当前位置 博文首页 > springboot源码解析-管中窥豹系列之项目类型（二）
这一节我们先讨论一下springboot项目的怎么自动加载applicationcontext实现类的。
那springboot用的是哪一种呢？
先说结论：关于类型的选择，springboot是根据class来判断的。
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
...
this.webApplicationType = WebApplicationType.deduceFromClasspath();
...
}
我们先看类型：
private static final String[] SERVLET_INDICATOR_CLASSES = { "javax.servlet.Servlet",
"org.springframework.web.context.ConfigurableWebApplicationContext" };
private static final String WEBMVC_INDICATOR_CLASS = "org.springframework.web.servlet.DispatcherServlet";
private static final String WEBFLUX_INDICATOR_CLASS = "org.springframework.web.reactive.DispatcherHandler";
private static final String JERSEY_INDICATOR_CLASS = "org.glassfish.jersey.servlet.ServletContainer";
static WebApplicationType deduceFromClasspath() {
if (ClassUtils.isPresent(WEBFLUX_INDICATOR_CLASS, null) && !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null)
&& !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) {
return WebApplicationType.REACTIVE;
}
for (String className : SERVLET_INDICATOR_CLASSES) {
if (!ClassUtils.isPresent(className, null)) {
return WebApplicationType.NONE;
}
}
return WebApplicationType.SERVLET;
}
类型确定之后，我们看SpringApplication的run方法：
public ConfigurableApplicationContext run(String... args) {
...
try {
...
context = createApplicationContext();
...
} catch (Throwable ex) {
...
}
...
return context;
}
ApplicationContext实现类就是在createApplicationContext（）里面确定的
public static final String DEFAULT_CONTEXT_CLASS = "org.springframework.context."
+ "annotation.AnnotationConfigApplicationContext";
public static final String DEFAULT_SERVLET_WEB_CONTEXT_CLASS = "org.springframework.boot."
+ "web.servlet.context.AnnotationConfigServletWebServerApplicationContext";
public static final String DEFAULT_REACTIVE_WEB_CONTEXT_CLASS = "org.springframework."
+ "boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext";
protected ConfigurableApplicationContext createApplicationContext() {
Class<?> contextClass = this.applicationContextClass;
if (contextClass == null) {
try {
switch (this.webApplicationType) {
case SERVLET:
contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
break;
case REACTIVE:
contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
break;
default:
contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
}
}
catch (ClassNotFoundException ex) {
throw new IllegalStateException(
"Unable create a default ApplicationContext, please specify an ApplicationContextClass", ex);
}
}
return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}
根据类型加载不同的class:
至此，一目了然了，想要不同的项目类型，添加对应的jar包，springboot自动帮你选择对应的ApplicationContext实现类
如果是普通的web项目：
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
如果是reactive项目：
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-webflux</artifactId>
</dependency>
如果是非web项目:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
</dependency>
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