Day40-Servlet原理、Mapping问题、ServletContext

Day40-Servlet原理、Mapping问题、ServletContext

Servlet原理

Servlet是由Web服务器调用，web服务器在收到浏览器请求之后

Mapping问题

1. 一个Servlet可以指定一个映射路径

  <servlet-mapping>
    <servlet-name>helloservlet-name>
    <url-pattern>/hellourl-pattern>
  servlet-mapping>

查看

2. 一个Servlet可以指定多个映射路径

  <servlet-mapping>
    <servlet-name>helloxiaozhaoservlet-name>
    <url-pattern>/helloxiaozhaourl-pattern>
  servlet-mapping>
  <servlet-mapping>
    <servlet-name>helloxiaozhaoservlet-name>
    <url-pattern>/helloxiaozhao1url-pattern>
  servlet-mapping>
  <servlet-mapping>
    <servlet-name>helloxiaozhaoservlet-name>
    <url-pattern>/helloxiaozhao2url-pattern>
  servlet-mapping>
  <servlet-mapping>
    <servlet-name>helloxiaozhaoservlet-name>
    <url-pattern>/helloxiaozhao3url-pattern>
  servlet-mapping>
  <servlet-mapping>
    <servlet-name>helloxiaozhaoservlet-name>
    <url-pattern>/helloxiaozhao4url-pattern>
  servlet-mapping>
  <servlet-mapping>
    <servlet-name>helloxiaozhaoservlet-name>
    <url-pattern>/helloxiaozhao5url-pattern>
  servlet-mapping>

查看

3. 一个Servlet可以指定通用映射路径

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

查看

4. 指定一些后缀或者前缀等等…

  
  <servlet-mapping>
    <servlet-name>helloxiaozhaoservlet-name>
    <url-pattern>*.xzurl-pattern>
  servlet-mapping>

查看

5. 优先级问题

  
  <servlet>
    <servlet-name>helloxiaozhaoservlet-name>
    <servlet-class>com.xz.servlet.HelloServletservlet-class>
  servlet>
  
  <servlet-mapping>
    <servlet-name>helloxiaozhaoservlet-name>
    <url-pattern>/helloxiaozhaourl-pattern>
  servlet-mapping>
  
  <servlet>
    <servlet-name>errorservlet-name>
    <servlet-class>com.xz.servlet.ErrorServletservlet-class>
  servlet>
  <servlet-mapping>
    <servlet-name>errorservlet-name>
    <url-pattern>/*url-pattern>
  servlet-mapping>

指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

查看

默认处理请求（自定义404）

ServletContext

web容器在启动的时候，它会为每个web程序都创建一个对应的ServletContext对象，它代表了当前的web应用。

共享数据

我在这个Servlet中保存的数据，可以在另一个servlet中拿到

package com.xz.servlet;

import javax.servlet.ServletContext;
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;

/**
 * @author 小龚
 * @create 2022-08-30 18:11
 */
public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //this.getInitParameter()初始化参数
        //this.getServletConfig()Servlet配置
        //this.getServletContext()Servlet上下文
        ServletContext context = this.getServletContext();

        String username = "小赵";//数据
        context.setAttribute("username",username);//将一个数据保存在了ServletContext中，名字为username，值为username（object）
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        PrintWriter out = resp.getWriter();
        out.print("已存放用户名");
    }

​ 获取数据的Servlet

package com.xz.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * @author 小龚
 * @create 2022-08-30 22:11
 */
public class GetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String username = (String) context.getAttribute("username");//需要强转

        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        resp.getWriter().print("用户名："+username);
    }

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

查看

• 未拿到数据

• 存放数据

• 再次运行

获取初始化参数

ServletDemo03

package com.xz.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * @author 小龚
 * @create 2022-08-30 22:50
 */
public class ServletDemo03 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String url = context.getInitParameter("url");
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");
        resp.getWriter().print(url);
    }

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

web.xml配置

    <context-param>
        <param-name>urlparam-name>
        <param-value>jdbc:mysql//localhost:3306/mybatisparam-value>
    context-param>
    <servlet>
        <servlet-name>gpservlet-name>
        <servlet-class>com.xz.servlet.ServletDemo03servlet-class>
    servlet>
    <servlet-mapping>
        <servlet-name>gpservlet-name>
        <url-pattern>/gpurl-pattern>
    servlet-mapping>

测试

请求转发

ServletDemo04

package com.xz.servlet;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
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;

/**
 * @author 小龚
 * @create 2022-08-30 23:18
 */
public class ServletDemo04 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        //请求转发
        //RequestDispatcher rc = context.getRequestDispatcher("/gp");//转发的请求路径
        //rc.forward(req,resp);//调用forward方法实现请求转发
        //以上两句合并成一句
        context.getRequestDispatcher("/gp").forward(req,resp);

    }

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

web.xml

    <servlet>
        <servlet-name>sd4servlet-name>
        <servlet-class>com.xz.servlet.ServletDemo04servlet-class>
    servlet>
    <servlet-mapping>
        <servlet-name>sd4servlet-name>
        <url-pattern>/sd4url-pattern>
    servlet-mapping>

测试

路径没有变化

读取资源文件

Properties类

• 在java目录下新建properties（需要在注意资源导出失败问题）
• 在resources目录下新建properties

发现：都被打包到了同一个路径下：classes，我们俗称这个路径为classPath

读取配置文件

ServletDemo05

package com.xz.servlet;

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.InputStream;
import java.util.Properties;

/**
 * @author 小龚
 * @create 2022-08-30 23:55
 */
public class ServletDemo05 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
        Properties pp= new Properties();
        pp.load(is);
        String username = pp.getProperty("username");
        String password = pp.getProperty("password");
        resp.setContentType("text/html");
        resp.getWriter().print(username+";"+password);
    }

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

db.properties

username=root
password=123456

web.xml

    <servlet>
        <servlet-name>sd5servlet-name>
        <servlet-class>com.xz.servlet.ServletDemo05servlet-class>
    servlet>
    <servlet-mapping>
        <servlet-name>sd5servlet-name>
        <url-pattern>/sd5url-pattern>
    servlet-mapping>

测试