内嵌tomcat最简单用法

maven项目引入内嵌tomcat依赖

<dependency>
    <groupId>org.apache.tomcat.embed</groupId>
    <artifactId>tomcat-embed-core</artifactId>
    <version>8.5.37</version>
</dependency>

编写如下main方法

 package com;

 import org.apache.catalina.Context;
 import org.apache.catalina.LifecycleException;
 import org.apache.catalina.startup.Tomcat;
 import org.apache.tomcat.util.descriptor.web.FilterDef;
 import org.apache.tomcat.util.descriptor.web.FilterMap;
 import org.springframework.web.filter.OncePerRequestFilter;

 import javax.servlet.Filter;
 import javax.servlet.FilterChain;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import java.io.IOException;
 import java.nio.charset.Charset;

 /**
  * @author allen
  * @date 2019-01-22 13:20
  */
 public class TomcatWebServer {
     public static void main(String[] args) {
         Tomcat tomcat = new Tomcat();
         HttpServlet httpServlet = new HttpServlet() {
             @Override
             protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
                 resp.getWriter().write("hello, i'm embed tomcat");
             }

             @Override
             protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException {
                 doGet(req, resp);
             }
         };
         tomcat.setHostname("localhost");
         tomcat.setPort(8080);
         final Context context = tomcat.addContext("/embed-tomcat", null);
         Tomcat.addServlet(context, "dispatch", httpServlet);
         context.addServletMappingDecoded("/dispatch", "dispatch");
         Filter filter = new OncePerRequestFilter() {
             @Override
             protected void doFilterInternal(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, FilterChain filterChain) throws ServletException, IOException {
                 System.out.println("filter do something");
                 filterChain.doFilter(httpServletRequest, httpServletResponse);
             }
         };
         FilterDef filterDef = new FilterDef();
         filterDef.setFilter(filter);
         filterDef.setFilterName("myFilter");
         filterDef.addInitParameter("userName", "Allen");

         FilterMap filterMap = new FilterMap();
         filterMap.addURLPatternDecoded("/*");
         filterMap.addServletName("*");
         filterMap.setFilterName("myFilter");
         filterMap.setCharset(Charset.forName("UTF-8"));

         context.addFilterDef(filterDef);
         context.addFilterMap(filterMap);
         try {
             tomcat.init();
             tomcat.start();
             tomcat.getServer().await();
         } catch (LifecycleException e) {
             e.printStackTrace();
         }
     }
 }

注意其中OncePerRequestFilter是spring提供的对filter接口的实现类，没有引入spring依赖的可自行改用其他实现类。

运行main方法，一个最简单的tomcat实例已经运行起来。浏览器打开http://localhost:8080/embed-tomcat/dispatch，页面可以看到输出内容，控制台也打印了过滤器执行的内容。

springboot默认就是使用tomcat作为内嵌容器的，基本原理通上述代码，只不过spring做了更深层次的封装，结合其ioc容器，可以实现只要往ioc容器中注入servlet、filter接口的实现类，spring的适配器可自动完成配置。