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spring boot容器启动流程

时间:2021-03-26 11:20     来源/作者:只会一点java

一、前言

spring cloud大行其道的当下,如果不了解基本原理那么是很纠结的(看见的都是 约定大于配置 ,但是原理呢?为什么要这么做?)。spring cloud是基于spring boot快速搭建的,今天咱们就看看spring boot容器启动流程。(本文不讲解如何快速启动spring boot,那些直接官方看即可, 官网文档飞机票 )

二、容器启动

spring boot一般是 指定容器启动main方法,然后以命令行方式启动jar包 ,如下图:

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@springbootapplication
public class application {
 public static void main(string[] args) {
 springapplication.run(application.class, args);
 }
 }

这里核心关注2个东西:

1.@springbootapplication注解

2. springapplication.run()静态方法

下面我们就分别探究这两块内容。

2.1 @springbootapplication注解

源码如下:  

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@target(elementtype.type)
@retention(retentionpolicy.runtime)
@documented
@inherited
@springbootconfiguration
@enableautoconfiguration
@componentscan(excludefilters = {
@filter(type = filtertype.custom, classes = typeexcludefilter.class),
@filter(type = filtertype.custom, classes = autoconfigurationexcludefilter.class) })
public @interface springbootapplication {

核心注解:

@springbootconfiguration(实际就是个@configuration):表示这是一个javaconfig配置类,可以在这个类中自定义bean,依赖关系等。-》这个是spring-boot特有的注解,常用到。

@enableautoconfiguration:借助@import的帮助,将所有符合自动配置条件的bean定义加载到ioc容器(建议放在根包路径下,这样可以扫描子包和类)。-》这个需要详细深挖!

@componentscan:spring的自动扫描注解,可定义扫描范围,加载到ioc容器。-》这个不多说,spring的注解大家肯定眼熟

其中@enableautoconfiguration这个注解的源码:

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@suppresswarnings("deprecation")
@target(elementtype.type)
@retention(retentionpolicy.runtime)
@documented
@inherited
@autoconfigurationpackage
@import(enableautoconfigurationimportselector.class)
public @interface enableautoconfiguration {

核心是一个enableautoconfigurationimportselector类图如下:

 spring boot容器启动流程

核心方法在顶级接口 importselector 的 selectimports() ,源码如下:

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@override
public string[] selectimports(annotationmetadata annotationmetadata) {
if (!isenabled(annotationmetadata)) {
return no_imports;
}
try { //1.从meta-inf/spring-autoconfigure-metadata.properties文件中载入483条配置属性(有一些有默认值),
autoconfigurationmetadata autoconfigurationmetadata = autoconfigurationmetadataloader
 .loadmetadata(this.beanclassloader);
annotationattributes attributes = getattributes(annotationmetadata);//2.获取注解属性
list<string> configurations = getcandidateconfigurations(annotationmetadata,//3.获取97个自动配置类
 attributes);
configurations = removeduplicates(configurations);//4.移除重复的
configurations = sort(configurations, autoconfigurationmetadata);//5.排序
set<string> exclusions = getexclusions(annotationmetadata, attributes);//6.获取需要排除的
checkexcludedclasses(configurations, exclusions);//7.校验排除类
configurations.removeall(exclusions);//8.删除所有需要排除的
configurations = filter(configurations, autoconfigurationmetadata);//9.过滤器onclasscondition(注解中配置的当存在某类才生效)
fireautoconfigurationimportevents(configurations, exclusions);//10.触发自动配置导入监听事件
return configurations.toarray(new string[configurations.size()]);
}
catch (ioexception ex) {
throw new illegalstateexception(ex);
}
}

这里注意3个核心方法:

1) loadmetadata 加载配置

其实就是用类加载器去加载: meta-inf/spring-autoconfigure-metadata.properties (spring-boot-autoconfigure-1.5.9.release-sources.jar) 文件中定义的配置,返回propertiesautoconfigurationmetadata(实现了autoconfigurationmetadata接口,封装了属性的get set方法)

2) getcandidateconfigurations 获取默认支持的自动配置类名列表

自动配置灵魂方法, springfactoriesloader.loadfactorynames 从 meta-inf/spring.factories (spring-boot-autoconfigure-1.5.9.release-sources.jar)文件中获取自动配置类key=enableautoconfiguration.class的配置。 

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protected list<string> getcandidateconfigurations(annotationmetadata metadata,
 annotationattributes attributes) {//话说这里2个入参没啥用啊...谁来给我解释一下...
 list<string> configurations = springfactoriesloader.loadfactorynames(
  getspringfactoriesloaderfactoryclass(), getbeanclassloader());
 assert.notempty(configurations,
  "no auto configuration classes found in meta-inf/spring.factories. if you "
  + "are using a custom packaging, make sure that file is correct.");
 return configurations;
 }
 //返回的是enableautoconfiguration类
 protected class<?> getspringfactoriesloaderfactoryclass() {
 return enableautoconfiguration.class;
 }

实际获取了什么? spring.factories 文件如下,实际获取了 # auto configure 自动配置模块的所有类。

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# initializers
org.springframework.context.applicationcontextinitializer=\
org.springframework.boot.autoconfigure.sharedmetadatareaderfactorycontextinitializer,\
org.springframework.boot.autoconfigure.logging.autoconfigurationreportlogginginitializer
# application listeners
org.springframework.context.applicationlistener=\
org.springframework.boot.autoconfigure.backgroundpreinitializer
# auto configuration import listeners
org.springframework.boot.autoconfigure.autoconfigurationimportlistener=\
org.springframework.boot.autoconfigure.condition.conditionevaluationreportautoconfigurationimportlistener
# auto configuration import filters
org.springframework.boot.autoconfigure.autoconfigurationimportfilter=\
org.springframework.boot.autoconfigure.condition.onclasscondition
# auto configure 这里就是全部的自动配置类
org.springframework.boot.autoconfigure.enableautoconfiguration=\
org.springframework.boot.autoconfigure.admin.springapplicationadminjmxautoconfiguration,\
org.springframework.boot.autoconfigure.aop.aopautoconfiguration,\
org.springframework.boot.autoconfigure.amqp.rabbitautoconfiguration,\
org.springframework.boot.autoconfigure.batch.batchautoconfiguration,\
org.springframework.boot.autoconfigure.cache.cacheautoconfiguration,\
org.springframework.boot.autoconfigure.cassandra.cassandraautoconfiguration,\
org.springframework.boot.autoconfigure.cloud.cloudautoconfiguration,\
org.springframework.boot.autoconfigure.context.configurationpropertiesautoconfiguration,\
org.springframework.boot.autoconfigure.context.messagesourceautoconfiguration,\
org.springframework.boot.autoconfigure.context.propertyplaceholderautoconfiguration,\
org.springframework.boot.autoconfigure.couchbase.couchbaseautoconfiguration,\
org.springframework.boot.autoconfigure.dao.persistenceexceptiontranslationautoconfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.cassandradataautoconfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.cassandrarepositoriesautoconfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.couchbasedataautoconfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.couchbaserepositoriesautoconfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.elasticsearchautoconfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.elasticsearchdataautoconfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.elasticsearchrepositoriesautoconfiguration,\
org.springframework.boot.autoconfigure.data.jpa.jparepositoriesautoconfiguration,\
org.springframework.boot.autoconfigure.data.ldap.ldapdataautoconfiguration,\
org.springframework.boot.autoconfigure.data.ldap.ldaprepositoriesautoconfiguration,\
org.springframework.boot.autoconfigure.data.mongo.mongodataautoconfiguration,\
org.springframework.boot.autoconfigure.data.mongo.mongorepositoriesautoconfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.neo4jdataautoconfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.neo4jrepositoriesautoconfiguration,\
org.springframework.boot.autoconfigure.data.solr.solrrepositoriesautoconfiguration,\
org.springframework.boot.autoconfigure.data.redis.redisautoconfiguration,\
org.springframework.boot.autoconfigure.data.redis.redisrepositoriesautoconfiguration,\
org.springframework.boot.autoconfigure.data.rest.repositoryrestmvcautoconfiguration,\
org.springframework.boot.autoconfigure.data.web.springdatawebautoconfiguration,\
org.springframework.boot.autoconfigure.elasticsearch.jest.jestautoconfiguration,\
org.springframework.boot.autoconfigure.freemarker.freemarkerautoconfiguration,\
org.springframework.boot.autoconfigure.gson.gsonautoconfiguration,\
org.springframework.boot.autoconfigure.h2.h2consoleautoconfiguration,\
org.springframework.boot.autoconfigure.hateoas.hypermediaautoconfiguration,\
org.springframework.boot.autoconfigure.hazelcast.hazelcastautoconfiguration,\
org.springframework.boot.autoconfigure.hazelcast.hazelcastjpadependencyautoconfiguration,\
org.springframework.boot.autoconfigure.info.projectinfoautoconfiguration,\
org.springframework.boot.autoconfigure.integration.integrationautoconfiguration,\
org.springframework.boot.autoconfigure.jackson.jacksonautoconfiguration,\
org.springframework.boot.autoconfigure.jdbc.datasourceautoconfiguration,\
org.springframework.boot.autoconfigure.jdbc.jdbctemplateautoconfiguration,\
org.springframework.boot.autoconfigure.jdbc.jndidatasourceautoconfiguration,\
org.springframework.boot.autoconfigure.jdbc.xadatasourceautoconfiguration,\
org.springframework.boot.autoconfigure.jdbc.datasourcetransactionmanagerautoconfiguration,\
org.springframework.boot.autoconfigure.jms.jmsautoconfiguration,\
org.springframework.boot.autoconfigure.jmx.jmxautoconfiguration,\
org.springframework.boot.autoconfigure.jms.jndiconnectionfactoryautoconfiguration,\
org.springframework.boot.autoconfigure.jms.activemq.activemqautoconfiguration,\
org.springframework.boot.autoconfigure.jms.artemis.artemisautoconfiguration,\
org.springframework.boot.autoconfigure.flyway.flywayautoconfiguration,\
org.springframework.boot.autoconfigure.groovy.template.groovytemplateautoconfiguration,\
org.springframework.boot.autoconfigure.jersey.jerseyautoconfiguration,\
org.springframework.boot.autoconfigure.jooq.jooqautoconfiguration,\
org.springframework.boot.autoconfigure.kafka.kafkaautoconfiguration,\
org.springframework.boot.autoconfigure.ldap.embedded.embeddedldapautoconfiguration,\
org.springframework.boot.autoconfigure.ldap.ldapautoconfiguration,\
org.springframework.boot.autoconfigure.liquibase.liquibaseautoconfiguration,\
org.springframework.boot.autoconfigure.mail.mailsenderautoconfiguration,\
org.springframework.boot.autoconfigure.mail.mailsendervalidatorautoconfiguration,\
org.springframework.boot.autoconfigure.mobile.deviceresolverautoconfiguration,\
org.springframework.boot.autoconfigure.mobile.devicedelegatingviewresolverautoconfiguration,\
org.springframework.boot.autoconfigure.mobile.sitepreferenceautoconfiguration,\
org.springframework.boot.autoconfigure.mongo.embedded.embeddedmongoautoconfiguration,\
org.springframework.boot.autoconfigure.mongo.mongoautoconfiguration,\
org.springframework.boot.autoconfigure.mustache.mustacheautoconfiguration,\
org.springframework.boot.autoconfigure.orm.jpa.hibernatejpaautoconfiguration,\
org.springframework.boot.autoconfigure.reactor.reactorautoconfiguration,\
org.springframework.boot.autoconfigure.security.securityautoconfiguration,\
org.springframework.boot.autoconfigure.security.securityfilterautoconfiguration,\
org.springframework.boot.autoconfigure.security.fallbackwebsecurityautoconfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.oauth2autoconfiguration,\
org.springframework.boot.autoconfigure.sendgrid.sendgridautoconfiguration,\
org.springframework.boot.autoconfigure.session.sessionautoconfiguration,\
org.springframework.boot.autoconfigure.social.socialwebautoconfiguration,\
org.springframework.boot.autoconfigure.social.facebookautoconfiguration,\
org.springframework.boot.autoconfigure.social.linkedinautoconfiguration,\
org.springframework.boot.autoconfigure.social.twitterautoconfiguration,\
org.springframework.boot.autoconfigure.solr.solrautoconfiguration,\
org.springframework.boot.autoconfigure.thymeleaf.thymeleafautoconfiguration,\
org.springframework.boot.autoconfigure.transaction.transactionautoconfiguration,\
org.springframework.boot.autoconfigure.transaction.jta.jtaautoconfiguration,\
org.springframework.boot.autoconfigure.validation.validationautoconfiguration,\
org.springframework.boot.autoconfigure.web.dispatcherservletautoconfiguration,\
org.springframework.boot.autoconfigure.web.embeddedservletcontainerautoconfiguration,\
org.springframework.boot.autoconfigure.web.errormvcautoconfiguration,\
org.springframework.boot.autoconfigure.web.httpencodingautoconfiguration,\
org.springframework.boot.autoconfigure.web.httpmessageconvertersautoconfiguration,\
org.springframework.boot.autoconfigure.web.multipartautoconfiguration,\
org.springframework.boot.autoconfigure.web.serverpropertiesautoconfiguration,\
org.springframework.boot.autoconfigure.web.webclientautoconfiguration,\
org.springframework.boot.autoconfigure.web.webmvcautoconfiguration,\
org.springframework.boot.autoconfigure.websocket.websocketautoconfiguration,\
org.springframework.boot.autoconfigure.websocket.websocketmessagingautoconfiguration,\
org.springframework.boot.autoconfigure.webservices.webservicesautoconfiguration
# failure analyzers
org.springframework.boot.diagnostics.failureanalyzer=\
org.springframework.boot.autoconfigure.diagnostics.analyzer.nosuchbeandefinitionfailureanalyzer,\
org.springframework.boot.autoconfigure.jdbc.datasourcebeancreationfailureanalyzer,\
org.springframework.boot.autoconfigure.jdbc.hikaridriverconfigurationfailureanalyzer
# template availability providers
org.springframework.boot.autoconfigure.template.templateavailabilityprovider=\
org.springframework.boot.autoconfigure.freemarker.freemarkertemplateavailabilityprovider,\
org.springframework.boot.autoconfigure.mustache.mustachetemplateavailabilityprovider,\
org.springframework.boot.autoconfigure.groovy.template.groovytemplateavailabilityprovider,\
org.springframework.boot.autoconfigure.thymeleaf.thymeleaftemplateavailabilityprovider,\
org.springframework.boot.autoconfigure.web.jsptemplateavailabilityprovider

3)filter过滤器 根据 onclasscondition 注解把不满足条件的过滤掉

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private list<string> filter(list<string> configurations,
autoconfigurationmetadata autoconfigurationmetadata) {
long starttime = system.nanotime();
string[] candidates = configurations.toarray(new string[configurations.size()]);
boolean[] skip = new boolean[candidates.length];
boolean skipped = false;
//获取需要过滤的自动配置导入拦截器,spring.factories配置中就一个:org.springframework.boot.autoconfigure.condition.onclasscondition
for (autoconfigurationimportfilter filter : getautoconfigurationimportfilters()) {
invokeawaremethods(filter);
boolean[] match = filter.match(candidates, autoconfigurationmetadata);
for (int i = 0; i < match.length; i++) {
 if (!match[i]) {
 skip[i] = true;
 skipped = true;
 }
}
}
if (!skipped) {//多条件只要有一个不匹配->skipped = true,全部匹配-》skipped = false->直接返回
return configurations;
}
list<string> result = new arraylist<string>(candidates.length);
for (int i = 0; i < candidates.length; i++) {
if (!skip[i]) {//匹配-》不跳过-》添加进result
 result.add(candidates[i]);
}
}
if (logger.istraceenabled()) {
int numberfiltered = configurations.size() - result.size();
logger.trace("filtered " + numberfiltered + " auto configuration class in "
 + timeunit.nanoseconds.tomillis(system.nanotime() - starttime)
 + " ms");
}
return new arraylist<string>(result);
}

2.2 springapplication .run()静态方法

springapplication.run 

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public configurableapplicationcontext run(string... args) {
stopwatch stopwatch = new stopwatch();
stopwatch.start();
configurableapplicationcontext context = null;
failureanalyzers analyzers = null;
configureheadlessproperty();
springapplicationrunlisteners listeners = getrunlisteners(args);//1.获取监听器
listeners.starting();-->启动!
try {
applicationarguments applicationarguments = new defaultapplicationarguments(
 args);
configurableenvironment environment = prepareenvironment(listeners,//2.准备好环境,触发applicationenvironmentpreparedevent事件
 applicationarguments);
banner printedbanner = printbanner(environment);//打印启动提示字符,默认spring的字符图
context = createapplicationcontext();//实例化一个可配置应用上下文
analyzers = new failureanalyzers(context);
preparecontext(context, environment, listeners, applicationarguments,//3.准备上下文
 printedbanner);
refreshcontext(context);//4.刷新上下文
afterrefresh(context, applicationarguments);//5.刷新上下文后
listeners.finished(context, null);--关闭!
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. getrunlisteners 获取监听器( springapplicationrunlisteners )

实际是 springapplicationrunlistener 类

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private springapplicationrunlisteners getrunlisteners(string[] args) {
class<?>[] types = new class<?>[] { springapplication.class, string[].class };
return new springapplicationrunlisteners(logger, getspringfactoriesinstances(
springapplicationrunlistener.class, types, this, args));
}
private <t> collection<? extends t> getspringfactoriesinstances(class<t> type) {
return getspringfactoriesinstances(type, new class<?>[] {});
}
private <t> collection<? extends t> getspringfactoriesinstances(class<t> type,
class<?>[] parametertypes, object... args) {
classloader classloader = thread.currentthread().getcontextclassloader();
// 使用set确保的字符串的唯一性
set<string> names = new linkedhashset<string>(
springfactoriesloader.loadfactorynames(type, classloader));// 1.载入工厂名称集合
list<t> instances = createspringfactoriesinstances(type, parametertypes,// 2.创建工厂实例
classloader, args, names);
annotationawareordercomparator.sort(instances);// 排序
return instances;
}

1.1 载入工厂名称(loadfactorynames)

当前类的类加载器从 meta-inf/spring.factories 文件中获取springapplicationrunlistener类的配置

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public static list<string> loadfactorynames(class<?> factoryclass, classloader classloader) {
 string factoryclassname = factoryclass.getname();
 try {
 enumeration<url> urls = (classloader != null ? classloader.getresources(factories_resource_location) :
  classloader.getsystemresources(factories_resource_location));
 list<string> result = new arraylist<string>();
 while (urls.hasmoreelements()) {
  url url = urls.nextelement();
  properties properties = propertiesloaderutils.loadproperties(new urlresource(url));
  string factoryclassnames = properties.getproperty(factoryclassname);
  result.addall(arrays.aslist(stringutils.commadelimitedlisttostringarray(factoryclassnames)));
 }
 return result;
 }
 catch (ioexception ex) {
 throw new illegalargumentexception("unable to load [" + factoryclass.getname() +
  "] factories from location [" + factories_resource_location + "]", ex);
 }
 }

上图,获取到工厂类名后,下面来看看meta-inf/spring.factories中定义了啥:

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# propertysource loaders
org.springframework.boot.env.propertysourceloader=\
org.springframework.boot.env.propertiespropertysourceloader,\
org.springframework.boot.env.yamlpropertysourceloader
# run listeners 这里呢,看这里!!!!
org.springframework.boot.springapplicationrunlistener=\
org.springframework.boot.context.event.eventpublishingrunlistener
# application context initializers
org.springframework.context.applicationcontextinitializer=\
org.springframework.boot.context.configurationwarningsapplicationcontextinitializer,\
org.springframework.boot.context.contextidapplicationcontextinitializer,\
org.springframework.boot.context.config.delegatingapplicationcontextinitializer,\
org.springframework.boot.context.embedded.serverportinfoapplicationcontextinitializer
# application listeners
org.springframework.context.applicationlistener=\
org.springframework.boot.clearcachesapplicationlistener,\
org.springframework.boot.builder.parentcontextcloserapplicationlistener,\
org.springframework.boot.context.fileencodingapplicationlistener,\
org.springframework.boot.context.config.ansioutputapplicationlistener,\
org.springframework.boot.context.config.configfileapplicationlistener,\
org.springframework.boot.context.config.delegatingapplicationlistener,\
org.springframework.boot.liquibase.liquibaseservicelocatorapplicationlistener,\
org.springframework.boot.logging.classpathloggingapplicationlistener,\
org.springframework.boot.logging.loggingapplicationlistener
# environment post processors
org.springframework.boot.env.environmentpostprocessor=\
org.springframework.boot.cloud.cloudfoundryvcapenvironmentpostprocessor,\
org.springframework.boot.env.springapplicationjsonenvironmentpostprocessor
# failure analyzers
org.springframework.boot.diagnostics.failureanalyzer=\
org.springframework.boot.diagnostics.analyzer.beancurrentlyincreationfailureanalyzer,\
org.springframework.boot.diagnostics.analyzer.beannotofrequiredtypefailureanalyzer,\
org.springframework.boot.diagnostics.analyzer.bindfailureanalyzer,\
org.springframework.boot.diagnostics.analyzer.connectorstartfailureanalyzer,\
org.springframework.boot.diagnostics.analyzer.nouniquebeandefinitionfailureanalyzer,\
org.springframework.boot.diagnostics.analyzer.portinusefailureanalyzer,\
org.springframework.boot.diagnostics.analyzer.validationexceptionfailureanalyzer
# failureanalysisreporters
org.springframework.boot.diagnostics.failureanalysisreporter=\
org.springframework.boot.diagnostics.loggingfailureanalysisreporter

哇,都是些类全名称,且key都是接口,value都是实现类。我们根据key=“ org.springframework.boot.springapplicationrunlistener ”查询得到实现类value=" org.springframework.boot.context.event.eventpublishingrunlistener" 事件发布启动监听器 , 一猜也知道肯定要用” 反射 ”根据类名获取类实例,下面很快得到验证...

1.2 创建spring工厂实例(createspringfactoriesinstances)

根据第一步得到的set<string> names(springapplicationrunlistener的唯一实现类 eventpublishingrunlistener )生成" 事件发布启动监听器 " 工厂实例

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@suppresswarnings("unchecked")
private <t> list<t> createspringfactoriesinstances(class<t> type,
class<?>[] parametertypes, classloader classloader, object[] args,
set<string> names) {
list<t> instances = new arraylist<t>(names.size());
for (string name : names) {
try {
 class<?> instanceclass = classutils.forname(name, classloader);// 利用反射获取类
 assert.isassignable(type, instanceclass);
 constructor<?> constructor = instanceclass
 .getdeclaredconstructor(parametertypes);// 得到构造器
 t instance = (t) beanutils.instantiateclass(constructor, args);// 根据构造器和参数构造实例
 instances.add(instance);
}
catch (throwable ex) {
 throw new illegalargumentexception(
 "cannot instantiate " + type + " : " + name, ex);
}
}
return instances;
}

准备上下文

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private void preparecontext(configurableapplicationcontext context,
configurableenvironment environment, springapplicationrunlisteners listeners,
applicationarguments applicationarguments, banner printedbanner) {
context.setenvironment(environment);
postprocessapplicationcontext(context);//单例一个beannamegenerator,把resourceloader设置进应用上下文
applyinitializers(context);//执行初始化器
listeners.contextprepared(context);// 监听器执行上下文"已准备好"方法
if (this.logstartupinfo) {
logstartupinfo(context.getparent() == null);
logstartupprofileinfo(context);
}
// 添加spring boot特殊单例bean
context.getbeanfactory().registersingleton("springapplicationarguments",
 applicationarguments);
if (printedbanner != null) {
context.getbeanfactory().registersingleton("springbootbanner", printedbanner);
}
// 载入资源
set<object> sources = getsources();
assert.notempty(sources, "sources must not be empty");
load(context, sources.toarray(new object[sources.size()]));
listeners.contextloaded(context);// 监听器执行"上下文已加载"方法
}

刷新上下文

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private void refreshcontext(configurableapplicationcontext context) {
refresh(context);//核心类
if (this.registershutdownhook) {
try {
context.registershutdownhook();//注册关闭钩子,容器关闭时执行
}
catch (accesscontrolexception ex) {
// not allowed in some environments.
}
}
}
protected void refresh(applicationcontext applicationcontext) {
assert.isinstanceof(abstractapplicationcontext.class, applicationcontext);
((abstractapplicationcontext) applicationcontext).refresh();
}

最终执行的是abstractapplicationcontext抽象类的 refresh 方法。

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public void refresh() throws beansexception, illegalstateexception {
synchronized (this.startupshutdownmonitor) {
//准备刷新的上下文环境,例如对系统属性或者环境变量进行准备及验证。
preparerefresh();
//启动子类的refreshbeanfactory方法.解析xml
configurablelistablebeanfactory beanfactory = obtainfreshbeanfactory();
//为beanfactory配置容器特性,例如类加载器、事件处理器等.
preparebeanfactory(beanfactory);
try {
 //设置beanfactory的后置处理. 空方法,留给子类拓展用。
 postprocessbeanfactory(beanfactory);
 //调用beanfactory的后处理器, 这些后处理器是在bean定义中向容器注册的.
 invokebeanfactorypostprocessors(beanfactory);
 //注册bean的后处理器, 在bean创建过程中调用.
 registerbeanpostprocessors(beanfactory);
 //初始化上下文中的消息源,即不同语言的消息体进行国际化处理
 initmessagesource();
 //初始化applicationeventmulticaster bean,应用事件广播器
 initapplicationeventmulticaster();
 //初始化其它特殊的bean, 空方法,留给子类拓展用。
 onrefresh();
 //检查并向容器注册监听器bean
 registerlisteners();
 //实例化所有剩余的(non-lazy-init) 单例bean.
 finishbeanfactoryinitialization(beanfactory);
 //发布容器事件, 结束refresh过程.
 finishrefresh();
}
catch (beansexception ex) {
 if (logger.iswarnenabled()) {
 logger.warn("exception encountered during context initialization - " +
 "cancelling refresh attempt: " + ex);
 }
 //销毁已经创建的单例bean, 以避免资源占用.
 destroybeans();
 //取消refresh操作, 重置active标志.
 cancelrefresh(ex);
 // propagate exception to caller.
 throw ex;
}
finally {
 //重置spring的核心缓存
 resetcommoncaches();
}
}
}

刷新完上下文后

spring boot提供的2个供用户自己拓展的接口: applicationrunner和 commandlinerunner。可以在容器启动完毕后(上下文刷新后)执行,做一些类似数据初始化的操作。

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private void callrunners(applicationcontext context, applicationarguments args) {
list<object> runners = new arraylist<object>();
runners.addall(context.getbeansoftype(applicationrunner.class).values());//从上下文中获取applicationrunner类型的bean
runners.addall(context.getbeansoftype(commandlinerunner.class).values());//从上下文中获取commandlinerunner类型的bean
annotationawareordercomparator.sort(runners);//排序
for (object runner : new linkedhashset<object>(runners)) {
if (runner instanceof applicationrunner) {
 callrunner((applicationrunner) runner, args);//执行
}
if (runner instanceof commandlinerunner) {
 callrunner((commandlinerunner) runner, args);
}
}
}

两个区别在于入参不同,根据实际情况自己选择。

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public interface commandlinerunner {
void run(string... args) throws exception;
}
public interface applicationrunner {
void run(applicationarguments args) throws exception;
}

commandlinerunner中执行参数是原始的 java启动类main方法的string[] args字符串数组参数; applicationrunner中的参数经过处理提供一些方法例如:

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list<string> getoptionvalues(string name);

根据名称获取值list,java 启动命令中 --foo=bar --foo=baz,则根据foo参数名返回list ["bar", "baz"]

三、总结

spring boot容器启动流程

按照前面的分析,spring-boot容器启动流程总体可划分为2部分:

1) 执行注解 :扫描指定范围下的bean、载入自动配置类对应的bean加载到ioc容器。

2)man方法中具体springappliocation.run() ,全流程贯穿springapplicationevent,有6个子类:

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applicationfailedevent.class
applicationpreparedevent.class
applicationreadyevent.class
applicationstartedevent.class
applicationstartingevent.class
springapplicationevent.class

这里用到了很经典的 spring事件驱动模型 ,飞机票: spring事件驱动模型和观察者模式

类图如下:

spring boot容器启动流程

如上图,就是一个经典spring 事件驱动模型,包含3种角色:事件发布者、事件、监听者。对应到spring-boot中就是:

1 .eventpublishingrunlistener 这个类封装了 事件发布 ,

2. springapplicationevent 是spring-boot中定义的事件(上面说的6种事件),继承自 applicationevent (spring中定义的)

3. 监听者 spring-boot并没有实现针对上述6种事件的监听者(我没找到...), 这里用户可以自己实现监听者(上述6种事件)来注入spring boot容器启动流程,触发相应的事件。

例如:实现applicationlistener<applicationreadyevent>这个接口,在容器启动完毕时最后一步listener.finished时,如果启动没有异常,就会执行!可以做一些数据初始化之类的操作。

总结

以上所述是小编给大家介绍的spring boot容器启动的相关知识,希望对大家有所帮助,如果大家有任何疑问请给我留言,小编会及时回复大家的。在此也非常感谢大家对服务器之家网站的支持!

原文链接:http://www.cnblogs.com/dennyzhangdd/p/8028950.html

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