Spring Boot自动配置源码

SpringBoot初始化上下文环境

SpringBoot会从

META-INF/spring.factories

文件中加载Initializers,Auto Configure

Initializers用于加载配置(Environment)

Auto Configure用于自动配置类

如果是web类型的工程,SpringBoot会创建EmbeddedWebApplicationContext上下文 -> 使用createEmbeddedServletContainer方法创建内嵌的servlet服务容器( 由工厂类EmbeddedServletContainerFactory -> getEmbeddedServletContainer()创建Servlet容器, ->initialize() 同时进行容器初始化及运行 )

容器类EmbeddedServletContainer控制着内嵌服务器的生命周期以及配置.

加载AutoConfiguration

AutoConfiguration初始化对应的实例

我们来看下Mongo的AutoConfiguration,如下:

@Configuration
@ConditionalOnClass(MongoClient.class)
@EnableConfigurationProperties(MongoProperties.class)
@ConditionalOnMissingBean(type = "org.springframework.data.mongodb.MongoDbFactory")
public class MongoAutoConfiguration {

@Autowired
private MongoProperties properties;

@Autowired(required = false)
private MongoClientOptions options;

@Autowired
private Environment environment;

private MongoClient mongo;

@PreDestroy
public void close() {
if (this.mongo != null) {
this.mongo.close();
}
}

@Bean
@ConditionalOnMissingBean
public MongoClient mongo() throws UnknownHostException {
this.mongo = this.properties.createMongoClient(this.options, this.environment);
return this.mongo;
}

}

Mongo的AutoConfiguration将会在用户引入Mongo相关包时,并且没有自定义MongoDbFactory时被激活,同时配置文件(application.properties之类的)将注入到MongoProperties中.MongoProperties类由@ConfigurationProperties标注:

@ConfigurationProperties(prefix = "spring.data.mongodb")
public class MongoProperties {

/**
* Default port used when the configured port is {@code null}.
*/
public static final int DEFAULT_PORT = 27017;

/**
* Mongo server host.
*/
private String host;
//...省略...
//根据配置创建MongoClient
public MongoClient createMongoClient(MongoClientOptions options,
Environment environment) throws UnknownHostException {
try {
if (hasCustomAddress() || hasCustomCredentials()) {
if (options == null) {
options = MongoClientOptions.builder().build();
}
List<MongoCredential> credentials = null;
if (hasCustomCredentials()) {
String database = this.authenticationDatabase == null
? getMongoClientDatabase() : this.authenticationDatabase;
credentials = Arrays.asList(MongoCredential.createMongoCRCredential(
this.username, database, this.password));
}
String host = this.host == null ? "localhost" : this.host;
int port = determinePort(environment);
return new MongoClient(Arrays.asList(new ServerAddress(host, port)),
credentials, options);
}
// The options and credentials are in the URI
return new MongoClient(new MongoClientURI(this.uri, builder(options)));
}
finally {
clearPassword();
}
}

可以看到MongoClient最终由MongoAutoConfiguration调用MongoProperties的createMongoClient()方法创建.通过标注@Bean将MongoClient发布到Spring容器中.

如果用户已经用@Bean自定义了一个MongoClient,那么Mongo AutoConfig就不会做去初始化MongoClient,配置文件中的配置也就不生效了.

Embedded Tomcat初始化过程

内嵌式Tomcat通过Tomcat类创建并配置的,我们可以看看Spring是如何包装的,使用工厂类TomcatEmbeddedServletContainerFactory -> getEmbeddedServletContainer() :

@Override
public EmbeddedServletContainer getEmbeddedServletContainer(
ServletContextInitializer... initializers) {
//通常创建内嵌Tomcat时的流程,使用Tomcat类
Tomcat tomcat = new Tomcat();
File baseDir = (this.baseDirectory != null ? this.baseDirectory
: createTempDir("tomcat"));
tomcat.setBaseDir(baseDir.getAbsolutePath());
Connector connector = new Connector(this.protocol);
tomcat.getService().addConnector(connector);
//用户可以通过这个接口做额外配置
customizeConnector(connector);
tomcat.setConnector(connector);
tomcat.getHost().setAutoDeploy(false);
tomcat.getEngine().setBackgroundProcessorDelay(-1);
for (Connector additionalConnector : this.additionalTomcatConnectors) {
tomcat.getService().addConnector(additionalConnector);
}
prepareContext(tomcat.getHost(), initializers);
return getTomcatEmbeddedServletContainer(tomcat);
}

Spring使用EmbeddedServletContainer包装了Tomcat,封装了内嵌容器的生命周期.

所有用户通过工厂类EmbeddedServletContainerFactory配置容器,例如:application.properties中的

server.port=8099

,

带有@ConfigurationProperties注解的ServerProperties,自动注入了application.properties中关于server.*的配置.

由于ServerProperties实现了EmbeddedServletContainerCustomizer接口,ServerProperties通过该接口的方法,对EmbeddedServletContainerFactory进行配置:

if (getPort() != null) {
container.setPort(getPort());
}
if (getAddress() != null) {
container.setAddress(getAddress());
}
if (getContextPath() != null) {
container.setContextPath(getContextPath());
}
if (getDisplayName() != null) {
container.setDisplayName(getDisplayName());
}
if (getSession().getTimeout() != null) {
container.setSessionTimeout(getSession().getTimeout());
}
if (getSsl() != null) {
container.setSsl(getSsl());
}
if (getJspServlet() != null) {
container.setJspServlet(getJspServlet());
}
if (getCompression() != null) {
container.setCompression(getCompression());
}

除了配置文件方式,我们还可以:

@Bean
public EmbeddedServletContainerFactory servletContainer() {
TomcatEmbeddedServletContainerFactory factory = new TomcatEmbeddedServletContainerFactory();
factory.addConnectorCustomizers(connector -> {
Http11NioProtocol protocol = ((Http11NioProtocol) connector.getProtocolHandler());
connector.setPort(8989);
protocol.setConnectionTimeout(10000);
});
return factory;
}

直接自己创建工厂类,并实现addConnectorCustomizers接口中的customizer.这部分会覆盖配置文件的配置,在TomcatEmbeddedServletContainerFactory的getEmbeddedServletContainer() -> customizeConnector() 中会调用我们自定义的customizer:

for (TomcatConnectorCustomizer customizer : this.tomcatConnectorCustomizers) {
customizer.customize(connector);
}

如果用户没有自定义EmbeddedServletContainerFactory的话,EmbeddedServletContainerAutoConfiguration就默认初始化一个.

@Configuration
@ConditionalOnClass({ Servlet.class, Tomcat.class })
@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
public static class EmbeddedTomcat {

@Bean
public TomcatEmbeddedServletContainerFactory tomcatEmbeddedServletContainerFactory() {
return new TomcatEmbeddedServletContainerFactory();
}

}

Reference

http://geowarin.github.io/understanding-spring-boot.html

http://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#howto-troubleshoot-auto-configuration

http://blog.csdn.net/liaokailin/article/category/5765237