Spring Boot Servlet、Filter、Listener 配置

如果在我们的 Spring Boot 项目使用到了 Servlet、Filter、Listener，可以使用如下三种方式配置。

自定义 Servlet、Filter、Listener

/**
 * 自定义 servlet
 */
public class CustomServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        System.out.println("servlet get method");
        doPost(request, response);
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        System.out.println("servlet post method");
        response.getWriter().write("hello world");
    }
}

/**
 * 自定义 filter
 */
public class CustomFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("init filter");
    }
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
        throws IOException, ServletException {
        System.out.println("do filter");
        chain.doFilter(request, response);
    }
    @Override
    public void destroy() {
        System.out.println("destroy filter");
    }
}

/**
 * 自定义 listener
 */
public class CustomListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        System.out.println("contextInitialized");
    }
    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        System.out.println("contextDestroyed");
    }
}

方式一：注册 Bean

创建自定义的 Servlet、Filter、Listener 类，然后通过在 Spring Boot 入口启动类中注册 ServletRegistrationBean、 FilterRegistrationBean 和 ServletListenerRegistrationBean 的方式使用。

@SpringBootApplication
public class DemoApplication {
    @Bean
    public ServletRegistrationBean servletRegistrationBean() {
        return new ServletRegistrationBean(new CustomServlet(), "/test");
    }
    @Bean
    public FilterRegistrationBean filterRegistrationBean() {
        return new FilterRegistrationBean(new CustomFilter(), servletRegistrationBean());
    }
    @Bean
    public ServletListenerRegistrationBean<CustomListener> servletListenerRegistrationBean() {
        return new ServletListenerRegistrationBean<CustomListener>(new CustomListener());
    }
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

方式二：实现 ServletContextInitializer 接口

通过实现 ServletContextInitializer 接口，实现其中的 onStartup 方法。

@SpringBootApplication
public class DemoApplication implements ServletContextInitializer {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
    @Override
    public void onStartup(ServletContext servletContext) throws ServletException {
        servletContext.addServlet("customServlet", new CustomServlet()).addMapping("/test");
        servletContext.addFilter("customFilter", new CustomFilter())
            .addMappingForServletNames(EnumSet.of(DispatcherType.REQUEST), true, "customServlet");
        servletContext.addListener(new CustomListener());
    }
}

方法三：通过注解

在 SpringBootApplication 上使用 @ServletComponentScan 注解后，直接通过@WebServlet、@WebFilter、@WebListener 注解自动注册。

@SpringBootApplication
@ServletComponentScan
public class DemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

/**
 * 自定义 servlet
 */
@WebServlet(name = "customServlet", urlPatterns = "/test")
public class CustomServlet extends HttpServlet {
/**
 * 自定义 filter
 */
@WebFilter(filterName = "customFilter", urlPatterns = "/*")
public class CustomFilter implements Filter {
/**
 * 自定义 listener
 */
 @WebListener
public class CustomListener implements ServletContextListener {