JavaServlet原理

servlet原理

servlet是由web服务器调用

1.1Mapping问题#

一个servlet可以指定一个映射路径

  <!--  一个servlet对应一个Mapping:映射-->
  <servlet-mapping>
    <servlet-name>helloServlet</servlet-name>
    <!--    请求路径-->
    <url-pattern>/hello</url-pattern>
  </servlet-mapping>

一个servlet可以指定多个映射路径

  <servlet-mapping>
    <servlet-name>helloServlet</servlet-name>
    <url-pattern>/hello</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>helloServlet</servlet-name>
    <url-pattern>/hello2</url-pattern>
  </servlet-mapping>

一个servlet可以指定通用映射路径

  <servlet-mapping>
    <servlet-name>helloServlet</servlet-name>
    <url-pattern>/hello/*</url-pattern>
  </servlet-mapping>

注意下面这样重启服务就不会默认进入到index.jsp页面了(不推荐使用)

  <servlet-mapping>
    <servlet-name>helloServlet</servlet-name>
    <url-pattern>/*</url-pattern>
  </servlet-mapping>

指定一些后缀或者前缀等等

  <!--  可以自定义后缀实现请求映射
  注意点：*前民不能加项目映射的路径    /hello/*.do   是不可以的
  但是/hello/hi.do是可以的
  -->  
  <servlet-mapping>
    <servlet-name>helloServlet</servlet-name>
    <url-pattern>*.do</url-pattern>
  </servlet-mapping>

优先级问题

制定了固有的映射路径优先级最高，如果找不到就会走默认的处理请求

  <servlet>
    <servlet-name>helloServlet</servlet-name>
    <servlet-class>com.zyy.servlet.HelloServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>helloServlet</servlet-name>
    <url-pattern>/hello/hi.do</url-pattern>
  </servlet-mapping>
  <!--  404-->
  <servlet>
    <servlet-name>errorServlet</servlet-name>
    <servlet-class>com.zyy.servlet.ErrorServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>errorServlet</servlet-name>
    <url-pattern>/*</url-pattern>
  </servlet-mapping>

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.io.PrintWriter;

public class HelloServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        response.setCharacterEncoding("utf-8");
        PrintWriter out = response.getWriter();
        out.println("<html>");
        out.println("<head>");
        out.println("<title>Hello World!</title>");
        out.println("</head>");
        out.println("<body>");
        out.println("<h1>你好！</h1>");
        out.println("</body>");
        out.println("</html>");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}