• 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 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();
    	}
    
    	@Override
    	public 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 {
    
    	@Bean
    	public 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。

    1、spring-boot:run运行的在对话框Enviroment中加入debug=true变量
    2、java -jar xx.jar --debug
    3、main方法运行,在VM Argumanets加入-Ddebug
    4、直接在application文件中加入debug=true
    5、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。

    推荐:Spring Boot & Cloud 最强技术教程

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  • 原文地址:https://www.cnblogs.com/javastack/p/9153974.html
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