SpringBoot启动源码分析

Z时代
2024-01-10
分类：综合

SpringBoot自启动源码分析

项目启动代码

publicstaticvoidmain(String[] args) {
    // springboot项目启动方式 
        SpringApplication.run(DemoApplication.class, args);
    }

springApplication.java

publicstaticConfigurableApplicationContextrun(Class<?>primarySource, String... args) {
    // 调用run方法
returnrun(newClass<?>[] { primarySource }, args);
}

publicstaticConfigurableApplicationContextrun(Class<?>[] primarySources, String[] args) {
        // 最终创建了一个SpringApplication对象
returnnewSpringApplication(primarySources).run(args);
}

publicSpringApplication(ResourceLoaderresourceLoader, Class<?>... primarySources) {
this.resourceLoader=resourceLoader;
    // 必须传一个类
Assert.notNull(primarySources, "PrimarySources must not be null");
    // 用一个Set集合存储我们的启动类
this.primarySources=newLinkedHashSet<>(Arrays.asList(primarySources));
    // webApplication的枚举类型
    // 主要判断我们启动的类型是什么，一般我们启动的是servlet
this.webApplicationType=WebApplicationType.deduceFromClasspath();
    // 初始化一些应用上下文
    // 加载springboot包下的/META-INF/spring.facotries中的8个类
setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
    // 初始化监听器
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
    // 通过类加载器启动我们的类
    // Class.forName()
this.mainApplicationClass=deduceMainApplicationClass();
}

setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));

我们来看看初始化应用上下文中做了什么

private<T>Collection<T>getSpringFactoriesInstances(Class<T>type, Class<?>[] parameterTypes, Object... args) {
    // 获取类加载器，我们传入的ApplicationContextInitializer.class
ClassLoaderclassLoader=getClassLoader();
// Use names and ensure unique to protect against duplicates
    // 这个方法重点
    // 这个方法里会加载spring.factories文件里的东西
Set<String>names=newLinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
    // 实例化对象
List<T>instances=createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
AnnotationAwareOrderComparator.sort(instances);
returninstances;
}

SpringFactoriesLoader.loadFactoryNames(type, classLoader)

privatestaticMap<String, List<String>>loadSpringFactories(@NullableClassLoaderclassLoader) {
    // 初始化监听器的时候就会直接取了
MultiValueMap<String, String>result=cache.get(classLoader);
if (result!=null) {
returnresult;
}
try {
            // 扫描我们类路径下META-INF/spring.factories文件
Enumeration<URL>urls= (classLoader!=null?
classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
result=newLinkedMultiValueMap<>();
while (urls.hasMoreElements()) {
URLurl=urls.nextElement();
UrlResourceresource=newUrlResource(url);
Propertiesproperties=PropertiesLoaderUtils.loadProperties(resource);
for (Map.Entry<?, ?>entry : properties.entrySet()) {
StringfactoryTypeName= ((String) entry.getKey()).trim();
for (StringfactoryImplementationName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {
                        // 添加到map中
                        // 这里map的映射关系是 接口-> 实现类
result.add(factoryTypeName, factoryImplementationName.trim());
}
}
}
cache.put(classLoader, result);
returnresult;
}
catch (IOExceptionex) {
thrownewIllegalArgumentException("Unable to load factories from location ["+
FACTORIES_RESOURCE_LOCATION+"]", ex);
}
}

// 这个方法进行实例化
private<T>List<T>createSpringFactoriesInstances(Class<T>type, Class<?>[] parameterTypes,
ClassLoaderclassLoader, Object[] args, Set<String>names) {
List<T>instances=newArrayList<>(names.size());
    // 获取该类加载器下对应的实现类
    // 我们可以手动实现ApplicationInitialzer和Listener
for (Stringname : names) {
try {
Class<?>instanceClass=ClassUtils.forName(name, classLoader);
Assert.isAssignable(type, instanceClass);
Constructor<?>constructor=instanceClass.getDeclaredConstructor(parameterTypes);
Tinstance= (T) BeanUtils.instantiateClass(constructor, args);
instances.add(instance);
}
catch (Throwableex) {
thrownewIllegalArgumentException("Cannot instantiate "+type+" : "+name, ex);
}
}
returninstances;
}

通过查看源码可知，如果要加载自己的类也可以通过自己建一个/META-INF/spring.factories文件

# PropertySource Loaders

com.example.demo.service.NewService=

com.example.demo.service.NewServiceImpl

org.springframework.context.ApplicationContextInitializer=

com.example.demo.service.TextApplicationInitializer

springApplication对象建好以后就是调用我们的run方法了

publicConfigurableApplicationContextrun(String... args) {
    // 秒表
StopWatchstopWatch=newStopWatch();
stopWatch.start();
ConfigurableApplicationContextcontext=null;
Collection<SpringBootExceptionReporter>exceptionReporters=newArrayList<>();
configureHeadlessProperty();
SpringApplicationRunListenerslisteners=getRunListeners(args);
    // 启动监听,SpringApplicationRunListeners
listeners.starting();
try {
ApplicationArgumentsapplicationArguments=newDefaultApplicationArguments(args);
            // 配置环境
ConfigurableEnvironmentenvironment=prepareEnvironment(listeners, applicationArguments);
configureIgnoreBeanInfo(environment);
            // 打印图标
BannerprintedBanner=printBanner(environment);
            // 默认加载AnnotationConfigServletWebServerApplicationContext.class
context=createApplicationContext();
exceptionReporters=getSpringFactoriesInstances(SpringBootExceptionReporter.class,
newClass[] { ConfigurableApplicationContext.class }, context);
            // 这里面调用了applyInitializers()方法 执行了 ApplicationContextInitialzer的initialize()方法
prepareContext(context, environment, listeners, applicationArguments, printedBanner);
refreshContext(context);
afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
newStartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
}
listeners.started(context);
callRunners(context, applicationArguments);
}
catch (Throwableex) {
handleRunFailure(context, ex, exceptionReporters, listeners);
thrownewIllegalStateException(ex);
}
try {
listeners.running(context);
}
catch (Throwableex) {
handleRunFailure(context, ex, exceptionReporters, null);
thrownewIllegalStateException(ex);
}
returncontext;
}

springboot配置

附录

1.WebApplicationType枚举

publicenumWebApplicationType {

/**

* 该应用程序不应作为Web应用程序运行，也不应启动嵌入式Web服务器。

NONE,

/**

* 该应用程序应作为基于Servlet的Web应用程序运行，并应启动嵌入式Servlet Web服务器。

SERVLET,

/**

* 该应用程序应作为反应式Web应用程序运行，并应启动嵌入式反应式Web服务器。

REACTIVE;

privatestaticfinalString[] SERVLET_INDICATOR_CLASSES= { "javax.servlet.Servlet",

"org.springframework.web.context.ConfigurableWebApplicationContext" };

privatestaticfinalStringWEBMVC_INDICATOR_CLASS="org.springframework.web.servlet.DispatcherServlet";

privatestaticfinalStringWEBFLUX_INDICATOR_CLASS="org.springframework.web.reactive.DispatcherHandler";

privatestaticfinalStringJERSEY_INDICATOR_CLASS="org.glassfish.jersey.servlet.ServletContainer";

privatestaticfinalStringSERVLET_APPLICATION_CONTEXT_CLASS="org.springframework.web.context.WebApplicationContext";

privatestaticfinalStringREACTIVE_APPLICATION_CONTEXT_CLASS="org.springframework.boot.web.reactive.context.ReactiveWebApplicationContext";

}

2.SpringApplicationBanner

通过类字段可以看到yml文件中配置banner的路径，以及将我们要展示的banner的文件名字取为banner.txt

staticfinalStringBANNER_LOCATION_PROPERTY="spring.banner.location";
staticfinalStringBANNER_IMAGE_LOCATION_PROPERTY="spring.banner.image.location";
staticfinalStringDEFAULT_BANNER_LOCATION="banner.txt";
staticfinalString[] IMAGE_EXTENSION= { "gif", "jpg", "png" };