javaweb-210329-01

javaweb - 210229 - 01

• 浏览器响应状态码
• Servlet原理
• Mapping问题
• ServletContext
• HttpServletResponse
• HttpServletRequest

浏览器响应状态码

200：请求响应成功
3xx:请求重定向
4xx：找不到资源（404）
5xx：服务器代码错误（500）	网关错误（502）

Servlet原理

Mapping问题

1.1 一个Servlet可以指定一个映射路径

1.2 一个Servlet可以指定多个路径

1.3 一个Servlet可以指定通用映射路径

1.4 默认请求路径

1.5 指定一些后缀或者前缀

自定义后缀实现映射，，，，注意：  *前面不能加项目的路径

注意：下面是错的：

---

ServletContext

ServletContext官方叫servlet上下文。服务器会为每一个工程创建一个对象，这个对象就是ServletContext对象。这个对象全局唯一，而且工程内部的所有servlet都共享这个对象。所以叫全局应用程序共享对象。web容器在启动的时候，它会为每一个web程序都创建一个对应的ServletContext对象，它代表了当前的web应用

域对象介绍
     域对象是服务器在内存上创建的存储空间，用于在不同动态资源（servlet）之间传递与共享数据。

1.  是一个域对象
2.  可以读取全局配置参数
3.  可以搜索当前工程目录下面的资源文件
4.  可以获取当前工程名字（了解）  

---

1.1 获取共享参数

TestServlet0201.java

package com.bgy.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;

public class TestServlet0201 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        context.setAttribute("userName","白光一");

        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");


        System.out.println("hello bgy,hahahaha");
    }

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

TestServlet0202.java

package com.bgy.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;

public class TestServlet0202 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");

        ServletContext context = this.getServletContext();
        String userName = (String) context.getAttribute("userName");
        resp.getWriter().print("名字："+userName);
    }

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

---

2.2获取初始化参数

配置初始化参数

---

TestServlet03.java

package com.bgy.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;

public class TestServlet03 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String url = context.getInitParameter("url");
        String user = context.getInitParameter("user");
        String password = context.getInitParameter("password");

        resp.getWriter().println(url+"\n"+user+"\n"+password);
    }

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

---

3.3 请求转发

TestServlet04.java

package com.bgy.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;

public class TestServlet04 extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            ServletContext context = this.getServletContext();
            // 转发的请求路径
            RequestDispatcher requestDispatcher = context.getRequestDispatcher("/test03");
            requestDispatcher.forward(req,resp);
        }

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

请求转发的方法：

你看，请求转发的url：http://localhost:8080/test/test04****

没有发生变化，，，但是访问到test03的内容

---

4.4 读取资源文件

test05.properties

url=jdbc:mysql://localhost:3306/test
user=root
password=admin

TestServlet05.java

package com.bgy.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;

public class TestServlet05 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
        InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/test05.properties");
        
        Properties prop = new Properties();
        prop.load(is);
        
        String url = prop.getProperty("url");
        String user = prop.getProperty("user");
        String password = prop.getProperty("password");

        resp.getWriter().print(url+"\n"+user+"\n"+password);
    }

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

生成的 test05.properties 的资源文件 在 WEB-INF/classes/test05.properties

---

HttpServletResponse

web服务器接收到客户端的http请求，针对这个请求，分别创建一个代表请求的HttpServletRequest对象，
代表响应的一个HttpServletResponse

获取客户端请求过来的参数：	HttpServletRequest
给客户端响应一些信息：		 HttpServletResponse

Web服务器收到一个http请求，会针对每个请求创建一个HttpServletRequest和HttpServletResponse对象，
向客户端发送数据找HttpServletResponse,
从客户端取数据找HttpServletRequest

---

HttpServletResponse继承了ServletResponse接口，并提供了与Http协议有关的方法，这些方法的主要功能是设置HTTP状态码和管理Cookie。HttpServletResponse对象代表服务器的响应。这个对象中封装了向客户端发送数据、发送响应头，发送响应状态码的方法
HttpServletResponse对象可以向客户端发送三种类型的数据:
a.响应头(Response headers)
b.状态码(Protocol—Status code—Description)
c.实体数据(Entity body )

负责向浏览器发送数据的方法（ServletResponse接口中的方法）
	ServletOutputStream getOutputStream() throws IOException;
    PrintWriter getWriter() throws IOException;

负责向浏览器发送响应头的方法
	void setCharacterEncoding(String var1);
    void setContentLength(int var1);
    void setContentLengthLong(long var1);
    void setContentType(String var1);
    void setBufferSize(int var1);

状态码：

HttpServletResponse常见应用

1.1向浏览器输出消息

2.2下载文件

package com.bgy.servlet;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.URLEncoder;
public class TestServlet06 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        // 1.获取下载文件的路径
        String realPath = this.getServletContext().getRealPath("WEB-INF/classes/test06.png");
        System.out.println("下载文件路径为："+realPath);
        // 2.下载文件名
        String fileName = realPath.substring(realPath.lastIndexOf("\\")+1);
        // 3.设置让浏览器能够支持下载我们需要的文件,,,设置编码，防止文件中文乱码
        resp.setHeader("Content-Disposition","attachment;filename="+URLEncoder.encode(fileName,"UTF-8"));
        // 4.获取下载文件的输入流
        FileInputStream in = new FileInputStream(realPath);
        // 5.创建缓冲区
        int len = 0;
        byte[] buffer = new byte[1024];
        // 6.获取OutputStream
        ServletOutputStream out = resp.getOutputStream();
        // 7.将FileOutputStream流写入到buffer缓冲区,使用OutputStream将缓冲区中的数据输入到客户端
        while ((len=in.read(buffer))>0){
            out.write(buffer,0,len);
        }

        in.close();;
        out.close();
    }

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

---

3.3验证码功能

package com.bgy.servlet;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

public class TestServlet07 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        // 让页面3秒刷新一次
//        resp.setHeader("refresh", "3");

        // 在内存中创建一个图片
        BufferedImage image = new BufferedImage(100,35,BufferedImage.TYPE_INT_RGB);
        // 得到图片
        Graphics2D g = (Graphics2D) image.getGraphics();  // 这是一只笔
        // 设置图片的背景颜色
        g.setColor(Color.white);
        g.fillRect(0,0,100,35);
        // 给图片写数据
        g.setColor(Color.BLUE);
        g.setFont(new Font(null,Font.BOLD,20));
        g.drawString(makeNumber(),0,35);
        // 告诉浏览器，用图片的形式打开
        resp.setContentType("image/jpg");
        // 网站会有缓存，不让浏览器有缓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");
        // 把图片写到浏览器
        ImageIO.write(image,"jpg",resp.getOutputStream());
    }

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

    // 生成随机数
    private String makeNumber(){
        Random random = new Random();
        String number = random.nextInt(99999999)+"";
        StringBuffer sb = new StringBuffer();
        // 如果生的的随机数不满8位，，后面追加0
        for (int i = 0; i < 8 - number.length(); i++  ) {
            sb.append("0");
        }
        number = sb.toString() + number;
        return number;
    }
}

---

4.4 实现重定向

重定向和转发区别：
	相同点：
		页面会跳转
	不同点：
		请求url不会发生改变
		重定向url会发生改变

package com.bgy.servlet;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class TestServlet08 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.sendRedirect("/test/test07");
    }

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

---

重定向运行前：

重定向运行后：

重定向代码：

转发代码：

---

HttpServletRequest

HttpServletRequest对象代表客户端的请求，当客户端通过HTTP协议访问服务器时，HTTP请求头中的所有信息都封装在这个对象中，通过这个对象提供的方法，可以获得客户端请求的所有信息。


应用：
	1. 获取前端传递的参数
	2. 请求转发

Demo01

TestServlet09.java

package com.bgy.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;

public class TestServlet09 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String loginName = req.getParameter("loginName");
        String loginPwd = req.getParameter("loginPwd");
        context.setAttribute("loginName",loginName);

        System.out.println(loginName);
        System.out.println(loginPwd);

        // 重定向
        resp.sendRedirect("/test/test10");
    }

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

TestServlet10.java

package com.bgy.servlet;

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

public class TestServlet10 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().print("hello,"+this.getServletContext().getAttribute("loginName"));
    }

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

index.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <title>$Title$</title>
  </head>
  <body>
    <h2>hello world</h2>
    <%--${pageContext.request.contextPath}代表当前项目--%>
    <form action="${pageContext.request.contextPath}/test09" method="get">
      <input type="text" name="loginName"/>
      <br/>
      <input type="password" name="loginPwd"/>
      <br/>
      <input type="submit" value="submit"/>
    </form>
  </body>
</html>

---

Demo02

login.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>login</title>
</head>
<body>
    <form action="${pageContext.request.contextPath}/test11" method="post">
        用户名：<input type="text" name="userName"/>
        <br/>
        密码：<input type="password" name="userPwd"/>
        <br/>
        爱好：<br/>
        <input type="checkbox" name="likes" value="音乐"/>音乐
        <br/>
        <input type="checkbox" name="likes" value="电影"/>电影
        <br/>
        <input type="checkbox" name="likes" value="动漫"/>动漫
        <br/>
        <input type="checkbox" name="likes" value="电视剧"/>电视剧
        <br/>
        <input type="submit" value="submit"/>
    </form>
</body>
</html>

TestServlet11.java

package com.bgy.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.util.Arrays;

public class TestServlet11 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("UTF-8");

        String userName = req.getParameter("userName");
        String userPwd = req.getParameter("userPwd");
        String[] likes = req.getParameterValues("likes");

        System.out.println(userName);
        System.out.println(userPwd);
        System.out.println(Arrays.toString(likes));

        // 重定向
        req.getRequestDispatcher("/WEB-INF/jsp/loginSuccess.jsp").forward(req,resp);
        resp.setCharacterEncoding("UTF-8");
    }

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

loginSuccess.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>LoginSuccessPage</title>
</head>
<body>
    <%
        String userName = request.getParameter("userName");
    %>
    <h3>hello,<%=userName%></h3>
</body>
</html>