从零学springboot—— servlet,过滤器，监听器，拦截器

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自定义servlet

@WebServlet(urlPatterns = "/myServlet/*")
public class MyServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
        System.out.println("********get请求***********");
    }

    protected void doPost(HttpServletRequest req, HttpServletResponse resp){
        System.out.println("********post请求***********");
    }
}

在启动类上添加注解@ServletComponentScan，过滤器和监听器也需要开启该注解。

过滤器实现

@WebFilter(urlPatterns="/*")
public class MyFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.err.println("********过滤器初始化*********");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.err.println("********过滤器执行*********");
        filterChain.doFilter(servletRequest,servletResponse);
    }

    @Override
    public void destroy() {
        System.err.println("********过滤器销毁*********");
    }
}

监听器实现

@WebListener
public class MyServletContextListen implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        System.err.println("***********容器启动**************");
    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        System.err.println("***********容器销毁**************");
    }
}

其中示例中的监听器为监听容器的启动及销毁，还存在其他的监听器接口，例如监听session的HttpSessionListener（多用于统计在线人数），监听ServletRequest对象的ServletRequestListener

拦截器实现

自定义拦截器：

public class MyInterceptor1 implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {
        System.err.println("*********拦截器1执行*********");
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {

    }

    @Override
    public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {

    }
}

public class MyInterceptor2 implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {
        System.err.println("***********拦截器2执行**************");
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {

    }

    @Override
    public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {

    }
}

将自定义拦截器加入到拦截器链：

@Configuration
public class MyWebAppConfigurer extends WebMvcConfigurerAdapter {

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new MyInterceptor1());
        registry.addInterceptor(new MyInterceptor2());
        super.addInterceptors(registry);
    }
}

这里过滤器，监听器，拦截器有个请求顺序，例如对于同一个请求，会先执行监听该请求的监听器，然后执行过滤器，再执行拦截器。