在ASP.NET Core中使用托管启动（hosting startup）程序集，实现批量注册service

在启动aspnet core时可以从外部程序集向应用添加增强功能。例如，外部库可以用托管启动（ hosting startup） 实现为应用程序提供附加配置（configuration）或服务（service）。

具体实现如下：

1、实现 ihostingstartup 接口

2、标注程序集（hostingstartup）属性。

[assembly: hostingstartup(typeof(startupenhancement.startupenhancementhostingstartup))]

3、在createhostbuilder中配置加载的程序集，如果多个程序集 分号 隔开

        public static ihostbuilder createhostbuilder(string[] args) =>
            host.createdefaultbuilder(args)
                .configurewebhostdefaults(webbuilder =>
                {
                    //增加外部启动项fap.core.di.servicesinjection，初始化所有service
                    webbuilder.usesetting(webhostdefaults.hostingstartupassemblieskey,"fap.core")
                    
                    .usestartup<startup>();
                });

如果阻止hosting startup加载，需要以下设置

 webbuilder.usesetting(webhostdefaults.preventhostingstartupkey, "true")

如果排除某些程序集的hosting startup加载

 webbuilder.usesetting(webhostdefaults.hostingstartupexcludeassemblieskey, "assembly1;assembly2; ...")

多个程序集 分号 隔开。

 

aspnet core 中的 di 没有批量注册service的功能。下面我就实现一个批量注册service的功能。

采用注解的形式，在需要注册为service的类上进行标注。

定义一个attribute

    [attributeusage(attributetargets.class)]
    public class serviceattribute:attribute
    {
        public serviceattribute(servicelifetime servicelifetime)
        {
            servicelifetime = servicelifetime;
        }
        public servicelifetime servicelifetime { get; set; } = servicelifetime.transient;
    }

定义需要注册的类和接口

    public interface iuser
    {
        string get(string username);
    }
    public interface iuser1
    {
        string get1(string username);
    }

    [service(microsoft.extensions.dependencyinjection.servicelifetime.singleton)]
    public class user : iuser,iuser1
    {
        private string s = guid.newguid().tostring();
        public string get(string username)
        {
            return $"{s}===={username}";
        }

        public string get1(string username)
        {
            return s;
        }
    }

如上，在user类上标注serviceattribute属性，设置servicelifetime为单利模式servicelifetime.singleton

接下来实现 利用host startup来实现自动注册功能。根据class上标注的service attribute 来自动注册service

//标注程序集属性 hostingstartup
[assembly: hostingstartup(typeof(fap.core.di.servicesinjection))]
namespace fap.core.di
{
    public class servicesinjection : ihostingstartup
    {
        public void configure(iwebhostbuilder builder)
        {
            builder.configureservices(services =>
            {
                var basepath = appdomain.currentdomain.relativesearchpath ?? appdomain.currentdomain.basedirectory;
                var assemblies = directory.getfiles(basepath, "*.dll").select(assembly.loadfrom).toarray();
                var types = assemblies.selectmany(a => a.definedtypes).select(type => type.astype()).where(t => t.getcustomattribute<serviceattribute>() != null).toarray();
                var implementtypes = types.where(t => t.isclass).toarray();
                foreach (var implementtype in implementtypes)
                {
                    var interfacetypes = implementtype.getinterfaces();
                    foreach (var interfacetype in interfacetypes)
                    {
                        var attr = implementtype.getcustomattribute<serviceattribute>();
　　　　　　　　　　　　　　//根据servicelifetime来向容器中注册
                        _ = (attr.servicelifetime switch
                        {
                            servicelifetime sl when sl == servicelifetime.scoped => services.addscoped(interfacetype, implementtype),
                            servicelifetime sl when sl == servicelifetime.singleton => services.addsingleton(interfacetype, implementtype),
                            servicelifetime sl when sl == servicelifetime.transient => services.addtransient(interfacetype, implementtype),
                            _ => throw new filenotfoundexception("未找到此类型")
                        });
                    }
                }
            });
        }
    }
}

下面在host builder时设置hoststartup

        public static ihostbuilder createhostbuilder(string[] args) =>
            host.createdefaultbuilder(args)
                .configurewebhostdefaults(webbuilder =>
                {
                    //增加外部启动项fap.core.di.servicesinjection，初始化所有service
                    webbuilder.usesetting(webhostdefaults.hostingstartupassemblieskey,"fap.core")
                    
                    .usestartup<startup>();
                });

 

这样我们在controller中就可以使用已经自动注册到servicecontainer中的service了。

   public class homecontroller : controller
    {
        private readonly ilogger<homecontroller> _logger;
        private readonly iuser1 _userservice1;
        private readonly iuser _userservice;
        public homecontroller(ilogger<homecontroller> logger,iuser1 userservice1,iuser user)
        {
            _logger = logger;
            _userservice1 = userservice1;
            _userservice = user;
        }

        public iactionresult index()
        {
            viewbag.cc = _userservice.get("zhangsan")+_userservice1.get1("lisi");
            return view();
        }
}

除了利用ihostingstartup为应用提供服务注册，还可以提供额外配置。

[assembly: hostingstartup(typeof(hostingstartuplibrary.servicekeyinjection))]

namespace hostingstartuplibrary
{
    public class servicekeyinjection : ihostingstartup
    {
        public void configure(iwebhostbuilder builder)
        {
            builder.configureappconfiguration(config =>
            {
                var dict = new dictionary<string, string>
                {
                    {"devaccount_fromlibrary", "dev_1111111-1111"},
                    {"prodaccount_fromlibrary", "prod_2222222-2222"}
                };

                config.addinmemorycollection(dict);
            });
        }
    }
}

在controller中就可以访问到如上配置项

        public indexmodel(iconfiguration config)
        {
            servicekey_development_library = config["devaccount_fromlibrary"];
            servicekey_production_library = config["prodaccount_fromlibrary"];
          
        }

 

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具体源码实现：

webbuilder.usesetting(webhostdefaults.hostingstartupassemblieskey,"fap.core")

设置了webhostoptions中的hostingstartupassemblies属性，存放我们要加载的ihostingstartup的程序集。

在iwebhostbuilder 调用 builder()返回iwebhost方法中进行调用。下面为关键代码

            _options = new webhostoptions(_config, assembly.getentryassembly()?.getname().name);
　　　　　　　//没有设置阻止加载webbuilder.usesetting( webhostdefaults.preventhostingstartupkey, "false")
            if (!_options.preventhostingstartup)
            {
                var exceptions = new list<exception>();

                // 执行 hosting startup assemblies
                foreach (var assemblyname in _options.getfinalhostingstartupassemblies().distinct(stringcomparer.ordinalignorecase))
                {
                    try
                    {
                        var assembly = assembly.load(new assemblyname(assemblyname));

                        foreach (var attribute in assembly.getcustomattributes<hostingstartupattribute>())
                        {
　　　　　　　　　　　　　　　　　//实例化自定义的hostingstartup
                            var hostingstartup = (ihostingstartup)activator.createinstance(attribute.hostingstartuptype);
　　　　　　　　　　　　　　　　　//调用configure方法，执行我们自定的逻辑
                            hostingstartup.configure(this);
                        }
                    }
                    catch (exception ex)
                    {
                        // capture any errors that happen during startup
                        exceptions.add(new invalidoperationexception($"startup assembly {assemblyname} failed to execute. see the inner exception for more details.", ex));
                    }
                }

                if (exceptions.count > 0)
                {
                    hostingstartuperrors = new aggregateexception(exceptions);
                }
            }

_options.getfinalhostingstartupassemblies()方法代码如下：

   public ienumerable<string> getfinalhostingstartupassemblies()
        {
　　　　　　　//返回hostingstartupassemblies中排除掉hostingstartupexcludeassemblies的程序集
            return hostingstartupassemblies.except(hostingstartupexcludeassemblies, stringcomparer.ordinalignorecase);
        }