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。