springboot servlet、filter、listener开发

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

springboot servlet、filter、listener开发

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