转发和重定向详解

转发与重定向的区别

前言：之前写了几篇JSP的博客，现在又回过头来看Servlet，温故而知新，再回顾回顾，总会有收获的。以前学习Servlet感觉内容很多，现在看的时候，其实也没多少东西，只需知道Servlet的生命周期，Servlet的实现方式，ServletContext作用域，接收和响应，转发和重定向，我觉得差不多够用了。当然，要是细究的话也不止这些，我针对的是新手。

转发与重定向简介

转发和重定向都是实现页面跳转，也就是说，当我们访问一个Servlet 的时候，Servlet帮我们跳转到另一个界面。

转发与重定向的区别

实现转发调用的是HttpServletRequest对象中的方法

实现重定向调用的是HttpServletResponse对象中的方法

转发时浏览器中的url地址不会发生改变

重定向时浏览器中的url地址会发生改变

转发时浏览器只请求一次服务器

重定向时浏览器请求两次服务器

转发能使用request带数据到跳转的页面

重定向能使用ServletContext带数据到跳转的页面

代码演示转发和重定向

package servlet;
 
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("/login")
public class ServletDemo extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取表单提交过来的数据
        //getParameter()方法可以获取请求的参数信息
        String name = req.getParameter("name");
        String password = req.getParameter("password");
 
        //打印获取到的参数信息
        System.out.println("name:"+name);
        System.out.println("password:"+password);
 
        //如果name=admin,password=123,则跳转到succee.jsp,否则跳转到fail.jsp
        if("admin".equals(name)&&"123".equals(password)){
            //通过转发实现跳转
            req.getRequestDispatcher("/success.jsp").forward(req,resp);
        }else {
            //通过重定向实现跳转
            resp.sendRedirect("/fail.jsp");
        }
    }
 
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
         
    }
}

JSP代码

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
 
<html>
 
<head>
 
    <title>登录</title>
 
</head>
 
<body>
 
<form action="/login">
 
    <table align="center">
 
        <tr>
 
            <td>账号:</td>
 
            <td><input type="text" name="name"></td>
 
        </tr>
 
        <tr>
 
            <td>密码:</td>
 
            <td><input type="text" name="password"></td>
 
        </tr>
 
        <tr>
 
            <td><input type="submit" value="登录"></td>
 
            <td><input type="reset" value="重置"></td>
 
        </tr>
 
    </table>
 
</form>
 
</body>
 
</html>

转发和重定向如何带数据到某个页面

package servlet;
 
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("/login")
 
public class ServletDemo extends HttpServlet {
 
    @Override
 
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 
            //通过转发带数据
 
            req.setAttribute("name","张三");
 
            req.getRequestDispatcher("/send.jsp").forward(req,resp);
 
    }
 
    @Override
 
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 
        doGet(req, resp);
 
    }
 
}

send.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
 
<html>
 
<head>
 
    <title>转发和重定向传代数据练习</title>
 
</head>
 
<body>
 
    <%
 
        //1、接收转发传代的数据
 
      String name =  (String) request.getAttribute("name");
 
      out.println("转发传代的数据："+name);
 
    %>
 
</body>
 
</html>

package servlet;
 
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("/login")
 
public class ServletDemo extends HttpServlet {
 
    @Override
 
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 
            //通过重定向带数据
 
        ServletContext servletContext = this.getServletContext();
 
        servletContext.setAttribute("name","王二麻子");
 
            resp.sendRedirect("/send2.jsp");
 
    }
 
    @Override
 
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 
        doGet(req, resp);
 
    }
 
}

send2.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
 
<html>
 
<head>
 
    <title>转发和重定向传代数据练习</title>
 
</head>
 
<body>
 
    <%
 
        //1、接收重定向传代的数据
 
        String name1 = (String)application.getAttribute("name");
 
        out.println("重定向传代的数据："+name1);
 
    %>
 
</body>
 
</html>

练习

index.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
 
<html>
 
<head>
 
    <title>Title</title>
 
</head>
 
<body>
 
<form action="CountServlet" method="post">
 
    <h3>加法计算器</h3>
 
    加数1：<input type="number" name="one">
 
    加数2：<input type="number" name="two">
 
    <input type="submit" value="计算">
 
</form>
 
</body>
 
</html>

count.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
 
<html>
 
<head>
 
    <title>Title</title>
 
</head>
 
<body>
 
计算结果：<%=request.getAttribute("count")%>
 
<!--计算结果：<%=application.getAttribute("count")%>-->
 
</body>
 
</html>

Servlet

package servlet;
 
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("/CountServlet")
public class CountServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
String one=request.getParameter("one");
 
int o=Integer.parseInt(one);//强制转换，将String类型的数据转换成int类型
 
String two=request.getParameter("two");
 
int t=Integer.parseInt(two);//强制转换，将String类型的数据转换成int类型
 
System.out.println(one+"   "+two);
 
int c=o+t;
 
String co=String.valueOf(c);//将int类型的数据转换成String类型
 
//转发，可以携带数据
 
request.setAttribute("count",co);
 
request.getRequestDispatcher("count.jsp").forward(request,response);
 
//用于存放数据
 
//        ServletContext s=this.getServletContext();
 
//        s.setAttribute("count",co);
 
//重定向只能依靠ServletContext获取数据
 
//  response.sendRedirect("count.jsp");
 
System.out.println(co);
 
}
 
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
doPost(request,response);
 
}
 
}