[Java知识库]Spring Boot实战清华版 Servlet Filter Listener

Servlet: 请求处理的鼻祖，不过现在基本废弃。

Filter：对一切请求均有效，可以实现敏感词过滤，请求响应的修改等等。

Listener: 对事件的监听，以ServletContentListener, SessionListener为主

Servlet的使用(不推荐使用)

使用@WebServlet注解声明，使用@ServletComponentScan开启扫描

? ? ? ? ?a. 使用@WebServlet注解声明

@WebServlet(name = "myServlet", urlPatterns = {"/test/mytest"})
public class MyServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("[MyServlet] doGet");
        resp.setContentType("application/json");
        resp.setStatus(200);
        PrintWriter writer = resp.getWriter();
        writer.write("{\"data\": 100}");
        writer.flush();
    }
}

????????b. 注解扫描

Filter的使用?

实现Filter接口的doFilter方法，使用@WebFilter进行注解, 开启ServletComponentScan

????????a.?实现Filter接口的doFilter方法，使用@WebFilter进行注解

@WebFilter(urlPatterns = "/*")
public class MyFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("[MyFilter] filter init");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("[MyFilter] do filter");
        filterChain.doFilter(servletRequest, servletResponse);
    }

    @Override
    public void destroy() {
        System.out.println("[MyFilter] filter destroy");
    }
}

????????b.开启ServletComponentScan

?

Listener的使用

使用@WebListener注解标记，同时实现ServletContextListener、HttpSessionListener接口

@WebListener
public class MyContextListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        System.out.println("[MyContextListener] context created");
    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        System.out.println("[MyContextListener] context destroyed");
    }
}

@WebListener
public class MySessionListener implements HttpSessionListener {
    @Override
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {
        System.out.println("[MySessionListener] session created");
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
        System.out.println("[MySessionListener] session destroyed");
    }
}

?开启ServletComponentScan