为什么我在servlet中使用"sendReditect"时得到空值，如下所示
我的代码如下：即使在FirstServlet和SecondServlet中，我也得到fname值null
索引.html：
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<form action="FirstServlet" method="get">
username<input type="text" name="fname"></br> <input type="submit"
value="SUBMIT">
</form>
</body>
</html>
FirstServlet：
package com.naveen;
import java.io.IOException;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class FirstServlet
*/
@WebServlet("/FirstServlet")
public class FirstServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse res) throws ServletException, IOException {
String s3=request.getParameter("fname");
// TODO Auto-generated method stub
/*String s1=request.getParameter("t1");*/
/*RequestDispatcher rd=request.getRequestDispatcher("SecondServlet");
rd.forward(request, response);*/
res.sendRedirect("SecondServlet");
System.out.println("your output as per" +s3);
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
}
}
SecondServlet：
package com.naveen;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class SecondServlet
*/
@WebServlet("/SecondServlet")
public class SecondServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
response.setContentType("text/html");
PrintWriter out=response.getWriter();
String s3=request.getParameter("fname");
out.print("hi i am siddharth");
out.println(s3);
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
}
}
为什么我在 servlet 中使用"sendReditect"时获得空值作为 根据下面的代码如下：即使在以下情况下，我也得到 fname 值为空 FirstServlet 和 SecondServlet，
因为您没有为请求设置任何值。您需要像这样为请求设置值：
@WebServlet("/FirstServlet")
public class FirstServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse res) throws ServletException, IOException {
String s3=request.getParameter("fname"); //get the value you set in your jsp/html/url
request.setAttribute("fname", s3); // set the s3 value to the request
res.sendRedirect("SecondServlet");
System.out.println("your output as per" +s3);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
}
我假设您在这里通过表单或其他东西发送了 fname 值。如果只需在 url 中键入FirstServlet来调用它，则会得到 null。
但是，如果您设置了某些内容，则不会，如果您不提交表单，请尝试这样做：
/FirstServlet?fname=helloworld
编辑：
只是注意到在您的表单中，您实际上并没有使用任何值设置 FNAME。您需要给它一个值：
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<form action="FirstServlet" method="get">
username<input type="text" name="fname" value="helloworld"></br> //add value to your input!!
<input type="submit" value="SUBMIT">
</form>
</body>
</html>