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的類可以找到下面的自動加載自動配置的映射。

org.springframework.core.io.support.SpringFactoriesLoader.loadFactoryNames(Class, ClassLoader)

public static List loadFactoryNames(Class factoryClass, ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
try {
Enumeration urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
lassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
List result = new ArrayList();
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);
}
}

這個方法會加載類路徑及所有jar包下META-INF / spring.factories配置中映射的自動配置的類。

/**
* The location to look for factories.
*

Can be present in multiple JAR files.
*/
public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";

查看Spring Boot自帶的自動配置的包： spring-boot-autoconfigure-1.5.6.RELEASE.jar，打開其中的META-INF / spring.factories文件會找到自動配置的映射。

# 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,\
...

再來看看數據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即自動配置的核心，首先它得是一個配置文件，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，了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。

添加配置類：

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();
}
}

創建META-INF / spring.factories文件，添加自動配置映射：

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

這樣就搞定了。

查看自動配置報告

怎麼看自己加的自動配置類有沒有被加載，或者查看所有自動配置激活的和未激活的可以通過以下幾次試查看。

spring-boot：在運行環境中加入debug = true變量
java -jar xx.jar —debug
main方法運行，在VM Argumanets中加入-Ddebug
直接在應用程序文件中加入debug = true
如果集成了spring-boot-starter-actuator監控，則通過autoconfig端點也可以查看。

啟動後會在控制台看到以下自動配置報告信息：

=========================
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)
...

正面匹配：已經啟用的自動配置

否定匹配項：未啟用的自動配置

從報告中看到自己添加的EnvAutoConfig已經自動配置了。