Headers 类型的Exchanges是不处理路由键的，而是根据发送的消息内容中的headers属性进行匹配。在绑定Queue与Exchange时指定一组键值对；当消息发送到RabbitMQ时会取到该消息的headers与Exchange绑定时指定的键值对进行匹配；如果完全匹配则消息会路由到该队列，否则不会路由到该队列。headers属性是一个键值对，可以是Hashtable，键值对的值可以是任何类型。而fanout，direct，topic 的路由键都需要要字符串形式的。
匹配规则x-match有下列两种类型：
- x-match = all ：表示所有的键值对都匹配才能接受到消息
- x-match = any ：表示只要有键值对匹配就能接受到消息
不过headers比较少用到，下面是headers的官方说明文档：
A headers exchange is designed to for routing on multiple attributes that are more easily expressed as message headers than a routing key. Headers exchanges ignore the routing key attribute. Instead, the attributes used for routing are taken from the headers attribute. A message is considered matching if the value of the header equals the value specified upon binding.
It is possible to bind a queue to a headers exchange using more than one header for matching. In this case, the broker needs one more piece of information from the application developer, namely, should it consider messages with any of the headers matching, or all of them? This is what the "x-match" binding argument is for. When the "x-match" argument is set to "any", just one matching header value is sufficient. Alternatively, setting "x-match" to "all" mandates that all the values must match.
Headers exchanges can be looked upon as "direct exchanges on steroids". Because they route based on header values, they can be used as direct exchanges where the routing key does not have to be a string; it could be an integer or a hash (dictionary) for example.
在Erlang里headers键值对表现的是一个三元组{Key,Type,Value} ， 如下：
-type(amqp_field_type() ::
'longstr' | 'signedint' | 'decimal' | 'timestamp' |
'table' | 'byte' | 'double' | 'float' | 'long' |
'short' | 'bool' | 'binary' | 'void' | 'array').
-type(amqp_property_type() ::
'shortstr' | 'longstr' | 'octet' | 'shortint' | 'longint' |
'longlongint' | 'timestamp' | 'bit' | 'table').
-type(amqp_table() :: [{binary(), amqp_field_type(), amqp_value()}]).
-type(amqp_array() :: [{amqp_field_type(), amqp_value()}]).
-type(amqp_value() :: binary() | % longstr
integer() | % signedint
{non_neg_integer(), non_neg_integer()} | % decimal
amqp_table() |
amqp_array() |
byte() | % byte
float() | % double
integer() | % long
integer() | % short
boolean() | % bool
binary() | % binary
'undefined' | % void
non_neg_integer() % timestamp
).
代码实现！！！！
消费者：
-module(mod_headers_receive).
-behaviour(gen_server).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]).
-export([start_link/0]).
-include("common.hrl").
-record(state, {}).
start_link() ->
gen_server:start_link({local,?MODULE}, ?MODULE, [], []).
init([]) ->
start(),
{ok, #state{}}.
handle_call(_Request, _From, State) ->
Reply = ok,
{reply, Reply, State}.
handle_cast(_Msg, State) ->
{noreply, State}.
handle_info({'basic.consume_ok',_}, State) ->
{noreply, State};
handle_info({#'basic.deliver'{},#amqp_msg{payload=Msg}}, State) ->
io:format(" receive messages is ~p~n",[Msg]),
{noreply, State};
handle_info(Info, State) ->
io:format(" unknown messages is ~p~n", [Info]),
{noreply, State}.
terminate(_Reason, _State) ->
ok.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
start() ->
Params = #amqp_params_network{host=?HOST,username=?USER_NAME,password=?PASSWORD},
case amqp_connection:start(Params) of
{ok,ConnectionPid} ->
{ok, Channel} = amqp_connection:open_channel(ConnectionPid),
%%生成队列名称
Queue = lists:concat([fanout_queue,now_time()]),
QueueName = erlang:list_to_binary(Queue),
%%声明队列
amqp_channel:call(Channel, #'queue.declare'{queue = QueueName,auto_delete=true}),
%%声明exchange
amqp_channel:call(Channel, #'exchange.declare'{auto_delete =true,exchange = <<"headers_test">>, type = ?EXCHANGE_TYPE_HEADERS}),
%%队列绑定到exchange,并设置headers
Headers = [{<<"x-match">>,longstr,<<"any">>},{<<"name">>,longstr,<<"jack">>},{<<"age">>,long,30}],
amqp_channel:call(Channel, #'queue.bind'{queue = QueueName, exchange = <<"headers_test">>, arguments = Headers}),
io:format("Waiting for messages......~n"),
amqp_channel:subscribe(Channel, #'basic.consume'{queue = QueueName,no_ack = true}, self());
{error,Resaon} ->
io:format("connection rabbit error: ~p~n", [Resaon]),
Resaon
end.
now_time()->
{A, B, _} = os:timestamp(),
A * 1000000 + B.
生产者：
-module(mod_headers_send).
-export([send/1]).
-include("common.hrl").
send(Msg) ->
Params = #amqp_params_network{host=?HOST,username=?USER_NAME,password=?PASSWORD},
case amqp_connection:start(Params) of
{ok,ConnectionPid} ->
{ok, Channel} = amqp_connection:open_channel(ConnectionPid),
Headers = [{<<"name">>,longstr,<<"jack">>},{<<"age">>,long,31}],
amqp_channel:cast(Channel,
#'basic.publish'{ exchange = <<"headers_test">>},
#amqp_msg{props= #'P_basic'{headers=Headers},payload = Msg}),
io:format("Sent '~p'~n",[Msg]),
amqp_channel:close(Channel),
amqp_connection:close(ConnectionPid);
{error,Reason} ->Reason
end.
Common头文件：
-include("amqp_client_internal.hrl").
-define(USER_NAME , <<"test">>).
-define(PASSWORD , <<"test">>).
-define(HOST , "192.168.249.128").
-define(PORT , 5672).
%%exchanges type
-define(EXCHANGE_TYPE_FANOUT , <<"fanout">> ).
-define(EXCHANGE_TYPE_DIRECT , <<"direct">> ).
-define(EXCHANGE_TYPE_TOPIC , <<"topic">> ).
-define(EXCHANGE_TYPE_HEADERS , <<"headers">>).
{<<"x-match">>,longstr,<<"any">>}运行结果如下：
{<<"x-match">>,longstr,<<"all">>}运行结果如下：
系统默认是{<<"x-match">>,longstr,<<"all">>}
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