首先来解释一下SpringBoot首页设置的三种方式
1.SpringBoot默认首页设置
编写一个最简单的html文件 index.html
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> </head> <body> <h1>首页</h1> </body> </html>
将index.html文件置于SpringBoot的任一静态资源目录下
http://localhost:8080/访问，成功显示
源码分析
首先找对应的自动配置类WebMvcAutoConfiguration中的对应代码
@Bean
public WelcomePageHandlerMapping welcomePageHandlerMapping(ApplicationContext applicationContext, FormattingConversionService mvcConversionService, ResourceUrlProvider mvcResourceUrlProvider) {
WelcomePageHandlerMapping welcomePageHandlerMapping =
new WelcomePageHandlerMapping(new TemplateAvailabilityProviders(applicationContext),
applicationContext, this.getWelcomePage(), this.mvcProperties.getStaticPathPattern());
welcomePageHandlerMapping.setInterceptors(this.getInterceptors(mvcConversionService, mvcResourceUrlProvider));
welcomePageHandlerMapping.setCorsConfigurations(this.getCorsConfigurations());
return welcomePageHandlerMapping;
}
可以看到 SpringBoot注册了WelcomePageHandlerMappingBean来处理项目的默认首页,构造器中的this.getWelcomePage()为首页资源。
private Resource getWelcomePage() {
String[] var1 = this.resourceProperties.getStaticLocations();
int var2 = var1.length;
for(int var3 = 0; var3 < var2; ++var3) {
String location = var1[var3];
Resource indexHtml = this.getIndexHtml(location);
if (indexHtml != null) {
return indexHtml;
}
}
ServletContext servletContext = this.getServletContext();
if (servletContext != null) {
return this.getIndexHtml((Resource)(new ServletContextResource(servletContext, "/")));
} else {
return null;
}
}
分析这段代码，首先获取了this.resourceProperties的StaticLocations字段，顾名思义就是静态路径，那就先跟踪StaticLocations
可以看出StaticLocations是WebPropertis中内部静态类Resources的属性，从构造器中可以看出它的值为
private static final String[] CLASSPATH_RESOURCE_LOCATIONS = new String[]{"classpath:/META-INF/resources/", "classpath:/resources/", "classpath:/static/", "classpath:/public/"};
显而易见，这其实就是SpringBoot的静态资源目录
/META-INF
/resources/
/resources/
/static/
/public/
回到之前的代码，获取了StaticLocations后，通过循环遍历，很明显可以看到一个新的方法this.getIndexHtml(location)
private Resource getIndexHtml(String location) {
return this.getIndexHtml(this.resourceLoader.getResource(location));
}
使用this.resourceLoader返回一个与location对应的Resource执行另一个getIndexHtml()函数
private Resource getIndexHtml(Resource location) {
try {
Resource resource = location.createRelative("index.html");
if (resource.exists() && resource.getURL() != null) {
return resource;
}
} catch (Exception var3) {
}
return null;
}
很明显，这个方法是获取对应目录下的index.html文件。再往回看
for(int var3 = 0; var3 < var2; ++var3) {
String location = var1[var3];
Resource indexHtml = this.getIndexHtml(location);
if (indexHtml != null) {
return indexHtml;
}
}
当找到对应文件的时候就返回对应的资源，这就是SpringBoot设置首页的默认方式的原理。
从源码中也可以看出另一个关于静态资源目录优先级的问题。getWelcomePage遍历静态资源目录，一旦找到就返回，所以优先级和staticLocations中的顺序相对，验证一下。
先在每一个目录下建立对应的indx.html文件
http://localhost:8080/访问
和得出的结论一样，优先级最高的是 /META-INF/resources/，把 /META-INF/resources/下的index.html文件删除再次验证
验证成功！
2.controller里添加"/"的映射路径
新建IndexController.java
package com.springboot04webapp.controller;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
@Controller
public class IndexController {
@RequestMapping("/")
public String index(){
return "indexController";
}
}
首页资源indexController.html
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> </head> <body> <h1>indexController首页</h1> </body> </html>
http://localhost:8080/访问
3.MVC扩展配置实现
新建MyMvcConfiguration配置类，扩展MVC配置，重写addViewControllers方法
package com.springboot04webapp.config;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.ViewControllerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
@Configuration
public class MyMvcConfiguration implements WebMvcConfigurer {
@Override
public void addViewControllers(ViewControllerRegistry registry) {
registry.addViewController("/").setViewName("indexMVC");
}
}
首页资源indexMVC.html
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> </head> <body> <h1>indexMVC首页</h1> </body> </html>
http://localhost:8080/访问
扩展：优先级问题
之前的三个方法都是单独设置的，现在把他们结合起来
http://localhost:8080/访问
优先级最高的是第二种方法，然后将indexController删除，再次验证
得出结论：Controller>MyMvcConfiguration>默认方法
