Springboot核心技術（二）

阿新 • • 發佈：2019-01-06

上一章節主要講解Spring核心功能，banner的設定，外部配置檔案，日誌等檔案。本章接著上章繼續完善。
轉載請註明出處。

SpringBoo執行原理

上一章我們見識了SpringBoot為我們做的自動配置，本節在瞭解SpringBoot執行原理後，用我們已經掌握的知識自定義一個starter pom.
SpringBoot關於自動配置的原始碼在下面jar中：
這裡寫圖片描述

想知道SpringBoot提供了哪些自動配置。檢視這裡的原始碼即可。

可以通過下列方式檢視專案中啟用和未啟用的自動配置：
（1）執行jar時增加–debug引數

java -jar xxx.jar -- 
debug

（2）在application.properties中增加

debug=true

（3）在STS中設定，eclipse中，
這裡寫圖片描述
在控制檯
已啟用自動配置：

未啟用自動配置：
這裡寫圖片描述

1.執行原理

關於SpringBoot執行原理，我們還是迴歸@SpringBootApplication註解上，這個註解是一個組合註解。

@SpringBootApplication原始碼：

@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 {

    /**
     * Exclude specific auto-configuration classes such that they will never be applied.
     * @return 
 the classes to exclude
     */
    @AliasFor(annotation = EnableAutoConfiguration.class, attribute = "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
     */
    @AliasFor(annotation = EnableAutoConfiguration.class, attribute = "excludeName")
    String[] excludeName() default {};

    /**
     * Base packages to scan for annotated components. Use {@link #scanBasePackageClasses}
     * for a type-safe alternative to String-based package names.
     * @return base packages to scan
     * @since 1.3.0
     */
    @AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
    String[] scanBasePackages() default {};

    /**
     * Type-safe alternative to {@link #scanBasePackages} for specifying the packages to
     * scan for annotated components. The package of each class specified will be scanned.
     * <p>
     * Consider creating a special no-op marker class or interface in each package that
     * serves no purpose other than being referenced by this attribute.
     * @return base packages to scan
     * @since 1.3.0
     */
    @AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
    Class<?>[] scanBasePackageClasses() default {};

}

它的核心功能主要由@EnableAutoConfiguration註解提供的，我們一起看下@EnableAutoConfiguration註解的原始碼。

@SuppressWarnings("deprecation")
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(EnableAutoConfigurationImportSelector.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 {};

}

這裡關鍵在於@Import(EnableAutoConfigurationImportSelector.class)

我們的spring-boot-autoconfigure.1.5.9.x.jar裡面META-INF有一個spring.factories檔案此檔案中聲明瞭哪些自動配置：

# Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
org.springframework.boot.autoconfigure.logging.AutoConfigurationReportLoggingInitializer

# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.autoconfigure.BackgroundPreinitializer

# Auto Configuration Import Listeners
org.springframework.boot.autoconfigure.AutoConfigurationImportListener=\
org.springframework.boot.autoconfigure.condition.ConditionEvaluationReportAutoConfigurationImportListener

# Auto Configuration Import Filters
org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
org.springframework.boot.autoconfigure.condition.OnClassCondition

# 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.CassandraRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\
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.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.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.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.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.flyway.FlywayAutoConfiguration,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\
org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\
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.mobile.DeviceResolverAutoConfiguration,\
org.springframework.boot.autoconfigure.mobile.DeviceDelegatingViewResolverAutoConfiguration,\
org.springframework.boot.autoconfigure.mobile.SitePreferenceAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\
org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\
org.springframework.boot.autoconfigure.reactor.ReactorAutoConfiguration,\
org.springframework.boot.autoconfigure.security.SecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.SecurityFilterAutoConfiguration,\
org.springframework.boot.autoconfigure.security.FallbackWebSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.OAuth2AutoConfiguration,\
org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\
org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\
org.springframework.boot.autoconfigure.social.SocialWebAutoConfiguration,\
org.springframework.boot.autoconfigure.social.FacebookAutoConfiguration,\
org.springframework.boot.autoconfigure.social.LinkedInAutoConfiguration,\
org.springframework.boot.autoconfigure.social.TwitterAutoConfiguration,\
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.DispatcherServletAutoConfiguration,\
org.springframework.boot.autoconfigure.web.EmbeddedServletContainerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.web.HttpEncodingAutoConfiguration,\
org.springframework.boot.autoconfigure.web.HttpMessageConvertersAutoConfiguration,\
org.springframework.boot.autoconfigure.web.MultipartAutoConfiguration,\
org.springframework.boot.autoconfigure.web.ServerPropertiesAutoConfiguration,\
org.springframework.boot.autoconfigure.web.WebClientAutoConfiguration,\
org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.WebSocketAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.WebSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration

# Failure analyzers
org.springframework.boot.diagnostics.FailureAnalyzer=\
org.springframework.boot.autoconfigure.diagnostics.analyzer.NoSuchBeanDefinitionFailureAnalyzer,\
org.springframework.boot.autoconfigure.jdbc.DataSourceBeanCreationFailureAnalyzer,\
org.springframework.boot.autoconfigure.jdbc.HikariDriverConfigurationFailureAnalyzer

# Template availability providers
org.springframework.boot.autoconfigure.template.TemplateAvailabilityProvider=\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.mustache.MustacheTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.web.JspTemplateAvailabilityProvider

核心註解
開啟上面任意一個AutoConfiguration檔案，一般都有下面的條件註解，在spring-boot-autoconfigure-1.5.9.x.jar的org.springframwork.boot.autoconfigure.condition包下:
這裡寫圖片描述

@ConditionalOnBean 當容器裡有指定的Bean的條件下。
@ConditionalOnClass 當類路徑下有指定的類的條件下
@ConditionalOnExpression 基於SpEL表示式作為條件判斷
@ConditionalOnJava 基於JVM版本作為判斷條件
@ConditionalOnJndi 在JNDI存在的條件下查詢指定位置
@ConditionalOn。。。。。。。。。。。
@ConditionalOn。。。。。。。。。。，
@ConditionalOnWebApplication 當前專案是Web專案的條件下。

這些註解都是組合了@Conditional元註解，只是使用了不同的條件（Condition）.

下面我們分析一下@ConditionalOnWebApplication註解
原始碼附上：

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.context.annotation.Conditional;

/**
 * {@link Conditional} that only matches when the application context is a web application
 * context.
 *
 * @author Dave Syer
 */
@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnWebApplicationCondition.class)
public @interface ConditionalOnWebApplication {

}

從原始碼可以看出，次註解使用的是OnWebApplicationCondition,下面我們看看它的構成：

@Order(Ordered.HIGHEST_PRECEDENCE + 20)
class OnWebApplicationCondition extends SpringBootCondition {

    private static final String WEB_CONTEXT_CLASS = "org.springframework.web.context."
            + "support.GenericWebApplicationContext";

    @Override
    public ConditionOutcome getMatchOutcome(ConditionContext context,
            AnnotatedTypeMetadata metadata) {
        boolean required = metadata
                .isAnnotated(ConditionalOnWebApplication.class.getName());
        ConditionOutcome outcome = isWebApplication(context, metadata, required);
        if (required && !outcome.isMatch()) {
            return ConditionOutcome.noMatch(outcome.getConditionMessage());
        }
        if (!required && outcome.isMatch()) {
            return ConditionOutcome.noMatch(outcome.getConditionMessage());
        }
        return ConditionOutcome.match(outcome.getConditionMessage());
    }

    private ConditionOutcome isWebApplication(ConditionContext context,
            AnnotatedTypeMetadata metadata, boolean required) {
        ConditionMessage.Builder message = ConditionMessage.forCondition(
                ConditionalOnWebApplication.class, required ? "(required)" : "");
        if (!ClassUtils.isPresent(WEB_CONTEXT_CLASS, context.getClassLoader())) {
            return ConditionOutcome
                    .noMatch(message.didNotFind("web application classes").atAll());
        }
        if (context.getBeanFactory() != null) {
            String[] scopes = context.getBeanFactory().getRegisteredScopeNames();
            if (ObjectUtils.containsElement(scopes, "session")) {
                return ConditionOutcome.match(message.foundExactly("'session' scope"));
            }
        }
        if (context.getEnvironment() instanceof StandardServletEnvironment) {
            return ConditionOutcome
                    .match(message.foundExactly("StandardServletEnvironment"));
        }
        if (context.getResourceLoader() instanceof WebApplicationContext) {
            return ConditionOutcome.match(message.foundExactly("WebApplicationContext"));
        }
        return ConditionOutcome.noMatch(message.because("not a web application"));
    }

}

從isWebApplication方法可以看出，判斷條件是
這裡寫圖片描述

例項分析

在瞭解SpringBoot運作原理和主要的條件註解後，現在分析一個簡單的SpringBoot內建的自動配置功能—http的編碼配置。

我們在常規的專案中是在web.xml中配置filter，如：
web.xml

 <filter>
    <filter-name>CharacterEncodingFilter</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <init-param>
      <param-name>encoding</param-name>
      <param-value>utf-8</param-value>
    </init-param>
     <init-param>
      <param-name>forceEncoding</param-name>
      <param-value>true</param-value>
    </init-param>
  </filter>

自動配置要滿足兩個條件：
（1）能配置CharacterEncodingFilter這個bean.
（2）能配置encoding和forceEncoding這兩個引數

1.配置引數

上一張章講了型別安全的配置，SpringBoot也是基於這一點配置的，
這裡的配置可以在application.properties中直接設定，也可以這樣，原始碼如下：

import java.nio.charset.Charset;
import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties(prefix="spring.http.encoding")
public class HttpEncodingProperties {

     public static final Charset DEFAULT_CHAESET=Charset.forName("UTF-8");

     private Charset charset = DEFAULT_CHAESET;

     private boolean force=true;

    public Charset getCharset() {
        return charset;
    }

    public void setCharset(Charset charset) {
        this.charset = charset;
    }

    public boolean isForce() {
        return force;
    }

    public void setForce(boolean force) {
        this.force = force;
    }


}

程式碼解釋：

在application.properties直接配置的時候字首為spring.http.encoding；

預設編碼方式為UTF-8,若修改可以配置spring.http.encoding.charset=編碼；

設定forceEncoding預設為true,若修改可以配置spring.http.encoding.force=false;

配置bean

通過條用上述配置，並根據條件配置CharacterEncodingFilter的bean,原始碼如下：

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.boot.web.filter.OrderedCharacterEncodingFilter;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.filter.CharacterEncodingFilter;

@Configuration
@EnableConfigurationProperties(HttpEncodingProperties.class)
@ConditionalOnClass(CharacterEncodingFilter.class)
@ConditionalOnProperty(prefix="spring.http.encoding",value="enabled",matchIfMissing=true)
public class HttpAutoEncodingBean {

    @Autowired
    private HttpEncodingProperties httpEncodingProperties;

    public CharacterEncodingFilter characterEncodingFilter(){
        CharacterEncodingFilter filter = new OrderedCharacterEncodingFilter();
        filter.setEncoding(this.httpEncodingProperties.getCharset().name());
        filter.setForceEncoding(this.httpEncodingProperties.isForce());
        return filter;

    }

}

程式碼解釋：

（1）開啟屬性注入，通過@EnableConfigurationProperties宣告，使用@Autowired注入。
（2）當CharacterEncodingFilter在類路徑的條件下、
（3）當設定spring.http.encoding=enabled的配置條件下，如果沒有配置則預設為true,即條件符合。
（4）像java配置的方式配置CharacterEncodingFilter這個bean.
（5）當容器中沒有這個bean的時候新建bean。

本章Springboot執行原理介紹完畢，下次介紹SpringBoot的web開發，SpringBoot結合redis,Docker等整合開發。

這裡寫圖片描述

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