11 Reponse对象+ServletContext对象
1.HTTP协议:
(1)请求消息:客户端发送给服务器端的数据
数据格式:
1. 请求行
2. 请求头
3. 请求空行
4. 请求体
(2)响应消息:服务器端发送给客户端的数据
* 数据格式:
1. 响应行
1. 组成:协议/版本 响应状态码 状态码描述
2. 响应状态码:服务器告诉客户端浏览器本次请求和响应的一个状态。
1. 状态码都是3位数字
2. 分类:
<1> 1xx:服务器就收客户端消息,但没有接受完成,等待一段时间后,发送1xx多状态码
<2> 2xx:成功。代表:200
<3> 3xx:重定向。代表:302(重定向),304(访问缓存)
<4> 4xx:客户端错误。
* 代表:
* 404(请求路径没有对应的资源)
* 405:请求方式没有对应的doXxx方法
<5> 5xx:服务器端错误。代表:500(服务器内部出现异常)
2. 响应头:
1. 格式:头名称: 值
2. 常见的响应头:
1. Content-Type:服务器告诉客户端本次响应体数据格式以及编码格式
2. Content-disposition:服务器告诉客户端以什么格式打开响应体数据
* 值:
* in-line:默认值,在当前页面内打开
* attachment;filename=xxx:以附件形式打开响应体。文件下载
3. 响应空行
4. 响应体:传输的数据
2.Response对象
功能:设置响应消息
注意:以下均是HttpServletResponse的成员方法。
(1)设置响应行
1. 格式:HTTP/1.1 200 ok
2. 设置状态码:setStatus(int sc)
(2) 设置响应头:setHeader(String name, String value)
(3)设置响应体:
使用步骤:
1. 获取输出流
* 字符输出流:PrintWriter getWriter()
* 字节输出流:ServletOutputStream getOutputStream()
2. 使用输出流,将数据输出到客户端浏览器
案例一:重定向
重定向过程:
(1)客户浏览器发送http请求
(2)web服务器接受后发送302状态码响应及对应新的location给客户浏览器
(3)客户浏览器发现是302响应,则自动再发送一个新的http请求,请求url是新的location地址。服务器根据此请求寻找资源并发送给客户。在这里location可以重定向到任意URL,既然是浏览器重新发出了请求,则就没有什么request传递的概念了。在客户浏览器路径栏显示的是其重定向的路径,客户可以观察到地址的变化的。重定向行为是浏览器做了至少两次的访问请求的。
ResponseTest01Servlet.java
package response; import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException; @WebServlet(name = "ResponseTest01Servlet",urlPatterns = "/responseTest01Servlet")
public class ResponseTest01Servlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("ResponseTest01Servlet被访问了");
//重定向
//方法一
/*//1.访问/responseTest01Servlet,会自动跳转到/responseTest02Servlet
response.setStatus(302);
//2.设置相应头location
response.setHeader("location","/day3/responseTest02Servlet");*/ //方法二
response.sendRedirect("/day3/responseTest02Servlet"); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
}
ResponseTest02Servlet.java
package response; import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException; @WebServlet(name = "ResponseTest02Servlet",urlPatterns = "/responseTest02Servlet")
public class ResponseTest02Servlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("ResponseTest02Servlet被访问了");
} protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
}
控制台输出:
重定向的特点:redirect
1. 地址栏发生变化
2. 重定向可以访问其他站点(服务器)的资源
3. 重定向是两次请求。不能使用request对象来共享数据
转发的特点:forward
1. 转发地址栏路径不变
2. 转发只能访问当前服务器下的资源
3. 转发是一次请求,可以使用request对象来共享数据
路径写法:
1. 路径分类
1. 相对路径:通过相对路径不可以确定唯一资源
如:./index.html
不以/开头,以.开头路径
规则:找到当前资源和目标资源之间的相对位置关系
./:当前目录(注意:当前目录是文件的父文件夹)
../:后退一级目录
2. 绝对路径:通过绝对路径可以确定唯一资源
如:http://localhost/day15/responseDemo2 或/day15/responseDemo2
以/开头的路径
规则:判断定义的路径是给谁用的?判断请求将来从哪儿发出
给客户端浏览器使用:需要加虚拟目录(项目的访问路径)
建议虚拟目录动态获取:request.getContextPath()
* <a> , <form> 重定向...
* 给服务器使用:不需要加虚拟目录
* 转发路径
案例二:服务器输出字符数据到浏览器
步骤:
1. 获取字符输出流
2. 输出数据
* 注意:
* 乱码问题:
1. PrintWriter pw = response.getWriter();获取的流的默认编码是ISO-8859-1
2. 设置该流的默认编码
3. 告诉浏览器响应体使用的编码
//简单的形式,设置编码,是在获取流之前设置
response.setContentType("text/html;charset=utf-8");
3. 服务器输出字节数据到浏览器
* 步骤:
1. 获取字节输出流
2. 输出数据
字符流:
package response; import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter; @WebServlet(name = "ResponseTest03Servlet",urlPatterns = "/responseTest03Servlet")
public class ResponseTest03Servlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");
//获取字符输出流
PrintWriter pw = response.getWriter();
pw.write("你好,hello response"); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
}
字节流:
package response; import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException; @WebServlet(name = "ResponseTest04Servlet",urlPatterns = "/responseTest04Servlet")
public class ResponseTest04Servlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");
//1.获取字节输出流
ServletOutputStream sos = response.getOutputStream();
//2.输出数据
sos.write("你好".getBytes("utf-8"));
} protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
}
案例三:验证码
1. 本质:图片
2. 目的:防止恶意表单注册
package response; import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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; @WebServlet(name = "CheckCodeServlet",urlPatterns = "/checkCodeServlet")
public class CheckCodeServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
int width=100;
int height=50;
//1.创建对象,验证码图片对象
BufferedImage image=new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB); //2.美化图片
//2.美化图片
//2.1 填充背景色
Graphics g = image.getGraphics();//画笔对象
g.setColor(Color.PINK);//设置画笔颜色
g.fillRect(0,0,width,height); //2.2画边框
g.setColor(Color.BLUE);
g.drawRect(0,0,width - 1,height - 1); String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghigklmnopqrstuvwxyz0123456789";
//生成随机角标
Random ran = new Random(); for (int i = 1; i <= 4; i++) {
int index = ran.nextInt(str.length());
//获取字符
char ch = str.charAt(index);//随机字符
//2.3写验证码
g.drawString(ch+"",width/5*i,height/2);
} //2.4画干扰线
g.setColor(Color.GREEN); //随机生成坐标点 for (int i = 0; i < 10; i++) {
int x1 = ran.nextInt(width);
int x2 = ran.nextInt(width); int y1 = ran.nextInt(height);
int y2 = ran.nextInt(height);
g.drawLine(x1,y1,x2,y2);
} //3.将图片输出到页面展示
ImageIO.write(image,"jpg",response.getOutputStream());
} protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
}
checkcode.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>验证码</title>
<script>
window.onload=function () {
//1.获取图片对象
var img = document.getElementById("code");
//2.绑定点击事件
img.onclick=function () {
var date=new Date().getTime();
img.src="/day3/checkCodeServlet?"+date;
} }
</script>
</head>
<body>
<img src="/day3/checkCodeServlet" id="code">
<a href="" id="change">看不清换一张</a>
</body>
</html>
效果图:
3.ServletContext对象:
(1)概念:代表整个web应用,可以和程序的容器(服务器)来通信
(2) 获取:
1. 通过request对象获取
request.getServletContext();
2. 通过HttpServlet获取
this.getServletContext();
(3)功能:
1. 获取MIME类型:
* MIME类型:在互联网通信过程中定义的一种文件数据类型
* 格式: 大类型/小类型 text/html image/jpeg
* 获取:String getMimeType(String file)
package servletContext; import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException; @WebServlet(name = "ContextTest01Servlet",urlPatterns = "/contextTest01Servlet")
public class ContextTest01Servlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1.获取servletContext
ServletContext servletContext = request.getServletContext();
//2.定义文件名称
String filename="a.jpg";
String mimeType = servletContext.getMimeType(filename);
System.out.println(mimeType); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
}
2. 域对象:共享数据
1. setAttribute(String name,Object value)
2. getAttribute(String name)
3. removeAttribute(String name)
* ServletContext对象范围:所有用户所有请求的数据。注意:ServletContext对象可能存在数据安全和内存溢出。
案例:
ContextTest02Servlet.java
package servletContext; import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException; @WebServlet(name = "ContextTest02Servlet",urlPatterns = "/contextTest02Servlet")
public class ContextTest02Servlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1.获取servletContext
ServletContext servletContext = request.getServletContext();
servletContext.setAttribute("msg","hello lucky"); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
}
ContextTest03Servlet.java
package servletContext; import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException; @WebServlet(name = "ContextTest03Servlet",urlPatterns = "/contextTest03Servlet")
public class ContextTest03Servlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1.获取servletContext
ServletContext servletContext = request.getServletContext(); Object msg = servletContext.getAttribute("msg");
System.out.println(msg); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
}
3. 获取文件的真实(服务器)路径
1. 方法:String getRealPath(String path)
package servletContext; import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException; @WebServlet(name = "ContextTest04Servlet",urlPatterns = "/contextTest04Servlet")
public class ContextTest04Servlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1.获取servletContext
ServletContext servletContext = request.getServletContext(); String realPath = servletContext.getRealPath("/linda.txt");
System.out.println(realPath); String haha = servletContext.getRealPath("/haha.html");
System.out.println(haha); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
}
4.综合应用案例
文件下载需求:
(1) 页面显示超链接
(2)点击超链接后弹出下载提示框
(3) 完成图片文件下载
分析:
(1)超链接指向的资源如果能够被浏览器解析,则在浏览器中展示,如果不能解析,则弹出下载提示框。不满足需求
(2)任何资源都必须弹出下载提示框
(3)使用响应头设置资源的打开方式:
content-disposition:attachment;filename=xxx
步骤:
(1) 定义页面,编辑超链接href属性,指向Servlet,传递资源名称filename
(2)定义Servlet
1. 获取文件名称
2. 使用字节输入流加载文件进内存
3. 指定response的响应头: content-disposition:attachment;filename=xxx
4. 将数据写出到response输出流
DownloadServlet.java
package download; import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException; @WebServlet(name = "DownloadServlet",urlPatterns = "/downloadServlet")
public class DownloadServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1.获取请求参数,文件名称
String filename = request.getParameter("filename");
//2.使用字节输入流加载文件进内存
//2.1 找到文件服务器路径
ServletContext servletContext = request.getServletContext();
String realPath = servletContext.getRealPath("/img/" + filename);
//2.2 用字节输入流关联
FileInputStream fis=new FileInputStream(realPath); //3.设置response的响应头
//3.1设置响应头类型,content-type
String mimeType = servletContext.getMimeType(filename); //获取文件的mime类型
response.setHeader("content-type",mimeType); //解决中文名称乱码问题
//1.获取user-agent请求头
String agent = request.getHeader("user-agent");
//2.使用工具类编码文件名
String fileName = DownLoadUtils.getFileName(agent, filename); //3.2设置响应头的打开方式,以下载提示框的方式
response.setHeader("content-disposition","attachment;filename="+fileName); //4.将输入流的数据写到输出流
ServletOutputStream sos = response.getOutputStream();
byte[] buffer=new byte[1024*8];
int len=0;
while ((len=fis.read(buffer))!=-1){
sos.write(buffer,0,len);
}
fis.close();//关闭输入流 } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
}
download.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>文件下载</title>
</head>
<body>
<a href="/day3/downloadServlet?filename=2.jpg">图片1</a>
<a href="/day3/downloadServlet?filename=九尾.jpg">图片九尾</a>
<a href="/day3/downloadServlet?filename=1.avi">视频1</a>
</body>
</html>
效果图:
* 问题:
* 中文文件问题
* 解决思路:利用工具类 DownLoadUtils
package download; import sun.misc.BASE64Encoder;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder; public class DownLoadUtils { public static String getFileName(String agent, String filename) throws UnsupportedEncodingException {
if (agent.contains("MSIE")) {
// IE浏览器
filename = URLEncoder.encode(filename, "utf-8");
filename = filename.replace("+", " ");
} else if (agent.contains("Firefox")) {
// 火狐浏览器
BASE64Encoder base64Encoder = new BASE64Encoder();
filename = "=?utf-8?B?" + base64Encoder.encode(filename.getBytes("utf-8")) + "?=";
} else {
// 其它浏览器
filename = URLEncoder.encode(filename, "utf-8");
}
return filename;
}
}
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