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();    }    @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。

推荐阅读

什么是Spring Boot?
Spring Boot开启的2种方式
Spring Boot Starters启动器
Spring Boot定制启动图案
Spring Boot核心配置
Spring Boot功能实战
Spring Boot自动配置原理、实战
Spring Boot Runner启动器
Spring Boot - Profile不同环境配置

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