HttpServletRequest 接口
获取前端浏览器用户提交的数据：
String getParameter(String name)
Map<String,String[]> getParameterMap()//这个是获取Map
Enumeration<String> getParameterNames()//这个是获取Map集合中所有的key
String[] getParameterValues(java.lang.String name)//根据Map的key获取获取value数组
//以上四个方法与获取用户提交的数据有关系
//前端获取的数据：username=abc
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<h2>学生登录系统</h2>
<form action="/htmm/htmservlet" method="post">
username<input type="text" name="username"/><br>
password<input type="password" name="userpwd"/><br>
interest:
smoke<input type="checkbox" name="hobby" value="s">
drink<input type="checkbox" name="hobby" value="d">
play<input type="checkbox" name="hobby" value="p">
<br>
<input type="submit" value="login">
</form>
</body>
</html>
//后端会收到这样的结果username=sza002415&userpwd=sadasda&hobby=s&hobby=d&hobby=p
Map<String,String[]>
key value
---------------------------------
username {"sza002415"}
userpwd {"sadasda"}
hobby {"s","d","p"}
//Map的使用以及遍历
Map<String,String[]> parameterMap = request.getParameterMap();
//遍历Map集合
Set<String> keys = parameterMap.keySet();
Iterator<String> it = keys.iterator();
while (it.hasNext()){
String key = it.next();
String[] values = parameterMap.get(key);//输出数组
//遍历一维数组
for (String value:values){
out.print(value + "<br>");
}
// out.print(key);
// out.print("<br>");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// super.doPost(req, resp);
response.setContentType("text/html");
PrintWriter out = response.getWriter();
//
Enumeration<String> names = request.getParameterNames();
while (names.hasMoreElements()){
String name = names.nextElement();
out.print(name+"<br>");
}
String[] usernames = request.getParameterValues("username");
String[] userpwds = request.getParameterValues("userpwd");
String[] interests = request.getParameterValues("hobby");
for (String username : usernames){
out.print(username);
}
for (String pwd : userpwds){
out.print(pwd);
}
for (String interest :interests){
out.print(interest);
}
}
使用Servlet的转发机制
执行Aservlet之后，跳转到Bservlet。
1.获取请求转发器对象
2.调用请求转发器RequestDispatcher的forward方法
//要转到类time，其是在请求域中拿出绑定的数据
package sza_htmservlet;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
public class time extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//从请求域当中取出绑定的数据
Object sysTime = request.getAttribute("sysTime");
//输出到服务器
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.print(sysTime);
}
}
//是类time_0其绑定了当前的系统时间，绑定了数据到请求域当中
package sza_htmservlet;
import jakarta.servlet.RequestDispatcher;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Date;
public class time_0 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//获得系统当前时间
Date nowtime = new Date();
//将系统当前时间绑定到请求域当中
request.setAttribute("sysTime",nowtime);
//第一步：获取请求转发器对象,这里的/time是xml文件里可以访问类的路径
RequestDispatcher requestDispatcher = request.getRequestDispatcher("/time");
//第二步调用请求转发器RequestDispatcher的forward方法参数为 本类的request和response
//此时便会自动转到/time 所指的类当中并执行doGet语句
requestDispatcher.forward(request,response);
}
}
两个servlet如何共享数据？
1.将数据放到servletContext当中，但是应用域范围太大，占用资源太多，不建议使用
2.放到request域当中要用时，使用转发机制
转发的下一个资源不一定是Servlet
比如html…
转发的路径以“/”开始，不加项目名
//可以合到一起写
request.getRequestDispatcher("time.html").forward(request,response);
关于request对象中两个非常容易混淆的方法
String username = request.getParameter("username");
//获取的是用户在浏览器上提交的数据
Object obj = request.getAttribute("name");
//获取的是请求域中绑定的数据