SpringBoot自动配置原理、实战
org.springframework.core.io.support.SpringFactoriesLoader.loadFactoryNames(Class<?>,ClassLoader)
publicstaticList<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 =newArrayList<String>();while(urls.hasMoreElements()){URL url = urls.nextElement();Properties properties =PropertiesLoaderUtils.loadProperties(newUrlResource(url));String factoryClassNames = properties.getProperty(factoryClassName);result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));}return result;}catch(IOException ex){thrownewIllegalArgumentException("Unable to load ["+ factoryClass.getName()+"] factories from location ["+ FACTORIES_RESOURCE_LOCATION +"]", ex);}}
这个方法会加载类路径及所有jar包下META-INF/spring.factories配置中映射的自动配置的类。
/*** The location to look for factories.* <p>Can be present in multiple JAR files.*/publicstaticfinalString FACTORIES_RESOURCE_LOCATION ="META-INF/spring.factories";
查看Spring Boot自带的自动配置的包： spring-boot-autoconfigure-1.5.6.RELEASE.jar，打开其中的META-INF/spring.factories文件会找到自动配置的映射。
# Auto Configureorg.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,...
再来看看数据源自动配置的实现注解
@Configuration@ConditionalOnClass({DataSource.class,EmbeddedDatabaseType.class})@EnableConfigurationProperties(DataSourceProperties.class)@Import({Registrar.class,DataSourcePoolMetadataProvidersConfiguration.class})publicclassDataSourceAutoConfiguration{...
@Configuration,@ConditionalOnClass就是自动配置的核心，首先它得是一个配置文件，其次根据类路径下是否有这个类去自动配置。
自动配置实战
所以，了解了自动配置的原理，来自己实现一个自动配置的玩意其实很简单。
添加配置类：
import org.slf4j.Logger;import org.springframework.context.EnvironmentAware;import org.springframework.core.env.Environment;import com.oceanpayment.common.utils.logger.LoggerUtils;publicclassEnvConfigimplementsEnvironmentAware{privatefinalLogger logger =LoggerUtils.getLogger(this);privateEnvironment env;publicString getStringValue(String key){return env.getProperty(key);}publicLong getLongValue(String key){String value = getStringValue(key);try{returnLong.parseLong(value);}catch(Exception e){logger.error("字符串转换Long失败：{} = {}", key, value);}return0L;}publicint getIntValue(String key){return getLongValue(key).intValue();}@Overridepublicvoid setEnvironment(Environment environment){this.env = environment;}}
添加自动配置类：
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)publicclassEnvAutoConfig{@BeanpublicEnvConfig envConfig(){returnnewEnvConfig();}}
创建META-INF/spring.factories文件，添加自动配置映射：
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\com.oceanpayment.common.config.env.EnvAutoConfig
这样就搞定了。
查看自动配置报告
怎么查看自己加的自动配置类有没有被加载，或者查看所有自动配置激活的和未激活的可以通过以下几种试查看。
spring-boot:run运行的在对话框Enviroment中加入debug=true变量
java -jar xx.jar --debug
main方法运行，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监控，通过autoconfig端点也可以查看。
启动后会在控制台看到以下自动配置报告信息：
=========================AUTO-CONFIGURATION REPORT=========================Positive matches:-----------------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:Didnot match:-@ConditionalOnClass did not find required classes "javax.jms.ConnectionFactory","org.apache.activemq.ActiveMQConnectionFactory"(OnClassCondition)AopAutoConfiguration.JdkDynamicAutoProxyConfiguration:Didnot match:-@ConditionalOnProperty(spring.aop.proxy-target-class=false) found different value inproperty"proxy-target-class"(OnPropertyCondition)ArtemisAutoConfiguration:Didnot match:-@ConditionalOnClass did not find required classes "javax.jms.ConnectionFactory","org.apache.activemq.artemis.jms.client.ActiveMQConnectionFactory"(OnClassCondition)BatchAutoConfiguration:Didnot match:-@ConditionalOnClass did not find required class"org.springframework.batch.core.launch.JobLauncher"(OnClassCondition)...
Positive matches：已经启用的自动配置
Negative matches：未启用的自动配置
从报告中看到自己添加的EnvAutoConfig已经自动配置了。
以上是 SpringBoot自动配置原理、实战 的全部内容， 来源链接： utcz.com/z/515920.html
