springboot servlet、filter、listener开发

落日映苍穹つ 2021-09-15 12:08 391阅读 0赞

springboot的最大特点是把底层的servlet和容器都屏蔽起来，给我们暴露的就是controller和各种注解。本文介绍如何在springboot上要做一些低层次的servlet、filter、listener之类的开发。

在spring boot中添加自己的Servlet有两种方法：（Filter和Listener也是如此）。

1、在代码中添加注册的方式：

1）自定义servlet、filter、listener类；

2）在springboot主类中通过ServletRegistrationBean、 FilterRegistrationBean 和 ServletListenerRegistrationBean 获得控制。

2、通过注解自动注册方式：

1）自定义servlet、filter、listener类，并且使用@WebServlet、@WebFilter、@WebListener 注解自动注册；

2）在SpringBootApplication 上使用@ServletComponentScan 注解；

servlet示例（使用代码的方式）：

1）自定义servlet：

package cn.edu.nuc.springbootmybatisdruid.servlet;
    
    import java.io.IOException;
    import java.io.PrintWriter;
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    //@WebServlet(urlPatterns="/lx/myservlet", description="Servlet的说明") // 不指定name的情况下，name默认值为类全路径，即org.springboot.sample.servlet.MyServlet2
    public class MyServlet extends HttpServlet{
    	private static final long serialVersionUID = 1L;
    
    	@Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            System.out.println(">>>>>>>>>>doGet2()<<<<<<<<<<<");
            doPost(req, resp);
        }
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            System.out.println(">>>>>>>>>>doPost2()<<<<<<<<<<<");
            resp.setContentType("text/html");  
            PrintWriter out = resp.getWriter();  
            out.println("<html>");  
            out.println("<head>");  
            out.println("<title>Hello World</title>");  
            out.println("</head>");  
            out.println("<body>");  
            out.println("<h1>大家好，我的名字叫Servlet2</h1>");  
            out.println("</body>");  
            out.println("</html>"); 
        }
    }

2）主类：

@SpringBootApplication
    //mapper 接口类扫描包配置
    @MapperScan("cn.edu.nuc.springbootmybatisdruid.dao.mysql")
    @EnableTransactionManagement
    public class App {
    	
    	@Bean
        public ServletRegistrationBean servletRegistrationBean() {
            return new ServletRegistrationBean(new MyServlet(), "/lx/*");// ServletName默认值为首字母小写，即myServlet
        }
    	
        public static void main( String[] args ) {
        	SpringApplication.run(App.class, args);
        }
    }

默认springboot中的DispatcherServlet 会拦截所有请求（/）。如果在浏览器上输入http://XXX/lx/a 这样的请求，会被自定义的servlet执行到，规则是：“匹配的优先级是从精确到模糊，复合条件的Servlet并不会都执行”。

既然系统DispatcherServlet 默认拦截“/”，那么我们是否能做修改呢，答案是肯定的，我们在springboot主类中添加代码：

@Bean
        public ServletRegistrationBean dispatcherRegistration(DispatcherServlet dispatcherServlet) {
            ServletRegistrationBean registration = new ServletRegistrationBean(dispatcherServlet);
            registration.getUrlMappings().clear();
            registration.addUrlMappings("*.do");
            registration.addUrlMappings("*.json");
            return registration;
        }

filter示例（使用注解的方式）：

1）自定义filter：

package cn.edu.nuc.springbootmybatisdruid.servlet;
    
    import java.io.IOException;
    import javax.servlet.Filter;
    import javax.servlet.FilterChain;
    import javax.servlet.FilterConfig;
    import javax.servlet.ServletException;
    import javax.servlet.ServletRequest;
    import javax.servlet.ServletResponse;
    import javax.servlet.annotation.WebFilter;
    import javax.servlet.http.HttpServletRequest;
    
    @WebFilter(filterName="myFilter",urlPatterns="/*")
    public class MyFilter implements Filter {
    
    	@Override
    	public void destroy() {
    		System.out.println("过滤器销毁");
    	}
    	@Override
    	public void init(FilterConfig arg0) throws ServletException {
    		 System.out.println("过滤器初始化");
    	}
    	
    	@Override
    	public void doFilter(ServletRequest request, ServletResponse response,
    			FilterChain chain) throws IOException, ServletException {
    		String uri = ((HttpServletRequest)request).getRequestURI();
    		System.out.println(uri+",执行过滤操作");
            chain.doFilter(request, response);
    	}
    }

2）主类：

@SpringBootApplication
    //mapper 接口类扫描包配置
    @MapperScan("cn.edu.nuc.springbootmybatisdruid.dao.mysql")
    @EnableTransactionManagement
    @ServletComponentScan
    public class App {
    	
        public static void main( String[] args ) {
        	SpringApplication.run(App.class, args);
        }
    }

或者在主类中加入：

@Bean  
    public FilterRegistrationBean filterRegistrationBean() {  
    	FilterRegistrationBean registrationBean = new FilterRegistrationBean();  
    	registrationBean.setFilter(new MyFilter());  
    	List<String> urlPatterns = new ArrayList<String>();  
    
    	urlPatterns.add("/api/dealer/out/list"); //这个请求会走filter。 比如是/api/product/out/list就不会走filter  
    	urlPatterns.add("/api/dealer/out/scanCheck");  
    	urlPatterns.add("/api/dealer/out/detail");  
    	urlPatterns.add("/api/dealer/out/scanStatus");  
    
    	registrationBean.setUrlPatterns(urlPatterns);  
    	return registrationBean;  
    }

同样，对于自定义listener也是如此。

参考：

https://blog.csdn.net/catoop/article/details/50501686

https://blog.csdn.net/catoop/article/details/50501688