spring boot 兼容servlet3.0

Spring 同时提醒我们，如果是比较早的servlet容器（低于Servlet 3.0），可能不支持ServletContextInitializer，这时我们需要给项目配置一个web.xml，并将配置类加载进项目。以下是spring官方给出的方案：

Deploying a WAR in an Old (Servlet 2.5) Container

Spring Boot uses Servlet 3.0 APIs to initialize the ServletContext (register Servlets etc.) so you can’t use the same application out of the box in a Servlet 2.5 container. It is however possible to run a Spring Boot application on an older container with some special tools. If you include org.springframework.boot:spring-boot-legacy as a dependency (maintained separately to the core of Spring Boot and currently available at 1.0.0.RELEASE), all you should need to do is create a web.xml and declare a context listener to create the application context and your filters and servlets. The context listener is a special purpose one for Spring Boot, but the rest of it is normal for a Spring application in Servlet 2.5.

e.g:



    
        contextConfigLocation
        
        demo.Application
    

    
    
        org.springframework.boot.legacy.context.web.SpringBootContextLoaderListener
    

    
        metricFilter
        org.springframework.web.filter.DelegatingFilterProxy
    

    
        metricFilter
        /*
    

    
        appServlet
        org.springframework.web.servlet.DispatcherServlet
        
            contextAttribute
            org.springframework.web.context.WebApplicationContext.ROOT
        
        1
    

    
        appServlet
        /