Springboot FatJa原理机制源码解析

Spring-Boot-Version: 2.1.3.RELEASE
Main-Class: org.springframework.boot.loader.JarLauncher
Start-Class: com.rock.springbootlearn.SpringbootLearnApplication
Spring-Boot-Classes: BOOT-INF/classes/
Spring-Boot-Lib: BOOT-INF/lib/
Build-Jdk: 1.8.0_131

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-loader</artifactId>
</dependency>

public ExecutableArchiveLauncher() {
	this.archive = createArchive();
}
protected final Archive createArchive() throws Exception {
	ProtectionDomain protectionDomain = getClass().getProtectionDomain();
	CodeSource codeSource = protectionDomain.getCodeSource();
	URI location = (codeSource != null) ? codeSource.getLocation().toURI() : null;
	String path = (location != null) ? location.getSchemeSpecificPart() : null;
	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));
}

@Override
protected List<Archive> getClassPathArchives() throws Exception {
	List<Archive> archives = new ArrayList<>(
			this.archive.getNestedArchives(this::isNestedArchive));
	postProcessClassPathArchives(archives);
	return archives;
}
protected boolean isNestedArchive(Archive.Entry entry) {
	if (entry.isDirectory()) {
		return entry.getName().equals(BOOT_INF_CLASSES);
	}
	return entry.getName().startsWith(BOOT_INF_LIB);
}

public static void main(String[] args) throws Exception {
	new JarLauncher().launch(args);
}

protected void launch(String[] args) throws Exception {
	JarFile.registerUrlProtocolHandler();
        //创建类加载器, 并指定归档文件
	ClassLoader classLoader = createClassLoader(getClassPathArchives());
	launch(args, getMainClass(), classLoader);
}
//创建类加载器, 将归档文件转换为URL
protected ClassLoader createClassLoader(List<Archive> archives) throws Exception {
	List<URL> urls = new ArrayList<>(archives.size());
	for (Archive archive : archives) {
		urls.add(archive.getUrl());
	}
	return createClassLoader(urls.toArray(new URL[0]));
}
//父加载器是AppClassLoader
protected ClassLoader createClassLoader(URL[] urls) throws Exception {
        //getClass().getClassLoader() 是系统类加载器,因为默认情况下main方法所在类是由SystemClassLoader加载的,默认情况下是AppClassLoader.
	return new LaunchedURLClassLoader(urls, getClass().getClassLoader());
}

public static void main(String[] args) throws Exception {
	new JarLauncher().launch(args);
}
protected void launch(String[] args, String mainClass, ClassLoader classLoader)
		throws Exception {
        //设置线程上下文类加载器
	Thread.currentThread().setContextClassLoader(classLoader);
	//调用MANIFEST.MF 中配置的Start-Class: xxx的main方法,还带入了参数
        createMainMethodRunner(mainClass, args, classLoader).run();