概念

springboot auto configuration的本質就是自動配置spring的各種bean。然後使應用可以通過@Autowired等注入方式來直接使用bean。

比如自動配置redisTemplate，jdbcTemplate等bean。

原理

1. 開啟@EnableAutoConfiguration注解

如果寫了@SpringBootApplication注解，不必再寫@EnableAutoConfiguration。

@SpringBootApplication = @Configuration + @EnableAutoConfiguration + @ComponentScan

@SpringCloudApplication = @SpringBootApplication + @EnableDiscoveryClient + @EnableCircuitBreaker

2. 開啟@EnableAutoConfiguration注解後，會引入一個AutoConfigurationImportSelector類

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

    String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";

    /**
     * Exclude specific auto-configuration classes such that they will never be applied.
     * @return the classes to exclude
     */
    Class<?>[] exclude() default {};

    /**
     * Exclude specific auto-configuration class names such that they will never be
     * applied.
     * @return the class names to exclude
     * @since 1.3.0
     */
    String[] excludeName() default {};

}

其會去掃描classpath下所有jar包内的META-INF/spring.factories檔案

3. spring.factories檔案

spring-boot-autoconfigure.jar的spring.factories檔案

springboot2.0 auto configuration自動配置概念原理

spring.factories檔案内會有一個org.springframework.boot.autoconfigure.EnableAutoConfiguration的key

# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\
org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\
org.springframework.boot.autoconfigure.cloud.CloudAutoConfiguration,\
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\
org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\
org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\
org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.ldap.LdapDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,\
org.springframework.boot.autoconfigure.elasticsearch.jest.JestAutoConfiguration,\
org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\
org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\
org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration,\
org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\
org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration,\
org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\
org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,\
org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\
org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\
org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\
org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\
org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\
org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\
org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\
org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\
org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\
org.springframework.boot.autoconfigure.reactor.core.ReactorCoreAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\
org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.OAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\
org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\
org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration

spring boot 會自動配置org.springframework.boot.autoconfigure.EnableAutoConfiguration的key下所有自動配置類。

可以看到這裡面包含RabbitMq，MongoDB，Redis，JdbcTemplate，Thymeleaf，WebFlux，WebSocket等等子產品的自動配置類。

4. 一般自動配置類都有@Configuration注解，相當于一個spring的xml檔案，裡面可以通過@Bean注解配置bean

@Configuration
@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(StringRedisTemplate.class)
    public StringRedisTemplate stringRedisTemplate(
            RedisConnectionFactory redisConnectionFactory) throws UnknownHostException {
        StringRedisTemplate template = new StringRedisTemplate();
        template.setConnectionFactory(redisConnectionFactory);
        return template;
    }

}

@ConditionalOnXXX：

@ConditionalOnBean（僅僅在目前上下文中存在某個對象時，才會執行個體化一個Bean
@ConditionalOnClass（某個class位于類路徑上，才會執行個體化一個Bean）
@ConditionalOnExpression（當表達式為true的時候，才會執行個體化一個Bean）
@ConditionalOnMissingBean（僅僅在目前上下文中不存在某個對象時，才會執行個體化一個Bean）
@ConditionalOnMissingClass（某個class類路徑上不存在的時候，才會執行個體化一個Bean）
@ConditionalOnProperty(value = “spring.cloud.config.enabled”, matchIfMissing = true)（當某個配置的值為一定條件時，才會執行個體化一個Bean）

5. 配置bean的時候，少不了要擷取properties或者yml檔案的屬性值

5.1 通過@ConfigurationProperties(prefix=”xxxx”)映射配置檔案的值到POJO

application.yml

test:
  id: 
  name: test

随意一個POJO類，例：Properties.java，類名随意，通過prefix指定配置屬性的字首

@ConfigurationProperties(prefix="test")
public class Properties {
    private int id;
    private String name;

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

5.2 将配置檔案的POJO類轉化為spring的bean

5.2.1. 在要使用配置的地方使用@EnableConfigurationProperties(Properties.class)将其轉化為spring的bean

@RestController
@EnableConfigurationProperties(Properties.class)
public class CommonController extends BaseController {
    //轉化為spring的bean後，就可以注入使用了
    @Autowired
    private Properties properties;

    @RequestMapping(value = "/properties", method = RequestMethod.GET)
    public Properties getProperties() {

        log.info(properties.toString());

        return properties;
    }

}

如果直接寫@EnableConfigurationProperties不指定Properties類的話，必須在同一目錄或者子目錄下才行。

5.2.2. 通過@Bean配置将其轉化為spring的bean

@Configuration
public class MyConfiguration {

    @Bean
    public Properties properties() {
        return new Properties();
    }

}

5.2.3. 通過@Component配置将其轉化為spring的bean

@Component
@ConfigurationProperties(prefix="test")
public class Properties {
    private int id;
    private String name;

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

轉化為spring的bean後，就可以在想用的地方通過任意注入方式注入bean來使用了。

5.2.4. 總結

在寫spring boot starter的時候，因為所有類都不在啟動的@ComponentScan目錄下，是以使用一般使用 5.2.1 或者 5.2.2 的方式擷取配置檔案資訊

在寫具體的spring boot應用服務時，配置類都在啟動的@ComponentScan目錄下，使用 5.2.3 的方式比較友善

springboot2.0 auto configuration自動配置概念原理

概念

原理

1. 開啟@EnableAutoConfiguration注解

2. 開啟@EnableAutoConfiguration注解後，會引入一個AutoConfigurationImportSelector類

3. spring.factories檔案

4. 一般自動配置類都有@Configuration注解，相當于一個spring的xml檔案，裡面可以通過@Bean注解配置bean

5. 配置bean的時候，少不了要擷取properties或者yml檔案的屬性值

5.1 通過@ConfigurationProperties(prefix=”xxxx”)映射配置檔案的值到POJO

5.2 将配置檔案的POJO類轉化為spring的bean

5.2.1. 在要使用配置的地方使用@EnableConfigurationProperties(Properties.class)将其轉化為spring的bean

5.2.2. 通過@Bean配置将其轉化為spring的bean

5.2.3. 通過@Component配置将其轉化為spring的bean

5.2.4. 總結

繼續閱讀

@Value的幾種常用用法

Android的前後端互動架構搭建（okhhtp+springboot+mysql完整版）

start to use skywalkingInstall JDK8Install ESInstall skywalkingRun Springboot JAR

關于Springboot中JSCH使用說明1. JSCH簡介2. JSCH依賴3. 使用方法4. 使用連接配接池

路徑錯誤Maven：Non-resolvable parent POM: Failure to find錯誤

jsch連接配接伺服器執行指令傳回的資料中文亂碼問題問題分析解決

springboot項目時間不一緻解決方案一、springboot項目時間不一緻解決方案

spring mvc 頁面傳遞數組背景接收方式spring mvc 頁面傳遞數組背景接收方式

Swagger-UI的使用一、添加依賴二、建立配置類三、注解

将swagger-ui中的接口導入postman

聊一聊Swagger-UI的那些事情軟體簡介Swagger 原生Bootstrap-ui Bootstrap的UIKnife4j Bootstrap的更新版的UI

springboot使用 swagger-ui 2.10.5 有關版本更新帶來的問題

微服務-性能壓測\緩存redis和分布式鎖redisson和SpringCache

java 8 Lamda 求 List 中 Bigdecimal類型的各種值求最大值求最小值求和求平均值

(SpringBoot)日志種類：log、monitor、access、out、gc、backup

spring boot @SpringBootApplication @EnableAutoConfiguration 的工作原理