目录

• 1、springboot自动配置的原理初探
• 2. 补充扩展（解释为什么引用的包都报红错了，项目还能启动）
• 3、又一个问题
• 总结

@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 {    //略……}

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

	//org.springframework.boot.autoconfigure.AutoConfigurationImportSelector//此处只贴了关键方法protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {		List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),				getBeanClassLoader());		Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you "				+ "are using a custom packaging, make sure that file is correct.");		return configurations;	}

//org.springframework.core.io.support.SpringFactoriesLoader//只贴了两个关键方法	public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";//此方法返回的是即将要被自动化配置的类的全限定类名，是从META-INF/spring.factories配置的，配置文件中有个org.springframework.boot.autoconfigure.EnableAutoConfiguration 其后面可配置多个想被自动花配置的类    public static List<String> loadFactoryNames(Class<?> factoryType, @Nullab等le ClassLoader classLoader) {            String factoryTypeName = factoryType.getName();            return loadSpringFactories(classLoader).getOrDefault(factoryTypeName, Collections.emptyList());     }	private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {		MultiValueMap<String, String> result = cache.get(classLoader);		if (result != null) {			return result;		}		try {			Enumeration<URL> urls = (classLoader != null ?					classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :					ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));//META-INF/spring.factories			result = new LinkedMultiValueMap<>();			while (urls.hasMoreElements()) {				URL url = urls.nextElement();				UrlResource resource = new UrlResource(url);				Properties properties = PropertiesLoaderUtils.loadProperties(resource);				for (Map.Entry<?, ?> entry : properties.entrySet()) {					String factoryTypeName = ((String) entry.getKey()).trim();					for (String factoryImplementationName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {						result.add(factoryTypeName, factoryImplementationName.trim());					}				}			}			cache.put(classLoader, result);			return result;		}		catch (IOException ex) {			throw new IllegalArgumentException("Unable to load factories from location [" +					FACTORIES_RESOURCE_LOCATION + "]", ex);		}	}

@Configuration(proxyBeanMethods = false)@ConditionalOnClass(RedisOperations.class)@EnableConfigurationProperties(RedisProperties.class)@Import({ LettuceConnectionConfiguration.class, JedisConnectionConfiguration.class })public class RedisAutoConfiguration {	@Bean	@ConditionalOnMissingBean(name = "redisTemplate")	public RedisTemplate<Object, Object> redisTemplate(RedisConnectionFactory redisConnectionFactory)			throws UnknownHostException {		RedisTemplate<Object, Object> template = new RedisTemplate<>();		template.setConnectionFactory(redisConnectionFactory);		return template;	}	@Bean	@ConditionalOnMissingBean	public StringRedisTemplate stringRedisTemplate(RedisConnectionFactory redisConnectionFactory)			throws UnknownHostException {		StringRedisTemplate template = new StringRedisTemplate();		template.setConnectionFactory(redisConnectionFactory);		return template;	}}

@Configurationpublic class RedisConfig {    /**     * 设置 redisTemplate 的序列化设置     *     * @param redisConnectionFactory     * @return     */    @Bean    public RedisTemplate<String, Object> redisTemplate(RedisConnectionFactory redisConnectionFactory) {        // 1.创建 redisTemplate 模版        RedisTemplate<String, Object> template = new RedisTemplate<>();        // 2.关联 redisConnectionFactory        template.setConnectionFactory(redisConnectionFactory);        // 3.创建 序列化类        Jackson2JsonRedisSerializer jackson2JsonRedisSerializer = new Jackson2JsonRedisSerializer(Object.class);        ObjectMapper om = new ObjectMapper();        // 4.设置可见度        om.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.ANY);        // 5.启动默认的类型        om.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL);        // 6.序列化类，对象映射设置        jackson2JsonRedisSerializer.setObjectMapper(om);        // 7.设置 value 的转化格式和 key 的转化格式        template.setValueSerializer(jackson2JsonRedisSerializer);        template.setKeySerializer(new StringRedisSerializer());        template.afterPropertiesSet();        return template;    }}

@EnableConfigurationProperties(RedisProperties.class)@Import({ LettuceConnectionConfiguration.class, JedisConnectionConfiguration.class })

@Target({ ElementType.TYPE, ElementType.METHOD })@Retention(RetentionPolicy.RUNTIME)@Documented@Conditional(OnClassCondition.class)public @interface ConditionalOnClass {	/**	 * The classes that must be present. Since this annotation is parsed by loading class	 * bytecode, it is safe to specify classes here that may ultimately not be on the	 * classpath, only if this annotation is directly on the affected component and	 * <b>not</b> if this annotation is used as a composed, meta-annotation. In order to	 * use this annotation as a meta-annotation, only use the {@link #name} attribute.	 * @return the classes that must be present	 */	Class<?>[] value() default {};	/**	 * The classes names that must be present.	 * @return the class names that must be present.	 */	String[] name() default {};}