版本2.1.1
springboot只有一个application的启动，我们就从这个启动开始分析，首先我们跟进注解@SpringBootApplication如下：
/** Class, interface (including annotation type), or enum declaration */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
@Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {
// ...
}这里我们看到开启了@EnableAutoConfiguration，通过字面意思我们就将要知道发生什么，下面我们看看@EnableAutoConfiguration干了什么
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
// ...
}他是通过AutoConfigurationImportSelector.class给容器导入了一些组件，让我们继续看下AutoConfigurationImportSelector到底做了些什么
/**
实现的若干个接口，有些一看名字就很熟悉，就是初始化Bean的那一套。。。
**/
public class AutoConfigurationImportSelector
implements DeferredImportSelector, BeanClassLoaderAware, ResourceLoaderAware,
BeanFactoryAware, EnvironmentAware, Ordered {
// 我们主要来看这个方法
@Override
public String[] selectImports(AnnotationMetadata annotationMetadata) {
if (!isEnabled(annotationMetadata)) {
return NO_IMPORTS;
}
// 从META-INF/spring-autoconfigure-metadata.properties加载配置属性
AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
.loadMetadata(this.beanClassLoader);
// 获取需要的自动配置类@
AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(
autoConfigurationMetadata, annotationMetadata);
return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
}
}接@继续跟踪 getAutoConfigurationEntry方法：
protected AutoConfigurationEntry getAutoConfigurationEntry(
AutoConfigurationMetadata autoConfigurationMetadata,
AnnotationMetadata annotationMetadata) {
if (!isEnabled(annotationMetadata)) {
return EMPTY_ENTRY;
}
AnnotationAttributes attributes = getAttributes(annotationMetadata);
// 通过spring-autoconfigure-metadata.properties配置类属性获取自动配置类，如图1所示，我们继续跟进这个方法@@
List<String> configurations = getCandidateConfigurations(annotationMetadata,
attributes);
// 移除重复的配置类，这个版本好像没有排序那个方法了。。
configurations = removeDuplicates(configurations);
Set<String> exclusions = getExclusions(annotationMetadata, attributes);
// 检查时候有需要排除的，如果有直接干掉
checkExcludedClasses(configurations, exclusions);
configurations.removeAll(exclusions);
// 执行过滤执行配置了@OnClassCondition才生效，如图1.1所示
configurations = filter(configurations, autoConfigurationMetadata);
// 触发自动配置导入监听事件
fireAutoConfigurationImportEvents(configurations, exclusions);
return new AutoConfigurationEntry(configurations, exclusions);
}
图1
图1.1
接@@我们继续跟进getCandidateConfigurations，里面还有好几层，我就不一一展示，直接看最后方法
/**
这个方法会通过每个jar下的META-INF/spring.factories，获得所有的自动配置类，如图2所示
**/
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
MultiValueMap<String, String> result = cache.get(classLoader);
if (result != null) {
return result;
}
try {
// FACTORIES_RESOURCE_LOCATION 的值为：META-INF/spring.factories
Enumeration<URL> urls = (classLoader != null ?
classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
result = new LinkedMultiValueMap<>();
while (urls.hasMoreElements()) {
URL url = urls.nextElement();
UrlResource resource = new UrlResource(url);
Properties properties = PropertiesLoaderUtils.loadProperties(resource);
for (Map.Entry<?, ?> entry : properties.entrySet()) {
String factoryClassName = ((String) entry.getKey()).trim();
for (String factoryName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {
result.add(factoryClassName, factoryName.trim());
}
}
}
cache.put(classLoader, result);
return result;
}
catch (IOException ex) {
throw new IllegalArgumentException("Unable to load factories from location [" +
FACTORIES_RESOURCE_LOCATION + "]", ex);
}
}
图2
下面我们找个具体配置类来具体看下，以HttpEncodingAutoConfiguration为例
// 标注为配置类，和之前spring的xml配置文件效果一样
@Configuration
// 启动指定类的ConfigurationProperties功能；将配置文件中对应的值和HttpEncodingProperties绑定起来；并把HttpEncodingProperties加入到ioc容器中，(prefix = "spring.http")我们在配置的key都是spring.http开始，如图3所示
@EnableConfigurationProperties(HttpProperties.class)
// 判断当前应用是否是web应用，如果是则生效
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)
// 判断项目中有没有CharacterEncodingFilter这个类，编码过滤器
@ConditionalOnClass(CharacterEncodingFilter.class)
// 如果2所示，判断配置文件中是否存在前缀为spring.http,encoding的配置
@ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true)
public class HttpEncodingAutoConfiguration {
private final HttpProperties.Encoding properties;
public HttpEncodingAutoConfiguration(HttpProperties properties) {
this.properties = properties.getEncoding();
}
// 给容器添加一个组件，组件的值从配置文件中获取，默认编码格式UTF-8
@Bean
@ConditionalOnMissingBean
public CharacterEncodingFilter characterEncodingFilter() {
CharacterEncodingFilter filter = new OrderedCharacterEncodingFilter();
filter.setEncoding(this.properties.getCharset().name());
filter.setForceRequestEncoding(this.properties.shouldForce(Type.REQUEST));
filter.setForceResponseEncoding(this.properties.shouldForce(Type.RESPONSE));
return filter;
}
@Bean
public LocaleCharsetMappingsCustomizer localeCharsetMappingsCustomizer() {
return new LocaleCharsetMappingsCustomizer(this.properties);
}
private static class LocaleCharsetMappingsCustomizer implements
WebServerFactoryCustomizer<ConfigurableServletWebServerFactory>, Ordered {
private final HttpProperties.Encoding properties;
LocaleCharsetMappingsCustomizer(HttpProperties.Encoding properties) {
this.properties = properties;
}
@Override
public void customize(ConfigurableServletWebServerFactory factory) {
if (this.properties.getMapping() != null) {
factory.setLocaleCharsetMappings(this.properties.getMapping());
}
}
@Override
public int getOrder() {
return 0;
}
}
}
图3
【自定义自动配置举例】
配置类：
package com.swk.springboot.config;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;
/**
* 只有这个组件是容器中的组件，才能容器提供的@ConfigurationProperties功能；
*/
@Component
@ConfigurationProperties(prefix = "start.info")
public class StartInfoConfig {
private String port;
private String name;
public String getPort() {
return port;
}
public void setPort(String port) {
this.port = port;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "StartInfoConfig{" +
"port='" + port + '\'' +
", name='" + name + '\'' +
'}';
}
}
properties配置：
#自定义配置
start.info.port=8080
start.info.name=sunwukong测试类：
package com.swk.springboot.springbootswk;
import com.swk.springboot.config.StartInfoConfig;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
@RunWith(SpringRunner.class)
@SpringBootTest
public class SpringbootSwkApplicationTests {
@Autowired
private StartInfoConfig startInfoConfig;
@Test
public void test(){
System.out.println(startInfoConfig.toString());
}
}
执行结果：
