1. ServletContext对象的获取
获取:
1. 通过request对象获取
request.getServletContext();
2. 通过HttpServlet获取
this.getServletContext();
package com.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("/servletContextDemo1")
public class ServletContextDemo1 extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1.通过request对象获取
ServletContext context1 = request.getServletContext();
//2.通过HttpServlet获取
ServletContext context2 = this.getServletContext();
System.out.println(context1);//org.apache.catalina.core.ApplicationContextFacade@1f01a450 System.out.println(context2);//org.apache.catalina.core.ApplicationContextFacade@1f01a450
System.out.println(context1==context2);//true
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
}
2. ServletContext对象的功能
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的扩展名是html或htm,
image/jpeg的扩展名是jpg
*获取:String getMimeType(String file)
代码1:
package com.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("/servletContextDemo2")
public class ServletContextDemo2 extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//(1)获取ServletContext对象:通过HttpServlet
ServletContext context = this.getServletContext();
//(2)定义文件名称
String filename="a.jpg";
//(3)获取MIME类型
String mimeType=context.getMimeType(filename);
System.out.println(mimeType);//image/jpeg 的扩展名是jpg
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
}
功能2. 域对象:共享数据
1.setAttribute(String name,Object value)
2.getAttribute(String name)
3.removeAttribute(String name)
代码2:servletContextDemo3和servletContextDemo4共享
package com.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("/servletContextDemo3")
public class ServletContextDemo3 extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//(1)通过HttpServlet获取ServletContext对象
ServletContext context = this.getServletContext();
//设置数据
context.setAttribute("msg","haha");
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
}
package com.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;
/**
* 与ServletContextDemo3共享数据
* */
@WebServlet("/servletContextDemo4")
public class ServletContextDemo4 extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
ServletContext context = this.getServletContext();
//获取共享数据
Object msg=context.getAttribute("msg");
System.out.println(msg);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
}
功能3.获取文件的真实(服务器)路径:
方法:String getRealPath(String path)
(1)String b = context.getRealPath("/b.txt");//web目录下资源访问System.out.println(b);
(2)String c = context.getRealPath("/WEB-INF/c.txt");//WEB-INF目录下的资源访问
System.out.println(c);
(3)String a = context.getRealPath("/WEB-INF/classes/a.txt");//src目录下的资源访问
System.out.println(a);
代码3:
package com.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.File;
import java.io.IOException;
@WebServlet("/servletContextDemo5")
public class ServletContextDemo5 extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//通过HttpServlet获取
ServletContext context = this.getServletContext();
//获取文件的服务器路径
String b= context.getRealPath("/b.txt");//web目录下资源访问
System.out.println(b);
//File file = new File(realPath);
String c = context.getRealPath("/WEB-INF/c.txt");//WEB-INF目录下的资源访问
System.out.println(c);
String a = context.getRealPath("/WEB-INF/classes/a.txt");//src目录下的资源访问
System.out.println(a);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
}
/**
* 结果:E:\JAVA\JAVA1\IDEA程序\Servlet\out\artifacts\Servlet_war_exploded\b.txt
* E:\JAVA\JAVA1\IDEA程序\Servlet\out\artifacts\Servlet_war_exploded\WEB-INF\c.txt
* E:\JAVA\JAVA1\IDEA程序\Servlet\out\artifacts\Servlet_war_exploded\WEB-INF\classes\a.txt
* */
3. 案例
1.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
2.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
3.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
- 获取文件名称
- 使用字节输入流加载文件进内存
- 指定response的响应头: content-disposition:attachment;filename=xxx
- 将数据写出到response输出流
4.问题:
中文文件问题
解决思路:(1). 获取客户端使用的浏览器版本信息
(2). 根据不同的版本信息,设置filename的编码方式不同
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<a href="/day15/img/1.jpg">图片1</a>
<a href="/day15/img/1.avi">视频</a>
<hr>
<a href="/day15/DownloadServlet?filename=九尾.jpg">图片1</a>
<a href="/day15/DownloadServlet?filename=1.avi">视频</a>
</body>
</html>
package com.download;
import com.utils.DownLoadUtils;
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("/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 = this.getServletContext();
String realPath = servletContext.getRealPath("/img/" + filename);
//2.2用字节流关联
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);
//解决中文文件名问题
//1.获取user-agent请求头、
String agent = request.getHeader("user-agent");
//2.使用工具类方法编码文件名即可
filename = DownLoadUtils.getFileName(agent, filename);
//3.2设置响应头打开方式:content-disposition
response.setHeader("content-disposition","attachment;filename="+filename);
//4.将输入流的数据写出到输出流中
ServletOutputStream sos = response.getOutputStream();
byte[] buff = new byte[1024 * 8];
int len = 0;
while((len = fis.read(buff)) != -1){
sos.write(buff,0,len);
}
fis.close();
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
}
重要的DownLoadUtils包:各种浏览器
package com.utils;
import java.util.Base64;
import java.util.Base64.*;
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
Encoder base64Encoder = Base64.getEncoder();
filename = "=?utf-8?B?" + base64Encoder.encode(filename.getBytes("utf-8")) + "?=";
} else {
// 其它浏览器
filename = URLEncoder.encode(filename, "utf-8");
}
return filename;
}
}
结果展示: