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Spring Boot自動配置原理

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Spring Boot的自動配置注解是@EnableAutoConfiguration， 從上面的@Import的類可以找到下面自動加載自動配置的映射。

org.springframework.core.io.support.SpringFactoriesLoader.loadFactoryNames(Class<?>, ClassLoader) public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {String factoryClassName = factoryClass.getName();try {Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :lassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));List<String> result = new ArrayList<String>();while (urls.hasMoreElements()) {URL url = urls.nextElement();Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));String factoryClassNames = properties.getProperty(factoryClassName);result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));}return result;}catch (IOException ex) {throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() +"] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex);}}

這個方法會加載類路徑及所有jar包下META-INF/spring.factories配置中映射的自動配置的類。

/** * The location to look for factories. * <p>Can be present in multiple JAR files. */ public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";

查看Spring Boot自帶的自動配置的包： spring-boot-autoconfigure-1.5.6.RELEASE.jar，打開其中的META-INF/spring.factories文件會找到自動配置的映射。

# 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,\ ...

再來看看數據源自動配置的實現注解

@Configuration @ConditionalOnClass({ DataSource.class, EmbeddedDatabaseType.class }) @EnableConfigurationProperties(DataSourceProperties.class) @Import({ Registrar.class, DataSourcePoolMetadataProvidersConfiguration.class }) public class DataSourceAutoConfiguration { ...

@Configuration,@ConditionalOnClass就是自動配置的核心，首先它得是一個配置文件，其次根據類路徑下是否有這個類去自動配置。

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自動配置實戰

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所以，了解了自動配置的原理，來自己實現一個自動配置的玩意其實很簡單。

添加配置類：

import org.slf4j.Logger; import org.springframework.context.EnvironmentAware; import org.springframework.core.env.Environment; import com.oceanpayment.common.utils.logger.LoggerUtils;public class EnvConfig implements EnvironmentAware {private final Logger logger = LoggerUtils.getLogger(this);private Environment env;public String getStringValue(String key) {return env.getProperty(key);}public Long getLongValue(String key) {String value = getStringValue(key);try {return Long.parseLong(value);} catch (Exception e) {logger.error("字符串轉換Long失敗：{} = {}", key, value);}return 0L;}public int getIntValue(String key) {return getLongValue(key).intValue();}@Overridepublic void setEnvironment(Environment environment) {this.env = environment;}}

添加自動配置類：

import org.springframework.boot.autoconfigure.condition.ConditionalOnClass; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.core.env.PropertyResolver;@Configuration @ConditionalOnClass(PropertyResolver.class) public class EnvAutoConfig {@Beanpublic EnvConfig envConfig() {return new EnvConfig();}}

創建META-INF/spring.factories文件，添加自動配置映射：

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\\ com.oceanpayment.common.config.env.EnvAutoConfig

這樣就搞定了。

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查看自動配置報告

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怎么查看自己加的自動配置類有沒有被加載，或者查看所有自動配置激活的和未激活的可以通過以下幾種試查看。

spring-boot:run運行的在對話框Enviroment中加入debug=true變量?

java -jar xx.jar --debug

main方法運行，在VM Argumanets加入-Ddebug

直接在application文件中加入debug=true

如果集成了spring-boot-starter-actuator監控，通過autoconfig端點也可以查看。

啟動后會在控制臺看到以下自動配置報告信息：

=========================

AUTO-CONFIGURATION REPORT

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Positive matches:

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??AopAutoConfiguration matched:
?????- @ConditionalOnClass found required classes 'org.springframework.context.annotation.EnableAspectJAutoProxy', 'org.aspectj.lang.annotation.Aspect', 'org.aspectj.lang.reflect.Advice'; @ConditionalOnMissingClass did not find unwanted class (OnClassCondition)
?????- @ConditionalOnProperty (spring.aop.auto=true) matched (OnPropertyCondition)

??...

??EnvAutoConfig matched:
?????- @ConditionalOnClass found required class 'org.springframework.core.env.PropertyResolver'; @ConditionalOnMissingClass did not find unwanted class (OnClassCondition)

??ErrorMvcAutoConfiguration matched:
?????- @ConditionalOnClass found required classes 'javax.servlet.Servlet', 'org.springframework.web.servlet.DispatcherServlet'; @ConditionalOnMissingClass did not find unwanted class (OnClassCondition)
?????- @ConditionalOnWebApplication (required) found StandardServletEnvironment (OnWebApplicationCondition)

??ErrorMvcAutoConfiguration#basicErrorController matched:
?????- @ConditionalOnMissingBean (types: org.springframework.boot.autoconfigure.web.ErrorController; SearchStrategy: current) did not find any beans (OnBeanCondition)

??...

Negative matches:
-----------------

??ActiveMQAutoConfiguration:
?????Did not match:
????????- @ConditionalOnClass did not find required classes 'javax.jms.ConnectionFactory', 'org.apache.activemq.ActiveMQConnectionFactory' (OnClassCondition)

??AopAutoConfiguration.JdkDynamicAutoProxyConfiguration:
?????Did not match:
????????- @ConditionalOnProperty (spring.aop.proxy-target-class=false) found different value in property 'proxy-target-class' (OnPropertyCondition)

??ArtemisAutoConfiguration:
?????Did not match:
????????- @ConditionalOnClass did not find required classes 'javax.jms.ConnectionFactory', 'org.apache.activemq.artemis.jms.client.ActiveMQConnectionFactory' (OnClassCondition)

??BatchAutoConfiguration:
?????Did not match:
????????- @ConditionalOnClass did not find required class 'org.springframework.batch.core.launch.JobLauncher' (OnClassCondition)

??...

Positive matches：已經啟用的自動配置

Negative matches：未啟用的自動配置

從報告中看到自己添加的EnvAutoConfig已經自動配置了。

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