Spring Boot啟動流程
君生我未生，君生我已老，君恨我生遲，我恨君生早，
一、簡述
Spring Boot啟動流程分析使用版本SpringBoot VERSION：版本 2.5.5-SNAPSHOT，
Spring Boot專案最簡單的Application啟動類，
可以看出Application啟動類中，包含了@SpringBootApplication 注解和 SpringApplication.run 啟動方法，所以SpringBoot的啟動可以分解為 注解 和 啟動方法 兩大程序，而仔細看啟動類中還引入了一個【org.springframework.boot.SpringApplication】包，所以啟動方法中又可以分為兩個階段即 創建SpringApplication 實體 和 執行run方法，
二、注解
注解暫且簡單了解，暫不深入，
1、@SpirngBootApplication注解
進入@SpringBootApplication注解內，
從@SpringBootApplication注解內部可以發現，它雖然定義使用了多個Annotation進行了原資訊標注，但實際上重要的只有三個Annotation：
- @SpringBootConfiguration（@SpringBootConfiguration注解點開查看發現里面還是應用了@Configuration）->Spring IOC容器配置類，
- @EnableAutoConfiguration ->使用@Import將所有符合自動配置條件的bean定義加載到IOC容器，
- @ComponentScan ->自動掃描并加載符合條件的組件或者bean定義，默認掃描SpringApplication的run方法里的class所在的包路徑下檔案，所以通常將該啟動類放到根包路徑下，
即 @SpringBootApplication = (默認屬性)@Configuration + @EnableAutoConfiguration + @ComponentScan，
三、啟動方法
啟動方法中分為兩個階段即 創建SpringApplication 實體 和 執行run方法，
1、創建SpringApplication實體
從啟動類中的run方法跟進去，SpringApplication.run -> return run -> return new SpringApplication(primarySources).run(args) -> this(null, primarySources) -> SpringApplication，
其中：return new SpringApplication(primarySources).run(args) ，如果跟new SpringApplication(primarySources) 方法則是啟動方法中的第一階段即創建SpringApplication實體，跟run(args) 方法進去就是啟動方法中的第二階段，
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources)
1 /**
2 * Create a new {@link SpringApplication} instance. The application context will load
3 * beans from the specified primary sources (see {@link SpringApplication class-level}
4 * documentation for details. The instance can be customized before calling
5 * {@link #run(String...)}.
6 *
7 * @param resourceLoader the resource loader to use
8 * @param primarySources the primary bean sources
9 * @see #run(Class, String[])
10 * @see #setSources(Set)
11 */
12 @SuppressWarnings({"unchecked", "rawtypes"})
13 public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
14 // 初始化類加載器
15 this.resourceLoader = resourceLoader;
16 // Assert 斷言非空，若傳入的class引數為null則列印例外并退出初始化
17 Assert.notNull(primarySources, "PrimarySources must not be null");
18 // 獲取main方法中的args，初始化啟動時配置的額外引數集合
19 this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
20 // 判斷專案啟動型別：NONE/SERVLET/REACTIVE
21 this.webApplicationType = WebApplicationType.deduceFromClasspath();
22 // 從 Spring 工廠獲取 Bootstrap Registry Initializers
23 this.bootstrapRegistryInitializers = getBootstrapRegistryInitializersFromSpringFactories();
24 // 獲取 Spring 工廠實體 -> 容器背景關系相關的初始化
25 setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
26 // 獲取 Spring 工廠實體 -> 設定應用程式監聽器
27 setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
28 // 推匯出主應用程式類，即從當前的堆疊資訊中尋找main所在主類：com.iot.SpringBootLoveApplication
29 this.mainApplicationClass = deduceMainApplicationClass();
30 }
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1.1、WebApplicationType
WebApplicationType 判斷專案型別，
public enum WebApplicationType
1 /*
2 * Copyright 2012-2019 the original author or authors.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * https://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package org.springframework.boot;
18
19 import org.springframework.util.ClassUtils;
20
21 /**
22 * An enumeration of possible types of web application.
23 *
24 * @author Andy Wilkinson
25 * @author Brian Clozel
26 * @since 2.0.0
27 */
28 public enum WebApplicationType {
29
30 /**
31 * The application should not run as a web application and should not start an
32 * embedded web server.
33 */
34 NONE,
35
36 /**
37 * The application should run as a servlet-based web application and should start an
38 * embedded servlet web server.
39 */
40 SERVLET,
41
42 /**
43 * The application should run as a reactive web application and should start an
44 * embedded reactive web server.
45 */
46 REACTIVE;
47
48 private static final String[] SERVLET_INDICATOR_CLASSES = {"javax.servlet.Servlet",
49 "org.springframework.web.context.ConfigurableWebApplicationContext"};
50
51 private static final String WEBMVC_INDICATOR_CLASS = "org.springframework.web.servlet.DispatcherServlet";
52
53 private static final String WEBFLUX_INDICATOR_CLASS = "org.springframework.web.reactive.DispatcherHandler";
54
55 private static final String JERSEY_INDICATOR_CLASS = "org.glassfish.jersey.servlet.ServletContainer";
56
57 private static final String SERVLET_APPLICATION_CONTEXT_CLASS = "org.springframework.web.context.WebApplicationContext";
58
59 private static final String REACTIVE_APPLICATION_CONTEXT_CLASS = "org.springframework.boot.web.reactive.context.ReactiveWebApplicationContext";
60
61 /**
62 * deduceFromClasspath
63 * 依次回圈遍歷當前應用中是否存在相關的類來判斷最終應用的啟動型別
64 *
65 * @return
66 */
67 static WebApplicationType deduceFromClasspath() {
68 /**
69 * REACTIVE：回應式WEB專案
70 * 若啟動型別為REACTIVE,
71 * 則類路徑下存在 org.springframework.web.reactive.DispatcherHandler 類
72 * 并且不存在 org.springframework.web.servlet.DispatcherServlet 和 org.glassfish.jersey.servlet.ServletContainer
73 * 兩者指的是SpringMVC/Tomcat和jersey容器
74 */
75 if (ClassUtils.isPresent(WEBFLUX_INDICATOR_CLASS, null) && !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null)
76 && !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) {
77 return WebApplicationType.REACTIVE;
78 }
79 /**
80 * NONE：非WEB專案,就是一個最簡單的Springboot應用
81 * 若啟動型別為NONE
82 * 則類路徑下 javax.servlet.Servlet 和org.springframework.web.context.ConfigurableWebApplicationContext都不存在
83 */
84 for (String className : SERVLET_INDICATOR_CLASSES) {
85 if (!ClassUtils.isPresent(className, null)) {
86 return WebApplicationType.NONE;
87 }
88 }
89 /**
90 * SERVLET：SERVLET WEB 專案
91 * 若啟動型別為Servlet，則必須有SERVLET_INDICATOR_CLASSES中的javax.servlet.Servlet
92 * 和org.springframework.web.context.ConfigurableWebApplicationContext
93 */
94 return WebApplicationType.SERVLET;
95 }
96
97 static WebApplicationType deduceFromApplicationContext(Class<?> applicationContextClass) {
98 if (isAssignable(SERVLET_APPLICATION_CONTEXT_CLASS, applicationContextClass)) {
99 return WebApplicationType.SERVLET;
100 }
101 if (isAssignable(REACTIVE_APPLICATION_CONTEXT_CLASS, applicationContextClass)) {
102 return WebApplicationType.REACTIVE;
103 }
104 return WebApplicationType.NONE;
105 }
106
107 private static boolean isAssignable(String target, Class<?> type) {
108 try {
109 return ClassUtils.resolveClassName(target, null).isAssignableFrom(type);
110 } catch (Throwable ex) {
111 return false;
112 }
113 }
114
115 }
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1.2、getBootstrapRegistryInitializersFromSpringFactories
getBootstrapRegistryInitializersFromSpringFactories方法從spring.factories 中獲取 BootstrapRegistryInitializer，
private List<BootstrapRegistryInitializer> getBootstrapRegistryInitializersFromSpringFactories()
1 private List<BootstrapRegistryInitializer> getBootstrapRegistryInitializersFromSpringFactories(){
2 ArrayList<BootstrapRegistryInitializer> initializers=new ArrayList<>();
3 /**
4 * 從spring.factories 中獲取Bootstrapper集合，
5 * 然后遍歷轉化為BootstrapRegistryInitializer，再存入 initializers
6 */
7 getSpringFactoriesInstances(Bootstrapper.class).stream()
8 .map((bootstrapper)->((BootstrapRegistryInitializer)bootstrapper::initialize))
9 .forEach(initializers::add);
10 /**
11 * 從spring.factories 中獲取BootstrapRegistryInitializer集合，再存入 initializers
12 * getSpringFactoriesInstances 該方法在整個啟動流程中會頻繁出現,下面集中介紹
13 */
14 initializers.addAll(getSpringFactoriesInstances(BootstrapRegistryInitializer.class));
15 return initializers;
16 }
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1.3、setInitializers && setListeners
setInitializers && setListeners 分別是容器背景關系初始化 & 監聽器初始化，
容器背景關系初始化setInitializers 和監聽器初始化setListeners 都是呼叫了getSpringFactoriesInstances() 方法，從spring.factories中獲取配置，不同的是傳給它的type引數，主要有一下幾種型別，
- ApplicationContextInitializer.class 背景關系相關
- ApplicationListener.class 監聽器相關
- SpringApplicationRunListener.class 運行時監聽器
- SpringBootExceptionReporter.class 例外類相關
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args)
1 /**
2 * The location to look for factories.
3 * <p>Can be present in multiple JAR files.
4 */
5 public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
6
7
8 /**
9 * 從spring.factories中獲取配置
10 */
11 private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
12 ClassLoader classLoader = getClassLoader();
13 // Use names and ensure unique to protect against duplicates
14 /**
15 * 加載各jar包中的"META-INF/spring.factories"配置
16 * 其中SpringFactoriesLoader.loadFactoryNames(type, classLoader) 方法
17 * 是獲取spring.factories組態檔中已經配置的指定型別的的實作類集合
18 * 其中FACTORIES_RESOURCE_LOCATION的值：META-INF/spring.factories
19 */
20 Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
21 // 通過反射創建這些類
22 List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
23 // 排序
24 AnnotationAwareOrderComparator.sort(instances);
25 return instances;
26 }
27
28
29 /**
30 * Load the fully qualified class names of factory implementations of the
31 * given type from {@value #FACTORIES_RESOURCE_LOCATION}, using the given
32 * class loader.
33 * <p>As of Spring Framework 5.3, if a particular implementation class name
34 * is discovered more than once for the given factory type, duplicates will
35 * be ignored.
36 *
37 * @param factoryType the interface or abstract class representing the factory
38 * @param classLoader the ClassLoader to use for loading resources; can be
39 * {@code null} to use the default
40 * @throws IllegalArgumentException if an error occurs while loading factory names
41 * @see #loadFactories
42 */
43 public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {
44 ClassLoader classLoaderToUse = classLoader;
45 if (classLoaderToUse == null) {
46 classLoaderToUse = SpringFactoriesLoader.class.getClassLoader();
47 }
48 String factoryTypeName = factoryType.getName();
49 return loadSpringFactories(classLoaderToUse).getOrDefault(factoryTypeName, Collections.emptyList());
50 }
51
52
53 /**
54 * Springboot自動配置的秘密
55 * Springboot在啟動時讀取了所有starter jar包里的META-INF/spring.factories組態檔，實作了所謂的自動化配置
56 * 這里jar包里的都是默認配置，后續Springboot也會從xml、yaml檔案中的用戶配置去覆寫同名的配置，
57 * 另外，這里的快取配置是保存在一個map型別的cache中，其中的key鍵對應上面提到的各種Type型別，value就是Type的各種初始jar包里的同型別Java類，
58 */
59 private static Map<String, List<String>> loadSpringFactories(ClassLoader classLoader) {
60 // 獲取相應類加載器中內容
61 Map<String, List<String>> result = cache.get(classLoader);
62 // 存在則直接回傳類加載器中內容
63 if (result != null) {
64 return result;
65 }
66 // 不存在則初始化類加載器中內容
67 result = new HashMap<>();
68 try {
69 /**
70 * 獲取資源 -> META-INF/spring.factories 串列
71 * 其中FACTORIES_RESOURCE_LOCATION的值：META-INF/spring.factories
72 */
73 Enumeration<URL> urls = classLoader.getResources(FACTORIES_RESOURCE_LOCATION);
74 // 可能存在多個META-INF/spring.factories 檔案,回圈加載
75 while (urls.hasMoreElements()) {
76 // 獲取 META-INF/spring.factories 檔案URL地址
77 URL url = urls.nextElement();
78 // 加載資源
79 UrlResource resource = new UrlResource(url);
80 // 加載資源配置
81 Properties properties = PropertiesLoaderUtils.loadProperties(resource);
82 // key:value形式回圈配置
83 for (Map.Entry<?, ?> entry : properties.entrySet()) {
84 String factoryTypeName = ((String) entry.getKey()).trim();
85 // 逗號分隔串列到字串陣列
86 String[] factoryImplementationNames =
87 StringUtils.commaDelimitedListToStringArray((String) entry.getValue());
88 // 回圈value中子項到串列中
89 for (String factoryImplementationName : factoryImplementationNames) {
90 result.computeIfAbsent(factoryTypeName, key -> new ArrayList<>())
91 .add(factoryImplementationName.trim());
92 }
93 }
94 }
95
96 // Replace all lists with unmodifiable lists containing unique elements
97 // 串列去重
98 result.replaceAll((factoryType, implementations) -> implementations.stream().distinct()
99 .collect(Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList)));
100 // 串列保存
101 cache.put(classLoader, result);
102 } catch (IOException ex) {
103 throw new IllegalArgumentException("Unable to load factories from location [" +
104 FACTORIES_RESOURCE_LOCATION + "]", ex);
105 }
106 return result;
107 }
108
109
110 /**
111 * 反射創建實作類
112 */
113 private <T> List<T> createSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes,
114 ClassLoader classLoader, Object[] args, Set<String> names) {
115 List<T> instances = new ArrayList<>(names.size());
116 for (String name : names) {
117 try {
118 Class<?> instanceClass = ClassUtils.forName(name, classLoader);
119 Assert.isAssignable(type, instanceClass);
120 Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);
121 T instance = (T) BeanUtils.instantiateClass(constructor, args);
122 instances.add(instance);
123 } catch (Throwable ex) {
124 throw new IllegalArgumentException("Cannot instantiate " + type + " : " + name, ex);
125 }
126 }
127 return instances;
128 }
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1.4、deduceMainApplicationClass
deduceMainApplicationClass 推導主應用程式類，
private Class<?> deduceMainApplicationClass()
1 /**
2 * 推導主應用程式類
3 * @return
4 */
5 private Class<?> deduceMainApplicationClass() {
6 try {
7 // 獲取當前的堆疊資訊
8 StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();
9 for (StackTraceElement stackTraceElement : stackTrace) {
10 // 獲取main方法所在的類class，此處即com.iot.SpringBootLoveApplication
11 if ("main".equals(stackTraceElement.getMethodName())) {
12 return Class.forName(stackTraceElement.getClassName());
13 }
14 }
15 }
16 catch (ClassNotFoundException ex) {
17 // Swallow and continue
18 }
19 return null;
20 }
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2、run方法
初始化完SpringApplication 就可以運行他的run方法了，也就是啟動方法中的第二階段，
public ConfigurableApplicationContext run(String... args)
1 /**
2 * Run the Spring application, creating and refreshing a new
3 * {@link ApplicationContext}.
4 *
5 * @param args the application arguments (usually passed from a Java main method)
6 * @return a running {@link ApplicationContext}
7 */
8 public ConfigurableApplicationContext run(String... args) {
9 // 啟動一個秒表計時器，用于統計專案啟動時間
10 StopWatch stopWatch = new StopWatch();
11 stopWatch.start();
12 // 創建啟動背景關系物件即spring根容器
13 DefaultBootstrapContext bootstrapContext = createBootstrapContext();
14 // 定義可配置的應用程式背景關系變數
15 ConfigurableApplicationContext context = null;
16 /**
17 * 設定jdk系統屬性
18 * headless直譯就是無頭模式，
19 * headless模式的意思就是明確Springboot要在無鼠鍵支持的環境中運行，一般程式也都跑在Linux之類的服務器上，無鼠鍵支持，這里默認值是true；
20 */
21 configureHeadlessProperty();
22 /**
23 * 獲取運行監聽器 getRunListeners, 其中也是呼叫了上面說到的getSpringFactoriesInstances 方法
24 * 從spring.factories中獲取配置
25 */
26 SpringApplicationRunListeners listeners = getRunListeners(args);
27 // 啟動監聽器
28 listeners.starting(bootstrapContext, this.mainApplicationClass);
29 try {
30 // 包裝默認應用程式引數，也就是在命令列下啟動應用帶的引數，如--server.port=9000
31 ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
32 //
33 /**
34 * 準備環境 prepareEnvironment 是個硬茬，里面主要涉及到
35 * getOrCreateEnvironment、configureEnvironment、configurePropertySources、configureProfiles
36 * environmentPrepared、bindToSpringApplication、attach諸多方法可以在下面的例子中查看
37 */
38 ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
39 // 配置忽略的 bean
40 configureIgnoreBeanInfo(environment);
41 // 列印 SpringBoot 標志，即啟動的時候在控制臺的圖案logo，可以在src/main/resources下放入名字是banner的自定義檔案
42 Banner printedBanner = printBanner(environment);
43 // 創建 IOC 容器
44 context = createApplicationContext();
45 // 設定一個啟動器，設定應用程式啟動
46 context.setApplicationStartup(this.applicationStartup);
47 // 配置 IOC 容器的基本資訊 (spring容器前置處理)
48 prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
49 /**
50 * 重繪IOC容器
51 * 這里會涉及Spring容器啟動、自動裝配、創建 WebServer啟動Web服務即SpringBoot啟動內嵌的 Tomcat
52 */
53 refreshContext(context);
54 /**
55 * 留給用戶自定義容器重繪完成后的處理邏輯
56 * 重繪容器后的擴展介面(spring容器后置處理)
57 */
58 afterRefresh(context, applicationArguments);
59 // 結束計時器并列印，這就是我們啟動后console的顯示的時間
60 stopWatch.stop();
61 if (this.logStartupInfo) {
62 // 列印啟動完畢的那行日志
63 new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
64 }
65 // 發布監聽應用背景關系啟動完成（發出啟動結束事件），所有的運行監聽器呼叫 started() 方法
66 listeners.started(context);
67 // 執行runner，遍歷所有的 runner，呼叫 run 方法
68 callRunners(context, applicationArguments);
69 } catch (Throwable ex) {
70 // 例外處理，如果run程序發生例外
71 handleRunFailure(context, ex, listeners);
72 throw new IllegalStateException(ex);
73 }
74
75 try {
76 // 所有的運行監聽器呼叫 running() 方法,監聽應用背景關系
77 listeners.running(context);
78 } catch (Throwable ex) {
79 // 例外處理
80 handleRunFailure(context, ex, null);
81 throw new IllegalStateException(ex);
82 }
83 // 回傳最終構建的容器物件
84 return context;
85 }
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2.1、configureHeadlessProperty
configureHeadlessProperty 設定headless無頭模式，
private void configureHeadlessProperty()
1 private static final String SYSTEM_PROPERTY_JAVA_AWT_HEADLESS = "java.awt.headless";
2
3 /**
4 * headless直譯就是無頭模式，
5 * headless模式的意思就是明確Springboot要在無鼠鍵支持的環境中運行，一般程式也都跑在Linux之類的服務器上，無鼠鍵支持，這里默認值是true；
6 */
7 private void configureHeadlessProperty() {
8 // SYSTEM_PROPERTY_JAVA_AWT_HEADLESS = "java.awt.headless";
9 System.setProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS,
10 System.getProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, Boolean.toString(this.headless)));
11 }
2.2、prepareEnvironment
prepareEnvironment 準備環境是個硬茬，里面主要涉及到getOrCreateEnvironment、configureEnvironment、configurePropertySources、configureProfilesenvironmentPrepared、bindToSpringApplication、attach諸多方法，
private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners, DefaultBootstrapContext bootstrapContext, ApplicationArguments applicationArguments)
1 /**
2 * 準備環境
3 *
4 * @param listeners
5 * @param bootstrapContext
6 * @param applicationArguments
7 * @return
8 */
9 private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,
10 DefaultBootstrapContext bootstrapContext, ApplicationArguments applicationArguments) {
11 // Create and configure the environment 創建和配置環境
12 // 根據專案型別建環境ConfigurableEnvironment
13 ConfigurableEnvironment environment = getOrCreateEnvironment();
14 // 從環境中獲取并設定 PropertySources 和 activeProfiles
15 configureEnvironment(environment, applicationArguments.getSourceArgs());
16 // 把 PropertySources 設定在自己PropertySources的第一個位置
17 ConfigurationPropertySources.attach(environment);
18 /**
19 * 運行監聽器呼叫
20 * 廣播事件，listeners環境準備(就是廣播ApplicationEnvironmentPreparedEvent事件)
21 * 發布事件通知所有的監聽器當前環境準備完成
22 */
23 listeners.environmentPrepared(bootstrapContext, environment);
24 // 移動 defaultProperties 屬性源到環境中的最后一個源
25 DefaultPropertiesPropertySource.moveToEnd(environment);
26 // 斷言 拋例外
27 Assert.state(!environment.containsProperty("spring.main.environment-prefix"),
28 "Environment prefix cannot be set via properties.");
29 // 與容器系結當前環境
30 bindToSpringApplication(environment);
31 // 若非web環境，將環境轉換成StandardEnvironment
32 if (!this.isCustomEnvironment) {
33 environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,
34 deduceEnvironmentClass());
35 }
36 // 配置PropertySources對它自己的遞回依賴
37 ConfigurationPropertySources.attach(environment);
38 return environment;
39 }
40
41
42 /**
43 * 獲取或創建環境Environment
44 *
45 * @return
46 */
47 private ConfigurableEnvironment getOrCreateEnvironment() {
48 // 存在則直接回傳
49 if (this.environment != null) {
50 return this.environment;
51 }
52 /**
53 * 根據webApplicationType創建對應的Environment
54 */
55 switch (this.webApplicationType) {
56 // SERVLET WEB 專案
57 case SERVLET:
58 return new ApplicationServletEnvironment();
59 // REACTIVE：回應式WEB專案
60 case REACTIVE:
61 return new ApplicationReactiveWebEnvironment();
62 // 非WEB專案,就是一個最簡單的Springboot應用
63 default:
64 return new ApplicationEnvironment();
65 }
66 }
67
68 /**
69 * 從環境中獲取并設定 PropertySources 和 activeProfiles
70 * 將配置任務按順序委托給configurePropertySources和configureProfiles
71 * Template method delegating to
72 * {@link #configurePropertySources(ConfigurableEnvironment, String[])} and
73 * {@link #configureProfiles(ConfigurableEnvironment, String[])} in that order.
74 * Override this method for complete control over Environment customization, or one of
75 * the above for fine-grained control over property sources or profiles, respectively.
76 *
77 * @param environment this application's environment
78 * @param args arguments passed to the {@code run} method
79 * @see #configureProfiles(ConfigurableEnvironment, String[])
80 * @see #configurePropertySources(ConfigurableEnvironment, String[])
81 */
82 protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) {
83 if (this.addConversionService) {
84 environment.setConversionService(new ApplicationConversionService());
85 }
86 // 配置PropertySources
87 configurePropertySources(environment, args);
88 // 配置Profiles
89 configureProfiles(environment, args);
90 }
91
92 /**
93 * 配置PropertySources
94 * Add, remove or re-order any {@link PropertySource}s in this application's
95 * environment.
96 *
97 * @param environment this application's environment
98 * @param args arguments passed to the {@code run} method
99 * @see #configureEnvironment(ConfigurableEnvironment, String[])
100 */
101 protected void configurePropertySources(ConfigurableEnvironment environment, String[] args) {
102 MutablePropertySources sources = environment.getPropertySources();
103 // 初始化 defaultProperties
104 if (!CollectionUtils.isEmpty(this.defaultProperties)) {
105 // 存在的話將其放到最后位置
106 DefaultPropertiesPropertySource.addOrMerge(this.defaultProperties, sources);
107 }
108 /**
109 * 存在命令列引數，則決議它并封裝進SimpleCommandLinePropertySource物件
110 * 同時將此物件放到sources的第一位置（優先級最高）
111 */
112 if (this.addCommandLineProperties && args.length > 0) {
113 String name = CommandLinePropertySource.COMMAND_LINE_PROPERTY_SOURCE_NAME;
114 if (sources.contains(name)) {
115 PropertySource<?> source = sources.get(name);
116 CompositePropertySource composite = new CompositePropertySource(name);
117 composite.addPropertySource(
118 new SimpleCommandLinePropertySource("springApplicationCommandLineArgs", args));
119 composite.addPropertySource(source);
120 sources.replace(name, composite);
121 } else {
122 // 放到首位
123 sources.addFirst(new SimpleCommandLinePropertySource(args));
124 }
125 }
126 }
127
128 /**
129 * 配置Profiles
130 *
131 * @param environment
132 * @param args
133 */
134 protected void configureProfiles(ConfigurableEnvironment environment, String[] args) {
135 /**
136 * 保證environment的activeProfiles屬性被初始化了，從PropertySources中查找spring.profiles.active屬性
137 * 存在則將其值添加activeProfiles集合中，
138 * 配置應用環境中的哪些組態檔處于激活狀態(或默認激活)
139 * 可以通過spring.profiles.active屬性在組態檔處理期間激活其他組態檔
140 * 就是我們專案中通常配置的dev、sit、prod等環境配置資訊設定哪些Profiles是激活的，
141 */
142 environment.getActiveProfiles(); // ensure they are initialized
143 // But these ones should go first (last wins in a property key clash)
144 // 如果存在其他的Profiles，則將這些Profiles放到第一的位置
145 Set<String> profiles = new LinkedHashSet<>(this.additionalProfiles);
146 profiles.addAll(Arrays.asList(environment.getActiveProfiles()));
147 environment.setActiveProfiles(StringUtils.toStringArray(profiles));
148 }
149
150 /**
151 * 運行監聽器呼叫
152 *
153 * @param bootstrapContext
154 * @param environment
155 */
156 void environmentPrepared(ConfigurableBootstrapContext bootstrapContext, ConfigurableEnvironment environment) {
157 doWithListeners("spring.boot.application.environment-prepared",
158 (listener) -> listener.environmentPrepared(bootstrapContext, environment));
159 }
160
161 /**
162 * 運行監聽器呼叫
163 * Called once the environment has been prepared, but before the
164 * {@link ApplicationContext} has been created.
165 *
166 * @param environment the environment
167 * @deprecated since 2.4.0 for removal in 2.6.0 in favor of
168 * {@link #environmentPrepared(ConfigurableBootstrapContext, ConfigurableEnvironment)}
169 */
170 @Deprecated
171 default void environmentPrepared(ConfigurableEnvironment environment) {
172 for (SpringApplicationRunListener listener : this.listeners) {
173 // 廣播ApplicationEnvironmentPreparedEvent事件,后面再看
174 listener.environmentPrepared(environment);
175 }
176 }
177
178 /**
179 * 與容器系結當前環境
180 * Bind the environment to the {@link SpringApplication}.
181 *
182 * @param environment the environment to bind
183 */
184 protected void bindToSpringApplication(ConfigurableEnvironment environment) {
185 try {
186 // 將environment系結到SpringApplication
187 Binder.get(environment).bind("spring.main", Bindable.ofInstance(this));
188 } catch (Exception ex) {
189 throw new IllegalStateException("Cannot bind to SpringApplication", ex);
190 }
191 }
192
193 /**
194 * 配置PropertySources對它自己的遞回依賴
195 * Attach a {@link ConfigurationPropertySource} support to the specified
196 * {@link Environment}. Adapts each {@link PropertySource} managed by the environment
197 * to a {@link ConfigurationPropertySource} and allows classic
198 * {@link PropertySourcesPropertyResolver} calls to resolve using
199 * {@link ConfigurationPropertyName configuration property names}.
200 * <p>
201 * The attached resolver will dynamically track any additions or removals from the
202 * underlying {@link Environment} property sources.
203 *
204 * @param environment the source environment (must be an instance of
205 * {@link ConfigurableEnvironment})
206 * @see #get(Environment)
207 */
208 public static void attach(Environment environment) {
209 // 判斷environment是否是ConfigurableEnvironment的實體
210 Assert.isInstanceOf(ConfigurableEnvironment.class, environment);
211 // 從environment獲取PropertySources
212 MutablePropertySources sources = ((ConfigurableEnvironment) environment)
213 .getPropertySources();
214 PropertySource<?> attached = sources.get(ATTACHED_PROPERTY_SOURCE_NAME);
215 if (attached != null && attached.getSource() != sources) {
216 sources.remove(ATTACHED_PROPERTY_SOURCE_NAME);
217 attached = null;
218 }
219 if (attached == null) {
220 // 將sources封裝成ConfigurationPropertySourcesPropertySource物件，并把這個物件放到sources的第一位置
221 sources.addFirst(new ConfigurationPropertySourcesPropertySource(
222 ATTACHED_PROPERTY_SOURCE_NAME,
223 new SpringConfigurationPropertySources(sources)));
224 }
225 }
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2.3、printBanner
printBanner 列印SpringBoot標志，printBanner(environment)方法就是列印Banner，Banner就是專案啟動時看到的那個logo，在工程專案src/main/resources路徑下下放入名字是banner的檔案，后綴后可以是SpringApplicationBannerPrinter.java類里的{ "gif", "jpg", "png" }，或者是txt、圖片也可以的，但是圖片列印時會字符化，而不是列印圖片本身，自定義banner鏈接
private Banner printBanner(ConfigurableEnvironment environment)
1 /** 2 * 列印SpringBoot標志 3 * banner的輸出默認有三種種模式，LOG、CONSOLE、OFF， 4 * 1. LOG：將banner資訊輸出到日志檔案， 5 * 2. CONSOLE：將banner資訊輸出到控制臺， 6 * 3. OFF：禁用banner的資訊輸出， 7 * 8 * @param environment 9 * @return 10 */ 11 private Banner printBanner(ConfigurableEnvironment environment) { 12 // 判斷Banner的模式是否關閉，如果關閉直接回傳， 13 if (this.bannerMode == Banner.Mode.OFF) { 14 return null; 15 } 16 ResourceLoader resourceLoader = (this.resourceLoader != null) ? this.resourceLoader 17 : new DefaultResourceLoader(null); 18 // 創建SpringApplicationBannerPrinter 列印類 19 SpringApplicationBannerPrinter bannerPrinter = new SpringApplicationBannerPrinter(resourceLoader, this.banner); 20 // LOG：將banner資訊輸出到日志檔案 21 if (this.bannerMode == Mode.LOG) { 22 return bannerPrinter.print(environment, this.mainApplicationClass, logger); 23 } 24 //banner沒有關閉且沒有指定是寫到log檔案中 將banner資訊輸出到控制臺 25 return bannerPrinter.print(environment, this.mainApplicationClass, System.out); 26 } 27 28 /** 29 * 列印 30 * 31 * @param environment 32 * @param sourceClass 33 * @param logger 34 * @return 35 */ 36 Banner print(Environment environment, Class<?> sourceClass, Log logger) { 37 // 獲取banner內容 38 Banner banner = getBanner(environment); 39 try { 40 logger.info(createStringFromBanner(banner, environment, sourceClass)); 41 } catch (UnsupportedEncodingException ex) { 42 logger.warn("Failed to create String for banner", ex); 43 } 44 return new PrintedBanner(banner, sourceClass); 45 } 46 47 /** 48 * 獲取banner內容 49 * 50 * @param environment 51 * @return 52 */ 53 private Banner getBanner(Environment environment) { 54 Banners banners = new Banners(); 55 // 圖片型別的banner內容 56 banners.addIfNotNull(getImageBanner(environment)); 57 // 文本型別的banner內容 58 banners.addIfNotNull(getTextBanner(environment)); 59 if (banners.hasAtLeastOneBanner()) { 60 return banners; 61 } 62 if (this.fallbackBanner != null) { 63 return this.fallbackBanner; 64 } 65 return DEFAULT_BANNER; 66 } 67 68 static final String BANNER_LOCATION_PROPERTY = "spring.banner.location"; 69 static final String DEFAULT_BANNER_LOCATION = "banner.txt"; 70 71 /** 72 * 文本型別的banner內容獲取 73 * 74 * @param environment 75 * @return 76 */ 77 private Banner getTextBanner(Environment environment) { 78 /** 79 * 拿到自定義配置的banner檔案地址 80 * BANNER_LOCATION_PROPERTY = "spring.banner.location" 81 * DEFAULT_BANNER_LOCATION = "banner.txt"; 82 */ 83 String location = environment.getProperty(BANNER_LOCATION_PROPERTY, DEFAULT_BANNER_LOCATION); 84 Resource resource = this.resourceLoader.getResource(location); 85 try { 86 if (resource.exists() && !resource.getURL().toExternalForm().contains("liquibase-core")) { 87 return new ResourceBanner(resource); 88 } 89 } catch (IOException ex) { 90 // Ignore 91 } 92 return null; 93 }View Code
2.4、createApplicationContext
createApplicationContext創建IOC容器，
protected ConfigurableApplicationContext createApplicationContext()
1 /**
2 * 創建 IOC 容器
3 * A default {@link ApplicationContextFactory} implementation that will create an
4 * appropriate context for the {@link WebApplicationType}.
5 */
6 ApplicationContextFactory DEFAULT = (webApplicationType) -> {
7 try {
8 // 根據當前應用的型別創建 IOC 容器
9 switch (webApplicationType) {
10 // Web 應用環境對應 AnnotationConfigServletWebServerApplicationContext
11 case SERVLET:
12 return new AnnotationConfigServletWebServerApplicationContext();
13 // 回應式編程對應 AnnotationConfigReactiveWebServerApplicationContext
14 case REACTIVE:
15 return new AnnotationConfigReactiveWebServerApplicationContext();
16 // 默認為 Spring 環境 AnnotationConfigApplicationContext
17 default:
18 return new AnnotationConfigApplicationContext();
19 }
20 }
21 catch (Exception ex) {
22 throw new IllegalStateException("Unable create a default ApplicationContext instance, "
23 + "you may need a custom ApplicationContextFactory", ex);
24 }
25 };
26
27 /**
28 * 設定一個啟動器
29 * Set the {@link ApplicationStartup} for this application context.
30 * <p>This allows the application context to record metrics
31 * during startup.
32 * @param applicationStartup the new context event factory
33 * @since 5.3
34 */
35 void setApplicationStartup(ApplicationStartup applicationStartup);
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2.5、prepareContext
prepareContext 配置 IOC 容器的基本資訊，
private void prepareContext(引數此處省略)
1 /**
2 * 準備IOC容器基本資訊
3 * @param bootstrapContext
4 * @param context
5 * @param environment
6 * @param listeners
7 * @param applicationArguments
8 * @param printedBanner
9 */
10 private void prepareContext(DefaultBootstrapContext bootstrapContext, ConfigurableApplicationContext context,
11 ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
12 ApplicationArguments applicationArguments, Banner printedBanner) {
13 // 設定容器環境，包括各種變數
14 context.setEnvironment(environment);
15 /**
16 * 后置處理流程
17 * 設定IOC容器的 bean 生成器和資源加載器
18 */
19 postProcessApplicationContext(context);
20 /**
21 * 獲取所有的初始化器呼叫 initialize() 方法進行初始化
22 * 執行容器中的ApplicationContextInitializer（包括從 spring.factories和自定義的實體）初始化
23 */
24 applyInitializers(context);
25 /**
26 * 觸發所有 SpringApplicationRunListener 監聽器的 contextPrepared 事件方法
27 * 所有的運行監聽器呼叫 environmentPrepared() 方法，EventPublishingRunListener 發布事件通知 IOC 容器準備完成
28 */
29 listeners.contextPrepared(context);
30 bootstrapContext.close(context);
31 // 列印啟動日志
32 if (this.logStartupInfo) {
33 logStartupInfo(context.getParent() == null);
34 logStartupProfileInfo(context);
35 }
36 // Add boot specific singleton beans
37 ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
38 // 注冊添加特定的單例bean
39 beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
40 if (printedBanner != null) {
41 beanFactory.registerSingleton("springBootBanner", printedBanner);
42 }
43 if (beanFactory instanceof DefaultListableBeanFactory) {
44 ((DefaultListableBeanFactory) beanFactory)
45 .setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
46 }
47 if (this.lazyInitialization) {
48 context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
49 }
50 // Load the sources
51 // 加載所有資源
52 Set<Object> sources = getAllSources();
53 // 斷言資源費控
54 Assert.notEmpty(sources, "Sources must not be empty");
55 // 創建BeanDefinitionLoader，加載啟動類，將啟動類注入容器
56 load(context, sources.toArray(new Object[0]));
57 // 觸發所有 SpringApplicationRunListener 監聽器的 contextLoaded 事件方法
58 listeners.contextLoaded(context);
59 }
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2.6、refresh
refresh 重繪應用背景關系，即重繪Spring背景關系資訊refreshContext，這里會涉及Spring容器啟動、SpringBoot自動裝配、創建 WebServer啟動Web服務即SpringBoot啟動內嵌的 Tomcat，
private void refreshContext(ConfigurableApplicationContext context)
1 /**
2 * 重繪應用背景關系
3 *
4 * @param context
5 */
6 private void refreshContext(ConfigurableApplicationContext context) {
7 if (this.registerShutdownHook) {
8 // 判斷是否注冊關閉的鉤子，是則注冊鉤子
9 shutdownHook.registerApplicationContext(context);
10 }
11 refresh(context);
12 }
13
14 /**
15 * Refresh the underlying {@link ApplicationContext}.
16 *
17 * @param applicationContext the application context to refresh
18 */
19 protected void refresh(ConfigurableApplicationContext applicationContext) {
20 applicationContext.refresh();
21 }
22
23 /**
24 * 重繪IOC容器
25 *
26 * @throws BeansException
27 * @throws IllegalStateException
28 */
29 @Override
30 public void refresh() throws BeansException, IllegalStateException {
31 synchronized (this.startupShutdownMonitor) {
32 StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");
33
34 // Prepare this context for refreshing. 準備重繪背景關系
35 prepareRefresh();
36
37 // Tell the subclass to refresh the internal bean factory. 通知子類重繪內部工廠
38 ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
39
40 // Prepare the bean factory for use in this context. 準備Bean工廠
41 prepareBeanFactory(beanFactory);
42
43 try {
44 // Allows post-processing of the bean factory in context subclasses.
45 // 允許在背景關系子類中對bean工廠進行后處理,這部分涉及Web服務器的啟動，如servlet
46 postProcessBeanFactory(beanFactory);
47
48 StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
49 // Invoke factory processors registered as beans in the context.
50 // 呼叫在背景關系中注冊為 bean 的工廠處理器
51 invokeBeanFactoryPostProcessors(beanFactory);
52
53 // Register bean processors that intercept bean creation. 注冊攔截 bean 創建的 bean 處理器
54 registerBeanPostProcessors(beanFactory);
55 beanPostProcess.end();
56
57 // Initialize message source for this context. 初始化此背景關系的訊息源
58 initMessageSource();
59
60 // Initialize event multicaster for this context. 為該背景關系初始化事件多播器
61 initApplicationEventMulticaster();
62
63 // Initialize other special beans in specific context subclasses. 初始化特定背景關系子類中的其他特殊 bean
64 /**
65 * SpringBoot 一鍵啟動web工程的關鍵方法
66 * 創建 WebServer啟動Web服務
67 * SpringBoot啟動內嵌的 Tomcat 首先要在pom檔案配置內嵌容器為tomcat
68 * SpringBoot 嵌入式 Servlet 容器，默認支持的 webServe：Tomcat、Jetty、Undertow
69 * <exclusion>
70 * <groupId>org.springframework.boot</groupId>
71 * <artifactId>spring-boot-starter-tomcat</artifactId>
72 * </exclusion>
73 */
74 onRefresh();
75
76 // Check for listener beans and register them. 檢查偵聽器 bean 并注冊
77 registerListeners();
78
79 // Instantiate all remaining (non-lazy-init) singletons. 實體化所有剩余的（非延遲初始化）單例
80 finishBeanFactoryInitialization(beanFactory);
81
82 // Last step: publish corresponding event. 發布事件
83 finishRefresh();
84 } catch (BeansException ex) {
85 if (logger.isWarnEnabled()) {
86 logger.warn("Exception encountered during context initialization - " +
87 "cancelling refresh attempt: " + ex);
88 }
89
90 // Destroy already created singletons to avoid dangling resources. 銷毀bean
91 destroyBeans();
92
93 // Reset 'active' flag.
94 cancelRefresh(ex);
95
96 // Propagate exception to caller.
97 throw ex;
98 } finally {
99 // Reset common introspection caches in Spring's core, since we
100 // might not ever need metadata for singleton beans anymore...
101 resetCommonCaches();
102 contextRefresh.end();
103 }
104 }
105 }
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2.7、onRefresh
onRefresh方法中創建WebServer、創建Tomcat物件，是SpringBoot一鍵啟動web工程的關鍵，SpringBoot 嵌入式 Servlet 容器，默認支持的 webServe：Tomcat、Jetty、Undertow，但要在POM檔案加入tomcat相關配置，
1 <dependency>
2 <groupId>org.springframework.boot</groupId>
3 <artifactId>spring-boot-starter-web</artifactId>
4 <exclusions>
5 <exclusion> <!--必須要把內嵌的 Tomcat 容器-->
6 <groupId>org.springframework.boot</groupId>
7 <artifactId>spring-boot-starter-tomcat</artifactId>
8 </exclusion>
9 </exclusions>
10 </dependency>
11 <dependency>
12 <groupId>org.springframework.boot</groupId>
13 <artifactId>spring-boot-starter-jetty</artifactId>
14 </dependency>
View Code
protected void onRefresh() throws BeansException
1 /**
2 * 創建 WebServer啟動Web服務
3 */
4 @Override
5 protected void onRefresh() {
6 // 初始化給定應用程式背景關系的主題資源
7 super.onRefresh();
8 try {
9 // 創建Web 服務
10 createWebServer();
11 }
12 catch (Throwable ex) {
13 throw new ApplicationContextException("Unable to start web server", ex);
14 }
15 }
16
17 /**
18 * super.onRefresh();
19 * Initialize the theme capability.
20 */
21 @Override
22 protected void onRefresh() {
23 /**
24 * 初始化給定應用程式背景關系的主題資源，自動檢測一個名為“themeSource”的bean，
25 * 如果沒有這樣的，將使用默認的(空的)ThemeSource，
26 */
27 this.themeSource = UiApplicationContextUtils.initThemeSource(this);
28 }
29
30 /**
31 * 創建Web 服務
32 */
33 private void createWebServer() {
34 WebServer webServer = this.webServer;
35 ServletContext servletContext = getServletContext();
36 if (webServer == null && servletContext == null) {
37 // 獲取web server
38 StartupStep createWebServer = this.getApplicationStartup().start("spring.boot.webserver.create");
39 // 獲取創建容器的工廠
40 ServletWebServerFactory factory = getWebServerFactory();
41 createWebServer.tag("factory", factory.getClass().toString());
42 /**
43 * 獲取 tomcat 、Jetty 或 Undertow 容器
44 * 從 getWebServer 方法點進去，找到 TomcatServletWebServerFactory 的實作方法，
45 * 與之對應的還有 Jetty 和 Undertow，這里配置了基本的連接器、引擎、虛擬站點等配置，
46 * 自動配置類 ServletWebServerFactoryAutoConfiguration 匯入了 ServletWebServerFactoryConfiguration（配置類）,
47 * 根據條件裝配判斷系統中到底匯入了哪個 Web 服務器的包，創建出服務器并啟動
48 * 默認是 web-starter 匯入 tomcat 包，容器中就有 TomcatServletWebServerFactory，創建出 Tomcat 服務器并啟動
49 */
50 this.webServer = factory.getWebServer(getSelfInitializer());
51 createWebServer.end();
52 getBeanFactory().registerSingleton("webServerGracefulShutdown",
53 new WebServerGracefulShutdownLifecycle(this.webServer));
54 getBeanFactory().registerSingleton("webServerStartStop",
55 new WebServerStartStopLifecycle(this, this.webServer));
56 }
57 else if (servletContext != null) {
58 try {
59 // 啟動web server
60 getSelfInitializer().onStartup(servletContext);
61 }
62 catch (ServletException ex) {
63 throw new ApplicationContextException("Cannot initialize servlet context", ex);
64 }
65 }
66 initPropertySources();
67 }
68
69 /**
70 * 獲取tomcat 容器
71 * 配置了基本的連接器、引擎、虛擬站點等配置
72 * @param initializers
73 * @return
74 */
75 @Override
76 public WebServer getWebServer(ServletContextInitializer... initializers) {
77 if (this.disableMBeanRegistry) {
78 Registry.disableRegistry();
79 }
80 /**
81 * 創建了Tomcat物件，并設定引數
82 */
83 Tomcat tomcat = new Tomcat();
84 // 設定作業忙碌
85 File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");
86 tomcat.setBaseDir(baseDir.getAbsolutePath());
87 // 初始化tomcat 連接，默認NIO
88 Connector connector = new Connector(this.protocol);
89 connector.setThrowOnFailure(true);
90 tomcat.getService().addConnector(connector);
91 customizeConnector(connector);
92 // 配置基本的連接器、引擎、虛擬站點
93 tomcat.setConnector(connector);
94 // 設定自動部署為false
95 tomcat.getHost().setAutoDeploy(false);
96 configureEngine(tomcat.getEngine());
97 for (Connector additionalConnector : this.additionalTomcatConnectors) {
98 tomcat.getService().addConnector(additionalConnector);
99 }
100 // 準備背景關系
101 prepareContext(tomcat.getHost(), initializers);
102 // 回傳TomcatWebServer服務
103 return getTomcatWebServer(tomcat);
104 }
105
106 /**
107 * Create a new {@link TomcatWebServer} instance.
108 * @param tomcat the underlying Tomcat server
109 * @param autoStart if the server should be started
110 * @param shutdown type of shutdown supported by the server
111 * @since 2.3.0
112 */
113 public TomcatWebServer(Tomcat tomcat, boolean autoStart, Shutdown shutdown) {
114 Assert.notNull(tomcat, "Tomcat Server must not be null");
115 this.tomcat = tomcat;
116 this.autoStart = autoStart;
117 this.gracefulShutdown = (shutdown == Shutdown.GRACEFUL) ? new GracefulShutdown(tomcat) : null;
118 // 初始化Tomcat
119 initialize();
120 }
121
122 /**
123 * 初始化Tomcat
124 * @throws WebServerException
125 */
126 private void initialize() throws WebServerException {
127 logger.info("Tomcat initialized with port(s): " + getPortsDescription(false));
128 synchronized (this.monitor) {
129 try {
130 addInstanceIdToEngineName();
131
132 Context context = findContext();
133 context.addLifecycleListener((event) -> {
134 if (context.equals(event.getSource()) && Lifecycle.START_EVENT.equals(event.getType())) {
135 // Remove service connectors so that protocol binding doesn't
136 // happen when the service is started.
137 removeServiceConnectors();
138 }
139 });
140
141 // Start the server to trigger initialization listeners
142 this.tomcat.start();
143
144 // We can re-throw failure exception directly in the main thread
145 rethrowDeferredStartupExceptions();
146
147 try {
148 ContextBindings.bindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());
149 }
150 catch (NamingException ex) {
151 // Naming is not enabled. Continue
152 }
153
154 // Unlike Jetty, all Tomcat threads are daemon threads. We create a
155 // blocking non-daemon to stop immediate shutdown
156 startDaemonAwaitThread();
157 }
158 catch (Exception ex) {
159 stopSilently();
160 destroySilently();
161 throw new WebServerException("Unable to start embedded Tomcat", ex);
162 }
163 }
164 }
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2.8、afterRefresh
afterReftesh() 重繪后處理，是個一空實作的擴展介面，留著后期擴展如用戶自定義容器重繪后的處理邏輯，
2.9、停止計時并列印啟動完畢相關日志
2.10、started
started 發布監聽應用啟動事件，
void started(ConfigurableApplicationContext context)
1 /**
2 * 發布應用監聽啟動事件
3 * @param context
4 */
5 void started(ConfigurableApplicationContext context) {
6 // listener.started(context) 中交由context.publishEvent（）方法處理
7 // 實際上是發送了一個ApplicationStartedEvent的事件
8 doWithListeners("spring.boot.application.started", (listener) -> listener.started(context));
9 }
10
11 /**
12 * 發布應用啟動事件ApplicationStartedEvent.
13 * @param context
14 */
15 @Override
16 public void started(ConfigurableApplicationContext context) {
17 context.publishEvent(new ApplicationStartedEvent(this.application, this.args, context));
18 AvailabilityChangeEvent.publish(context, LivenessState.CORRECT);
19 }
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2.11、callRunners
callRunners，執行runner主要是遍歷所有的runner獲取所有的ApplicationRuner 和CommandLineRunner 來初始化引數，其中callRuner（是一個回呼函式)，
private void callRunners(ApplicationContext context, ApplicationArguments args)
1 /**
2 * 執行runner 初始化引數
3 * @param context
4 * @param args
5 */
6 private void callRunners(ApplicationContext context, ApplicationArguments args) {
7 List<Object> runners = new ArrayList<>();
8 runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());
9 runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());
10 AnnotationAwareOrderComparator.sort(runners);
11 // 遍歷所有runner
12 for (Object runner : new LinkedHashSet<>(runners)) {
13 if (runner instanceof ApplicationRunner) {
14 /**
15 * 回呼函式callRunner 處理 ApplicationRunner
16 */
17 callRunner((ApplicationRunner) runner, args);
18 }
19 if (runner instanceof CommandLineRunner) {
20 /**
21 * 回呼函式callRunner 處理 CommandLineRunner
22 */
23 callRunner((CommandLineRunner) runner, args);
24 }
25 }
26 }
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2.12、running
running 發布背景關系完成準備事件，listeners.running() 發布背景關系完成準備事件同前面的listeners.started() 方法一樣，都是發布了一個running事件，代碼也相同，
void running(ConfigurableApplicationContext context)
1 /**
2 * 發布背景關系完成準備事件
3 * 與上面的 listeners.started() 方法一樣
4 * @param context
5 */
6 void running(ConfigurableApplicationContext context) {
7 // listener.started(context) 中交由context.publishEvent（）方法處理
8 // 實際上是發送了一個ApplicationStartedEvent的事件
9 doWithListeners("spring.boot.application.running", (listener) -> listener.running(context));
10 }
11
12 /**
13 * 發布背景關系完成準備事件
14 * Called immediately before the run method finishes, when the application context has
15 * been refreshed and all {@link CommandLineRunner CommandLineRunners} and
16 * {@link ApplicationRunner ApplicationRunners} have been called.
17 * @param context the application context.
18 * @since 2.0.0
19 */
20 @Override
21 public void running(ConfigurableApplicationContext context) {
22 context.publishEvent(new ApplicationReadyEvent(this.application, this.args, context));
23 AvailabilityChangeEvent.publish(context, ReadinessState.ACCEPTING_TRAFFIC);
24 }
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這也是SpringBoot啟動流程兩大程序中的第二階段的啟動方法run中最后一個方法了，該方法執行完成后，SpringApplication的run(String... args)方法執行結束，至此Spring Boot的ApplicationContext 啟動結束，
四、總結
SpringBoot啟動流程總結就是下面兩張圖片，一個創建SpringApplication實體，一個執行run方法，所有的貓膩都在其中，
君生我未生
君生我已老
君恨我生遲
我恨君生早
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