主入口代码
@SpringBootApplication
public class HelloWorldMainApplication {
public static void main(String[] args) {
// 让Spring应用启动起来，这个原理就是启动spring的主入口
SpringApplication.run(HelloWorldMainApplication.class,args);
}
}
设置：这个类是SpringBoot的主配置类（HelloWorldMainApplication ），SpringBoot就应该运行这个类的main方法来启动SpringBoot应用；
SpringApplication.run(主配置类的类对象，main方法的参数);这个功能就像很久以前Java的启动类，args就是启动类参数。
@SpringBootApplication类
容器初始化的时候会读取配置类信息到容器中，相当于配置web.xml读取配置文件
@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 {
Spring Boot的配置类，标注在某个类上，表示这是一个Spring Boot的配置类；
@Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Configuration//配置类上来标注这个注解，初始化配置类的信息到容器中 public @interface SpringBootConfiguration { }
1.11@Configuration
用于定义配置类，可替换xml配置文件，被注解的类内部包含有一个或多个被@Bean注解的方法，这些方法将会被AnnotationConfigApplicationContext或AnnotationConfigWebApplicationContext类进行扫描，并用于构建bean定义，初始化Spring容器。
换句话说：使用这个注解将将某个包下的配置类初始化到容器中。
@Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Component public @interface Configuration { String value() default ""; }
1.12@EnableAutoConfiguration:
开启自动配置功能,打个比方说，项目中集成redis，那么一定要有redis.xml的配置。当我们开启这个注解后，它会去自动配置redis的配置信息。
@SuppressWarnings("deprecation") @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @AutoConfigurationPackage @Import(EnableAutoConfigurationImportSelector.class) public @interface EnableAutoConfiguration {
1.121@AutoConfigurationPackage
自动配置包，相当于spring扫描包的功能（
@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @Import(AutoConfigurationPackages.Registrar.class)//将主配置类（@SpringBootApplication标注的类）的所在包及下面所有子包里面的所有组件扫描到Spring容器； public @interface AutoConfigurationPackage { }
@Import(AutoConfigurationPackages.Registrar.class)//将主配置类（@SpringBootApplication标注的类）的所在包及下面所有子包里面的所有组件扫描到Spring容器；
@Order(Ordered.HIGHEST_PRECEDENCE) static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports { @Override public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) { //注册主入口类的包名 register(registry, new PackageImport(metadata).getPackageName()); }
1.122@Import(EnableAutoConfigurationImportSelector.class)
给容器中导入选择器中的组件。
EnableAutoConfigurationImportSelector：导入的组件选择器；
将所有需要导入的组件以全类名的方式返回；这些组件就会被添加到容器中；
会给容器中导入非常多的自动配置类（xxxAutoConfiguration）；就是给容器中导入这个场景需要的所有组件，并配置好这些组件。
换句话说：当我们需要redis组件的时候，使用这个注解，redis的所有配置就会导入进来。
@Deprecated public class EnableAutoConfigurationImportSelector extends AutoConfigurationImportSelector { @Override protected boolean isEnabled(AnnotationMetadata metadata) { if (getClass().equals(EnableAutoConfigurationImportSelector.class)) { return getEnvironment().getProperty( EnableAutoConfiguration.ENABLED_OVERRIDE_PROPERTY, Boolean.class, true); } return true; } }
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;
}
public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
try {
Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");
ArrayList result = new ArrayList();
while(urls.hasMoreElements()) {
URL url = (URL)urls.nextElement();
Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
String factoryClassNames = properties.getProperty(factoryClassName);
result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
}
retur
META-INF/spring.factories
这些值作为自动配置类导入到容器中，自动配置类就生效，帮我们进行自动配置工作；
比如说：这里面有redis配置。
@Configuration @ConditionalOnClass({ JedisConnection.class, RedisOperations.class, Jedis.class }) @EnableConfigurationProperties(RedisProperties.class) public class RedisAutoConfiguration { /** * Redis connection configuration. */ @Configuration @ConditionalOnClass(GenericObjectPool.class) protected static class RedisConnectionConfiguration { private final RedisProperties properties; private final RedisSentinelConfiguration sentinelConfiguration; private final RedisClusterConfiguration clusterConfiguration; public RedisConnectionConfiguration(RedisProperties properties, ObjectProvider<RedisSentinelConfiguration> sentinelConfiguration, ObjectProvider<RedisClusterConfiguration> clusterConfiguration) { this.properties = properties; this.sentinelConfiguration = sentinelConfiguration.getIfAvailable(); this.clusterConfiguration = clusterConfiguration.getIfAvailable(); } @Bean @ConditionalOnMissingBean(RedisConnectionFactory.class) public JedisConnectionFactory redisConnectionFactory() throws UnknownHostException { return applyProperties(createJedisConnectionFactory()); }
RedisProperties.class
@ConfigurationProperties(prefix = "spring.redis")
public class RedisProperties {
/**
* Database index used by the connection factory.
*/
private int database = 0;
/**
* Redis url, which will overrule host, port and password if set.
*/
private String url;
/**
* Redis server host.
*/
private String host = "localhost";
/**
* Login password of the redis server.
*/
private String password;