u5982\u4e0b\uff1a<\/p>\n

1.\u4f7f\u7528\u53d1\u5e03\/\u8ba2\u9605\u6d88\u606f\u6a21\u5f0f\uff0c\u63d0\u4f9b\u4e00\u5bf9\u591a\u7684\u6d88\u606f\u53d1\u5e03\uff0c\u89e3\u9664\u5e94\u7528\u7a0b\u5e8f\u8026\u5408\u3002\r\n2. \u5bf9\u8d1f\u8f7d\u5185\u5bb9\u5c4f\u853d\u7684\u6d88\u606f\u4f20\u8f93\u3002\r\n3. \u4f7f\u7528 TCP\/IP \u63d0\u4f9b\u7f51\u7edc\u8fde\u63a5\u3002\r\n4. \u6709\u4e09\u79cd\u6d88\u606f\u53d1\u5e03\u670d\u52a1\u8d28\u91cf\uff1a\r\n    \u201c\u81f3\u591a\u4e00\u6b21\u201d\uff0c\u6d88\u606f\u53d1\u5e03\u5b8c\u5168\u4f9d\u8d56\u5e95\u5c42 TCP\/IP \u7f51\u7edc\u3002\u4f1a\u53d1\u751f\u6d88\u606f\u4e22\u5931\u6216\u91cd\u590d\u3002\u8fd9\u4e00\u7ea7\u522b\u53ef\u7528\u4e8e\u5982\u4e0b\u60c5\u51b5\uff0c\u73af\u5883\u4f20\u611f\u5668\u6570\u636e\uff0c\u4e22\u5931\u4e00\u6b21\u8bfb\u8bb0\u5f55\u65e0\u6240\u8c13\uff0c\u56e0\u4e3a\u4e0d\u4e45\u540e\u8fd8\u4f1a\u6709\u7b2c\u4e8c\u6b21\u53d1\u9001\u3002\r\n    \u201c\u81f3\u5c11\u4e00\u6b21\u201d\uff0c\u786e\u4fdd\u6d88\u606f\u5230\u8fbe\uff0c\u4f46\u6d88\u606f\u91cd\u590d\u53ef\u80fd\u4f1a\u53d1\u751f\u3002\r\n    \u201c\u53ea\u6709\u4e00\u6b21\u201d\uff0c\u786e\u4fdd\u6d88\u606f\u5230\u8fbe\u4e00\u6b21\u3002\u8fd9\u4e00\u7ea7\u522b\u53ef\u7528\u4e8e\u5982\u4e0b\u60c5\u51b5\uff0c\u5728\u8ba1\u8d39\u7cfb\u7edf\u4e2d\uff0c\u6d88\u606f\u91cd\u590d\u6216\u4e22\u5931\u4f1a\u5bfc\u81f4\u4e0d\u6b63\u786e\u7684\u7ed3\u679c\u3002\r\n5. \u5c0f\u578b\u4f20\u8f93\uff0c\u5f00\u9500\u5f88\u5c0f\uff08\u56fa\u5b9a\u957f\u5ea6\u7684\u5934\u90e8\u662f 2 \u5b57\u8282\uff09\uff0c\u534f\u8bae\u4ea4\u6362\u6700\u5c0f\u5316\uff0c\u4ee5\u964d\u4f4e\u7f51\u7edc\u6d41\u91cf\u3002\r\n6. \u4f7f\u7528 Last Will \u548c Testament \u7279\u6027\u901a\u77e5\u6709\u5173\u5404\u65b9\u5ba2\u6237\u7aef\u5f02\u5e38\u4e2d\u65ad\u7684\u673a\u5236\u3002<\/pre>\n
MQTT 3.1\u534f\u8bae\u5728\u7ebf\u7248\u672c\uff1a <\/span>http:\/\/public.dhe.ibm.com\/software\/dw\/webservices\/ws-mqtt\/mqtt-v3r1.html<\/a><\/p>\n
\u5b98\u65b9\u4e0b\u8f7d\u5730\u5740\uff1a <\/span>http:\/\/public.dhe.ibm.com\/software\/dw\/webservices\/ws-mqtt\/MQTT_V3.1_Protocol_Specific.pdf<\/a><\/p>\n
PDF\u7248\u672c\uff0c42\u9875\uff0c\u4e0d\u7b97\u591a\u3002<\/p>\n
\u53e6\u5916\uff0c\u76ee\u524dMQTT\u5927\u5bb6\u90fd\u7528\u5728\u4e86\u624b\u673a\u63a8\u9001\uff0c\u53ef\u80fd\u8fd8\u6709\u5f88\u591a\u7684\u4f7f\u7528\u65b9\u5f0f\uff0c\u6709\u5f85\u8fdb\u4e00\u6b65\u7684\u63a2\u7d22\u3002<\/p>\n
\u534f\u8bae\u65b9\u9762\uff0c\u4ee5\u524d\u66fe\u7b80\u5355\u5b9e\u73b0\u8fc7\u4e00\u70b9HTTP\u534f\u8bae\uff0c\u57fa\u4e8eHTTP\u4e0a\u6784\u5efa\u82e5\u5e72\u79cd\u901a\u4fe1\u7ba1\u9053\u7684socket.io<\/a>\u534f\u8bae\uff0c\u4e0d\u8fc7socket.io 0.9\u7248\u672c\u7684\u534f\u8bae\u624d\u4e24\u4e09\u9875\u800c\u5df2\u3002\u9762\u5bf9\u9886\u57df\u4e0d\u540c\uff0c\u81ea\u7136\u89e3\u51b3\u7684\u65b9\u5f0f\u4e5f\u4e0d\u4e00\u6837\u3002<\/p>\n
\u9605\u8bfb\u5b8c\u6bd5MQTT\u534f\u8bae\uff0c\u6709\u4e00\u4e2a\u60f3\u6cd5\uff0c\u5176\u5b9e\u53ef\u4ee5\u57fa\u4e8eMQTT\u534f\u8bae\uff0c\u6253\u9020\u66f4\u52a0\u79c1\u6709\u3001\u7cbe\u7b80\uff08\u534f\u8bae\u4e00\u4e9b\u5730\u65b9\uff0c\u7565\u663e\u591a\u4f59\uff09\u7684\u4f20\u8f93\u534f\u8bae\uff0c\u6bd4\u5982\u4e00\u4e2a\u5b57\u8282\u7684\u4f20\u8f93\u5f00\u9500\u3002\u6709\u65f6\u95f4\uff0c\u4f1a\u8be6\u7ec6\u8bf4\u4e00\u4e0b\u3002<\/p>\n
\u56fa\u5b9a\u5934\u90e8<\/h2>\n
\u56fa\u5b9a\u5934\u90e8\uff0c\u4f7f\u7528\u4e24\u4e2a\u5b57\u8282\uff0c\u517116\u4f4d\uff1a<\/p>\n\n\n\n\n\n\n
bit<\/th>\n7<\/th>\n6<\/th>\n5<\/th>\n4<\/th>\n3<\/th>\n2<\/th>\n1<\/th>\n0<\/th>\n<\/tr>\n<\/thead>\n
byte 1<\/td>\nMessage Type<\/td>\nDUP flag<\/td>\nQoS level<\/td>\nRETAIN<\/td>\n<\/tr>\n
byte 2<\/td>\nRemaining Length<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\u7b2c\u4e00\u4e2a\u5b57\u8282(byte 1)<\/h3>\n
\u6d88\u606f\u7c7b\u578b(4-7)\uff0c\u4f7f\u75284\u4f4d\u4e8c\u8fdb\u5236\u8868\u793a\uff0c\u53ef\u4ee3\u886816\u79cd\u6d88\u606f\u7c7b\u578b\uff1a<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Mnemonic<\/th>\nEnumeration<\/th>\nDescription<\/th>\n<\/tr>\n<\/thead>\n
Reserved<\/td>\n0<\/td>\nReserved<\/td>\n<\/tr>\n
CONNECT<\/td>\n1<\/td>\nClient request to connect to Server<\/td>\n<\/tr>\n
CONNACK<\/td>\n2<\/td>\nConnect Acknowledgment<\/td>\n<\/tr>\n
PUBLISH<\/td>\n3<\/td>\nPublish message<\/td>\n<\/tr>\n
PUBACK<\/td>\n4<\/td>\nPublish Acknowledgment<\/td>\n<\/tr>\n
PUBREC<\/td>\n5<\/td>\nPublish Received (assured delivery part 1)<\/td>\n<\/tr>\n
PUBREL<\/td>\n6<\/td>\nPublish Release (assured delivery part 2)<\/td>\n<\/tr>\n
PUBCOMP<\/td>\n7<\/td>\nPublish Complete (assured delivery part 3)<\/td>\n<\/tr>\n
SUBSCRIBE<\/td>\n8<\/td>\nClient Subscribe request<\/td>\n<\/tr>\n
SUBACK<\/td>\n9<\/td>\nSubscribe Acknowledgment<\/td>\n<\/tr>\n
UNSUBSCRIBE<\/td>\n10<\/td>\nClient Unsubscribe request<\/td>\n<\/tr>\n
UNSUBACK<\/td>\n11<\/td>\nUnsubscribe Acknowledgment<\/td>\n<\/tr>\n
PINGREQ<\/td>\n12<\/td>\nPING Request<\/td>\n<\/tr>\n
PINGRESP<\/td>\n13<\/td>\nPING Response<\/td>\n<\/tr>\n
DISCONNECT<\/td>\n14<\/td>\nClient is Disconnecting<\/td>\n<\/tr>\n
Reserved<\/td>\n15<\/td>\nReserved<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\u9664\u53bb0\u548c15\u4f4d\u7f6e\u5c5e\u4e8e\u4fdd\u7559\u5f85\u7528\uff0c\u517114\u79cd\u6d88\u606f\u4e8b\u4ef6\u7c7b\u578b\u3002<\/p>\n
DUP flag\uff08\u6253\u5f00\u6807\u5fd7\uff09<\/h3>\n
\u4fdd\u8bc1\u6d88\u606f\u53ef\u9760\u4f20\u8f93\uff0c\u9ed8\u8ba4\u4e3a0\uff0c\u53ea\u5360\u7528\u4e00\u4e2a\u5b57\u8282\uff0c\u8868\u793a\u7b2c\u4e00\u6b21\u53d1\u9001\u3002\u4e0d\u80fd\u7528\u4e8e\u68c0\u6d4b\u6d88\u606f\u91cd\u590d\u53d1\u9001\u7b49\u3002\u53ea\u9002\u7528\u4e8e\u5ba2\u6237\u7aef\u6216\u670d\u52a1\u5668\u7aef\u5c1d\u8bd5\u91cd\u53d1PUBLISH, PUBREL, SUBSCRIBE \u6216 UNSUBSCRIBE\u6d88\u606f\uff0c\u6ce8\u610f\u9700\u8981\u6ee1\u8db3\u4ee5\u4e0b\u6761\u4ef6\uff1a<\/p>\n
 \u5f53QoS > 0\r\n \u6d88\u606f\u9700\u8981\u56de\u590d\u786e\u8ba4<\/pre>\n
\u6b64\u65f6\uff0c\u5728\u53ef\u53d8\u5934\u90e8\u9700\u8981\u5305\u542b\u6d88\u606fID\u3002\u5f53\u503c\u4e3a1\u65f6\uff0c\u8868\u793a\u5f53\u524d\u6d88\u606f\u5148\u524d\u5df2\u7ecf\u88ab\u4f20\u9001\u8fc7\u3002<\/p>\n
QoS(Quality of Service,\u670d\u52a1\u8d28\u91cf)<\/h3>\n
\u4f7f\u7528\u4e24\u4e2a\u4e8c\u8fdb\u5236\u8868\u793aPUBLISH\u7c7b\u578b\u6d88\u606f\uff1a<\/p>\n\n\n\n\n\n\n\n\n
QoS value<\/th>\nbit 2<\/th>\nbit 1<\/th>\nDescription<\/th>\n<\/tr>\n<\/thead>\n
0<\/td>\n0<\/td>\n0<\/td>\n\u81f3\u591a\u4e00\u6b21<\/td>\n\u53d1\u5b8c\u5373\u4e22\u5f03<\/td>\n<=1<\/td>\n<\/tr>\n
1<\/td>\n0<\/td>\n1<\/td>\n\u81f3\u5c11\u4e00\u6b21<\/td>\n\u9700\u8981\u786e\u8ba4\u56de\u590d<\/td>\n>=1<\/td>\n<\/tr>\n
2<\/td>\n1<\/td>\n0<\/td>\n\u53ea\u6709\u4e00\u6b21<\/td>\n\u9700\u8981\u786e\u8ba4\u56de\u590d<\/td>\n=1<\/td>\n<\/tr>\n
3<\/td>\n1<\/td>\n1<\/td>\n\u5f85\u7528\uff0c\u4fdd\u7559\u4f4d\u7f6e<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
RETAIN(\u4fdd\u6301)<\/h3>\n
\u4ec5\u9488\u5bf9PUBLISH\u6d88\u606f\u3002\u4e0d\u540c\u503c\uff0c\u4e0d\u540c\u542b\u4e49\uff1a<\/p>\n
1<\/strong>\uff1a\u8868\u793a\u53d1\u9001\u7684\u6d88\u606f\u9700\u8981\u4e00\u76f4\u6301\u4e45\u4fdd\u5b58\uff08\u4e0d\u53d7\u670d\u52a1\u5668\u91cd\u542f\u5f71\u54cd\uff09\uff0c\u4e0d\u4f46\u8981\u53d1\u9001\u7ed9\u5f53\u524d\u7684\u8ba2\u9605\u8005\uff0c\u5e76\u4e14\u4ee5\u540e\u65b0\u6765\u7684\u8ba2\u9605\u4e86\u6b64Topic name\u7684\u8ba2\u9605\u8005\u4f1a\u9a6c\u4e0a\u5f97\u5230\u63a8\u9001\u3002<\/p>\n
\u5907\u6ce8\uff1a\u65b0\u6765\u4e4d\u5230\u7684\u8ba2\u9605\u8005\uff0c\u53ea\u4f1a\u53d6\u51fa\u6700\u65b0\u7684\u4e00\u4e2aRETAIN flag = 1\u7684\u6d88\u606f\u63a8\u9001\u3002<\/p>\n
0<\/strong>\uff1a\u4ec5\u4ec5\u4e3a\u5f53\u524d\u8ba2\u9605\u8005\u63a8\u9001\u6b64\u6d88\u606f\u3002<\/p>\n
\u5047\u5982\u670d\u52a1\u5668\u6536\u5230\u4e00\u4e2a\u7a7a\u6d88\u606f\u4f53(zero-length payload)\u3001RETAIN = 1\u3001\u5df2\u5b58\u5728Topic name\u7684PUBLISH\u6d88\u606f\uff0c\u670d\u52a1\u5668\u53ef\u4ee5\u5220\u9664\u6389\u5bf9\u5e94\u7684\u5df2\u88ab\u6301\u4e45\u5316\u7684PUBLISH\u6d88\u606f\u3002<\/p>\n
\u5982\u4f55\u89e3\u6790<\/h3>\n
\u56e0\u4e3ajava\u4f7f\u7528\u6709\u7b26\u53f7(\u6700\u9ad8\u4f4d\u4e3a\u7b26\u53f7\u4f4d)\u6570\u636e\u8868\u793a\uff0cbyte\u8303\u56f4\uff1a-128-127\u3002\u8be5\u5b57\u8282\u7684\u6700\u9ad8\u4f4d\uff08\u5de6\u8fb9\u7b2c\u4e00\u4f4d\uff09\uff0c\u53ef\u80fd\u4e3a1\u3002\u82e5\u76f4\u63a5\u8f6c\u6362\u4e3abyte\u7c7b\u578b\uff0c\u4f1a\u51fa\u73b0\u8d1f\u6570\uff0c\u8fd9\u662f\u4e00\u4e2a\u96f7\u533a\u3002DataInputStream\u63d0\u4f9b\u4e86int readUnsignedByte()\u8bfb\u53d6\u65b9\u5f0f\uff0c\u8bf7\u6ce8\u610f\u3002\u4e0b\u9762\u6f14\u793a\u4e86\uff0c\u5982\u4f55\u4ece\u4e00\u4e2a\u5b57\u8282\u4e2d\uff0c\u83b7\u53d6\u5230\u6240\u6709\u5b9a\u4e49\u7684\u4fe1\u606f\uff0c\u540c\u65f6\u7ed5\u8fc7\u96f7\u533a\uff1a<\/p>\n
public static void main(String[] args) {\r\n    byte publishFixHeader = 50;\/\/ 0 0 1 1 0 0 1 0\r\n\r\n    doGetBit(publishFixHeader);\r\n    int ori = 224;\/\/1110000,DISCONNECT ,Message Type (14)\r\n    byte flag = (byte) ori; \/\/\u6709\u7b26\u53f7byte       \r\n    doGetBit(flag);\r\n    doGetBit_v2(ori);\r\n}\r\n\r\n\r\npublic static void doGetBit(byte flags) {\r\n    boolean retain = (flags & 1) > 0;\r\n    int qosLevel = (flags & 0x06) >> 1;\r\n    boolean dupFlag = (flags & 8) > 0;\r\n    int messageType = (flags >> 4) & 0x0f;\r\n\r\n    System.out.format(\r\n            \"Message type:%d, DUP flag:%s, QoS level:%d, RETAIN:%s\\n\",\r\n            messageType, dupFlag, qosLevel, retain);\r\n}\r\n\r\npublic static void doGetBit_v2(int flags) {\r\n    boolean retain = (flags & 1) > 0;\r\n    int qosLevel = (flags & 0x06) >> 1;\r\n    boolean dupFlag = (flags & 8) > 0;\r\n    int messageType = flags >> 4;\r\n\r\n    System.out.format(\r\n            \"Message type:%d, DUP flag:%s, QoS level:%d, RETAIN:%s\\n\",\r\n            messageType, dupFlag, qosLevel, retain);\r\n}<\/pre>\n
\u5904\u7406Remaining Length\uff08\u5269\u4f59\u957f\u5ea6\uff09<\/h3>\n
\u5728\u5f53\u524d\u6d88\u606f\u4e2d\u5269\u4f59\u7684byte(\u5b57\u8282)\u6570\uff0c\u5305\u542b\u53ef\u53d8\u5934\u90e8\u548c\u8d1f\u8377(\u79f0\u4e4b\u4e3a\u5185\u5bb9\/body\uff0c\u66f4\u4e3a\u5408\u9002)\u3002\u5355\u4e2a\u5b57\u8282\u6700\u5927\u503c\uff1a01111111\uff0c16\u8fdb\u5236\uff1a0x7F\uff0c10\u8fdb\u5236\u4e3a127\u3002\u5355\u4e2a\u5b57\u8282\u4e3a\u4ec0\u4e48\u4e0d\u80fd\u662f11111111\uff080xFF\uff09\u5462\uff1f\u56e0\u4e3aMQTT\u534f\u8bae\u89c4\u5b9a\uff0c\u7b2c\u516b\u4f4d\uff08\u6700\u9ad8\u4f4d\uff09\u82e5\u4e3a1\uff0c\u5219\u8868\u793a\u8fd8\u6709\u540e\u7eed\u5b57\u8282\u5b58\u5728\u3002\u540c\u65f6MQTT\u534f\u8bae\u6700\u591a\u5141\u8bb84\u4e2a\u5b57\u8282\u8868\u793a\u5269\u4f59\u957f\u5ea6\u3002\u90a3\u4e48\u6700\u5927\u957f\u5ea6\u4e3a\uff1a0xFF,0xFF,0xFF,0x7F\uff0c\u4e8c\u8fdb\u5236\u8868\u793a\u4e3a:11111111,11111111,11111111,01111111\uff0c\u5341\u8fdb\u5236\uff1a268435455 byte=261120KB=256MB=0.25GB \u56db\u4e2a\u5b57\u8282\u4e4b\u95f4\u503c\u7684\u8303\u56f4\uff1a<\/p>\n\n\n\n\n\n\n\n\n
Digits<\/th>\nFrom<\/th>\nTo<\/th>\n<\/tr>\n<\/thead>\n
1<\/td>\n0 (0x00)<\/td>\n127 (0x7F)<\/td>\n<\/tr>\n
2<\/td>\n128 (0x80, 0x01)<\/td>\n16 383 (0xFF, 0x7F)<\/td>\n<\/tr>\n
3<\/td>\n16 384 (0x80, 0x80, 0x01)<\/td>\n2 097 151 (0xFF, 0xFF, 0x7F)<\/td>\n<\/tr>\n
4<\/td>\n2 097 152 (0x80, 0x80, 0x80, 0x01)<\/td>\n268 435 455 (0xFF, 0xFF, 0xFF, 0x7F)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\u5982\u4f55\u6362\u7b97\u6210\u5341\u8fdb\u5236\u5462 ? \u4f7f\u7528java\u8bed\u8a00\u8868\u793a\u5982\u4e0b\uff1a<\/p>\n
public static void main(String[] args) throws IOException {\r\n    \/\/ \u6a21\u62df\u5ba2\u6237\u7aef\u5199\u5165\r\n   ByteArrayOutputStream arrayOutputStream = new ByteArrayOutputStream();\r\n   DataOutputStream dataOutputStream = new DataOutputStream(arrayOutputStream);\r\n   dataOutputStream.write(0xff);\r\n   dataOutputStream.write(0xff);\r\n   dataOutputStream.write(0xff);\r\n   dataOutputStream.write(0x7f);\r\n\r\n   InputStream arrayInputStream = new ByteArrayInputStream(arrayOutputStream.toByteArray());\r\n\r\n    \/\/ \u6a21\u62df\u670d\u52a1\u5668\/\u5ba2\u6237\u7aef\u89e3\u6790\r\n   System. out.println( \"result is \" + bytes2Length(arrayInputStream));\r\n}\r\n\r\n\/**\r\n* \u8f6c\u5316\u5b57\u8282\u4e3a int\u7c7b\u578b\u957f\u5ea6\r\n* @param in\r\n* @return\r\n* @throws IOException\r\n*\/\r\nprivate static int bytes2Length(InputStream in) throws IOException {\r\n    int multiplier = 1;\r\n    int length = 0;\r\n    int digit = 0;\r\n    do {\r\n        digit = in.read(); \/\/\u4e00\u4e2a\u5b57\u8282\u7684\u6709\u7b26\u53f7\u6216\u8005\u65e0\u7b26\u53f7\uff0c\u8f6c\u6362\u8f6c\u6362\u4e3a\u56db\u4e2a\u5b57\u8282\u6709\u7b26\u53f7 int\u7c7b\u578b\r\n        length += (digit & 0x7f) * multiplier;\r\n        multiplier *= 128;\r\n   } while ((digit & 0x80) != 0);\r\n\r\n    return length;\r\n}<\/pre>\n
\u4e00\u822c\u6700\u540e\u4e00\u4e2a\u5b57\u8282\u5c0f\u4e8e127\uff0801111111\uff09\uff0c\u548c0x80\uff0810000000\uff09\u8fdb\u884c&\u64cd\u4f5c\uff0c\u6700\u7ec8\u7ed3\u679c\u90fd\u4e3a0\uff0c\u56e0\u6b64\u8ba1\u7b97\u4f1a\u7ec8\u6b62\u3002\u4ee3\u7406\u4e2d\u95f4\u4ef6\u548c\u8bf7\u6c42\u8005\uff0c\u4e2d\u95f4\u4f20\u9012\u7684\u662f\u5b57\u8282\u6d41Stream\uff0c\u81ea\u7136\u8981\u4ece\u6d41\u4e2d\u8bfb\u53d6\uff0c\u9010\u4e00\u89e3\u6790\u51fa\u6765\u3002<\/p>\n
\u90a3\u4e48\u5982\u4f55\u5c06int\u7c7b\u578b\u957f\u5ea6\u89e3\u6790\u4e3a\u4e0d\u786e\u5b9a\u7684\u5b57\u8282\u503c\u5462\uff1f<\/p>\n
public static void main(String[] args) throws IOException {\r\n    \/\/ \u6a21\u62df\u670d\u52a1\u5668\/\u5ba2\u6237\u7aef\u5199\u5165\r\n   ByteArrayOutputStream arrayOutputStream = new ByteArrayOutputStream();\r\n   DataOutputStream dataOutputStream = new DataOutputStream(\r\n             arrayOutputStream);\r\n\r\n    \/\/ \u6a21\u62df\u670d\u52a1\u5668\/\u5ba2\u6237\u7aef\u89e3\u6790\r\n    length2Bytes(dataOutputStream, 128);\r\n}\r\n\r\n\/**\r\n* int\u7c7b\u578b\u957f\u5ea6\u89e3\u6790\u4e3a1-4\u4e2a\u5b57\u8282\r\n* @param out\r\n* @param length\r\n* @throws IOException\r\n*\/\r\nprivate static void length2Bytes(OutputStream out, int length)\r\n         throws IOException {\r\n    int val = length;\r\n    do {\r\n         int digit = val % 128;\r\n        val = val \/ 128;\r\n         if (val > 0)\r\n             digit = digit | 0x80;\r\n\r\n        out.write(digit);\r\n   } while (val > 0);\r\n}<\/pre>\n
digit\u5bf9val\u6c42\u6a21\uff0c\u6700\u5927\u503c\u53ef\u80fd\u662f127\uff0c\u4e00\u65e6127 | 10000000 = 11111111 = 0xff = 255 \u8bf7\u6ce8\u610f\uff1a\u5269\u4f59\u957f\u5ea6\uff0c\u53ea\u5728\u56fa\u5b9a\u5934\u90e8\u4e2d\uff0c\u65e0\u8bba\u662f\u4e00\u4e2a\u5b57\u8282\uff0c\u8fd8\u662f\u56db\u4e2a\u5b57\u8282\uff0c\u4e0d\u80fd\u88ab\u7b97\u4f5c\u53ef\u53d8\u5934\u90e8\u4e2d\u3002<\/p>\n
\u53ef\u53d8\u5934\u90e8<\/h2>\n
\u56fa\u5b9a\u5934\u90e8\u4ec5\u5b9a\u4e49\u4e86\u6d88\u606f\u7c7b\u578b\u548c\u4e00\u4e9b\u6807\u5fd7\u4f4d\uff0c\u4e00\u4e9b\u6d88\u606f\u7684\u5143\u6570\u636e\uff0c\u9700\u8981\u653e\u5165\u53ef\u53d8\u5934\u90e8\u4e2d\u3002\u53ef\u53d8\u5934\u90e8\u5185\u5bb9\u5b57\u8282\u957f\u5ea6 + Playload\/\u8d1f\u8377\u5b57\u8282\u957f\u5ea6 = \u5269\u4f59\u957f\u5ea6\uff0c\u8fd9\u4e2a\u662f\u9700\u8981\u7262\u8bb0\u7684\u3002\u53ef\u53d8\u5934\u90e8\uff0c\u5305\u542b\u4e86\u534f\u8bae\u540d\u79f0\uff0c\u7248\u672c\u53f7\uff0c\u8fde\u63a5\u6807\u5fd7\uff0c\u7528\u6237\u6388\u6743\uff0c\u5fc3\u8df3\u65f6\u95f4\u7b49\u5185\u5bb9\uff0c\u8fd9\u90e8\u5206\u548c\u540e\u9762\u8981\u8bb2\u5230\u7684CONNECT\u6d88\u606f\u7c7b\u578b\uff0c\u6709\u91cd\u590d\uff0c\u6682\u65f6\u7565\u8fc7\u3002<\/p>\n
Playload\/\u6d88\u606f\u4f53\/\u8d1f\u8377<\/h3>\n
\u6d88\u606f\u4f53\u4e3b\u8981\u662f\u4e3a\u914d\u5408\u56fa\u5b9a\/\u53ef\u53d8\u5934\u90e8\u547d\u4ee4\uff08\u6bd4\u5982CONNECT\u53ef\u53d8\u5934\u90e8User name\u6807\u8bb0\u82e5\u4e3a1\u5219\u9700\u8981\u5728\u6d88\u606f\u4f53\u4e2d\u9644\u52a0\u7528\u6237\u540d\u79f0\u5b57\u7b26\u4e32\uff09\u800c\u5b58\u5728\u3002<\/p>\n
CONNECT\/SUBSCRIBE\/SUBACK\/PUBLISH\u7b49\u6d88\u606f\u6709\u6d88\u606f\u4f53\u3002PUBLISH\u7684\u6d88\u606f\u4f53\u4ee5\u4e8c\u8fdb\u5236\u5f62\u5f0f\u5bf9\u5f85\u3002<\/p>\n
\u8bf7\u8bb0\u4f4f\uff0cMQTT\u534f\u8bae\u53ea\u5141\u8bb8\u5728PUBLISH\u7c7b\u578b\u6d88\u606f\u4f53\u4e2d\u4f7f\u7528\u81ea\u5b9a\u4e49\u7279\u6027\uff0c\u5728\u56fa\u5b9a\/\u53ef\u53d8\u5934\u90e8\u60f3\u52a0\u5165\u81ea\u5b9a\u4e49\u79c1\u6709\u7279\u6027\uff0c\u5c31\u514d\u4e86\u5427\u3002\u8fd9\u4e5f\u662f\u4e3a\u4e86\u534f\u8bae\u514d\u4e8e\u6d41\u4e8e\u5f62\u5f0f\uff0c\u53d8\u5f97\u5f88\u5206\u88c2\u4e5f\u4e3a\u4e86\u517c\u987e\u73b0\u6709\u5ba2\u6237\u7aef\u7b49\u3002\u6bd4\u5982\u652f\u6301\u538b\u7f29\u7b49\uff0c\u90a3\u5c31\u53ef\u4ee5\u5728Playload\u4e2d\u5b9a\u4e49\u6570\u636e\u652f\u6301\uff0c\u5728\u5e94\u7528\u4e2d\u8fdb\u884c\u8bfb\u53d6\u5904\u7406\u3002<\/p>\n
\u8fd9\u90e8\u5206\u4f1a\u5728\u540e\u9762\u8be6\u7ec6\u8bba\u8ff0\u3002<\/p>\n
\u6d88\u606f\u6807\u8bc6\u7b26\/\u6d88\u606fID<\/h3>\n
\u56fa\u5b9a\u5934\u4e2d\u7684QoS level\u6807\u5fd7\u503c\u4e3a1\u62162\u65f6\u624d\u4f1a\u5728\uff1aPUBLISH\uff0cPUBACK\uff0cPUBREC\uff0cPUBREL\uff0cPUBCOMP\uff0cSUBSCRIBE\uff0cSUBACK\uff0cUNSUBSCRIBE\uff0cUNSUBACK\u7b49\u6d88\u606f\u7684\u53ef\u53d8\u5934\u4e2d\u51fa\u73b0\u3002<\/p>\n
\u4e00\u4e2a16\u4f4d\u65e0\u7b26\u53f7\u4f4d\u7684short\u7c7b\u578b\u503c\uff08\u503c\u4e0d\u80fd\u4e3a 0\uff0c0\u505a\u4fdd\u7559\u4f5c\u4e3a\u65e0\u6548\u7684\u6d88\u606fID\uff09\uff0c\u4ec5\u4ec5\u8981\u6c42\u5728\u4e00\u4e2a\u7279\u5b9a\u65b9\u5411\uff08\u670d\u52a1\u5668\u53d1\u5f80\u5ba2\u6237\u7aef\u4e3a\u4e00\u4e2a\u65b9\u5411\uff0c\u5ba2\u6237\u7aef\u53d1\u9001\u5230\u670d\u52a1\u5668\u7aef\u4e3a\u53e6\u4e00\u4e2a\u65b9\u5411\uff09\u7684\u901a\u4fe1\u6d88\u606f\u4e2d\u5fc5\u987b\u552f\u4e00\u3002\u6bd4\u5982\u5ba2\u6237\u7aef\u53d1\u5f80\u670d\u52a1\u5668\uff0c\u6709\u53ef\u80fd\u5b58\u5728\u670d\u52a1\u5668\u53d1\u5f80\u5ba2\u6237\u7aef\u4f1a\u540c\u65f6\u5b58\u5728\u91cd\u590d\uff0c\u4f46\u4e0d\u788d\u4e8b\u3002<\/p>\n
\u53ef\u53d8\u5934\u90e8\u4e2d\uff0c\u9700\u8981\u4e24\u4e2a\u5b57\u8282\u7684\u987a\u5e8f\u662fMSB(Most Significant Bit) LSB(Last\/Least Significant Bit)\uff0c\u7ffb\u8bd1\u6210\u4e2d\u6587\u5c31\u662f\uff0c\u6700\u9ad8\u6709\u6548\u4f4d\uff0c\u6700\u4f4e\u6709\u6548\u4f4d\u3002\u6700\u9ad8\u6709\u6548\u4f4d\u5728\u6700\u4f4e\u6709\u6548\u4f4d\u5de6\u8fb9\/\u4e0a\u9762\uff0c\u8868\u793a\u8fd9\u662f\u4e00\u4e2a\u5927\u7aef\u5b57\u8282\/\u7f51\u7edc\u5b57\u8282\u5e8f\uff0c\u7b26\u5408\u4eba\u7684\u9605\u8bfb\u4e60\u60ef\uff0c\u9ad8\u4f4d\u5728\u6700\u5de6\u8fb9\u3002<\/p>\n\n\n\n\n\n\n
bit<\/th>\n7<\/th>\n6<\/th>\n5<\/th>\n4<\/th>\n3<\/th>\n2<\/th>\n1<\/th>\n0<\/th>\n<\/tr>\n<\/thead>\n
 <\/td>\nMessage Identifier MSB<\/td>\n<\/tr>\n
 <\/td>\nMessage Identifier LSB<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\u4f46\u51e1\u5982\u6b64\u8868\u793a\u7684\uff0c\u90fd\u53ef\u4ee5\u89c6\u4e3a\u4e00\u4e2a16\u4f4d\u65e0\u7b26\u53f7short\u7c7b\u578b\u6574\u6570\uff0c\u4e24\u4e2a\u5b57\u8282\u8868\u793a\u3002\u5728JAVA\u4e2d\u5904\u7406\u6bd4\u8f83\u7b80\u5355\uff1a<\/p>\n
DataInputStream.readUnsignedShort<\/pre>\n
\u6216\u8005<\/p>\n
in.read() * 0xFF + in.read();<\/pre>\n
\u6700\u5927\u957f\u5ea6\u53ef\u4e3a\uff1a 65535<\/p>\n
UTF-8\u7f16\u7801<\/h3>\n
\u6709\u5173\u5b57\u7b26\u4e32\uff0cMQTT\u91c7\u7528\u7684\u662f\u4fee\u6539\u7248\u7684UTF-8\u7f16\u7801\uff0c\u4e00\u822c\u5f62\u5f0f\u4e3a\u5982\u4e0b\uff0c\u9700\u8981\u7262\u8bb0\uff1a<\/p>\n\n\n\n\n\n\n\n
bit<\/th>\n7<\/th>\n6<\/th>\n5<\/th>\n4<\/th>\n3<\/th>\n2<\/th>\n1<\/th>\n0<\/th>\n<\/tr>\n<\/thead>\n
byte 1<\/td>\nString Length MSB<\/td>\n<\/tr>\n
byte 2<\/td>\nString Length LSB<\/td>\n<\/tr>\n
bytes 3 ...<\/td>\nEncoded Character Data

\n
\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\u6bd4\u5982AVA\uff0c\u4f7f\u7528writeUTF()\u65b9\u6cd5\u5199\u5165\u4e00\u4e32\u6587\u5b57\u201cOTWP\u201d\uff0c\u5934\u4e24\u4e2a\u5b57\u8282\u4e3a\u4e00\u4e2a\u5b8c\u6574\u7684\u65e0\u7b26\u53f7\u6570\u5b57\uff0c\u4ee3\u8868\u5b57\u7b26\u4e32\u5b57\u8282\u957f\u5ea6\uff0c\u540e\u9762\u56db\u4e2a\u5b57\u8282\u624d\u662f\u5b57\u7b26\u4e32\u771f\u6b63\u7684\u957f\u5ea6\uff0c\u5171\u516d\u4e2a\u5b57\u8282\uff1a<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
bit<\/th>\n7<\/th>\n6<\/th>\n5<\/th>\n4<\/th>\n3<\/th>\n2<\/th>\n1<\/th>\n0<\/th>\n<\/tr>\n<\/thead>\n
byte 1<\/td>\nMessage Length MSB (0x00)<\/td>\n<\/tr>\n
 <\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n<\/tr>\n
byte 2<\/td>\nMessage Length LSB (0x04)<\/td>\n<\/tr>\n
 <\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n<\/tr>\n
byte 3<\/td>\n'O' (0x4F)<\/td>\n<\/tr>\n
 <\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n1<\/td>\n1<\/td>\n<\/tr>\n
byte 4<\/td>\n'T' (0x54)<\/td>\n<\/tr>\n
 <\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n<\/tr>\n
byte 5<\/td>\n'W' (0x57)<\/td>\n<\/tr>\n
 <\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n1<\/td>\n<\/tr>\n
byte 6<\/td>\n'P' (0x50)<\/td>\n<\/tr>\n
 <\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\u8fd9\u70b9\uff0c\u5728\u7a0b\u5e8f\u4e2d\uff0c\u53ef\u4e0d\u7528\u5355\u72ec\u5904\u7406\u9ed8\u8ba4\uff0c\u76f4\u63a5\u4f7f\u7528readUTF()<\/strong>\u65b9\u6cd5\uff0c\u53ef\u81ea\u52a8\u7701\u53bb\u4e86\u5904\u7406\u5b57\u7b26\u4e32\u957f\u5ea6\u7684\u9ebb\u70e6\u3002\u5f53\u7136\uff0c\u53ef\u4ee5\u624b\u52a8\u8bfb\u53d6\u5b57\u7b26\u4e32\uff1a<\/p>\n
\/\/ \u6a21\u62df\u5199\u5165\r\ndataOutputStream.writeUTF( \"abcd\");\/\/ 2 + 4 = 6 byte\r\n......\r\n\/\/ \u6a21\u62df\u8bfb\u53d6 \r\nint decodedLength = dataInputStream.readUnsignedShort();\/\/2 byte\r\nbyte[] decodedString = new byte[decodedLength]; \/\/ 4 bytes\r\ndataInputStream.read(decodedString);\r\nString target = new String(decodedString, \"UTF-8\");<\/pre>\n
\u7b49\u540c\u4e8e\uff1a<\/p>\n
String target = dataInputStream.readUTF();<\/pre>\n
MQTT\u65e0\u8bba\u662f\u53ef\u53d8\u5934\u90e8\u8fd8\u662f\u6d88\u606f\u4f53\u4e2d\uff0c\u53ea\u8981\u662f\u5b57\u7b26\u4e32\u90e8\u5206\uff0c\u90fd\u662f\u91c7\u7528\u4e86\u4fee\u6539\u7248\u7684UTF-8\u7f16\u7801\uff0c\u8bfb\u53d6\u548c\u5199\u5165\uff0c\u501f\u52a9DataInputStream\/DataOutputStream\u7684\u5e2e\u52a9\uff0c\u4e00\u884c\u8bed\u53e5\uff0c\u7565\u53bb\u4e86\u624b\u52a8\u5904\u7406\u7684\u9ebb\u70e6\u3002<\/p>\n
\u5c0f\u7ed3<\/h2>\n
\u603b\u4e4b\uff0c\u638c\u63e1\u56fa\u5b9a\u5934\u90e8\u7684QoS level\u3001RETAIN\u6807\u8bb0\u3001\u53ef\u53d8\u5934\u90e8\u7684Connect flags\u4f5c\u7528\u548c\u610f\u4e49\uff0c\u5bf9\u603b\u4f53\u7406\u89e3MQTT\u4f5c\u7528\u5f88\u5927\u3002<\/p>\n
 <\/p>\n
\u8f6c\u81ea\uff1ahttp:\/\/www.blogjava.net\/yongboy\/archive\/2014\/02\/07\/409587.html<\/a><\/p>\n
 <\/p>\n
<\/code><\/code><\/code><\/code><\/code><\/code><\/code><\/code><\/code><\/p>\n","protected":false},"excerpt":{"rendered":"
MQTT\uff08Message Queue Telemetry Transport\uff09,\u9065\u6d4b\u4f20\u8f93\u534f\u8bae\uff0c\u63d0\u4f9b\u8ba2\u9605\/\u53d1\u5e03\u6a21\u5f0f\uff0c\u66f4\u4e3a\u7b80\u7ea6\u3001\u8f7b\u91cf\uff0c\u6613\u4e8e\u4f7f\u7528\uff0c\u9488\u5bf9\u53d7\u9650\u73af\u5883\uff08\u5e26\u5bbd\u4f4e\u3001\u7f51\u7edc\u5ef6\u8fdf\u9ad8\u3001\u7f51\u7edc\u901a\u4fe1\u4e0d\u7a33\u5b9a\uff09\uff0c\u53ef\u4ee5\u7b80\u5355\u6982\u62ec\u4e3a\u7269\u8054\u7f51\u6253\u9020\uff0c\u5b98\u65b9\u603b\u7ed3\u7279\u70b9\u5982\u4e0b\uff1a<\/p>\n
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