Spring Boot本身並不提供Spring框架的核心特性以及擴展功能,只是用於快速、敏捷地開發新一代基於Spring框架的應用程序。也就是說,它並不是用來替代Spring的解決方案,而是和Spring框架緊密結合用於提升Spring開發者體驗的工具。
Spring Boot繼承了Spring的優點,並新增了一些新功能和特性
(0)從字面理解,Boot是引導的意思,因此SpringBoot幫助開發者快速搭建Spring框架,Spring 項目引導頁面可以在幾秒構建一個項目
(1)Spring Boot 內置了多種種強大的測試框架,只需要在項目中引入spring-boot-start-test依賴包
(2)Spring Boot 的自動配置讓配置變簡單;
(3)SpringBoot的起步依賴讓依賴管理更加簡單;
(4)Spring Boot Actuator對應用系統監控的集成功能;
(5)現在spring boot和spring cloud是現在java開發框架的主流了
Spring Boot提供了一種新的編程範式,能在最小的阻力下開發Spring應用程序。有了它,你可以更加敏捷地開發Spring應用程序,專注於應用程序的功能,不用在Spring的配置上多花功夫,甚至完全不用配置。實際上,Spring Boot的一項重要工作就是讓Spring不再成爲你成功路上的絆腳石。 ——《SpringBoot實戰》
springboot如何做到
構建springboot項目
訪問http://start.spring.io/
選擇構建工具Maven Project、Spring Boot版本以及一些工程基本信息
下載壓縮包以後直接導入到ide中就可以了,大概就是這個樣子
這個是我大致畫的一些spring的東西,先從代碼結構說吧
http://naotu.baidu.com/file/e8972e3eff7fc8a1a54dd7c2d6d946d5
這是一般的主程序入口,當然在我們的項目中,因爲並沒有使用springboot內置的tomcat,所以啓動方式有所不同
@SpringBootApplication
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
}123456
不適用內置tomcat的情況,原理沒有區別
@SpringBootApplication
@EnableAutoConfiguration(exclude = { DataSourceAutoConfiguration.class, RedisAutoConfiguration.class,
DataSourceTransactionManagerAutoConfiguration.class, })
@ComponentScan({ "com.fanli.*" })
public class Application extends SpringBootServletInitializer {
@Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
return application.sources(Application.class);
}
}12345678910
按照下圖分別講一下源碼
@SpringBootApplication
/**
* Indicates a {@link Configuration configuration} class that declares one or more
* {@link Bean @Bean} methods and also triggers {@link EnableAutoConfiguration
* auto-configuration} and {@link ComponentScan component scanning}. This is a convenience
* annotation that is equivalent to declaring {@code @Configuration},
* {@code @EnableAutoConfiguration} and {@code @ComponentScan}.
*
* @author Phillip Webb
* @author Stephane Nicoll
* @since 1.2.0
*/
@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 {
......
}1234567891011121314151617181920212223
@SpringBootApplication實際是@SpringBootConfiguration,@EnableAutoConfiguration以及@ComponentScan的組合
/**
* Indicates that a class provides Spring Boot application
* {@link Configuration @Configuration}. Can be used as an alternative to the Spring's
* standard {@code @Configuration} annotation so that configuration can be found
* automatically (for example in tests).
* <p>
* Application should only ever include <em>one</em> {@code @SpringBootConfiguration} and
* most idiomatic Spring Boot applications will inherit it from
* {@code @SpringBootApplication}.
*
* @author Phillip Webb
* @since 1.4.0
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {
}12345678910111213141516171819
@SpringBootConfiguration而@Configuration有相同的作用,配備了該註解的類就能夠以JavaConfig的方式完成一些配置,可以不再使用XML配置
@ComponentScan註解完成的是自動掃描的功能,相當於Spring XML配置文件中的
<context:component-scan >1
如果不設置的話默認掃描@ComponentScan註解所在類的同級類和同級目錄下的所有類,所以對於一個Spring Boot項目,一般會把入口類放在頂層目錄中,這樣就能夠保證源碼目錄下的所有類都能夠被掃描到。如果需要設置的話如下代碼
@SpringBootApplication
@EnableAutoConfiguration(exclude = { DataSourceAutoConfiguration.class, RedisAutoConfiguration.class,
DataSourceTransactionManagerAutoConfiguration.class, })
@ComponentScan({ "com.fanli.*" })
public class Application extends SpringBootServletInitializer {。。。。。。12345
@EnableAutoConfiguration(核心)
這個註釋告訴SpringBoot“猜”你將如何想配置Spring,基於你已經添加的依賴項,如果我們使用了spring-boot-starter-web並且已經添加Tomcat和Spring MVC,@EnableAutoConfiguration自動將假設您正在開發一個web應用程序並添加相應的Spring設置。
Spring Boot的自動配置是一個運行時(更準確地說,是應用程序啓動時)的過程,考慮了衆多因素,才決定Spring配置應該用哪個,不該用哪個。舉個例子。Spring的JdbcTemplate是不是在Classpath裏?如果是,並且有DataSource的Bean,則自動配置一個JdbcTemplate的Bean。每當應用程序啓動的時候,Spring Boot的自動配置都要做將近200個這樣的決定,涵蓋安全、集成、持久化、Web開發等諸多方面。所有這些自動配置就是爲了儘量不讓你自己寫配置。
在嚮應用程序加入Spring Boot時,有個名爲spring-boot-autoconfigure的JAR文件,其中包含了很多自動配置類(自動配置類就是普通的Spring @Configuration類,通過SpringFactoriesLoader機制完成加載,實現上通常使用@Conditional(比如@ConditionalOnClass或者@ConditionalOnMissingBean))。
每個配置類都在應用程序的Classpath裏,都有機會爲應用程序的配置添磚加瓦。這些配置類裏有用於AOP的配置,有用於Spring Data JPA的配置,有用於Spiring MVC的配置,還有很多其他東西的配置,你可以自己選擇是否在Spring應用程序裏使用它們。
@SuppressWarnings("deprecation")
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(EnableAutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration { // ... }12345678
這個@AutoConfigurationPackage僅限於引入@Import(AutoConfigurationPackages.Registrar.class)
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(AutoConfigurationPackages.Registrar.class)
public @interface AutoConfigurationPackage { }123456
@Order(Ordered.HIGHEST_PRECEDENCE)
static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports {
@Override
public void registerBeanDefinitions(AnnotationMetadata metadata,
BeanDefinitionRegistry registry) {
register(registry, new PackageImport(metadata).getPackageName());
}
@Override
public Set<Object> determineImports(AnnotationMetadata metadata) {
return Collections.<Object>singleton(new PackageImport(metadata));
}
}123456789101112
/**
* Programmatically registers the auto-configuration package names. Subsequent
* invocations will add the given package names to those that have already been
* registered. You can use this method to manually define the base packages that will
* be used for a given {@link BeanDefinitionRegistry}. Generally it's recommended that
* you don't call this method directly, but instead rely on the default convention
* where the package name is set from your {@code @EnableAutoConfiguration}
* configuration class or classes.
* @param registry the bean definition registry
* @param packageNames the package names to set
*/
public static void register(BeanDefinitionRegistry registry, String... packageNames) {
if (registry.containsBeanDefinition(BEAN)) {
BeanDefinition beanDefinition = registry.getBeanDefinition(BEAN);
ConstructorArgumentValues constructorArguments = beanDefinition
.getConstructorArgumentValues();
constructorArguments.addIndexedArgumentValue(0,
addBasePackages(constructorArguments, packageNames));
}
else {
GenericBeanDefinition beanDefinition = new GenericBeanDefinition();
beanDefinition.setBeanClass(BasePackages.class);
beanDefinition.getConstructorArgumentValues().addIndexedArgumentValue(0,
packageNames);
beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
registry.registerBeanDefinition(BEAN, beanDefinition);
}
}1234567891011121314151617181920212223242526272829
從註釋中可以看出,它的功能簡單說就是將應用的 package給註冊到Spring容器中,供後續使用,還說了不推薦手動來註冊
然後debug的時候看一下,packageNames只有我們的rootpackage(com.example.demo),這裏也就是將應用的root package給註冊到Spring容器中,供後續使用。
順便還可以看看調用棧,調用register方法的時間在容器刷新期間:
refresh -> invokeBeanFactoryPostProcessors -> invokeBeanDefinitionRegistryPostProcessors -> postProcessBeanDefinitionRegistry -> processConfigBeanDefinitions(開始處理配置Bean的定義) -> loadBeanDefinitions -> loadBeanDefinitionsForConfigurationClass(讀取配置Class中的Bean定義) -> loadBeanDefinitionsFromRegistrars(這裏開始準備進入上面的register方法) -> registerBeanDefinitions(即上述方法)
@Import(AutoConfigurationImportSelector.class)
/**
* 最主要的方法
* annotationMetadata
* [@org.springframework.boot.autoconfigure.SpringBootApplication
* (scanBasePackageClasses=[], excludeName=[], exclude=[], scanBasePackages=[])]
* @param annotationMetadata
* @return
*/
@Override
public String[] selectImports(AnnotationMetadata annotationMetadata) {
if (!isEnabled(annotationMetadata)) {
return NO_IMPORTS;
}
/**
* 加載META-INF/spring-autoconfigure-metadata.properties,獲取所有支持自動配置的信息
*/
AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
.loadMetadata(this.beanClassLoader);
/**
* 得到註解中的所有屬性信息{excludeName=[], exclude=[]}
*/
AnnotationAttributes attributes = getAttributes(annotationMetadata);
/**
* 獲取所有支持EnableAutoConfiguration的組件信息,這部分信息配置在spring-boot-autoconfig包下的spring.factories下
*
* 使用了內部工具使用SpringFactoriesLoader,查找classpath上所有jar包中的
* META-INF\spring.factories,找出其中key爲
* org.springframework.boot.autoconfigure.EnableAutoConfiguration
* 的屬性定義的工廠類名稱。
*/
List<String> configurations = getCandidateConfigurations(annotationMetadata,
attributes);
configurations = removeDuplicates(configurations);
/**
* 去除不需要的
* @EnableAutoConfiguration(exclude = { DataSourceAutoConfiguration.class, RedisAutoConfiguration.class,
DataSourceTransactionManagerAutoConfiguration.class, })
*/
Set<String> exclusions = getExclusions(annotationMetadata, attributes);
checkExcludedClasses(configurations, exclusions);
configurations.removeAll(exclusions);
/**
* 然後使用AutoConfigurationImportFilter進行過濾,過濾的方式基本上是判斷現有系統是否引入了某個組件,(系統是否使用哪個組件是在pom定義的時候就確定了的)
* ,如果有的話則進行相關配置。比如ServletWebServerFactoryAutoConfiguration
* ,會在ServletRequest.class等條件存在的情況下進行配置,
* 而EmbeddedTomcat會在Servlet.class, Tomcat.class存在的情況下創建TomcatServletWebServerFactory
*
* org.springframework.boot.autoconfigure.condition.OnClassCondition
* 總而言之,此過濾器會檢查候選配置類的註解@ConditionalOnClass,如果要求的類在classpath 中不存在,則這個候選配置類會被排除掉
*/
configurations = filter(configurations, autoConfigurationMetadata);
/**
* 現在已經找到所有需要被應用的候選配置類
* 廣播事件AutoConfigurationImportEvent
*/
fireAutoConfigurationImportEvents(configurations, exclusions);
return StringUtils.toStringArray(configurations);
}
private void fireAutoConfigurationImportEvents(List<String> configurations,
Set<String> exclusions) {
List<AutoConfigurationImportListener> listeners = getAutoConfigurationImportListeners();
if (!listeners.isEmpty()) {
AutoConfigurationImportEvent event = new AutoConfigurationImportEvent(this,
configurations, exclusions);
for (AutoConfigurationImportListener listener : listeners) {
invokeAwareMethods(listener);
listener.onAutoConfigurationImportEvent(event);
}
}
}123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172
# Auto Configuration Import Listeners
org.springframework.boot.autoconfigure.AutoConfigurationImportListener=\
org.springframework.boot.autoconfigure.condition.ConditionEvaluationReportAutoConfigurationImportListener123
protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
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;
}123456
// 傳入的factoryClass:org.springframework.boot.autoconfigure.EnableAutoConfiguration
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);
}
}
// 相關常量 public static final String FACTORIES_RESOURCE_LOCATION =
// "META-INF/spring.factories";123456789101112131415161718192021
這段代碼的意圖很明確,在第一篇文章討論Spring Boot啓動過程的時候就已經接觸到了。它會從類路徑中拿到所有名爲META-INF/spring.factories的配置文件,然後按照factoryClass的名稱取到對應的值。那麼我們就來找一個META-INF/spring.factories配置文件看看。
# Auto Configure
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,\
。。。。。。12345678910111213
列舉了非常多的自動配置候選項,挑一個AOP相關的AopAutoConfiguration看看究竟:
/ 如果設置了spring.aop.auto=false,那麼AOP不會被配置
// 需要檢測到@EnableAspectJAutoProxy註解存在纔會生效
// 默認使用JdkDynamicAutoProxyConfiguration,如果設置了spring.aop.proxy-target-class=true,那麼使用CglibAutoProxyConfiguration
@Configuration
@ConditionalOnClass({ EnableAspectJAutoProxy.class, Aspect.class, Advice.class })
@ConditionalOnProperty(prefix = “spring.aop”, name = “auto”, havingValue = “true”, matchIfMissing = true)
public class AopAutoConfiguration {
@Configuration
@EnableAspectJAutoProxy(proxyTargetClass = false)
@ConditionalOnProperty(prefix = “spring.aop”, name = “proxy-target-class”, havingValue = “false”, matchIfMissing = true)
public static class JdkDynamicAutoProxyConfiguration {
}
@Configuration
@EnableAspectJAutoProxy(proxyTargetClass = true)
@ConditionalOnProperty(prefix = “spring.aop”, name = “proxy-target-class”, havingValue = “true”, matchIfMissing = false)
public static class CglibAutoProxyConfiguration {
}
}
如果存在並且值爲true的話使用基於CGLIB字節碼操作的動態代理方案,否則使用JDK自帶的動態代理機制。在這個配置類中,使用到了兩個全新的註解:
@ConditionalOnClass
@ConditionalOnProperty
從這兩個註解的名稱,就大概能夠猜出它們的功能了:
@ConditionalOnClass
當類路徑上存在指定的類時,滿足條件。
@ConditionalOnProperty
當配置中存在指定的屬性時,滿足條件。
其實除了這兩個註解之外,還有幾個類似的,它們都在org.springframework.boot.autoconfigure.condition這個包下,在具體介紹實現之前,下面先來看看Spring Boot對於@Conditional的擴展。
Spring Boot對於@Conditional的擴展Spring Boot提供了一個實現了Condition接口的抽象類SpringBootCondition。這個類的主要作用是打印一些用於診斷的日誌,告訴用戶哪些類型被自動配置了。它實現Condition接口的方法:
@Override
public final boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
String classOrMethodName = getClassOrMethodName(metadata);
try {
ConditionOutcome outcome = getMatchOutcome(context, metadata);
logOutcome(classOrMethodName, outcome);
recordEvaluation(context, classOrMethodName, outcome);
return outcome.isMatch();
} catch (NoClassDefFoundError ex) {
throw new IllegalStateException("Could not evaluate condition on " + classOrMethodName + " due to "
+ ex.getMessage() + " not " + "found. Make sure your own configuration does not rely on "
+ "that class. This can also happen if you are "
+ "@ComponentScanning a springframework package (e.g. if you "
+ "put a @ComponentScan in the default package by mistake)", ex);
} catch (RuntimeException ex) {
throw new IllegalStateException("Error processing condition on " + getName(metadata), ex);
}
}
/**
* * Determine the outcome of the match along with suitable log output. * @param
* context the condition context * @param metadata the annotation metadata
* * @return the condition outcome
*/
public abstract ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata);
123456789101112131415161718192021222324
在Spring裏可以很方便地編寫你自己的條件,你所要做的就是實現Condition接口,覆蓋它的matches()方法
Spring Boot定義了很多更有趣的條件,並把它們運用到了配置類上,這些配置類構成了Spring Boot的自動配置。Spring Boot運用條件化配置的方法是,定義
多個特殊的條件化註解,並將它們用到配置類上。
https://github.com/spring-projects/spring-boot/blob/master/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/condition/OnClassCondition.java
看一下這個calss的調用棧
在說一下springboot的啓動過程
@SpringBootApplication
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
}
/**
* Static helper that can be used to run a {@link SpringApplication} from the
* specified sources using default settings and user supplied arguments.
* @param primarySources the primary sources to load
* @param args the application arguments (usually passed from a Java main method)
* @return the running {@link ApplicationContext}
*/
public static ConfigurableApplicationContext run(Class<?>[] primarySources,
String[] args) {
return new SpringApplication(primarySources).run(args);
}1234567891011121314151617181920
它實際上會構造一個SpringApplication的實例,然後運行它的run方法,而run方法返回一個ConfigurableApplicationContext,看一下構造SpringApplication實列的地方
/**
* Create a new {@link SpringApplication} instance. The application context will load
* beans from the specified primary sources (see {@link SpringApplication class-level}
* documentation for details. The instance can be customized before calling
* {@link #run(String...)}.
* @param resourceLoader the resource loader to use
* @param primarySources the primary bean sources
* @see #run(Class, String[])
* @see #setSources(Set)
*/
@SuppressWarnings({ "unchecked", "rawtypes" })
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
this.resourceLoader = resourceLoader;//resourceLoader接口,提供資源導入,見鏈接https://www.cnblogs.com/doit8791/p/5774743.html
Assert.notNull(primarySources, "PrimarySources must not be null");
this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources)); //此處爲DemoApplication.class
//推斷應用類型,Standard還是Web
this.webApplicationType = deduceWebApplicationType();
//
/**
* 設置初始化器(Initializer)
* getSpringFactoriesInstances(ApplicationContextInitializer.class)
* 從類路徑的META-INF/spring.factories處讀取相應配置文件,然後進行遍歷,讀取配置文件中Key爲:
* org.springframework.context.ApplicationContextInitializer的value
* value是一系列類名,實例化後this.initializers.addAll(initializers);全部set到SpringApplication中
* 在Spring上下文被刷新之前進行初始化的操作。典型地比如在Web應用中,註冊Property Sources或者是激活Profiles。
* Property Sources比較好理解,就是配置文件。Profiles是Spring爲了在不同環境下(如DEV,TEST,PRODUCTION等),加載不同的配置項而抽象出來的一個實體
*ConfigurableApplicationContext.refresh()或SpringApplication.run()中用到
*
*/
setInitializers((Collection) getSpringFactoriesInstances(
ApplicationContextInitializer.class));
/**
* 設置setListeners,設置方式和初始化器一樣
*/
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
/**
* 獲取入口類的信息
*/
this.mainApplicationClass = deduceMainApplicationClass();
}
其實就是獲得容器ConfigurableApplicationContext之前初始化了一系列Initializers和Listeners
實際run方法:
public ConfigurableApplicationContext run(String... args) {
// 計時工具
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
// 設置java.awt.headless系統屬性爲true - 沒有圖形化界面
configureHeadlessProperty();
/**
* 獲取SpringApplicationRunListeners
* getSpringFactoriesInstances方法,從META-INF/spring.factories中讀取
* Key爲org.springframework.boot.SpringApplicationRunListener的Values
* SpringApplicationEvent:它會利用一個內部的ApplicationEventMulticaster在上下文實際被刷新之前對事件進行處理
* 它實際上是一個事件中轉器,它能夠感知到Spring Boot啓動過程中產生的事件,然後有選擇性的將事件進行中轉
*/
// Spring事件體系 https://blog.csdn.net/caihaijiang/article/details/7460888
SpringApplicationRunListeners listeners = getRunListeners(args);
// 發出開始執行的事件
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
// 根據SpringApplicationRunListeners以及參數來準備環境
ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
configureIgnoreBeanInfo(environment);
// 準備Banner打印器 - 就是啓動Spring Boot的時候打印在console上的ASCII藝術字體
Banner printedBanner = printBanner(environment);
// 創建Spring上下文,根據之前獲得的應用類型,創建ConfigurableApplicationContext實列可以看到實際上創建的是AnnotationConfigApplicationContext或AnnotationConfigEmbeddedWebApplicationContext。
context = createApplicationContext();
//SpringBootExceptionReporter,在spring.factories中能看到
exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
// Spring上下文前置處理,prepareContext方法中將會執行每個initializers的邏輯
prepareContext(context, environment, listeners, applicationArguments, printedBanner);
// Spring上下文刷新
refreshContext(context);
// Spring上下文後置處理
afterRefresh(context, applicationArguments);
// 發出結束執行的事件
stopWatch.stop();
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;
}
private void prepareContext(ConfigurableApplicationContext context,
ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments, Banner printedBanner) {
context.setEnvironment(environment);
postProcessApplicationContext(context);
//調用之前準備好的ApplicationContextInitializer
applyInitializers(context);
listeners.contextPrepared(context);
if (this.logStartupInfo) {
logStartupInfo(context.getParent() == null);
logStartupProfileInfo(context);
}
// Add boot specific singleton beans
context.getBeanFactory().registerSingleton("springApplicationArguments",
applicationArguments);
if (printedBanner != null) {
context.getBeanFactory().registerSingleton("springBootBanner", printedBanner);
}
// Load the sources
Set<Object> sources = getAllSources();
Assert.notEmpty(sources, "Sources must not be empty");
load(context, sources.toArray(new Object[0]));
//將SpringApplication自己擁有的ApplicationListener加入到ApplicationContext,發送ApplicationPreparedEvent
listeners.contextLoaded(context);
}123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130
# Application Context Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\ // to report warnings for common misconfiguration,用來報告Spring容器的一些常見的錯誤配置的
org.springframework.boot.context.ContextIdApplicationContextInitializer,\//爲ApplicationContext設置id
org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\//委派處理ApplicationContext初始化器
org.springframework.boot.web.context.ServerPortInfoApplicationContextInitializer//添加一個EmbeddedServletContainerInitializedEvent事件監聽,觸發設置嵌入的WEB服務啓動端口。通過屬性local.[namespace].port來設置啓動端口,其中namespace爲ApplicationContext指定的命名空間,如果命名空間爲空,則使用local.server.port屬性來表示配置的端口1234567
最終可以看到AbstractApplicationContext的refresh方法
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}123456789101112131415161718192021222324252627282930313233343536373839404142434445464748
在之前的的講解中可以看到調用棧 invokeBeanFactoryPostProcessors(beanFactory);這裏的時候,自動配置會起作用
SpringApplication實例的構建過程
其中主要涉及到了初始化器(Initializer)以及監聽器(Listener)這兩大概念,它們都通過META-INF/spring.factories完成定義。
SpringApplication實例run方法的執行過程
其中主要有一個SpringApplicationRunListeners的概念,它作爲Spring Boot容器初始化時各階段事件的中轉器,將事件派發給感興趣的Listeners(在SpringApplication實例的構建過程中得到的)。這些階段性事件將容器的初始化過程給構造起來,提供了比較強大的可擴展性。
改造過程中遇到的坑
1.原先項目改造中,有大量的xml配置文件,如果單純的改爲springboot項目的無xml配置,反而很麻煩,和springboot的某些目的背道而馳
@Configuration
@ImportResource(locations={"classpath:context/ehcache.xml"})
public class EncacheConfig {
}1234
2.在一個系統中,出現多個datasource時候出現的問題
自動裝配(autowiring)要求bean的匹配具備唯一性,否則就會產生歧義,從而拋出異常
@EnableAutoConfiguration(exclude = { DataSourceAutoConfiguration.class, RedisAutoConfiguration.class,
DataSourceTransactionManagerAutoConfiguration.class, })12
3.spring項目啓動太慢的問題
54607 ms
刪除@SpringBootApplication 52118ms 幾乎沒有區別
修改import 36238 ms
最終改爲
@Configuration
@Import({
DispatcherServletAutoConfiguration.class,
// EmbeddedServletContainerAutoConfiguration.class,
// ErrorMvcAutoConfiguration.class,
// HttpEncodingAutoConfiguration.class,
HttpMessageConvertersAutoConfiguration.class,
// JacksonAutoConfiguration.class,
// JmxAutoConfiguration.class,
// MultipartAutoConfiguration.class,
ServerPropertiesAutoConfiguration.class,
WebMvcAutoConfiguration.class,
// WebSocketAutoConfiguration.class,
})
@ComponentScan({ "com.fanli.*" })
public class Application extends SpringBootServletInitializer {12345678910111213141516
@SpringBootApplication註解來自動獲取應用的配置信息,但這樣也會帶來一些副作用。使用這個註解後,會觸發自動配置(auto-configuration)和組件掃描(component scanning),這跟使用@Configuration、@EnableAutoConfiguration和@ComponentScan三個註解的作用是
可以通過Actuator的/autoconfig接口去看
4.多個springboot項目在同一臺機器上啓動(內測)時候的問題,多應用在同一個容器中
spring.jmx.default-domain=opendomain
endpoints.jmx.domain=opendomain
指定JMX domain name
https://www.zhihu.com/question/36688387
https://stackoverflow.com/questions/28197414/spring-cloud-error-deploying-two-eureka-clients-in-one-container12345
5.log日誌的問題
@Order(1)
public class CommonInitializer implements WebApplicationInitializer {
@Override
public void onStartup(ServletContext servletContext)
throws ServletException {
//Log4jConfigListener
servletContext.setInitParameter("webAppRootKey", "mall-open-api.root");
servletContext.setInitParameter("log4jConfigLocation", "classpath:properties/log4j.properties");
servletContext.addListener(Log4jConfigListener.class);
//OpenSessionInViewFilter
}
}12345678910111213
ServletContainerInitializer
Servlet 3.0引入的接口,用於在web應用啓動時動態添加servlet、filter和listener;
基於spi機制,META-INF/services/javax.servlet.ServletContainerInitializer文件中存放實現該接口的類,這些類會被容器調用
SpringServletContainerInitializer作爲ServletContainerInitializer的實現類,通過SPI機制,在web容器加載的時候會自動的被調用。(這個類上還有一個註解@HandlesTypes,它的作用是將感興趣的一些類注入到ServletContainerInitializerde), 而這個類的方法又會掃描找到WebApplicationInitializer的實現類,調用它的onStartup方法,從而起到啓動web.xml相同的作用。
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