SpringBoot AutoConfiguration

Spring boot auto-configuration 初探

1、打印 AUTO-CONFIGURATION REPORT
2、从@SpringBootApplication开始；
3、spring.factories;
4、org.springframework.boot.autoconfigure.*;
5、实践

1、打印 AUTO-CONFIGURATION REPORT

mvn spring-boot:run -Dlogging.level.org.springframework.boot.autoconfigure.logging=DEBUG

在每个Spring Boot ApplicationContext中都存在一个相当有用的ConditionEvaluationReport。如果开启DEBUG日志输出,你将会看到它:

=========================
AUTO-CONFIGURATION REPORT
=========================


Positive matches:
-----------------

   DataSourceAutoConfiguration matched
      - @ConditionalOnClass classes found: javax.sql.DataSource,org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseType (OnClassCondition)

   DataSourceAutoConfiguration#dataSourceInitializer matched
      - @ConditionalOnMissingBean (types: org.springframework.boot.autoconfigure.jdbc.DataSourceInitializer; SearchStrategy: all) found no beans (OnBeanCondition)

   DataSourceAutoConfiguration.PooledDataSourceConfiguration matched
      - supported DataSource class found (DataSourceAutoConfiguration.PooledDataSourceCondition)
      - @ConditionalOnMissingBean (types: javax.sql.DataSource,javax.sql.XADataSource; SearchStrategy: all) found no beans (OnBeanCondition)

   ......    

Negative matches:
-----------------

   ActiveMQAutoConfiguration did not match
      - required @ConditionalOnClass classes not found: javax.jms.ConnectionFactory,org.apache.activemq.ActiveMQConnectionFactory (OnClassCondition)

   AopAutoConfiguration did not match
      - required @ConditionalOnClass classes not found: org.aspectj.lang.annotation.Aspect,org.aspectj.lang.reflect.Advice (OnClassCondition)

   ArtemisAutoConfiguration did not match
      - required @ConditionalOnClass classes not found: javax.jms.ConnectionFactory,org.apache.activemq.artemis.jms.client.ActiveMQConnectionFactory (OnClassCondition)

   ......

Exclusions:
-----------

    None


Unconditional classes:
----------------------

    org.springframework.boot.autoconfigure.PropertyPlaceholderAutoConfiguration

    org.springframework.boot.autoconfigure.web.WebClientAutoConfiguration

    org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration

    org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration

这份report清楚完整地报告了spring boot做了哪些auto-config以及它们各自需要满足的条件，没有做哪些auto-config(因为不满足哪些条件)，开发者可以根据这份报告对程序进行调试，以求达到自己想要的效果。

2、从@SpringBootApplication开始；

（1）、@SpringBootApplication

我们的App启动类注解了@SpringBootApplication。从源码上来看，这个注解糅合了

@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan

这三个注解，其中@SpringBootConfiguration是@Configuration的一个替代;@EnableAutoConfiguration的作用是启用Spring应用程序上下文的自动配置，尝试猜测和配置可能需要的bean，即Spring Boot的auto-config是由这个注解实现的;@ComponentScan的作用是扫描@Configuration注解的类的目录及子目录下的Components并装载。

（2）@EnableAutoConfiguration、：

其源码如下:

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import({EnableAutoConfigurationImportSelector.class})
public @interface EnableAutoConfiguration {
    String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";

    Class<?>[] exclude() default {};

    String[] excludeName() default {};
}

EnableAutoConfigurationImportSelector：使用的是spring-core模块中的SpringFactoriesLoader#loadFactoryNames()方法，它的作用是在类路径上扫描META-INF/spring.factories文件中定义的类。

3、spring.factories

在org.springframework.boot.autoconfigure包下找到/META-INF/spring.factories:

# Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
org.springframework.boot.autoconfigure.logging.AutoConfigurationReportLoggingInitializer

# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.autoconfigure.BackgroundPreinitializer

# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
...... 

# Failure analyzers
org.springframework.boot.diagnostics.FailureAnalyzer=\
org.springframework.boot.autoconfigure.jdbc.DataSourceBeanCreationFailureAnalyzer

# Template availability providers
org.springframework.boot.autoconfigure.template.TemplateAvailabilityProvider=\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerTemplateAvailabilityProvider,\
......

Auto Configure模块是spring boot启动时加载的配置类，让我们看一下JerseyAutoConfiguration:

@Configuration
@ConditionalOnClass(
    name = {"org.glassfish.jersey.server.spring.SpringComponentProvider", "javax.servlet.ServletRegistration"}
)
@ConditionalOnBean(
    type = {"org.glassfish.jersey.server.ResourceConfig"}
)
@ConditionalOnWebApplication
@AutoConfigureOrder(-2147483648)
@AutoConfigureBefore({DispatcherServletAutoConfiguration.class})
@AutoConfigureAfter({JacksonAutoConfiguration.class})
@EnableConfigurationProperties({JerseyProperties.class})
public class JerseyAutoConfiguration implements ServletContextAware {
    ...
}

让我们先来看一下JerseyAutoConfiguration上的几个注解：

@Configuration指明这是个配置类
@Conditional此注释使得只有在特定条件满足时才启用一些配置 Spring还提供了很多Condition给我们用 @ConditionalOnBean（仅仅在当前上下文中存在某个对象时，才会实例化一个Bean） @ConditionalOnClass（某个class位于类路径上，才会实例化一个Bean） @ConditionalOnExpression（当表达式为true的时候，才会实例化一个Bean） @ConditionalOnMissingBean（仅仅在当前上下文中不存在某个对象时，才会实例化一个Bean） @ConditionalOnMissingClass（某个class类路径上不存在的时候，才会实例化一个Bean） @ConditionalOnNotWebApplication（不是web应用）也就是说，只用满足以下两个条件，spring boot才会帮我们自动配置。当我们配置Jersey时，我们在pom中引入了相关的package，包括org.glassfish.jersey.server.spring.SpringComponentProvider, javax.servlet.ServletRegistration满足了第一个条件；然后我们还写了public class JerseyConfig extends ResourceConfig注册endpoint，第二个条件也满足了，spring boot启动的是web application,地三个条件也满足了：

JerseyAutoConfiguration matched
- @ConditionalOnClass classes found: org.glassfish.jersey.server.spring.SpringComponentProvider,javax.servlet.ServletRegistration (OnClassCondition)
- found web application StandardServletEnvironment (OnWebApplicationCondition)
- @ConditionalOnBean (types: org.glassfish.jersey.server.ResourceConfig; SearchStrategy: all) found the following [jerseyConfig] (OnBeanCondition)
JerseyAutoConfiguration#jerseyServletRegistration matched
- @ConditionalOnMissingBean (names: jerseyServletRegistration; SearchStrategy: all) found no beans (OnBeanCondition)
- matched (OnPropertyCondition)
JerseyAutoConfiguration#requestContextFilter matched
- @ConditionalOnMissingBean (types: org.springframework.boot.web.servlet.FilterRegistrationBean; SearchStrategy: all) found no beans (OnBeanCondition)
JerseyAutoConfiguration.JacksonResourceConfigCustomizer matched
- @ConditionalOnClass classes found: org.glassfish.jersey.jackson.JacksonFeature (OnClassCondition)
- @ConditionalOnSingleCandidate (types: com.fasterxml.jackson.databind.ObjectMapper; SearchStrategy: all) found a primary candidate amongst the following [jacksonObjectMapper] (OnBeanCondition) JerseyAutoConfiguration中用@Bean自动注入了以上三个变量，@Bean注解的方法上也可以使用@Conditional。

3、动手试一试

我们已经知道了spring-boot auto-configuration的流程，spring-boot也允许我们实现自己的auto-config。

（1）写一个简单的TestBean，假设它是我们需要引入的库包：

package com.example.zhuangqf;

/**
 * Created by zhuangqf on 11/27/16.
 */
public class TestBean {

    private String testString;

    public TestBean(String testString){
        this.testString = testString;
    }

    public String showTest(){
        return testString;
    }

}

在这个类中，我们并没有用到spring相关的东西，包括注解。

（2）编写我们的TestBeanAutoConfiguration

package com.example.zhuangqf.config;

import com.example.zhuangqf.TestBean;
import com.example.zhuangqf.properties.TestBeanProperties;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
* Created by zhuangqf on 11/27/16.
*/
@Configuration
@EnableConfigurationProperties(TestBeanProperties.class)
public class TestBeanAutoConfiguration {

   @Autowired TestBeanProperties testBeanProperties;

   @Bean
   @ConditionalOnMissingBean(TestBean.class)
   public TestBean testBean() {
       return new TestBean(testBeanProperties.getTestString());
   }
}

@EnableConfigurationProperties(TestBeanProperties.class)告诉spring boot帮我们自动加载TestBeanProperties.class，这个类是用来读取properties外部文件的。

（3）TestBeanProperties.class：

package com.example.zhuangqf.properties;

import org.springframework.boot.context.properties.ConfigurationProperties;

/**
 * Created by zhuangqf on 11/27/16.
 */
@ConfigurationProperties(prefix = "com.example.zhuangqf")
public class TestBeanProperties {

    private String testString;

    public String getTestString() {
        return testString;
    }

    public void setTestString(String testString) {
        this.testString = testString;
    }
}

这个类从项目依赖的properties文件中读取com.example.zhuangqf前缀的key（properties文件以key-value格式存属性）

（4）application.properties：

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.example.zhuangqf.config.TestBeanAutoConfiguration
com.example.zhuangqf.testString=test

第一句告诉spring boot自动加载com.example.zhuangqf.config.TestBeanAutoConfiguration中的配置，第二句配置（3）中的testString

(5)测试

在之前的endpoint中加:

@Autowired
TestBean testBean;

@GET
@Path("/test")
public String test(){
    System.out.println(testBean.showTest());
    return testBean.showTest();
}

启动程序，访问对应的网址：

test

查看report：

TestBeanAutoConfiguration#testBean matched - @ConditionalOnMissingBean (types: com.zhuangqf.TestBean; SearchStrategy: all) found no beans (OnBeanCondition) 我们自定义的类成功auto-config！！！

Name		Name	Last commit message	Last commit date
Latest commit History 2 Commits
.idea		.idea
src		src
AutoConfigDemo.iml		AutoConfigDemo.iml
README.md		README.md
pom.xml		pom.xml

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SpringBoot AutoConfiguration

1、打印 AUTO-CONFIGURATION REPORT

2、从@SpringBootApplication开始；

（1）、@SpringBootApplication

（2）@EnableAutoConfiguration、：

3、spring.factories

3、动手试一试

（1）写一个简单的TestBean，假设它是我们需要引入的库包：

（2）编写我们的TestBeanAutoConfiguration

（3）TestBeanProperties.class：

（4）application.properties：

(5)测试

参考：

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SpringBoot AutoConfiguration

1、打印 AUTO-CONFIGURATION REPORT

2、从@SpringBootApplication开始；

（1）、@SpringBootApplication

（2）@EnableAutoConfiguration、：

3、spring.factories

3、动手试一试

（1）写一个简单的TestBean，假设它是我们需要引入的库包：

（2）编写我们的TestBeanAutoConfiguration

（3）TestBeanProperties.class：

（4）application.properties：

(5)测试

参考：

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