// 默认容器实现
DefaultListableBeanFactory beanRegistry = new DefaultListableBeanFactory();
// 根据业务对象构造相应的BeanDefinition
AbstractBeanDefinition definition = new RootBeanDefinition(Business.class,true);
// 将bean定义注册到容器中
beanRegistry.registerBeanDefinition("beanName",definition);
// 如果有多个bean，还可以指定各个bean之间的依赖关系
// ........

// 然后可以从容器中获取这个bean的实例
// 注意：这里的beanRegistry其实实现了BeanFactory接口，所以可以强转，
// 单纯的BeanDefinitionRegistry是无法强制转换到BeanFactory类型的
BeanFactory container = (BeanFactory)beanRegistry;
Business business = (Business)container.getBean("beanName");

// 通常为BeanDefinitionRegistry的实现类，这里以DeFaultListabeBeanFactory为例
BeanDefinitionRegistry beanRegistry = new DefaultListableBeanFactory(); 
// XmlBeanDefinitionReader实现了BeanDefinitionReader接口，用于解析XML文件
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReaderImpl(beanRegistry);
// 加载配置文件
beanDefinitionReader.loadBeanDefinitions("classpath:spring-bean.xml");

// 从容器中获取bean实例
BeanFactory container = (BeanFactory)beanRegistry;
Business business = (Business)container.getBean("beanName");

public interface BeanPostProcessor {
    // 前置处理
    Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;
    // 后置处理
    Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;
}

// 代码来自：org.springframework.context.support.ApplicationContextAwareProcessor
// 其postProcessBeforeInitialization方法调用了invokeAwareInterfaces方法
private void invokeAwareInterfaces(Object bean) {
    if (bean instanceof EnvironmentAware) {
        ((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
    }
    if (bean instanceof ApplicationContextAware) {
        ((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
    }
    // ......
}

<bean id="bookService" class="cn.moondev.service.BookServiceImpl"></bean>

@Configuration
public class MoonBookConfiguration {

    // 任何标志了@Bean的方法，其返回值将作为一个bean注册到Spring的IOC容器中
    // 方法名默认成为该bean定义的id
    @Bean
    public BookService bookService() {
        return new BookServiceImpl();
    }
}

<bean id="bookService" class="cn.moondev.service.BookServiceImpl">
    <property name="dependencyService" ref="dependencyService"/>
</bean>
<bean id="otherService" class="cn.moondev.service.OtherServiceImpl">
    <property name="dependencyService" ref="dependencyService"/>
</bean>
<bean id="dependencyService" class="DependencyServiceImpl"/>

@Configuration
public class MoonBookConfiguration {

    // 如果一个bean依赖另一个bean，则直接调用对应JavaConfig类中依赖bean的创建方法即可
    // 这里直接调用dependencyService()
    @Bean
    public BookService bookService() {
        return new BookServiceImpl(dependencyService());
    }

    @Bean
    public OtherService otherService() {
        return new OtherServiceImpl(dependencyService());
    }

    @Bean
    public DependencyService dependencyService() {
        return new DependencyServiceImpl();
    }
}

@Configuration
public class MoonBookConfiguration {
    @Bean
    public BookService bookService() {
        return new BookServiceImpl();
    }
}

@Configuration
// 可以同时导入多个配置类，比如：@Import({A.class,B.class})
@Import(MoonBookConfiguration.class)
public class MoonUserConfiguration {
    @Bean
    public UserService userService(BookService bookService) {
        return new BookServiceImpl(bookService);
    }
}

public class JdbcTemplateCondition implements Condition {

    @Override
    public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {
        try {
        conditionContext.getClassLoader().loadClass("org.springframework.jdbc.core.JdbcTemplate");
            return true;
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        return false;
    }
}

@Conditional(JdbcTemplateCondition.class)
@Service
public MyService service() {
    ......
}

// jdbc config
jdbc.mysql.url=jdbc:mysql://localhost:3306/sampledb
jdbc.mysql.username=root
jdbc.mysql.password=123456
......

// 配置数据源
@Configuration
public class HikariDataSourceConfiguration {

    @Value("jdbc.mysql.url")
    public String url;
    @Value("jdbc.mysql.username")
    public String user;
    @Value("jdbc.mysql.password")
    public String password;

    @Bean
    public HikariDataSource dataSource() {
        HikariConfig hikariConfig = new HikariConfig();
        hikariConfig.setJdbcUrl(url);
        hikariConfig.setUsername(user);
        hikariConfig.setPassword(password);
        // 省略部分代码
        return new HikariDataSource(hikariConfig);
    }
}

@Component
//  还可以通过@PropertySource("classpath:jdbc.properties")来指定配置文件
@ConfigurationProperties("jdbc.mysql")
// 前缀=jdbc.mysql，会在配置文件中寻找jdbc.mysql.*的配置项
pulic class JdbcConfig {
    public String url;
    public String username;
    public String password;
}

@Configuration
public class HikariDataSourceConfiguration {

    @AutoWired
    public JdbcConfig config;

    @Bean
    public HikariDataSource dataSource() {
        HikariConfig hikariConfig = new HikariConfig();
        hikariConfig.setJdbcUrl(config.url);
        hikariConfig.setUsername(config.username);
        hikariConfig.setPassword(config.password);
        // 省略部分代码
        return new HikariDataSource(hikariConfig);
    }
}

#App
app.menus[0].title=Home
app.menus[0].name=Home
app.menus[0].path=/
app.menus[1].title=Login
app.menus[1].name=Login
app.menus[1].path=/login

app.compiler.timeout=5
app.compiler.output-folder=/temp/

app.error=/error/

@Component
@ConfigurationProperties("app")
public class AppProperties {

    public String error;
    public List<Menu> menus = new ArrayList<>();
    public Compiler compiler = new Compiler();

    public static class Menu {
        public String name;
        public String path;
        public String title;
    }

    public static class Compiler {
        public String timeout;
        public String outputFolder;
    }
}

protected Class<?> loadClass(String name, boolean resolve) {
    synchronized (getClassLoadingLock(name)) {
    // 首先，检查该类是否已经被加载，如果从JVM缓存中找到该类，则直接返回
    Class<?> c = findLoadedClass(name);
    if (c == null) {
        try {
            // 遵循双亲委派的模型，首先会通过递归从父加载器开始找，
            // 直到父类加载器是BootstrapClassLoader为止
            if (parent != null) {
                c = parent.loadClass(name, false);
            } else {
                c = findBootstrapClassOrNull(name);
            }
        } catch (ClassNotFoundException e) {}
        if (c == null) {
            // 如果还找不到，尝试通过findClass方法去寻找
            // findClass是留给开发者自己实现的，也就是说
            // 自定义类加载器时，重写此方法即可
           c = findClass(name);
        }
    }
    if (resolve) {
        resolveClass(c);
    }
    return c;
    }
}

for (String aDriver : driversList) {
    try {
        // 直接使用AppClassLoader
        Class.forName(aDriver, true, ClassLoader.getSystemClassLoader());
    } catch (Exception ex) {
        println("DriverManager.Initialize: load failed: " + ex);
    }
}

public Enumeration<URL> getResources(String name) throws IOException {
    Enumeration<URL>[] tmp = (Enumeration<URL>[]) new Enumeration<?>[2];
    if (parent != null) {
        tmp[0] = parent.getResources(name);
    } else {
        tmp[0] = getBootstrapResources(name);
    }
    tmp[1] = findResources(name);
    return new CompoundEnumeration<>(tmp);
}

// 寻找Array.class文件
public static void main(String[] args) throws Exception{
    // Array.class的完整路径
    String name = "java/sql/Array.class";
    Enumeration<URL> urls = Thread.currentThread().getContextClassLoader().getResources(name);
    while (urls.hasMoreElements()) {
        URL url = urls.nextElement();
        System.out.println(url.toString());
    }
}

$JAVA_HOME/jre/lib/rt.jar!/java/sql/Array.class

public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
// spring.factories文件的格式为：key=value1,value2,value3
// 从所有的jar包中找到META-INF/spring.factories文件
// 然后从文件中解析出key=factoryClass类名称的所有value值
public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
    String factoryClassName = factoryClass.getName();
    // 取得资源文件的URL
    Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) : ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
    List<String> result = new ArrayList<String>();
    // 遍历所有的URL
    while (urls.hasMoreElements()) {
        URL url = urls.nextElement();
        // 根据资源文件URL解析properties文件
        Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
        String factoryClassNames = properties.getProperty(factoryClassName);
        // 组装数据，并返回
        result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
    }
    return result;
}

// 来自 org.springframework.boot.autoconfigure下的META-INF/spring.factories
// EnableAutoConfiguration后文会讲到，它用于开启Spring Boot自动配置功能
org.springframework.boot.autoconfigure.EnableAutoConfiguration=
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration

public class MethodMonitorEvent extends EventObject {
    // 时间戳，用于记录方法开始执行的时间
    public long timestamp;

    public MethodMonitorEvent(Object source) {
        super(source);
    }
}

// 1、定义事件监听接口
public interface MethodMonitorEventListener extends EventListener {
    // 处理方法执行之前发布的事件
    public void onMethodBegin(MethodMonitorEvent event);
    // 处理方法结束时发布的事件
    public void onMethodEnd(MethodMonitorEvent event);
}
// 2、事件监听接口的实现：如何处理
public class AbstractMethodMonitorEventListener implements MethodMonitorEventListener {

    @Override
    public void onMethodBegin(MethodMonitorEvent event) {
        // 记录方法开始执行时的时间
        event.timestamp = System.currentTimeMillis();
    }

    @Override
    public void onMethodEnd(MethodMonitorEvent event) {
        // 计算方法耗时
        long duration = System.currentTimeMillis() - event.timestamp;
        System.out.println("耗时：" + duration);
    }
}

public class MethodMonitorEventPublisher {

    private List<MethodMonitorEventListener> listeners = new ArrayList<MethodMonitorEventListener>();

    public void methodMonitor() {
        MethodMonitorEvent eventObject = new MethodMonitorEvent(this);
        publishEvent("begin",eventObject);
        // 模拟方法执行：休眠5秒钟
        TimeUnit.SECONDS.sleep(5);
        publishEvent("end",eventObject);

    }

    private void publishEvent(String status,MethodMonitorEvent event) {
        // 避免在事件处理期间，监听器被移除，这里为了安全做一个复制操作
        List<MethodMonitorEventListener> copyListeners =  new ArrayList<MethodMonitorEventListener>(listeners);
        for (MethodMonitorEventListener listener : copyListeners) {
            if ("begin".equals(status)) {
                listener.onMethodBegin(event);
            } else {
                listener.onMethodEnd(event);
            }
        }
    }

    public static void main(String[] args) {
        MethodMonitorEventPublisher publisher = new MethodMonitorEventPublisher();
        publisher.addEventListener(new AbstractMethodMonitorEventListener());
        publisher.methodMonitor();
    }
    // 省略实现
    public void addEventListener(MethodMonitorEventListener listener) {}
    public void removeEventListener(MethodMonitorEventListener listener) {}
    public void removeAllListeners() {}

@SpringBootApplication
public class MoonApplication {

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

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
        @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
        @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {
    // ......
}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(EnableAutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
    // ......
}

public String[] selectImports(AnnotationMetadata annotationMetadata) {
    // 省略了大部分代码，保留一句核心代码
    // 注意：SpringBoot最近版本中，这句代码被封装在一个单独的方法中
    // SpringFactoriesLoader相关知识请参考前文
    List<String> factories = new ArrayList<String>(new LinkedHashSet<String>(  
        SpringFactoriesLoader.loadFactoryNames(EnableAutoConfiguration.class, this.beanClassLoader)));
}

// 来自 org.springframework.boot.autoconfigure下的META-INF/spring.factories
// 配置的key = EnableAutoConfiguration，与代码中一致
org.springframework.boot.autoconfigure.EnableAutoConfiguration=
org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration
.....

@Configuration
@ConditionalOnClass({ DataSource.class, EmbeddedDatabaseType.class })
@EnableConfigurationProperties(DataSourceProperties.class)
@Import({ Registrar.class, DataSourcePoolMetadataProvidersConfiguration.class })
public class DataSourceAutoConfiguration {
}

// 提供对datasource配置信息的支持，所有的配置前缀为：spring.datasource
@ConfigurationProperties(prefix = "spring.datasource")
public class DataSourceProperties  {
    private ClassLoader classLoader;
    private Environment environment;
    private String name = "testdb";
    ......
}

@Configuration
public class DataSourcePoolMetadataProvidersConfiguration {

    @Configuration
    @ConditionalOnClass(org.apache.tomcat.jdbc.pool.DataSource.class)
    static class TomcatDataSourcePoolMetadataProviderConfiguration {
        @Bean
        public DataSourcePoolMetadataProvider tomcatPoolDataSourceMetadataProvider() {
            .....
        }
    }
  ......
}

private void initialize(Object[] sources) {
     if (sources != null && sources.length > 0) {
         this.sources.addAll(Arrays.asList(sources));
     }
     // 判断是否是Web项目
     this.webEnvironment = deduceWebEnvironment();
     setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
     setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
     // 找到入口类
     this.mainApplicationClass = deduceMainApplicationClass();
}

org.springframework.context.ApplicationListener=
cn.moondev.listeners.xxxxListener

public ConfigurableApplicationContext run(String... args) {
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        FailureAnalyzers analyzers = null;
        configureHeadlessProperty();
        // ①
        SpringApplicationRunListeners listeners = getRunListeners(args);
        listeners.starting();
        try {
            // ②
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            ConfigurableEnvironment environment = prepareEnvironment(listeners,applicationArguments);
            // ③
            Banner printedBanner = printBanner(environment);
            // ④
            context = createApplicationContext();
            // ⑤
            analyzers = new FailureAnalyzers(context);
            // ⑥
            prepareContext(context, environment, listeners, applicationArguments,printedBanner);
            // ⑦ 
            refreshContext(context);
            // ⑧
            afterRefresh(context, applicationArguments);
            // ⑨
            listeners.finished(context, null);
            stopWatch.stop();
            return context;
        }
        catch (Throwable ex) {
            handleRunFailure(context, listeners, analyzers, ex);
            throw new IllegalStateException(ex);
        }
    }

public interface SpringApplicationRunListener {

    // 运行run方法时立即调用此方法，可以用户非常早期的初始化工作
    void starting();

    // Environment准备好后，并且ApplicationContext创建之前调用
    void environmentPrepared(ConfigurableEnvironment environment);

    // ApplicationContext创建好后立即调用
    void contextPrepared(ConfigurableApplicationContext context);

    // ApplicationContext加载完成，在refresh之前调用
    void contextLoaded(ConfigurableApplicationContext context);

    // 当run方法结束之前调用
    void finished(ConfigurableApplicationContext context, Throwable exception);

}

public void starting() {
    // 发布一个ApplicationStartedEvent
    this.initialMulticaster.multicastEvent(new ApplicationStartedEvent(this.application, this.args));
}