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。

1. org.springframework.core.io.support.SpringFactoriesLoader.loadFactoryNames(Class<?>, ClassLoader)

1. public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {

2.    String factoryClassName = factoryClass.getName();

3.    try {

4.        Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :

5.                lassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));

6.        List<String> result = new ArrayList<String>();

7.        while (urls.hasMoreElements()) {

8.            URL url = urls.nextElement();

9.            Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));

10.            String factoryClassNames = properties.getProperty(factoryClassName);

11.            result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));

12.        }

13.        return result;

14.    }

15.    catch (IOException ex) {

16.        throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() +

17.                "] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex);

18.    }

19. }

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。

1. /**

2. * The location to look for factories.

3. * <p>Can be present in multiple JAR files.

4. */

5. 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。

1. # Auto Configure

2. org.springframework.boot.autoconfigure.EnableAutoConfiguration=

3. org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,

4. org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,

5. org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,

6. org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,

7. org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,

8. org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,

9. org.springframework.boot.autoconfigure.cloud.CloudAutoConfiguration,

10. ...

再来看看数据源自动配置的实现注解

1. @Configuration

2. @ConditionalOnClass({ DataSource.class, EmbeddedDatabaseType.class })

3. @EnableConfigurationProperties(DataSourceProperties.class)

4. @Import({ Registrar.class, DataSourcePoolMetadataProvidersConfiguration.class })

5. public class DataSourceAutoConfiguration {

6. ...

@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：

1. import org.slf4j.Logger;

2. import org.springframework.context.EnvironmentAware;

3. import org.springframework.core.env.Environment;

5. import com.oceanpayment.common.utils.logger.LoggerUtils;

7. public class EnvConfig implements EnvironmentAware {

9.    private final Logger logger = LoggerUtils.getLogger(this);

11.    private Environment env;

13.    public String getStringValue(String key) {

14.        return env.getProperty(key);

15.    }

17.    public Long getLongValue(String key) {

18.        String value = getStringValue(key);

19.        try {

20.            return Long.parseLong(value);

21.        } catch (Exception e) {

22.            logger.error("字符串转换Long失败：{} = {}", key, value);

23.        }

24.        return 0L;

25.    }

27.    public int getIntValue(String key) {

28.        return getLongValue(key).intValue();

29.    }

31.    @Override

32.    public void setEnvironment(Environment environment) {

33.        this.env = environment;

34.    }

36. }

添加自动配置类：

1. import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;

2. import org.springframework.context.annotation.Bean;

3. import org.springframework.context.annotation.Configuration;

4. import org.springframework.core.env.PropertyResolver;

6. @Configuration

7. @ConditionalOnClass(PropertyResolver.class)

8. public class EnvAutoConfig {

10.    @Bean

11.    public EnvConfig envConfig() {

12.        return new EnvConfig();

13.    }

15. }

创建META-INF/spring.factories文件，添加自动配置映射：

1. org.springframework.boot.autoconfigure.EnableAutoConfiguration=\

2. 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：

1. =========================

2. AUTO-CONFIGURATION REPORT

3. =========================

6. Positive matches:

7. -----------------

9.   AopAutoConfiguration matched:

10.      - @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)

11.      - @ConditionalOnProperty (spring.aop.auto=true) matched (OnPropertyCondition)

13.   ...

15.   EnvAutoConfig matched:

16.      - @ConditionalOnClass found required class 'org.springframework.core.env.PropertyResolver'; @ConditionalOnMissingClass did not find unwanted class (OnClassCondition)

18.   ErrorMvcAutoConfiguration matched:

19.      - @ConditionalOnClass found required classes 'javax.servlet.Servlet', 'org.springframework.web.servlet.DispatcherServlet'; @ConditionalOnMissingClass did not find unwanted class (OnClassCondition)

20.      - @ConditionalOnWebApplication (required) found StandardServletEnvironment (OnWebApplicationCondition)

22.   ErrorMvcAutoConfiguration#basicErrorController matched:

23.      - @ConditionalOnMissingBean (types: org.springframework.boot.autoconfigure.web.ErrorController; SearchStrategy: current) did not find any beans (OnBeanCondition)

25.   ...

28. Negative matches:

29. -----------------

31.   ActiveMQAutoConfiguration:

32.      Did not match:

33.         - @ConditionalOnClass did not find required classes 'javax.jms.ConnectionFactory', 'org.apache.activemq.ActiveMQConnectionFactory' (OnClassCondition)

35.   AopAutoConfiguration.JdkDynamicAutoProxyConfiguration:

36.      Did not match:

37.         - @ConditionalOnProperty (spring.aop.proxy-target-class=false) found different value in property 'proxy-target-class' (OnPropertyCondition)

39.   ArtemisAutoConfiguration:

40.      Did not match:

41.         - @ConditionalOnClass did not find required classes 'javax.jms.ConnectionFactory', 'org.apache.activemq.artemis.jms.client.ActiveMQConnectionFactory' (OnClassCondition)

43.   BatchAutoConfiguration:

44.      Did not match:

45.         - @ConditionalOnClass did not find required class 'org.springframework.batch.core.launch.JobLauncher' (OnClassCondition)

47.   ...

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。