Cookie+Session+ServletContentext的区别和用法

//总结一下：Cookie和Session都是通过request得到，ServletContext是通过this得到。Cookie通过getValue取值，Session和ServletContext通过getAttribute取值。Cookie通过setMaxAge来清空，Session通过setMaxActiveInterval来清空。

Cookie的创建：Cookie通过new，add,setMaxAge的方式设定值，Session和ServletContext通过setAttribute的方式设定值。

//演示了一个Cookie的创建的案例

package Model;

import javax.servlet.*;

import javax.servlet.http.*;

import java.io.*;

public class CookieTest1 extends HttpServlet{

//处理doGet请求

public void doGet(HttpServletRequest request,HttpServletResponse response)

throws IOException,ServletException{

try{

response.setCharacterEncoding("UTF-8");

response.setContentType("text/html");

PrintWriter pw=response.getWriter();

//当有用户访问该Servlet时，就将信息创建到该用户的Cookie中

//1.现在服务器端创建一个cookie

Cookie myCookie =new Cookie("color1","red");

Cookie name=new Cookie("myname",u);

Cookie pass=new Cookie("mypasswd",p);

//2.设置改cookie存在的时间，如果你不设置存在时间，那么该cookie将不会保存

myCookie.setMaxAge(30);

name.setMaxAge(14*24*3600);

pass.setMaxAge(14*24*3600);

//3.将该cookie写回到客户端

response.addCookie(myCookie);

res.addCookie(name);

res.addCookie(pass);

pw.println("已经创建了cookie");

}catch(Exception e){

e.printStackTrace();

}

}

}

//如何读取cookie案例

package Model;

import javax.servlet.ServletException;

import javax.servlet.http.*;

import java.io.*;

public class CookieTest2 extends HttpServlet{

//处理get请求

public void doGet(HttpServletRequest request,HttpServletResponse response)

throws IOException,ServletException{

try{

response.setContentType("text/html;charset=UTF-8");

PrintWriter pw=response.getWriter();

//从客户端得到所有的cookie信息

Cookie[] allCookie=request.getCookies();

int i=0;

//如果allCookie不为空..

if(allCookie!=null){

//从中取出cookie

for(i=0;i<allCookie.length;i++){

//依次取出

Cookie temp=allCookie[i];

if(temp.getName().equals("color1")){

//得到cookie的值

String val=temp.getValue();

pw.println("color1="+val);

break;

}

if(allCookie.length==i){

pw.println("Cookie已过期！！！");

}

}

}else{

pw.println("不存在color1这个cookie或者已经过期了！！！");

}

}catch(Exception e){

e.printStackTrace();

}

}

}

//如何删除cookie案例

package Model;

import javax.servlet.ServletException;

import javax.servlet.http.*;

import java.io.*;

public class CookieTest3 extends HttpServlet{

//处理get请求

public void doGet(HttpServletRequest request,HttpServletResponse response)

throws IOException,ServletException{

response.setContentType("text/html;charset=UTF-8");

PrintWriter pw=response.getWriter();

//从客户端得到所有cookie信息

Cookie[] allCookies=request.getCookies();

int i=0;

//如果allCookies不为空..

if(allCookies!=null){

//从中取出cookie

for(i=0;i<allCookies.length;i++){

Cookie temp=allCookies[i];

if(temp.getName().equals("color1")){

//如果取出的是该cookie则将其删除

temp.setMaxAge(0);

pw.println("删除了color这个cookie");

break;

}

}

}else{

pw.println("所有cookie都为空！！！");

}

}

}

Session:

//session案例--如何得到session/和在session中添加属性

package Model;

import javax.servlet.*;

import javax.servlet.http.*;

import java.io.*;

public class SessionTest1 extends HttpServlet{

//处理get请求

//request：用于获得客户端（浏览器）信息

//response:用于向客户端（浏览器）返回信息

public void doGet(HttpServletRequest request,HttpServletResponse response)

throws IOException,ServletException{

//处理中文乱码

response.setContentType("text/html;charset=UTF-8");

PrintWriter pw=response.getWriter();

//得到和request相关联的session，如果没有就创建session

HttpSession hs=request.getSession(true);

//得到session的id，这是由容器分配的

String sessionId=hs.getId();

pw.println("sessionTest1的session id="+sessionId);

//向session中添加一个属性(String类型的)

hs.setAttribute("name", "李世荣");

//如果不指定时间，那么该session的有效期是30秒

hs.setMaxInactiveInterval(20);

pw.println("在session中放入了一个属性 name=李世荣");

}

public void doPost(HttpServletRequest request,HttpServletResponse response)

throws IOException,ServletException{

this.doGet(request, response);

}

}

package Model;

import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;

public class SessionTest2 {

//处理get请求

//request:用于获得客户端（浏览器）的信息

//response:用于向客户端（浏览器）返回信息

public void doGet(HttpServletRequest request,HttpServletResponse response)

throws IOException,ServletException{

response.setContentType("text/html;charset=UTF-8");

PrintWriter pw=response.getWriter();

//得到和req相关联的session，如果没有就创建session

HttpSession ht=request.getSession(true);

//得到sessionId

String sessionId=ht.getId();

pw.println("sessionTest2的session id="+sessionId);

//得到session中的某个属性

String myName=(String)ht.getAttribute("name");

pw.println("name="+myName);

}

}

package Model;

import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;

public class SessionTest3 extends HttpServlet{

public void doGet(HttpServletRequest request,HttpServletResponse response)

throws IOException,ServletException{

response.setContentType("text/html;charset=UTF-8");

PrintWriter pw=response.getWriter();

//得到和request相关联的session，如果没有就创建session

HttpSession ht=request.getSession(true);

//向session中添加一个属性(String类型的)

ht.setAttribute("you", "周星星");

ht.setAttribute("I", "lishirong");

pw.println("在没有删除you属性前you的值="+ht.getAttribute("you")+"<br>");

//从session中删除you属性

ht.removeAttribute("you");

ht.setMaxInactiveInterval(0);

pw.println("删除you属性后you的值="+ht.getAttribute("you")+"<br>");

pw.println("删除you属性后he的值="+ht.getAttribute("he")+"<br>");

}

}

ServletContext:

package Model;

import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;

public class ServletContext extends HttpServlet{

public void init(){

//重写init函数

try{

//只会被调用一次

//创建一个FileReader

FileReader fr=new FileReader("F:\\counter.txt");

BufferedReader br=new BufferedReader(fr);

//读出一行数据

String numVal=br.readLine();

//一定要关闭文件流

br.close();

//将times放入到ServletContext

this.getServletContext().setAttribute("visitTimes",numVal);

System.out.println("init被调用！");

}catch(Exception e){

e.printStackTrace();

}

}

//重写destroy函数

public void destroy(){

try{

FileWriter fw=new FileWriter("f:\\counter.txt");

BufferedWriter bw=new BufferedWriter(fw);

//在文件中写入数据

bw.write(this.getServletContext().getAttribute("visitTimes").toString());

//关闭文件流

bw.close();

System.out.println("destroy被调用");

}catch(Exception e){

e.printStackTrace();

}

}

//处理get请求

public void doGet(HttpServletRequest request,HttpServletResponse response){

try{

String u=request.getParameter("username");

String p=request.getParameter("password");

//将servletContext中的visitTime所对应的值++

String times=this.getServletContext().getAttribute("visitTimes").toString();

//对times++再重新放回servlet

this.getServletContext().setAttribute("visitTimes", (Integer.parseInt(times)+1)+"");

//跳转到wel

response.sendRedirect("Main");

}catch(Exception e){

e.printStackTrace();

}

}

}