SpringBoot啟動的主入口註解SpringBootApplication分析
主入口程式碼
@SpringBootApplication
public class HelloWorldMainApplication {
public static void main(String[] args) {
// 讓Spring應用啟動起來，這個原理就是啟動spring的主入口
SpringApplication.run(HelloWorldMainApplication.class,args);
}
}
[email protected]:
設定：這個類是SpringBoot的主配置類（HelloWorldMainApplication ），SpringBoot就應該執行這個類的main方法來啟動SpringBoot應用；
SpringApplication.run(主配置類的類物件，main方法的引數);這個功能就像很久以前Java的啟動類，args就是啟動類引數。
@SpringBootApplication類
[email protected]
容器初始化的時候會讀取配置類資訊到容器中，相當於配置web.xml讀取配置檔案
@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的配置類，標註在某個類上，表示這是一個Spring Boot的配置類；
@Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Configuration//配置類上來標註這個註解，初始化配置類的資訊到容器中 public @interface SpringBootConfiguration { }
1.11@Configuration
用於定義配置類，可替換xml配置檔案，被註解的類內部包含有一個或多個被@Bean註解的方法，這些方法將會被AnnotationConfigApplicationContext或AnnotationConfigWebApplicationContext類進行掃描，並用於構建bean定義，初始化Spring容器。
換句話說：使用這個註解將將某個包下的配置類初始化到容器中。
@Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Component public @interface Configuration { String value() default ""; }
1.12@EnableAutoConfiguration:
開啟自動配置功能,打個比方說，專案中整合redis，那麼一定要有redis.xml的配置。當我們開啟這個註解後，它會去自動配置redis的配置資訊。
@SuppressWarnings("deprecation") @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @AutoConfigurationPackage @Import(EnableAutoConfigurationImportSelector.class) public @interface EnableAutoConfiguration {
1.121@AutoConfigurationPackage
自動配置包，相當於spring掃描包的功能（
@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @Import(AutoConfigurationPackages.Registrar.class)//將主配置類（@SpringBootApplication標註的類）的所在包及下面所有子包裡面的所有元件掃描到Spring容器； public @interface AutoConfigurationPackage { }
@Import(AutoConfigurationPackages.Registrar.class)//將主配置類（@SpringBootApplication標註的類）的所在包及下面所有子包裡面的所有元件掃描到Spring容器；
@Order(Ordered.HIGHEST_PRECEDENCE) static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports { @Override public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) { //註冊主入口類的包名 register(registry, new PackageImport(metadata).getPackageName()); }
1.122@Import(EnableAutoConfigurationImportSelector.class)
給容器中匯入選擇器中的元件。
EnableAutoConfigurationImportSelector：匯入的元件選擇器；
將所有需要匯入的元件以全類名的方式返回；這些元件就會被新增到容器中；
會給容器中匯入非常多的自動配置類（xxxAutoConfiguration）；就是給容器中匯入這個場景需要的所有元件，並配置好這些元件。
換句話說：當我們需要redis元件的時候，使用這個註解，redis的所有配置就會匯入進來。
@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
這些值作為自動配置類匯入到容器中，自動配置類就生效，幫我們進行自動配置工作；
比如說：這裡面有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;