Spring Boot自动配置原理、实战
Spring Boot自动配置原理
Spring Boot的自动配置注解是@EnableAutoConfiguration， 从上面的@Import的类可以找到下面自动加载自动配置的映射。
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);}}
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.*/public static final String 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 })public class DataSourceAutoConfiguration {...
@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;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("字符串转换Long失败：{} = {}", key, value);}return 0L;}public int getIntValue(String key) {return getLongValue(key).intValue();}@Overridepublic void 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)public class EnvAutoConfig {@Beanpublic EnvConfig envConfig() {return new EnvConfig();}}
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: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。
看完是否收获良多？
分享到朋友圈给更多的人吧。