详解spring boot应用启动原理分析

git clone git@github.com:hengyunabc/spring-boot-demo.git
mvn spring-boot-demo
java -jar target/demo-0.0.1-SNAPSHOT.jar

demo-0.0.1-SNAPSHOT.jar
demo-0.0.1-SNAPSHOT.jar.original

├── META-INF
│ ├── MANIFEST.MF
├── application.properties
├── com
│ └── example
│  └── SpringBootDemoApplication.class
├── lib
│ ├── aopalliance-1.0.jar
│ ├── spring-beans-4.2.3.RELEASE.jar
│ ├── ...
└── org
 └── springframework
  └── boot
   └── loader
    ├── ExecutableArchiveLauncher.class
    ├── JarLauncher.class
    ├── JavaAgentDetector.class
    ├── LaunchedURLClassLoader.class
    ├── Launcher.class
    ├── MainMethodRunner.class
    ├── ...

Manifest-Version: 1.0
Start-Class: com.example.SpringBootDemoApplication
Implementation-Vendor-Id: com.example
Spring-Boot-Version: 1.3.0.RELEASE
Created-By: Apache Maven 3.3.3
Build-Jdk: 1.8.0_60
Implementation-Vendor: Pivotal Software, Inc.
Main-Class: org.springframework.boot.loader.JarLauncher

@SpringBootApplication
public class SpringBootDemoApplication {

 public static void main(String[] args) {
  SpringApplication.run(SpringBootDemoApplication.class, args);
 }
}

public abstract class Archive {
 public abstract URL getUrl();
 public String getMainClass();
 public abstract Collection<Entry> getEntries();
 public abstract List<Archive> getNestedArchives(EntryFilter filter);

jar:file:/tmp/target/demo-0.0.1-SNAPSHOT.jar!/

jar:file:/tmp/target/demo-0.0.1-SNAPSHOT.jar!/lib/aopalliance-1.0.jar
jar:file:/tmp/target/demo-0.0.1-SNAPSHOT.jar!/lib/spring-beans-4.2.3.RELEASE.jar

class JarLauncher extends ExecutableArchiveLauncher
class ExecutableArchiveLauncher extends Launcher

protected final Archive createArchive() throws Exception {
 ProtectionDomain protectionDomain = getClass().getProtectionDomain();
 CodeSource codeSource = protectionDomain.getCodeSource();
 URI location = (codeSource == null ? null : codeSource.getLocation().toURI());
 String path = (location == null ? null : location.getSchemeSpecificPart());
 if (path == null) {
 throw new IllegalStateException("Unable to determine code source archive");
 }
 File root = new File(path);
 if (!root.exists()) {
 throw new IllegalStateException(
 "Unable to determine code source archive from " + root);
 }
 return (root.isDirectory() ? new ExplodedArchive(root)
 : new JarFileArchive(root));
}

/**
 * Launch the application given the archive file and a fully configured classloader.
 */
protected void launch(String[] args, String mainClass, ClassLoader classLoader)
 throws Exception {
 Runnable runner = createMainMethodRunner(mainClass, args, classLoader);
 Thread runnerThread = new Thread(runner);
 runnerThread.setContextClassLoader(classLoader);
 runnerThread.setName(Thread.currentThread().getName());
 runnerThread.start();
}

/**
 * Create the {@code MainMethodRunner} used to launch the application.
 */
protected Runnable createMainMethodRunner(String mainClass, String[] args,
 ClassLoader classLoader) throws Exception {
 Class<?> runnerClass = classLoader.loadClass(RUNNER_CLASS);
 Constructor<?> constructor = runnerClass.getConstructor(String.class,
 String[].class);
 return (Runnable) constructor.newInstance(mainClass, args);
}

jar:file:/tmp/target/demo-0.0.1-SNAPSHOT.jar!/

public URL(String protocol,
   String host,
   int port,
   String file,
   URLStreamHandler handler)
 throws MalformedURLException

//org.springframework.boot.loader.jar.Handler
public class Handler extends URLStreamHandler {
 private static final String SEPARATOR = "!/";
 private static SoftReference<Map<File, JarFile>> rootFileCache;
 @Override
 protected URLConnection openConnection(URL url) throws IOException {
 if (this.jarFile != null) {
 return new JarURLConnection(url, this.jarFile);
 }
 try {
 return new JarURLConnection(url, getRootJarFileFromUrl(url));
 }
 catch (Exception ex) {
 return openFallbackConnection(url, ex);
 }
 }
 public JarFile getRootJarFileFromUrl(URL url) throws IOException {
 String spec = url.getFile();
 int separatorIndex = spec.indexOf(SEPARATOR);
 if (separatorIndex == -1) {
 throw new MalformedURLException("Jar URL does not contain !/ separator");
 }
 String name = spec.substring(0, separatorIndex);
 return getRootJarFile(name);
 }

public URL findResource(String name)
public InputStream getResourceAsStream(String name)

//org.springframework.boot.loader.jar.JarURLConnection
 @Override
 public InputStream getInputStream() throws IOException {
 connect();
 if (this.jarEntryName.isEmpty()) {
 throw new IOException("no entry name specified");
 }
 return this.jarEntryData.getInputStream();
 }

URLClassPath ucp = new URLClassPath(urls);

 Resource getResource(final String name, boolean check) {
 final URL url;
 try {
  url = new URL(base, ParseUtil.encodePath(name, false));
 } catch (MalformedURLException e) {
  throw new IllegalArgumentException("name");
 }
 final URLConnection uc;
 try {
  if (check) {
   URLClassPath.check(url);
  }
  uc = url.openConnection();
  InputStream in = uc.getInputStream();
  if (uc instanceof JarURLConnection) {
   /* Need to remember the jar file so it can be closed
    * in a hurry.
    */
   JarURLConnection juc = (JarURLConnection)uc;
   jarfile = JarLoader.checkJar(juc.getJarFile());
  }
 } catch (Exception e) {
  return null;
 }
 return new Resource() {
  public String getName() { return name; }
  public URL getURL() { return url; }
  public URL getCodeSourceURL() { return base; }
  public InputStream getInputStream() throws IOException {
   return uc.getInputStream();
  }
  public int getContentLength() throws IOException {
   return uc.getContentLength();
  }
 };
}

@SpringBootApplication
public class SpringBootDemoApplication {

 public static void main(String[] args) {
  SpringApplication.run(SpringBootDemoApplication.class, args);
 }
}

java org.springframework.boot.loader.JarLauncher

private static final String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet",
 "org.springframework.web.context.ConfigurableWebApplicationContext" };

private boolean deduceWebEnvironment() {
 for (String className : WEB_ENVIRONMENT_CLASSES) {
  if (!ClassUtils.isPresent(className, null)) {
   return false;
  }
 }
 return true;
}

//org.springframework.boot.SpringApplication
 protected ConfigurableApplicationContext createApplicationContext() {
 Class<?> contextClass = this.applicationContextClass;
 if (contextClass == null) {
 try {
 contextClass = Class.forName(this.webEnvironment
  ? DEFAULT_WEB_CONTEXT_CLASS : DEFAULT_CONTEXT_CLASS);
 }
 catch (ClassNotFoundException ex) {
 throw new IllegalStateException(
  "Unable create a default ApplicationContext, "
  + "please specify an ApplicationContextClass",
  ex);
 }
 }
 return (ConfigurableApplicationContext) BeanUtils.instantiate(contextClass);
 }

//TomcatEmbeddedServletContainerFactory
@Override
public EmbeddedServletContainer getEmbeddedServletContainer(
  ServletContextInitializer... initializers) {
 Tomcat tomcat = new Tomcat();
 File baseDir = (this.baseDirectory != null ? this.baseDirectory
   : createTempDir("tomcat"));
 tomcat.setBaseDir(baseDir.getAbsolutePath());
 Connector connector = new Connector(this.protocol);
 tomcat.getService().addConnector(connector);
 customizeConnector(connector);
 tomcat.setConnector(connector);
 tomcat.getHost().setAutoDeploy(false);
 tomcat.getEngine().setBackgroundProcessorDelay(-1);
 for (Connector additionalConnector : this.additionalTomcatConnectors) {
  tomcat.getService().addConnector(additionalConnector);
 }
 prepareContext(tomcat.getHost(), initializers);
 return getTomcatEmbeddedServletContainer(tomcat);
}

private void addDefaultServlet(Context context) {
 Wrapper defaultServlet = context.createWrapper();
 defaultServlet.setName("default");
 defaultServlet.setServletClass("org.apache.catalina.servlets.DefaultServlet");
 defaultServlet.addInitParameter("debug", "0");
 defaultServlet.addInitParameter("listings", "false");
 defaultServlet.setLoadOnStartup(1);
 // Otherwise the default location of a Spring DispatcherServlet cannot be set
 defaultServlet.setOverridable(true);
 context.addChild(defaultServlet);
 context.addServletMapping("/", "default");
}

private void addJspServlet(Context context) {
 Wrapper jspServlet = context.createWrapper();
 jspServlet.setName("jsp");
 jspServlet.setServletClass(getJspServletClassName());
 jspServlet.addInitParameter("fork", "false");
 jspServlet.setLoadOnStartup(3);
 context.addChild(jspServlet);
 context.addServletMapping("*.jsp", "jsp");
 context.addServletMapping("*.jspx", "jsp");
}

//ResourceProperties
public class ResourceProperties implements ResourceLoaderAware {

 private static final String[] SERVLET_RESOURCE_LOCATIONS = { "/" };

 private static final String[] CLASSPATH_RESOURCE_LOCATIONS = {
 "classpath:/META-INF/resources/", "classpath:/resources/",
 "classpath:/static/", "classpath:/public/" };
 

//WebMvcAutoConfigurationAdapter
 @Override
 public void addViewControllers(ViewControllerRegistry registry) {
 Resource page = this.resourceProperties.getWelcomePage();
 if (page != null) {
 logger.info("Adding welcome page: " + page);
 registry.addViewController("/").setViewName("forward:index.html");
 }
 }

public static final String DEFAULT_PREFIX = "classpath:/templates/";

spring.view.prefix: /WEB-INF/jsp/

@Controller
@RequestMapping("${server.error.path:${error.path:/error}}")
public class BasicErrorController extends AbstractErrorController

@Configuration
@ConditionalOnProperty(prefix = "server.error.whitelabel", name = "enabled", matchIfMissing = true)
@Conditional(ErrorTemplateMissingCondition.class)
protected static class WhitelabelErrorViewConfiguration {

 private final SpelView defaultErrorView = new SpelView(
 "<html><body><h2>Whitelabel Error Page</h2>"
  + "<p>This application has no explicit mapping for /error, so you are seeing this as a fallback.</p>"
  + "<div id='created'>${timestamp}</div>"
  + "<div>There was an unexpected error (type=${error}, status=${status}).</div>"
  + "<div>${message}</div></body></html>");

 @Bean(name = "error")
 @ConditionalOnMissingBean(name = "error")
 public View defaultErrorView() {
 return this.defaultErrorView;
 }

spring.output.ansi.enabled=false

public class LaunchedURLClassLoader extends URLClassLoader {

 private static LockProvider LOCK_PROVIDER = setupLockProvider();
 private static LockProvider setupLockProvider() {
 try {
 ClassLoader.registerAsParallelCapable();
 return new Java7LockProvider();
 }
 catch (NoSuchMethodError ex) {
 return new LockProvider();
 }
 }

 @Override
 protected Class<?> loadClass(String name, boolean resolve)
 throws ClassNotFoundException {
 synchronized (LaunchedURLClassLoader.LOCK_PROVIDER.getLock(this, name)) {
 Class<?> loadedClass = findLoadedClass(name);
 if (loadedClass == null) {
 Handler.setUseFastConnectionExceptions(true);
 try {
  loadedClass = doLoadClass(name);
 }
 finally {
  Handler.setUseFastConnectionExceptions(false);
 }
 }
 if (resolve) {
 resolveClass(loadedClass);
 }
 return loadedClass;
 }
 }

private static final String JAVA_AGENT_PREFIX = "-javaagent:";

 private String getPid() {
 try {
 String jvmName = ManagementFactory.getRuntimeMXBean().getName();
 return jvmName.split("@")[0];
 }
 catch (Throwable ex) {
 return null;
 }
}

 private Class<?> deduceMainApplicationClass() {
 try {
  StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();
  for (StackTraceElement stackTraceElement : stackTrace) {
   if ("main".equals(stackTraceElement.getMethodName())) {
    return Class.forName(stackTraceElement.getClassName());
   }
  }
 }
 catch (ClassNotFoundException ex) {
  // Swallow and continue
 }
 return null;
}