一、作用：

servlet3.0支持仅支持tomcat7以上版本，@WebServlet、@WebListener、@WebFilter等注解相当于web.xml配置<servlet-name>...</<servlet-name><servlet-url>....<servlet-url>。。。。，加了此注解后web应用可以不用配置web.xml，直接注解标注相应的servlet，listener，filter

二、例子：

@WebServlet("/hello")
public class HelloServlet extends HttpServlet{
    private static final long serialVersionUID = 1L;

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        resp.getWriter().write("hello,suxiaodong");
    }
}

index.jsp

<html>
<body>
    <a href="hello">servlet3.0</a>
</body>
</html>

  三、ServletContainerInitializer

容器在启动应用的时候，会扫描当前应用每一个jar包里面META-INF/services/javax.servlet.ServletContainerInitializer指定的实现类，启动并运行这个实现类的方法,传入感兴趣的类型:

ServletContainerInitializer:

@HandlesTypes:

@HandlesTypes(value = {HelloService.class})
public class MyServletContainerInitializer implements ServletContainerInitializer{
//set传入注解感兴趣类型的所有子类
    @Override
    public void onStartup(Set<Class<?>> set, ServletContext ctx)
            throws ServletException {
        System.out.println("感兴趣的类型：");
        for(Class<?> clazz: set) {
            System.out.println(clazz);
        }
    }

}

interface: HelloService

实现类：HelloServiceImpl

子接口：HelloServiceSub

抽象子类：AbstractHelloService

resource配置：

 

 容器启动打印：

2019-06-13 23:00:42.228:INFO:oejs.Server:main: jetty-9.3.12.v20160915
2019-06-13 23:00:48.602:INFO:oeja.AnnotationConfiguration:main: Scanning elapsed time=5269ms
感兴趣的类型：
interface com.suxiaodong.service.HelloServiceSub
class com.suxiaodong.service.HelloServiceImpl
class com.suxiaodong.service.AbstractHelloService
23:00:48,921 |-INFO in ch.qos.logback.classic.LoggerContext[xdsuLogging] - Could NOT find resource [logback-test.xml]
23:00:48,921 |-INFO in ch.qos.logback.classic.LoggerContext[xdsuLogging] - Could NOT find resource [logback.groovy]
23:00:48,921 |-INFO in ch.qos.logback.classic.LoggerContext[xdsuLogging] - Found resource [logback.xml] at [file:/D:/testwo