SpringBoot啟動(dòng)流程SpringApplication準(zhǔn)備階段源碼分析
更新時(shí)間：2023年04月03日 14:01:01 作者：唐小碼
這篇文章主要為大家介紹了SpringBoot啟動(dòng)流程SpringApplication準(zhǔn)備階段源碼分析，有需要的朋友可以借鑒參考下，希望能夠有所幫助，祝大家多多進(jìn)步，早日升職加薪
SpringBoot啟動(dòng)流程源碼分析一、入口參數(shù)研究和創(chuàng)建對(duì)象
我們?cè)谏弦黄臅r(shí)候主要針對(duì)入口參數(shù)和SpringApplication創(chuàng)建對(duì)象的過程進(jìn)行了研究，本篇主要針對(duì)執(zhí)行run方法之前的準(zhǔn)備過程進(jìn)行研究。
準(zhǔn)備階段分析
以下先看下SpringApplication的run()方法
package org.springframework.boot;
public ConfigurableApplicationContext run(String... args) {
//1.計(jì)時(shí)器
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
//2.headless配置
configureHeadlessProperty();
//3、獲取監(jiān)聽
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
try {
//應(yīng)用程序啟動(dòng)的參數(shù)
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
//4、準(zhǔn)備環(huán)境
ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
//環(huán)境創(chuàng)建成功后，配置bean信息，決定是否跳過 BeanInfo 類的掃描，如果設(shè)置為 true,則跳過
configureIgnoreBeanInfo(environment);
//打印banner信息
Banner printedBanner = printBanner(environment);
context = createApplicationContext();
exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
prepareContext(context, environment, listeners, applicationArguments, printedBanner);
refreshContext(context);
afterRefresh(context, applicationArguments);
//停止計(jì)時(shí)
stopWatch.stop();
//控制是否打印日志的,這里為true，即打印日志
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
}
listeners.started(context);
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, listeners);
throw new IllegalStateException(ex);
}
try {
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, null);
throw new IllegalStateException(ex);
}
return context;
}
我將會(huì)根據(jù)執(zhí)行過程逐行進(jìn)行分析
1、StopWatch計(jì)時(shí)器
此類實(shí)則為計(jì)時(shí)器，如下對(duì)具體使用進(jìn)行分析
StopWatch stopWatch = new StopWatch(); //開始計(jì)時(shí) stopWatch.start(); //停止計(jì)時(shí) stopWatch.stop();
對(duì)于具體打印的上面寫的為
//將當(dāng)前類傳入StartupInfoLogger創(chuàng)建了一個(gè)對(duì)象
//然后調(diào)用logStarted打印日志
new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
//創(chuàng)建一個(gè)Log類
protected Log getApplicationLog() {
if (this.mainApplicationClass == null) {
return logger;
}
return LogFactory.getLog(this.mainApplicationClass);
}
//調(diào)用log類的log.info()方法來打印日志
public void logStarted(Log log, StopWatch stopWatch) {
if (log.isInfoEnabled()) {
log.info(getStartedMessage(stopWatch));
}
}
//打印詳細(xì)的日志
private StringBuilder getStartedMessage(StopWatch stopWatch) {
StringBuilder message = new StringBuilder();
message.append("Started ");
message.append(getApplicationName());
message.append(" in ");
message.append(stopWatch.getTotalTimeSeconds());
try {
double uptime = ManagementFactory.getRuntimeMXBean().getUptime() / 1000.0;
message.append(" seconds (JVM running for " + uptime + ")");
}
catch (Throwable ex) {
// No JVM time available
}
return message;
}
這里可以看到stopWatch.getTotalTimeSeconds()方法就是來獲取實(shí)際的計(jì)時(shí)時(shí)間的。再者，通過這幾行代碼，我們也可以考慮下平常在寫代碼的時(shí)候，有幾種日志打印方式？SpringBoot是怎么集成日志框架的？
2、configureHeadlessProperty()
private static final String SYSTEM_PROPERTY_JAVA_AWT_HEADLESS = "java.awt.headless";
private void configureHeadlessProperty() {
System.setProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS,
System.getProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, Boolean.toString(this.headless)));
}
這一部分代碼這樣理解吧，首先java.awt包提供了用于創(chuàng)建用戶界面和繪制圖形圖像的所有分類,那么 屬性SYSTEM_PROPERTY_JAVA_AWT_HEADLESS就一定會(huì)和用戶界面相關(guān)了。 這里將SYSTEM_PROPERTY_JAVA_AWT_HEADLESS設(shè)置為true，其實(shí)就是表示在缺少顯示屏、鍵盤或者鼠標(biāo)中的系統(tǒng)配置，如果將其設(shè)置為true，那么headless工具包就會(huì)被使用。
3、getRunListeners(args) 獲取監(jiān)聽
總體上可以分這三步
- 獲取一個(gè)默認(rèn)的加載器
- 根據(jù)類型獲取spring.factories中符合的類名
- 創(chuàng)建類實(shí)例，返回
如下將跟下代碼
//獲取所有監(jiān)聽 SpringApplicationRunListeners listeners = getRunListeners(args); //啟動(dòng)監(jiān)聽 listeners.starting();
跳轉(zhuǎn)進(jìn)入getRunListeners方法
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<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
//3.1獲取類加載器
ClassLoader classLoader = getClassLoader();
// Use names and ensure unique to protect against duplicates
//3.2 根據(jù)類型獲取spring.factories中符合的類名
Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
//3.3 創(chuàng)建類實(shí)例
List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
//對(duì)實(shí)例進(jìn)行排序
AnnotationAwareOrderComparator.sort(instances);
return instances;
}
SpringApplicationRunListeners類解讀
先看下SpringApplicationRunListeners類
/**
* A collection of {@link SpringApplicationRunListener}.
*
* @author Phillip Webb
*/
class SpringApplicationRunListeners {
private final Log log;
private final List<SpringApplicationRunListener> listeners;
SpringApplicationRunListeners(Log log, Collection<? extends SpringApplicationRunListener> listeners) {
this.log = log;
this.listeners = new ArrayList<>(listeners);
}
SpringApplicationRunListeners類內(nèi)部關(guān)聯(lián)了SpringApplicationRunListener的集合，說白了就是用List集合存儲(chǔ)了SpringApplicationRunListeners類，那么，我們就需要了解一下這個(gè)類是干嘛的
老規(guī)矩，先把源碼抬上來
/**
*//可以理解為Spring Boot應(yīng)用的運(yùn)行時(shí)監(jiān)聽器
* Listener for the {@link SpringApplication} {@code run} method.
*//SpringApplicationRunListener的構(gòu)造器參數(shù)必須依次為SpringApplication和String[]類型
* {@link SpringApplicationRunListener}s are loaded via the {@link SpringFactoriesLoader}
* and should declare a public constructor that accepts a {@link SpringApplication}
* instance and a {@code String[]} of arguments.
*//每次運(yùn)行的時(shí)候?qū)?huì)創(chuàng)建一個(gè) SpringApplicationRunListener
A new
* {@link SpringApplicationRunListener} instance will be created for each run.
*
*/
public interface SpringApplicationRunListener {
/**
* Called immediately when the run method has first started. Can be used for very
* early initialization.
*/
//Spring應(yīng)用剛啟動(dòng)
void starting();
/**
* Called once the environment has been prepared, but before the
* {@link ApplicationContext} has been created.
* @param environment the environment
*/
//ConfigurableEnvironment準(zhǔn)備妥當(dāng)，允許將其調(diào)整
void environmentPrepared(ConfigurableEnvironment environment);
/**
* Called once the {@link ApplicationContext} has been created and prepared, but
* before sources have been loaded.
* @param context the application context
*/
//ConfigurableApplicationContext準(zhǔn)備妥當(dāng)，允許將其調(diào)整
void contextPrepared(ConfigurableApplicationContext context);
/**
* Called once the application context has been loaded but before it has been
* refreshed.
* @param context the application context
*/
//ConfigurableApplicationContext已裝載，但是任未啟動(dòng)
void contextLoaded(ConfigurableApplicationContext context);
/**
* The context has been refreshed and the application has started but
* {@link CommandLineRunner CommandLineRunners} and {@link ApplicationRunner
* ApplicationRunners} have not been called.
* @param context the application context.
* @since 2.0.0
*/
//ConfigurableApplicationContext已啟動(dòng)，此時(shí)Spring Bean已初始化完成
void started(ConfigurableApplicationContext context);
/**
* Called immediately before the run method finishes, when the application context has
* been refreshed and all {@link CommandLineRunner CommandLineRunners} and
* {@link ApplicationRunner ApplicationRunners} have been called.
* @param context the application context.
* @since 2.0.0
*/
//Spring應(yīng)用正在運(yùn)行
void running(ConfigurableApplicationContext context);
/**
* Called when a failure occurs when running the application.
* @param context the application context or {@code null} if a failure occurred before
* the context was created
* @param exception the failure
* @since 2.0.0
*/
//Spring應(yīng)用運(yùn)行失敗
void failed(ConfigurableApplicationContext context, Throwable exception);
}
單純的看源碼，是一個(gè)簡單的接口，這時(shí)候我們可以看下作者給的注釋。理解部分就直接加到上面源碼中了。
再看下他的實(shí)現(xiàn)類EventPublishingRunListener
public class EventPublishingRunListener implements SpringApplicationRunListener, Ordered {
private final SpringApplication application;
private final String[] args;
private final SimpleApplicationEventMulticaster initialMulticaster;
public EventPublishingRunListener(SpringApplication application, String[] args) {
this.application = application;
this.args = args;
this.initialMulticaster = new SimpleApplicationEventMulticaster();
for (ApplicationListener<?> listener : application.getListeners()) {
this.initialMulticaster.addApplicationListener(listener);
}
}
這里我們看到兩點(diǎn)：
- 構(gòu)造器參數(shù)和他實(shí)現(xiàn)的接口（上面剛分析了）注釋中規(guī)定的一致
- 將SpringApplication中的ApplicationListener實(shí)例列表全部添加到了SimpleApplicationEventMulticaster對(duì)象中
SimpleApplicationEventMulticaster是Spring框架的一個(gè)監(jiān)聽類，用于發(fā)布Spring應(yīng)用事件。因此EventPublishingRunListener實(shí)際充當(dāng)了Spring Boot事件發(fā)布者的角色。
這里我再跟進(jìn)源碼的時(shí)候發(fā)現(xiàn)，針對(duì)SpringBoot的事件/監(jiān)聽機(jī)制內(nèi)容還是挺多的，我們?cè)诔浞掷斫獾臅r(shí)候需要先了解Spring的事件/監(jiān)聽機(jī)制，后面將兩個(gè)結(jié)合后單獨(dú)進(jìn)行對(duì)比分析。
3.1獲取類加載器getClassLoader()
ClassLoader classLoader = getClassLoader();
public ClassLoader getClassLoader() {
if (this.resourceLoader != null) {
return this.resourceLoader.getClassLoader();
}
return ClassUtils.getDefaultClassLoader();
}
這里的類加載器獲取首先是獲取resourceLoader的類加載器，獲取不到則獲取默認(rèn)的類加載器。 resourceLoader是資源加載器類，有具體的實(shí)現(xiàn)類。
3.2 根據(jù)類型獲取spring.factories中符合的類名
SpringFactoriesLoader.loadFactoryNames(type, classLoader)
public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
//獲取類型名稱：org.springframework.context.ApplicationContextInitializer
String factoryClassName = factoryClass.getName();
return (List)loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
}
我們繼續(xù)對(duì)loadSpringFactories追下去
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
//從緩存里面獲取
MultiValueMap<String, String> result = (MultiValueMap)cache.get(classLoader);
if (result != null) {
return result;
} else {
try {
//執(zhí)行classLoader.getResources("META-INF/spring.factories")，表示通過加載器獲取META-INF/spring.factories下的資源
Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");
LinkedMultiValueMap result = new LinkedMultiValueMap();
while(urls.hasMoreElements()) {
//文件地址
URL url = (URL)urls.nextElement();
//從指定位置加載UrlResource
UrlResource resource = new UrlResource(url);
//加載里面的屬性，屬性見下圖
Properties properties = PropertiesLoaderUtils.loadProperties(resource);
Iterator var6 = properties.entrySet().iterator();
while(var6.hasNext()) {
Entry<?, ?> entry = (Entry)var6.next();
//獲取key值
String factoryClassName = ((String)entry.getKey()).trim();
//獲取value值
String[] var9 = StringUtils.commaDelimitedListToStringArray((String)entry.getValue());
int var10 = var9.length;
//這里是將查詢出來的key作為result的key,value轉(zhuǎn)換成字符數(shù)組存放到result的value中
for(int var11 = 0; var11 < var10; ++var11) {
String factoryName = var9[var11];
result.add(factoryClassName, factoryName.trim());
}
}
}
//將結(jié)果集存入緩存中
cache.put(classLoader, result);
return result;
} catch (IOException var13) {
throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var13);
}
}
}
default V getOrDefault(Object key, V defaultValue) {
V v;
return (((v = get(key)) != null) || containsKey(key))
? v
: defaultValue;
}
這個(gè)的意思是如果沒有，則獲取一個(gè)空的list
3.3創(chuàng)建實(shí)例createSpringFactoriesInstances()
這一步其實(shí)就是將上一步從META-INF/spring.factories加載進(jìn)來的資源進(jìn)行實(shí)例化。
private <T> List<T> createSpringFactoriesInstances()(Class<T> type, Class<?>[] parameterTypes,
ClassLoader classLoader, Object[] args, Set<String> names) {
List<T> instances = new ArrayList<>(names.size());
for (String name : names) {
try {
//根據(jù)類加載器獲取指定類
Class<?> instanceClass = ClassUtils.forName(name, classLoader);
Assert.isAssignable(type, instanceClass);
//根據(jù)參數(shù)獲取構(gòu)造器
Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);
//根據(jù)傳入的構(gòu)造器對(duì)象以及構(gòu)造器所需的參數(shù)創(chuàng)建一個(gè)實(shí)例
T instance = (T) BeanUtils.instantiateClass(constructor, args);
//添加實(shí)例到集合中
instances.add(instance);
}
catch (Throwable ex) {
throw new IllegalArgumentException("Cannot instantiate " + type + " : " + name, ex);
}
}
return instances;
}
4、環(huán)境準(zhǔn)備prepareEnvironment
prepareEnvironment(listeners, applicationArguments)
private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments) {
// Create and configure the environment
//4.1 創(chuàng)建一個(gè)環(huán)境
ConfigurableEnvironment environment = getOrCreateEnvironment();
//4.2 配置環(huán)境
configureEnvironment(environment, applicationArguments.getSourceArgs());
//4.3 ConfigurationPropertySourcesPropertySource對(duì)象存入到第一位
ConfigurationPropertySources.attach(environment);
//listeners環(huán)境準(zhǔn)備(就是廣播ApplicationEnvironmentPreparedEvent事件)
listeners.environmentPrepared(environment);
// 將環(huán)境綁定到SpringApplication
bindToSpringApplication(environment);
// 如果是非web環(huán)境，將環(huán)境轉(zhuǎn)換成StandardEnvironment
if (!this.isCustomEnvironment) {
environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,
deduceEnvironmentClass());
}
// 配置PropertySources對(duì)它自己的遞歸依賴
ConfigurationPropertySources.attach(environment);
return environment;
}
4.1創(chuàng)建一個(gè)環(huán)境getOrCreateEnvironment
private ConfigurableEnvironment getOrCreateEnvironment() {
//有的話，直接返回
if (this.environment != null) {
return this.environment;
}
//這里我們?cè)谏厦嬉姷竭^，通過WebApplicationType.deduceFromClasspath()方法獲取的
switch (this.webApplicationType) {
case SERVLET:
return new StandardServletEnvironment();
case REACTIVE:
return new StandardReactiveWebEnvironment();
default:
return new StandardEnvironment();
}
}
這里創(chuàng)建了一個(gè)StandardServletEnvironment實(shí)例的環(huán)境 systemProperties用來封裝了JDK相關(guān)的信息 如下圖
systemEnvironment用來封轉(zhuǎn)環(huán)境相關(guān)的信息
封裝的還是挺詳細(xì)的哈。
4.2 配置環(huán)境
protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) {
if (this.addConversionService) {
ConversionService conversionService = ApplicationConversionService.getSharedInstance();
environment.setConversionService((ConfigurableConversionService) conversionService);
}
configurePropertySources(environment, args);
configureProfiles(environment, args);
}
setConversionService(ConfigurableConversionService conversionService)方法繼承于ConfigurablePropertyResolver接口， 該接口是PropertyResolver類型都將實(shí)現(xiàn)的配置接口。提供用于訪問和自定義將屬性值從一種類型轉(zhuǎn)換為另一種類型時(shí)使用的ConversionService的工具。PropertyResolver是用于針對(duì)任何底層源解析屬性的接口。
configurePropertySources(environment, args);當(dāng)前方法主要是將啟動(dòng)命令中的參數(shù)和run 方法中的參數(shù)封裝為PropertySource。
protected void configurePropertySources(ConfigurableEnvironment environment, String[] args) {
//獲取所有的屬性源，就是獲取4.1的ConfigurableEnvironment上獲取到的屬性
MutablePropertySources sources = environment.getPropertySources();
if (this.defaultProperties != null && !this.defaultProperties.isEmpty()) {
sources.addLast(new MapPropertySource("defaultProperties", this.defaultProperties));
}
//是否添加命令啟動(dòng)參數(shù)，addCommandLineProperties為true，表示需要添加，但是前提是你得配置了參數(shù)
if (this.addCommandLineProperties && args.length > 0) {
String name = CommandLinePropertySource.COMMAND_LINE_PROPERTY_SOURCE_NAME;
if (sources.contains(name)) {
PropertySource<?> source = sources.get(name);
CompositePropertySource composite = new CompositePropertySource(name);
composite.addPropertySource(
new SimpleCommandLinePropertySource("springApplicationCommandLineArgs", args));
composite.addPropertySource(source);
sources.replace(name, composite);
}
else {
sources.addFirst(new SimpleCommandLinePropertySource(args));
}
}
}
configureProfiles(environment, args);環(huán)境配置
protected void configureProfiles(ConfigurableEnvironment environment, String[] args) {
//獲取激活的環(huán)境
environment.getActiveProfiles(); // ensure they are initialized
// But these ones should go first (last wins in a property key clash)
Set<String> profiles = new LinkedHashSet<>(this.additionalProfiles);
profiles.addAll(Arrays.asList(environment.getActiveProfiles()));
//設(shè)置當(dāng)前的環(huán)境
environment.setActiveProfiles(StringUtils.toStringArray(profiles));
}
4.3 ConfigurationPropertySourcesPropertySource對(duì)象存入
public static void attach(Environment environment) {
Assert.isInstanceOf(ConfigurableEnvironment.class, environment);
//獲取所有的屬性源，就是獲取4.1的ConfigurableEnvironment上獲取到的屬性
MutablePropertySources sources = ((ConfigurableEnvironment) environment).getPropertySources();
//判斷是否有 屬性 configurationProperties
PropertySource<?> attached = sources.get(ATTACHED_PROPERTY_SOURCE_NAME);
if (attached != null && attached.getSource() != sources) {
sources.remove(ATTACHED_PROPERTY_SOURCE_NAME);
attached = null;
}
if (attached == null) {
// 將sources封裝成ConfigurationPropertySourcesPropertySource對(duì)象，并把這個(gè)對(duì)象放到sources的第一位置
sources.addFirst(new ConfigurationPropertySourcesPropertySource(ATTACHED_PROPERTY_SOURCE_NAME,
new SpringConfigurationPropertySources(sources)));
}
}
總結(jié)
準(zhǔn)備階段主要干了如下幾件事情
- 設(shè)置headless為true（表示可以在缺少顯示屏、鍵盤或者鼠標(biāo)時(shí)候的系統(tǒng)配置）
- 文件META-INF\spring.factories中獲取SpringApplicationRunListener接口的實(shí)現(xiàn)類EventPublishingRunListener，主要發(fā)布SpringApplicationEvent。
- 創(chuàng)建Environment并設(shè)置比如環(huán)境信息，系統(tǒng)屬性，輸入?yún)?shù)和profile等信息
- 打印Banner信息
本文僅為個(gè)人能力范圍內(nèi)理解，旨在分享出來和大家討論技術(shù)，共同努力，共同進(jìn)步！
參考：《SpringBoot編程思想》
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