重定向与转发

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转发参数不会自动包含在新的请求中。若要将参数传递给重定向地址，可以在服务器端显式地添加参数到重定向URL中。

在重定向URL中包含参数

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/initialRequest")
public class InitialRequestServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 获取原始请求参数
        String param = request.getParameter("param");
        
        // 重定向到新的URL，并在重定向URL中包含原始参数
        response.sendRedirect("redirectedRequest?param=" + param);
    }
}

处理重定向后的请求

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/redirectedRequest")
public class RedirectedRequestServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 获取重定向后请求中的参数
        String param = request.getParameter("param");
        
        response.setContentType("text/html");
        response.getWriter().println("<h1>Redirected Request</h1>");
        response.getWriter().println("<p>Param: " + param + "</p>");
    }
}

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转发会携带初始请求的参数
转发

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/initialRequest")
public class InitialRequestServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 获取原始请求参数
        String param = request.getParameter("param");

        // 在请求属性中保存参数
        request.setAttribute("param", param);

        // 转发请求到新的Servlet
        request.getRequestDispatcher("/forwardedRequest").forward(request, response);
    }
}

转发之后

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/forwardedRequest")
public class ForwardedRequestServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 获取转发请求中的参数
        String param = (String) request.getAttribute("param");

        response.setContentType("text/html");
        response.getWriter().println("<h1>Forwarded Request</h1>");
        response.getWriter().println("<p>Param: " + param + "</p>");
    }
}