SpringBoot读取配置文件源码探究

1. springboot读取配置文件源码探究

1.1. 概览

• springboot的源码是再原来的spring源码上又包了一层，看过spring源码都知道，当我们从入口debug进去的时候，原来的spring源码都集中在refreshcontext方法，springboot的主要运行步骤，基本都包含在这个方法里了，而这个方法就是我们运行springboot的主函数springapplication.run(application.class, args);经过几步后到达的

    public configurableapplicationcontext run(string... args) {
        stopwatch stopwatch = new stopwatch();
        stopwatch.start();
        configurableapplicationcontext context = null;
        failureanalyzers analyzers = null;
        configureheadlessproperty();
        springapplicationrunlisteners listeners = getrunlisteners(args);
        listeners.starting();
        try {
            applicationarguments applicationarguments = new defaultapplicationarguments(
                    args);
            configurableenvironment environment = prepareenvironment(listeners,
                    applicationarguments);
            banner printedbanner = printbanner(environment);
            context = createapplicationcontext();
            analyzers = new failureanalyzers(context);
            preparecontext(context, environment, listeners, applicationarguments,
                    printedbanner);
            refreshcontext(context);
            afterrefresh(context, applicationarguments);
            listeners.finished(context, null);
            stopwatch.stop();
            if (this.logstartupinfo) {
                new startupinfologger(this.mainapplicationclass)
                        .logstarted(getapplicationlog(), stopwatch);
            }
            return context;
        }
        catch (throwable ex) {
            handlerunfailure(context, listeners, analyzers, ex);
            throw new illegalstateexception(ex);
        }
    }

1.2. 配置读取步骤

1.2.1. prepareenvironment

• 配置读取的步骤主要就在configurableenvironment environment = prepareenvironment(listeners, applicationarguments);这一步，我们继续深入

    private configurableenvironment prepareenvironment(
            springapplicationrunlisteners listeners,
            applicationarguments applicationarguments) {
        // create and configure the environment
        configurableenvironment environment = getorcreateenvironment();
        configureenvironment(environment, applicationarguments.getsourceargs());
        //主要是这步
        listeners.environmentprepared(environment);
        if (!this.webenvironment) {
            environment = new environmentconverter(getclassloader())
                    .converttostandardenvironmentifnecessary(environment);
        }
        return environment;
    }

• 创建基本的环境容器后，进入listeners.environmentprepared(environment);通过监听器来进行环境变量的初始化，同时读取配置也是一部分工作

1.2.2. environmentprepared

• 下一步，看到对监听器进行循环处理，这里的listeners中，默认只有一个eventpublishrunlistener

    public void environmentprepared(configurableenvironment environment) {
        for (springapplicationrunlistener listener : this.listeners) {
            listener.environmentprepared(environment);
        }
    }

• 继续如下，这一步它进行广播事件了

    @override
    public void environmentprepared(configurableenvironment environment) {
        this.initialmulticaster.multicastevent(new applicationenvironmentpreparedevent(
                this.application, this.args, environment));
    }

1.2.3. multicastevent

    @override
    public void multicastevent(applicationevent event) {
        multicastevent(event, resolvedefaulteventtype(event));
    }

继续，重点是invokelistener方法，去调用监听器事件，可以想象对配置文件来讲，这就是读取配置事件了。同时监听器有很多，读取配置文件的监听器是configfileaplicationlistener，看名字还是蛮明显的吧

    @override
    public void multicastevent(final applicationevent event, resolvabletype eventtype) {
        resolvabletype type = (eventtype != null ? eventtype : resolvedefaulteventtype(event));
        for (final applicationlistener<?> listener : getapplicationlisteners(event, type)) {
            executor executor = gettaskexecutor();
            if (executor != null) {
                executor.execute(new runnable() {
                    @override
                    public void run() {
                        invokelistener(listener, event);
                    }
                });
            }
            else {
                //重点
                invokelistener(listener, event);
            }
        }
    }

继续，和上一步类似，do真正的事件了

    protected void invokelistener(applicationlistener<?> listener, applicationevent event) {
        errorhandler errorhandler = geterrorhandler();
        if (errorhandler != null) {
            try {
                doinvokelistener(listener, event);
            }
            catch (throwable err) {
                errorhandler.handleerror(err);
            }
        }
        else {
            //重点
            doinvokelistener(listener, event);
        }
    }

    private void doinvokelistener(applicationlistener listener, applicationevent event) {
        try {
            // 入口
            listener.onapplicationevent(event);
        }
        catch (classcastexception ex) {
            string msg = ex.getmessage();
            if (msg == null || matchesclasscastmessage(msg, event.getclass())) {
                // possibly a lambda-defined listener which we could not resolve the generic event type for
                // -> let's suppress the exception and just log a debug message.
                log logger = logfactory.getlog(getclass());
                if (logger.isdebugenabled()) {
                    logger.debug("non-matching event type for listener: " + listener, ex);
                }
            }
            else {
                throw ex;
            }
        }
    }

1.2.4. onapplicationevent

• 在configfileapplicationlistener类中继续

    @override
    public void onapplicationevent(applicationevent event) {
        if (event instanceof applicationenvironmentpreparedevent) {
            //配置入口
            onapplicationenvironmentpreparedevent(
                    (applicationenvironmentpreparedevent) event);
        }
        if (event instanceof applicationpreparedevent) {
            onapplicationpreparedevent(event);
        }
    }

继续，可以看到处理器有这些，我们关注configfileapplicationlistener

    private void onapplicationenvironmentpreparedevent(
            applicationenvironmentpreparedevent event) {
        list<environmentpostprocessor> postprocessors = loadpostprocessors();
        postprocessors.add(this);
        annotationawareordercomparator.sort(postprocessors);
        for (environmentpostprocessor postprocessor : postprocessors) {
            //入口
            postprocessor.postprocessenvironment(event.getenvironment(),
                    event.getspringapplication());
        }
    }

1.2.5. postprocessenvironment

    @override
    public void postprocessenvironment(configurableenvironment environment,
            springapplication application) {
        //重点入口
        addpropertysources(environment, application.getresourceloader());
        configureignorebeaninfo(environment);
        bindtospringapplication(environment, application);
    }

继续

    protected void addpropertysources(configurableenvironment environment,
            resourceloader resourceloader) {
        randomvaluepropertysource.addtoenvironment(environment);
        //总算看到加载入口了
        new loader(environment, resourceloader).load();
    }

1.2.6. load

public void load() {
            this.propertiesloader = new propertysourcesloader();
            this.activatedprofiles = false;
            this.profiles = collections.aslifoqueue(new linkedlist<profile>());
            this.processedprofiles = new linkedlist<profile>();

            // pre-existing active profiles set via environment.setactiveprofiles()
            // are additional profiles and config files are allowed to add more if
            // they want to, so don't call addactiveprofiles() here.
            set<profile> initialactiveprofiles = initializeactiveprofiles();
            this.profiles.addall(getunprocessedactiveprofiles(initialactiveprofiles));
            if (this.profiles.isempty()) {
                for (string defaultprofilename : this.environment.getdefaultprofiles()) {
                    profile defaultprofile = new profile(defaultprofilename, true);
                    if (!this.profiles.contains(defaultprofile)) {
                        this.profiles.add(defaultprofile);
                    }
                }
            }

            // the default profile for these purposes is represented as null. we add it
            // last so that it is first out of the queue (active profiles will then
            // override any settings in the defaults when the list is reversed later).
            this.profiles.add(null);

            while (!this.profiles.isempty()) {
                profile profile = this.profiles.poll();
                for (string location : getsearchlocations()) {
                    if (!location.endswith("/")) {
                        // location is a filename already, so don't search for more
                        // filenames
                        load(location, null, profile);
                    }
                    else {
                        for (string name : getsearchnames()) {
                            //加载入口
                            load(location, name, profile);
                        }
                    }
                }
                this.processedprofiles.add(profile);
            }

            addconfigurationproperties(this.propertiesloader.getpropertysources());
        }

• 可以看到它的加载名从getsearchnames获取，那就看看这个方法

        private set<string> getsearchnames() {
            if (this.environment.containsproperty(config_name_property)) {
                return asresolvedset(this.environment.getproperty(config_name_property),
                        null);
            }
            return asresolvedset(configfileapplicationlistener.this.names, default_names);
        }

• config_name_property值为spring.config.name，default_names值为application，所以可以看出application这个名字就是默认的配置名了，但也可以用spring.config.name属性来修改

• 其实到这一步，后面已经没难度了，可以想象，接下去应该是拼接出完整的路径，找到文件读取，还是走完流程把

• 继续

        private void load(string location, string name, profile profile) {
            string group = "profile=" + ((profile != null) ? profile : "");
            if (!stringutils.hastext(name)) {
                // try to load directly from the location
                loadintogroup(group, location, profile);
            }
            else {
                // search for a file with the given name
                for (string ext : this.propertiesloader.getallfileextensions()) {
                    if (profile != null) {
                        // try the profile-specific file
                        loadintogroup(group, location + name + "-" + profile + "." + ext,
                                null);
                        for (profile processedprofile : this.processedprofiles) {
                            if (processedprofile != null) {
                                loadintogroup(group, location + name + "-"
                                        + processedprofile + "." + ext, profile);
                            }
                        }
                        // sometimes people put "spring.profiles: dev" in
                        // application-dev.yml (gh-340). arguably we should try and error
                        // out on that, but we can be kind and load it anyway.
                        loadintogroup(group, location + name + "-" + profile + "." + ext,
                                profile);
                    }
                    // also try the profile-specific section (if any) of the normal file
                    //加载重点
                    loadintogroup(group, location + name + "." + ext, profile);
                }
            }
        }

• 继续

        private propertysource<?> loadintogroup(string identifier, string location,
                profile profile) {
            try {
                //入口
                return doloadintogroup(identifier, location, profile);
            }
            catch (exception ex) {
                throw new illegalstateexception(
                        "failed to load property source from location '" + location + "'",
                        ex);
            }
        }

• do开头都是正式要干事了

        private propertysource<?> doloadintogroup(string identifier, string location,
                profile profile) throws ioexception {
            resource resource = this.resourceloader.getresource(location);
            propertysource<?> propertysource = null;
            stringbuilder msg = new stringbuilder();
            if (resource != null && resource.exists()) {
                string name = "applicationconfig: [" + location + "]";
                string group = "applicationconfig: [" + identifier + "]";
                // 加载入口
                propertysource = this.propertiesloader.load(resource, group, name,
                        (profile != null) ? profile.getname() : null);
                if (propertysource != null) {
                    msg.append("loaded ");
                    handleprofileproperties(propertysource);
                }
                else {
                    msg.append("skipped (empty) ");
                }
            }
            else {
                msg.append("skipped ");
            }
            msg.append("config file ");
            msg.append(getresourcedescription(location, resource));
            if (profile != null) {
                msg.append(" for profile ").append(profile);
            }
            if (resource == null || !resource.exists()) {
                msg.append(" resource not found");
                this.logger.trace(msg);
            }
            else {
                this.logger.debug(msg);
            }
            return propertysource;
        }

• load内容，这里有两个加载器，看名字也知道了，yml结尾的文件肯定用yamlpropertysourceloader才能加载，properties结尾的用另一个
  

    public propertysource<?> load(resource resource, string group, string name,
            string profile) throws ioexception {
        if (isfile(resource)) {
            string sourcename = generatepropertysourcename(name, profile);
            for (propertysourceloader loader : this.loaders) {
                if (canloadfileextension(loader, resource)) {
                    // 干事的入口
                    propertysource<?> specific = loader.load(sourcename, resource,
                            profile);
                    addpropertysource(group, specific);
                    return specific;
                }
            }
        }
        return null;
    }

• 我用的是yml，所以在yamlpropertysourceloader类

    @override
    public propertysource<?> load(string name, resource resource, string profile)
            throws ioexception {
        if (classutils.ispresent("org.yaml.snakeyaml.yaml", null)) {
            processor processor = new processor(resource, profile);
            //真正的处理类
            map<string, object> source = processor.process();
            if (!source.isempty()) {
                return new mappropertysource(name, source);
            }
        }
        return null;
    }

        public map<string, object> process() {
            final map<string, object> result = new linkedhashmap<string, object>();
            //接近了
            process(new matchcallback() {
                @override
                public void process(properties properties, map<string, object> map) {
                    result.putall(getflattenedmap(map));
                }
            });
            return result;
        }

1.2.7. process

    protected void process(matchcallback callback) {
        yaml yaml = createyaml();
        for (resource resource : this.resources) {
            //更近了
            boolean found = process(callback, yaml, resource);
            if (this.resolutionmethod == resolutionmethod.first_found && found) {
                return;
            }
        }
    }

• 继续深入
  
  
• 可以看到，总算把我配合文件的内容给读到了，然后放入callback

    private boolean process(matchcallback callback, yaml yaml, resource resource) {
        int count = 0;
        try {
            if (logger.isdebugenabled()) {
                logger.debug("loading from yaml: " + resource);
            }
            //读取文件
            reader reader = new unicodereader(resource.getinputstream());
            try {
                for (object object : yaml.loadall(reader)) {
                    //总算拿到了
                    if (object != null && process(asmap(object), callback)) {
                        count++;
                        if (this.resolutionmethod == resolutionmethod.first_found) {
                            break;
                        }
                    }
                }
                if (logger.isdebugenabled()) {
                    logger.debug("loaded " + count + " document" + (count > 1 ? "s" : "") +
                            " from yaml resource: " + resource);
                }
            }
            finally {
                reader.close();
            }
        }
        catch (ioexception ex) {
            handleprocesserror(resource, ex);
        }
        return (count > 0);
    }

• 结果就存入了result

• 这样之后返回去看，你就会看到它存入了mappropertysource属性资源，在之后就会被用上了

1.3. 总结

• 我通过一步步的代码跟踪，解析了springboot读取application.yml的整个流程，代码虽然贴的比较多，但可以让初学者也可以跟着这个步骤完整的理解一遍，代码中的关键步骤我都用中文标明了，其它没标注部分不是这章的重点，想研究的自行研究