springboot直接main方法就可以启动一个项目原因就其中内置了tomcat
原理：
new一个Tomcat对象
Tomcat tomcat = new Tomcat();
然后设置端口，名称，目录等
接着将我们的service服务映射为路径
Wrapper wrapper = tomcat.addServlet("/", "DemoServlet", new DemoServlet());
wrapper.addMapping("/helloworld");
手写嵌入式Tomcat
代码如下
加入依赖
<dependency>
<groupId>org.apache.tomcat.maven</groupId>
<artifactId>tomcat7-maven-plugin</artifactId>
<version>2.2</version>
</dependency>
两个类：
一个是配置tomcat类
一个自己项目的servlet类
public class EmbeddedTomcatServer {
public static void main(String[] args) throws Exception{
//把目录的绝对的路径获取到
String classpath = System.getProperty("user.dir");
System.out.println(classpath);
//D:\workspace-tomcat\tomcat-maven
//我们new一个Tomcat
Tomcat tomcat = new Tomcat();
//插件是6或者6以前的
//Embbedded
//设置Tomcat的端口
//tomcat.setPort(9090);
Connector connector = tomcat.getConnector();
connector.setPort(9091);
//设置Host
Host host = tomcat.getHost();
//我们会根据xml配置文件来
host.setName("localhost");
host.setAppBase("webapps");
//前面的那个步骤只是把Tomcat起起来了，但是没啥东西
//要把class加载进来,把启动的工程加入进来了
Context context =tomcat.addContext(host, "/", classpath);
if(context instanceof StandardContext){
StandardContext standardContext = (StandardContext)context;
standardContext.setDefaultContextXml("D:/tools/apache-tomcat-8.0.52/conf/web.xml");
// standardContext.setDefaultContextXml("E:/tomcat/tomcat8.5/conf/web.xml");
//我们要把Servlet设置进去
Wrapper wrapper = tomcat.addServlet("/", "DemoServlet", new DemoServlet());
wrapper.addMapping("/helloworld");
}
//Tomcat跑起来
tomcat.start();
//强制Tomcat server等待，避免main线程执行结束后关闭
tomcat.getServer().await();
}
}
servlet类
public class DemoServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
@Override
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws IOException, ServletException
{
response.setContentType("text/html");
response.setCharacterEncoding("UTF-8");
PrintWriter out = response.getWriter();
out.println("<!DOCTYPE html><html>");
out.println("<head>");
out.println("<meta charset=\"UTF-8\" />");
out.println("<title></title>");
out.println("</head>");
out.println("<body bgcolor=\"white\">");
out.println("<h1>嵌入式tomcat!</h1>");
out.println("</body>");
out.println("</html>");
}
}
然后输入地址http://localhost:9091/helloworld
