Spring Boot自動配置原理、實戰

轉載自 Spring Boot自動配置原理、實戰

Spring Boot自動配置原理

Spring Boot的自動配置註解是@EnableAutoConfiguration，從上面的@Import的類可以找到下面自動載入自動配置的對映。

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);
    }
}

這個方法會載入類路徑及所有jar包下META-INF/spring.factories配置中對映的自動配置的類。

/**
 * 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";

檢視Spring Boot自帶的自動配置的包：spring-boot-autoconfigure-1.5.6.RELEASE.jar，開啟其中的META-INF/spring.factories檔案會找到自動配置的對映。

# 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,\
...

再來看看資料來源自動配置的實現註解

@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檔案，其次根據類路徑下是否有這個類去自動配置。

自動配置實戰

所以，瞭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。

新增配置類：

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("字串轉換Long失敗：{} = {}", key, value);
        }
        return 0L;
    }

    public int getIntValue(String key) {
        return getLongValue(key).intValue();
    }

    @Override
    public void setEnvironment(Environment environment) {
        this.env = environment;
    }

}

新增自動配置類：

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 {

    @Bean
    public EnvConfig envConfig() {
        return new EnvConfig();
    }

}

建立META-INF/spring.factories檔案，新增自動配置對映：

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

這樣就搞定了。

檢視自動配置報告

怎麼檢視自己加的自動配置類有沒有被載入，或者檢視所有自動配置啟用的和未啟用的可以通過以下幾種試檢視。

1. spring-boot:run執行的在對話方塊Enviroment中加入debug=true變數 

2. java -jar xx.jar --debug

3. main方法執行，在VM Argumanets加入-Ddebug

4. 直接在application檔案中加入debug=true

5. 如果整合了spring-boot-starter-actuator監控，通過autoconfig端點也可以檢視。

啟動後會在控制檯看到以下自動配置報告資訊：

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

從報告中看到自己新增的EnvAutoConfig已經自動配置了。