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SpringBoot中使用Servlet，Filter，Listener
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项目最近在替换之前陈旧的框架，改用SpringBoot进行重构，初接触，暂时还没有用到Servlet，Filter，Listener的地方，但在之前回顾Servlet的生命周期时，https://www.cnblogs.com/qq931399960/p/10283952.html，想到SpringBoot如何使用原生Servlet，故简单调查了下。
目前SpringBoot官网GA版本为2.1.2，在官方文档中有对Servlet，Filter，Listener的具体描述
可以通过将Servlet， Filter，Listener注册为Spring Bean或者使用@ServletComponentScan注解扫描Servlet组件
一、注册Spring Bean方式使用Servlet，Filter，Listener
自定义Servlet
package com.demo.webtest.servlet;import java.io.IOException;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class MyServlet extends HttpServlet { @Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
} @Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println("do service");
} @Override
public void destroy() {
System.out.println("destory servlet");
} @Override
public void init() throws ServletException {
System.out.println("init servlet");
}}
自定义Filter
package com.demo.webtest.servlet;import java.io.IOException;import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;public class MyFilter implements Filter { @Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException { System.out.println("do filter");
// 使请求继续执行
chain.doFilter(request, response);
}}
自定义Listener（以ServletRequestListener为例）
package com.demo.webtest.servlet;import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;public class MyRequestListener implements ServletRequestListener { @Override
public void requestDestroyed(ServletRequestEvent sre) {
System.out.println("destory request");
} @Override
public void requestInitialized(ServletRequestEvent sre) {
System.out.println("init request");
}}
将自定义Servlet，Filter，Listener注册为Spring Bean
package com.demo.webtest.servletbean;import javax.servlet.Filter;
import javax.servlet.Servlet;
import javax.servlet.ServletRequestListener;import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.boot.web.servlet.ServletListenerRegistrationBean;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;import com.demo.webtest.servlet.MyFilter;
import com.demo.webtest.servlet.MyRequestListener;
import com.demo.webtest.servlet.MyServlet;@Component
public class ServletBean { @Bean
public ServletRegistrationBean<Servlet> registerServlet() {
ServletRegistrationBean<Servlet> servletRegistrationBean = new ServletRegistrationBean<Servlet>(new MyServlet(),
"/myservlet");
// 设置服务启动时初始化该servlet
servletRegistrationBean.setLoadOnStartup(1);
return servletRegistrationBean;
} @Bean
public FilterRegistrationBean<Filter> registerFilter() {
FilterRegistrationBean<Filter> filter = new FilterRegistrationBean<>();
filter.setFilter(new MyFilter());
filter.addUrlPatterns("/*");
return filter;
} @Bean
public ServletListenerRegistrationBean<ServletRequestListener> registerRequestListener() {
ServletListenerRegistrationBean<ServletRequestListener> servletListenerRegistrationBean = new ServletListenerRegistrationBean<>();
servletListenerRegistrationBean.setListener(new MyRequestListener());
return servletListenerRegistrationBean;
}}
启动服务
MyServlet设置了loadOnStartup，且其值大于等于0，故服务启动初始化MyServlet，调用了其init方法，页面访问http://localhost:8080/myservlet
上面日志省略。。。
2019-01-20 09:29:02.308 WARN 12592 --- [ main] ion$DefaultTemplateResolverConfiguration : Cannot find template location: classpath:/templates/ (please add some templates or check your Thymeleaf configuration)
init servlet
2019-01-20 09:29:02.710 INFO 12592 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
2019-01-20 09:29:02.712 INFO 12592 --- [ main] com.demo.webtest.WebtestApplication : Started WebtestApplication in 3.032 seconds (JVM running for 3.47)
init request
do filter
do service
destory request
1、程序启动，初始化Servlet
2、页面访问Servlet，初始化request
3、过滤器过滤请求
4、执行Servlet业务
5、销毁request
清空日志，再次访问http://localhost:8080/myservlet
init request
do filter
do service
destory request
1、初始化request
2、过滤器过滤请求
3、执行Servlet业务
4、销毁request
以上测试时使用的为ServletRequestListener ，LIstener还有其他多种形式，比如HttpSessionListener,HttpSessionBindingListener等，但比较重要的有一个ServletContextListener，在springmvc官网的配置文件中，配置了一个ContextLoaderListener,该Listener实现了ServletContextListener接口，并重写了contextInitialized和contextDestroyed方法，在contextInitialized中初始化了WebApplicationContext，服务器启动后，无论servlet是否配置有loadStartup，也不论该值是什么，contextInitialized始终都在servlet的初始化方法之前执行。每个应用只有一个ServletContext
二、使用注解扫描Servlet组件
删除或注释掉ServletBean类
修改自定义Servlet，Filter，Listener，添加Servlet相关组件注解
自定义Servlet，为与上面区分，将url将映射到/my
package com.demo.webtest.servlet;import java.io.IOException;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 = "/my", loadOnStartup = 0)
public class MyServlet extends HttpServlet {
...
}
自定义Filter
package com.demo.webtest.servlet;import java.io.IOException;import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;@WebFilter(urlPatterns="/*")
public class MyFilter implements Filter {
...
}
自定义Listener
package com.demo.webtest.servlet;import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.annotation.WebListener;@WebListener(value="/*")
public class MyRequestListener implements ServletRequestListener {
...
}
启动类添加Servlet组件扫描
package com.demo.webtest;import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.ServletComponentScan;@SpringBootApplication
@ServletComponentScan
public class WebtestApplication { public static void main(String[] args) {
SpringApplication springApplication = new SpringApplication(WebtestApplication.class);
springApplication.run(args);
}
}
服务启动，也会先进行servlet初始化，页面访问http://localhost:8080/my，日志输出与上述注册Spring Bean方式一致
