Question

我尝试获取用于打印的vsn信息。但返回值是[]。

app文件如下：

{application,john,
             [{description,[]},
              {vsn,"0.1.2.3"},
              {registered,[john]},
              {applications,[kernel,stdlib]},
              {mod,{john_app,[]}},
              {env,[]},
              {modules,[john_app,john_basic_rule,john_basic_sup,john_client,
                        john_cookie,john_env,john_file,john_framing_0_0_1,
                        john_framing_tests,john_group_sup,john_guid,john_ldap,
                        john_ldap_tests,john_local_message,john_log,
                        john_log_tests,john_message,john_mnesia,john_model,
                        john_rabbitmq,john_reader,john_reader_2_sup,
                        john_reader_sup,john_reader_tests,john_reader_tests_2,
                        john_store,john_store_tests,john_sup,john_upgrade,
                        john_version,john_worker,john_worker_tests]}]}.

xxx_app.erl文件如下：

start(normal, []) ->
    lager:md(?OP_ST),
    lager:debug("john_app_start_1"),
    case erts_version_check() of
        ok ->
            lager:debug("john_start_2"),
            try
                %% 是否需要启动john_sup依赖的服务器??
                true = register(john, self()),
                [ok = run_boot_step(Step) || Step <- boot_steps()],
                {ok,Sup_pid} = john_basic_sup:start_link(),
                ok = john_basic_sup:start_basic(),
                print_banner(),
                {ok, Sup_pid}
            catch Error_a:Reason_a->
                    lager:error("john_app_start_normal_3:~p,~p,~n~p",
                                [Error_a,Reason_a,erlang:get_stacktrace()]),
                    Reason_a                        
            end;
        Error ->
            lager:error("john_start_error:~p",[Error]),
            Error
    end.

print_banner() ->
    {ok, Product} = application:get_key(john,id),
    {ok, Version} = application:get_key(john,vsn),
    ProductLen = string:len(Product),
    lager:info("~n"
              "john--------------~n"
              "~s~n~s~n~s~n~s~n~s~n",
              [Product, string:right([$v|Version], ProductLen),
               ?PROTOCOL_VERSION,
               ?COPYRIGHT_MESSAGE, ?INFORMATION_MESSAGE]),

然后我尝试了application：get_all_key（），然后返回[]。

为什么？

我尝试了application:loaded_applications()和application:get_all_keys()。但结果不是预期的：

(zarah_john_slave_21@yus-iMac.local)3> application:loaded_applications().
[{goldrush,[],"0.1.0"},
 {kernel,"ERTS  CXC 138 10","2.16.2"},
 {lager,"Erlang logging framework","2.0.0"},
 {friar,[],"0.1.2"},
 {amqp_client,"RabbitMQ AMQP Client","2.8.2"},
 {mnesia,"MNESIA  CXC 138 12","4.9"},
 {inets,"INETS  CXC 138 49","5.9.5"},
 {john,[],"0.1.2.3"},
 {jotham,"pgsql jacob install","0.1.1"},
 {sasl,"SASL  CXC 138 11","2.3.2"},
 {stdlib,"ERTS  CXC 138 10","1.19.2"}]
(zarah_john_slave_21@yus-iMac.local)4> application:get_all_key().
[]
(zarah_john_slave_21@yus-iMac.local)5>

我尝试了应用程序：get_all_key（john）。

{ok,[{description,[]},
     {id,[]},
     {vsn,"0.1.2.3"},
     {modules,[john_app,john_basic_rule,john_basic_sup,
               john_client,john_cookie,john_env,john_file,
               john_framing_0_0_1,john_framing_tests,john_group_sup,
               john_guid,john_ldap,john_ldap_tests,john_local_message,
               john_log,john_log_tests,john_message,john_mnesia,john_model,
               john_rabbitmq,john_reader|...]},
     {maxP,infinity},
     {maxT,infinity},
     {registered,[john]},
     {included_applications,[]},
     {applications,[kernel,stdlib]},
     {env,[{db_host,"xxx.xxx.com"},
           {db_port,5432},
           {ldap_options,[{timeout,7000},{anon_auth,true}]},
           {mq_username,<<"john_2">>},
           {link_exchange,<<"exchange_john_2">>},
           {included_applications,[]},
           {ldap_password,"helloworld"},
           {ldap_user,"admin"},
           {mq_port,5672},
           {db_password,<<"xxxx">>},
           {is_direct_link,false},
           {db_database,"db_jotham"},
           {cluster_nodes,[...]},
           {mq_address,...},
           {...}|...]},
     {mod,{john_app,[]}},
     {start_phases,undefined}]}

另外，当get_key功能可用时？ {ok，Product} = application：get_key（john，id）， {ok，Version} = application：get_key（john，vsn），

在上面的start(normal,[])中，get_key功能不可用，但在服务器启动完成后，get_key(john,vsn)可用。我仍在努力寻找原因。

问题已经解决，它与“复制 - 不思考”有关。该代码最初来自rabbitmq的rabbit.erl文件。

以下代码导致了问题：

 [Product, string:right([$v|Version], ProductLen),

rabbitmq的“ProductLen”键不为0.但我的ProductLen为0，字符串：right（xxx，0）返回“”。所以出现了问题。

感谢您提供调试的线索。

Answer 1

应用程序资源文件应该称为Application.app，其中Application是应用程序的名称。该文件应位于应用程序的ebin目录中。

首先，检查app文件名是john.app？

其次，检查app文件是否在正确的目录中？

您可以使用loaded_applications() -> [{Application, Description, Vsn}]检查您的应用是否已成功加载。

为什么＆＃34;应用程序：get_key（x，x）＆＃34;不行？

1 个答案: