SpringBoot源码简易篇

@MySpringBootApplication
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class);
    }
}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Configuration
@ComponentScan
@Import(AutoConfigurationImportSelector.class)
public @interface MySpringBootApplication {
}

public class SpringApplication {
    public static void run(Class clazz){
        AnnotationConfigWebApplicationContext applicationContext=new AnnotationConfigWebApplicationContext();
        applicationContext.register(clazz);
        applicationContext.refresh();
        WebServer webServer = getWebServer(applicationContext);
        webServer.start(applicationContext);
    }
    private static WebServer getWebServer(ApplicationContext applicationContext){
        Map<String, WebServer> webServers = applicationContext.getBeansOfType(WebServer.class);
       if(webServers.isEmpty()){
           throw new NullPointerException();
       }
       if(webServers.size()>1){
           throw new IllegalStateException();
       }
        return webServers.values().stream().findFirst().get();
    }
}

@Configuration
public class WebServerAutoConfiguration implements AutoConfiguration{
    @Bean
    @ConditionalOnClass("org.apache.catalina.startup.Tomcat")
    public TomcatWebServer tomcatWebServer(){
        return new TomcatWebServer();
    }
}

public class TomcatWebServer implements WebServer{
     public void start(AnnotationConfigWebApplicationContext applicationContext) {
        Tomcat tomcat=new Tomcat();
        Server server = tomcat.getServer();
        Service service = server.findService("Tomcat");
        Connector connector=new Connector();
        connector.setPort(8081);
        Engine engine=new StandardEngine();
        engine.setDefaultHost("localhost");
        Host host=new StandardHost();
        host.setName("localhost");
        String contextPath="";
        Context context=new StandardContext();
        context.setPath(contextPath);
        context.addLifecycleListener(new Tomcat.FixContextListener());
        host.addChild(context);
        engine.addChild(host);
        service.setContainer(engine);
        service.addConnector(connector);
        //Springmvc
        tomcat.addServlet(contextPath,"dispatcher",new DispatcherServlet(applicationContext));
        context.addServletMappingDecoded("/*","dispatcher");
        try {
            tomcat.start();
        } catch (LifecycleException e) {
            e.printStackTrace();
        }
    }
}

public class MyCondition implements Condition {
    @Override
    public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {
        Map<String, Object> annotationAttributes = annotatedTypeMetadata.getAnnotationAttributes(ConditionalOnClass.class.getName());
        String className= (String) annotationAttributes.get("value");
        try {
            Class<?> aClass = conditionContext.getClassLoader().loadClass(className);
            return true;
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
            return false;
        }
    }
}

@Target({ElementType.TYPE,ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(MyCondition.class)
public @interface ConditionalOnClass {
    String value();
}

public class AutoConfigurationImportSelector implements DeferredImportSelector {
    @Override
    public String[] selectImports(AnnotationMetadata annotationMetadata) {
        //jdk SPI
        ServiceLoader<AutoConfiguration> serviceLoader = ServiceLoader.load(AutoConfiguration.class);
        List<String> list=new ArrayList<>();
        for (AutoConfiguration autoConfiguration : serviceLoader) {
            list.add(autoConfiguration.getClass().getName());
        }
        return list.toArray(new String[0]);
    }
}