spring boot jar的启动原理分析
1、前言
2、分模块后的结构
3、MANIFEST.MF文件
4、运行
5、main程序的启动流程
6、总结
1.前言
近来有空对公司的open api平台进行了些优化,然后在打出jar包的时候,突然想到以前都是对spring boot使用很熟练,但是从来都不知道spring boot打出的jar的启动原理,然后这回将jar解开了看了下,与想象中确实大不一样,以下就是对解压出来的jar的完整分析。
2.jar的结构
spring boot的应用程序就不贴出来了,一个较简单的demo打出的结构都是类似,另外我采用的spring boot的版本为1.4.1.RELEASE
网上有另外一篇文章对spring boot jar启动的分析,那个应该是1.4以下的,启动方式与当前版本也有着许多的不同。
在mvn clean install后,我们在查看target目录中时,会发现两个jar包,如下:
xxxx.jar
xxx.jar.original
这个则是归功于spring boot插件的机制,将一个普通的jar打成了一个可以执行的jar包,而xxx.jar.original则是maven打出的jar包,这些可以参考spring官网的文章来了解,如下:
http://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#executable-jar
以下是spring boot应用打出的jar的部分目录结构,大部分省略了,仅仅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
这个jar除了我们写的应用程序打出的class以外还有一个单独的org包,应该是spring boot应用在打包的使用spring boot插件将这个package打进来,也就是增强了mvn生命周期中的package阶段,而正是这个包在启动过程中起到了关键的作用,另外中jar中将应用所需的各种依赖都打进来,并且打入了spring boot额外的package,这种可以all-in-one的jar也被称之为fat.jar,下文我们将一直以fat.jar来代替打出的jar的名字。
3.MANIFEST.MF文件
这个时候我们再继续看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
这里指定的main-class是单独打入的包中的一个类文件而不是我们的启动程序,然后MANIFEST.MF文件有一个单独的start-class指定的是我们的应用的启动程序。
4.启动分析
首先我们找到类org.springframework.boot.loader.PropertiesLauncher,其中main方法为:
public static void main(String[] args) throws Exception {
PropertiesLauncher launcher = new PropertiesLauncher();
args = launcher.getArgs(args);
launcher.launch(args);
}
查看launch方法,这个方法在父类Launcher中,找到父类方法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方法最终调用了createMainMethodRunner方法,后者实例化了MainMethodRunner对象并运行了run方法,我们转到MainMethodRunner源码中,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,就很怎么将spring boot的jar怎么运行起来的了,由此分析基本也就结束了。
5、main程序的启动流程
讲完了jar的启动流程,现在来讲下spring boot应用中,main程序的启动与加载流程,首先我们看一个spring boot应用的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);
}
}
转到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);
}
这里的SpringApplication的实例化是关键,我们转到SpringApplication的构造函数。
/** * 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();
}
这里的initialize方法中的deduceWebEnvironment()确定了当前是以web应用启动还是以普通的jar启动,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为:
private static final String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet",
"org.springframework.web.context.ConfigurableWebApplicationContext" };
只要其中任何一个不存在,即当前应用以普通jar的形式启动。
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))**
这一步初始化所有Listener。
我们再回到之前的SpringApplication(sources).run(args);处,进入run方法,代码如下:
/** * 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);
}
}
这一步进行上下文的创建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());
这一步进行了环境的配置与加载。
if (this.bannerMode != Banner.Mode.OFF) {
printBanner(environment);
}
这一步进行了打印spring boot logo,需要更改的话,在资源文件中加入banner.txt,banner.txt改为自己需要的图案即可。
// Create, load, refresh and run the ApplicationContext context = createApplicationContext();
return (ConfigurableApplicationContext) BeanUtils.instantiate(contextClass)
创建上下文,这一步中真正包含了是创建什么容器,并进行了响应class的实例化,其中包括了EmbeddedServletContainerFactory的创建,是选择jetty还是tomcat,内容繁多,留待下一次再讲。
if (this.registerShutdownHook) {
try {
context.registerShutdownHook();
}
catch (AccessControlException ex) {
// Not allowed in some environments.
}
}
这一步就是当前上下文进行注册,当收到kill指令的时候进行容器的销毁等工作了。
基本到此,启动的分析就结束了,但是还有一些细节讲述起来十分耗时,这个留待后续的博文中再来讲述,今天就到这里。
6.总结
综上spring boot jar的启动流程基本就是下面几个步骤:
1、我们正常进行maven打包时,spring boot插件扩展maven生命周期,将spring boot相关package打入到jar中,这个jar中包含了应用所打出的jar以外还有spring boot启动程序相关的类文件。
2、我以前看过稍微低一些版本的spring boot的jar的启动流程,当时我记得是当前线程又起了一个新线程来运行main程序,而现在的已经改成了直接使用反射来启动main程序。
下一节我们讲述@EnableEurekaClient的服务注册过程。