<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
        </plugin>
    </plugins>
</build>

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <executions>
        <execution>
            <goals>
                <goal>repackage</goal>
            </goals>
        </execution>
    </executions>
</plugin>

Manifest-Version: 1.0
Archiver-Version: Plexus Archiver
Built-By: xxxx
Start-Class: com.xxxx.AppServer
Spring-Boot-Classes: BOOT-INF/classes/
Spring-Boot-Lib: BOOT-INF/lib/
Spring-Boot-Version: 2.1.6.RELEASE
Created-By: Apache Maven 3.3.9
Build-Jdk: 1.8.0_73
Main-Class: org.springframework.boot.loader.JarLauncher

public class JarLauncher extends ExecutableArchiveLauncher {

	static final String BOOT_INF_CLASSES = "BOOT-INF/classes/";

	static final String BOOT_INF_LIB = "BOOT-INF/lib/";

	public JarLauncher() {
	}

	protected JarLauncher(Archive archive) {
		super(archive);
	}

	@Override
	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 {
        //項目入口，重點在launch這個方法中
		new JarLauncher().launch(args);
	}

}

//launch方法
protected void launch(String[] args) throws Exception {
    JarFile.registerUrlProtocolHandler();
    //創(chuàng)建LaunchedURLClassLoader。如果根類加載器和擴展類加載器沒有加載到某個類的話，就會通過LaunchedURLClassLoader這個加載器來加載類。這個加載器會從Boot-INF下面的class目錄和lib目錄下加載類。
    ClassLoader classLoader = createClassLoader(getClassPathArchives());
    //這個方法會讀取jar描述文件中的Start-Class屬性，然后通過反射調(diào)用到這個類的main方法。
    launch(args, getMainClass(), classLoader);
}

 java -Xdebug -Xrunjdwp:transport=dt_socket,address=5005,server=y,suspend=y -jar App.jar