spring boot jar的啟動原理解析
1.前言
近來有空對公司的open api平臺進行了些優(yōu)化,然后在打出jar包的時候,突然想到以前都是對spring boot使用很熟練,但是從來都不知道spring boot打出的jar的啟動原理,然后這回將jar解開了看了下,與想象中確實大不一樣,以下就是對解壓出來的jar的完整分析。
2.jar的結構
spring boot的應用程序就不貼出來了,一個較簡單的demo打出的結構都是類似,另外我采用的spring boot的版本為1.4.1.RELEASE網(wǎng)上有另外一篇文章對spring boot jar啟動的分析,那個應該是1.4以下的,啟動方式與當前版本也有著許多的不同。
在mvn clean install后,我們在查看target目錄中時,會發(fā)現(xiàn)兩個jar包,如下:
xxxx.jar xxx.jar.original
這個則是歸功于spring boot插件的機制,將一個普通的jar打成了一個可以執(zhí)行的jar包,而xxx.jar.original則是maven打出的jar包,這些可以參考spring官網(wǎng)的文章來了解,如下:
http://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#executable-jar
以下是spring boot應用打出的jar的部分目錄結構,大部分省略了,僅僅展示出其中重要的部分。
.
├── BOOT-INF
│ ├── classes
│ │ ├── application-dev.properties
│ │ ├── application-prod.properties
│ │ ├── application.properties
│ │ ├── com
│ │ │ └── weibangong
│ │ │ └── open
│ │ │ └── openapi
│ │ │ ├── SpringBootWebApplication.class
│ │ │ ├── config
│ │ │ │ ├── ProxyServletConfiguration.class
│ │ │ │ └── SwaggerConfig.class
│ │ │ ├── oauth2
│ │ │ │ ├── controller
│ │ │ │ │ ├── AccessTokenController.class
│ │ ├── logback-spring.xml
│ │ └── static
│ │ ├── css
│ │ │ └── guru.css
│ │ ├── images
│ │ │ ├── FBcover1200x628.png
│ │ │ └── NewBannerBOOTS_2.png
│ └── lib
│ ├── accessors-smart-1.1.jar
├── META-INF
│ ├── MANIFEST.MF
│ └── maven
│ └── com.weibangong.open
│ └── open-server-openapi
│ ├── pom.properties
│ └── pom.xml
└── org
└── springframework
└── boot
└── loader
├── ExecutableArchiveLauncher$1.class
├── ExecutableArchiveLauncher.class
├── JarLauncher.class
├── LaunchedURLClassLoader$1.class
├── LaunchedURLClassLoader.class
├── Launcher.class
├── archive
│ ├── Archive$Entry.class
│ ├── Archive$EntryFilter.class
│ ├── Archive.class
│ ├── ExplodedArchive$1.class
│ ├── ExplodedArchive$FileEntry.class
│ ├── ExplodedArchive$FileEntryIterator$EntryComparator.class
├── ExplodedArchive$FileEntryIterator.class
這個jar除了我們寫的應用程序打出的class以外還有一個單獨的org包,應該是spring boot應用在打包的使用spring boot插件將這個package打進來,也就是增強了mvn生命周期中的package階段,而正是這個包在啟動過程中起到了關鍵的作用,另外中jar中將應用所需的各種依賴都打進來,并且打入了spring boot額外的package,這種可以all-in-one的jar也被稱之為fat.jar,下文我們將一直以fat.jar來代替打出的jar的名字。
3.MANIFEST.MF文件
這個時候我們再繼續(xù)看META-INF中的MANIFEST.MF文件,如下:
Manifest-Version: 1.0 Implementation-Title: open :: server :: openapi Implementation-Version: 1.0-SNAPSHOT Archiver-Version: Plexus Archiver Built-By: xiaxuan Implementation-Vendor-Id: com.weibangong.open Spring-Boot-Version: 1.4.1.RELEASE Implementation-Vendor: Pivotal Software, Inc. Main-Class: org.springframework.boot.loader.PropertiesLauncher Start-Class: com.weibangong.open.openapi.SpringBootWebApplication Spring-Boot-Classes: BOOT-INF/classes/ Spring-Boot-Lib: BOOT-INF/lib/ Created-By: Apache Maven 3.3.9 Build-Jdk: 1.8.0_20 Implementation-URL: http://maven.apache.org/open-server-openapi
這里指定的main-class是單獨打入的包中的一個類文件而不是我們的啟動程序,然后MANIFEST.MF文件有一個單獨的start-class指定的是我們的應用的啟動程序。
4.啟動分析
首先我們找到類org.springframework.boot.loader.PropertiesLauncher,其中main方法為:
public static void main(String[] args) throws Exception {
PropertiesLauncher launcher = new PropertiesLauncher();
args = launcher.getArgs(args);
launcher.launch(args);
}
查看launch方法,這個方法在父類Launcher中,找到父類方法launch方法,如下:
protected void launch(String[] args, String mainClass, ClassLoader classLoader) throws Exception {
Thread.currentThread().setContextClassLoader(classLoader);
this.createMainMethodRunner(mainClass, args, classLoader).run();
}
protected MainMethodRunner createMainMethodRunner(String mainClass, String[] args, ClassLoader classLoader) {
return new MainMethodRunner(mainClass, args);
}
launch方法最終調用了createMainMethodRunner方法,后者實例化了MainMethodRunner對象并運行了run方法,我們轉到MainMethodRunner源碼中,如下:
package org.springframework.boot.loader;
import java.lang.reflect.Method;
public class MainMethodRunner {
private final String mainClassName;
private final String[] args;
public MainMethodRunner(String mainClass, String[] args) {
this.mainClassName = mainClass;
this.args = args == null?null:(String[])args.clone();
}
public void run() throws Exception {
Class mainClass = Thread.currentThread().getContextClassLoader().loadClass(this.mainClassName);
Method mainMethod = mainClass.getDeclaredMethod("main", new Class[]{String[].class});
mainMethod.invoke((Object)null, new Object[]{this.args});
}
}
查看run方法,就很怎么將spring boot的jar怎么運行起來的了,由此分析基本也就結束了。
5、main程序的啟動流程
講完了jar的啟動流程,現(xiàn)在來講下spring boot應用中,main程序的啟動與加載流程,首先我們看一個spring boot應用的main方法。
package cn.com.devh;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.feign.EnableFeignClients;
/**
* Created by xiaxuan on 17/8/25.
*/
@SpringBootApplication
@EnableFeignClients
@EnableEurekaClient
public class A1ServiceApplication {
public static void main(String[] args) {
SpringApplication.run(A1ServiceApplication.class, args);
}
}
轉到SpringApplication中的run方法,如下:
/**
* Static helper that can be used to run a {@link SpringApplication} from the
* specified source using default settings.
* @param source the source to load
* @param args the application arguments (usually passed from a Java main method)
* @return the running {@link ApplicationContext}
*/
public static ConfigurableApplicationContext run(Object source, String... args) {
return run(new Object[] { source }, args);
}
/**
* Static helper that can be used to run a {@link SpringApplication} from the
* specified sources using default settings and user supplied arguments.
* @param sources the sources to load
* @param args the application arguments (usually passed from a Java main method)
* @return the running {@link ApplicationContext}
*/
public static ConfigurableApplicationContext run(Object[] sources, String[] args) {
return new SpringApplication(sources).run(args);
}
這里的SpringApplication的實例化是關鍵,我們轉到SpringApplication的構造函數(shù)。
/**
* Create a new {@link SpringApplication} instance. The application context will load
* beans from the specified sources (see {@link SpringApplication class-level}
* documentation for details. The instance can be customized before calling
* {@link #run(String...)}.
* @param sources the bean sources
* @see #run(Object, String[])
* @see #SpringApplication(ResourceLoader, Object...)
*/
public SpringApplication(Object... sources) {
initialize(sources);
}
private void initialize(Object[] sources) {
if (sources != null && sources.length > 0) {
this.sources.addAll(Arrays.asList(sources));
}
this.webEnvironment = deduceWebEnvironment();
setInitializers((Collection) getSpringFactoriesInstances(
ApplicationContextInitializer.class));
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
this.mainApplicationClass = deduceMainApplicationClass();
}
這里的initialize方法中的deduceWebEnvironment()確定了當前是以web應用啟動還是以普通的jar啟動,如下:
private boolean deduceWebEnvironment() {
for (String className : WEB_ENVIRONMENT_CLASSES) {
if (!ClassUtils.isPresent(className, null)) {
return false;
}
}
return true;
}
其中的WEB_ENVIRONMENT_CLASSES為:
private static final String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet",
"org.springframework.web.context.ConfigurableWebApplicationContext" };
只要其中任何一個不存在,即當前應用以普通jar的形式啟動。
然后setInitializers方法初始化了所有的ApplicationContextInitializer,
/**
* Sets the {@link ApplicationContextInitializer} that will be applied to the Spring
* {@link ApplicationContext}.
* @param initializers the initializers to set
*/
public void setInitializers(
Collection<? extends ApplicationContextInitializer<?>> initializers) {
this.initializers = new ArrayList<ApplicationContextInitializer<?>>();
this.initializers.addAll(initializers);
}
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class))**
這一步初始化所有Listener。
我們再回到之前的SpringApplication(sources).run(args);處,進入run方法,代碼如下:
/**
* Run the Spring application, creating and refreshing a new
* {@link ApplicationContext}.
* @param args the application arguments (usually passed from a Java main method)
* @return a running {@link ApplicationContext}
*/
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
configureHeadlessProperty();
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.started();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
context = createAndRefreshContext(listeners, applicationArguments);
afterRefresh(context, applicationArguments);
listeners.finished(context, null);
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass)
.logStarted(getApplicationLog(), stopWatch);
}
return context;
}
catch (Throwable ex) {
handleRunFailure(context, listeners, ex);
throw new IllegalStateException(ex);
}
}
這一步進行上下文的創(chuàng)建createAndRefreshContext(listeners, applicationArguments),
private ConfigurableApplicationContext createAndRefreshContext(
SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments) {
ConfigurableApplicationContext context;
// Create and configure the environment
ConfigurableEnvironment environment = getOrCreateEnvironment();
configureEnvironment(environment, applicationArguments.getSourceArgs());
listeners.environmentPrepared(environment);
if (isWebEnvironment(environment) && !this.webEnvironment) {
environment = convertToStandardEnvironment(environment);
}
if (this.bannerMode != Banner.Mode.OFF) {
printBanner(environment);
}
// Create, load, refresh and run the ApplicationContext
context = createApplicationContext();
context.setEnvironment(environment);
postProcessApplicationContext(context);
applyInitializers(context);
listeners.contextPrepared(context);
if (this.logStartupInfo) {
logStartupInfo(context.getParent() == null);
logStartupProfileInfo(context);
}
// Add boot specific singleton beans
context.getBeanFactory().registerSingleton("springApplicationArguments",
applicationArguments);
// Load the sources
Set<Object> sources = getSources();
Assert.notEmpty(sources, "Sources must not be empty");
load(context, sources.toArray(new Object[sources.size()]));
listeners.contextLoaded(context);
// Refresh the context
refresh(context);
if (this.registerShutdownHook) {
try {
context.registerShutdownHook();
}
catch (AccessControlException ex) {
// Not allowed in some environments.
}
}
return context;
}
// Create and configure the environment
ConfigurableEnvironment environment = getOrCreateEnvironment();
configureEnvironment(environment, applicationArguments.getSourceArgs());
這一步進行了環(huán)境的配置與加載。
if (this.bannerMode != Banner.Mode.OFF) {
printBanner(environment);
}
這一步進行了打印spring boot logo,需要更改的話,在資源文件中加入banner.txt,banner.txt改為自己需要的圖案即可。
// Create, load, refresh and run the ApplicationContext context = createApplicationContext(); return (ConfigurableApplicationContext) BeanUtils.instantiate(contextClass)
創(chuàng)建上下文,這一步中真正包含了是創(chuàng)建什么容器,并進行了響應class的實例化,其中包括了EmbeddedServletContainerFactory的創(chuàng)建,是選擇jetty還是tomcat,內容繁多,留待下一次再講。
if (this.registerShutdownHook) {
try {
context.registerShutdownHook();
}
catch (AccessControlException ex) {
// Not allowed in some environments.
}
}
這一步就是當前上下文進行注冊,當收到kill指令的時候進行容器的銷毀等工作了。
基本到此,啟動的分析就結束了,但是還有一些細節(jié)講述起來十分耗時,這個留待后續(xù)的博文中再來講述,今天就到這里。
6.總結
綜上spring boot jar的啟動流程基本就是下面幾個步驟:
1、我們正常進行maven打包時,spring boot插件擴展maven生命周期,將spring boot相關package打入到jar中,這個jar中包含了應用所打出的jar以外還有spring boot啟動程序相關的類文件。
2、我以前看過稍微低一些版本的spring boot的jar的啟動流程,當時我記得是當前線程又起了一個新線程來運行main程序,而現(xiàn)在的已經改成了直接使用反射來啟動main程序。
總結
以上所述是小編給大家介紹的spring boot jar的啟動原理解析,希望對大家有所幫助,如果大家有任何疑問請給我留言,小編會及時回復大家的。在此也非常感謝大家對腳本之家網(wǎng)站的支持!

