Question

提前感谢您的帮助。我试图通过使用单选按钮对象从jsp获得答案，然后发送到servlet，该servlet将管理请求并发送到特定的servlet以影响数据库。我在管理请求的servlet中遇到问题。我无法将请愿书重新发送到最终的servlet。源代码的部分是下一个：

PolicyManager.jsp：

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
    <h1>Change the current policy</h1>
     <form action="ManageRequest" method="Post">
        Which action would you like to apply?<br><br>
        <input type="radio" name="policy" value="add">Add<br>
        <input type="radio" name="policy" value="delete">Delete
        <br><br>
        <input type="submit" value="submit"/>       
     </form>

</body>
</html>

ManageRequest.java：

import java.io.IOException;
import java.io.PrintWriter;    
import javax.servlet.RequestDispatcher;
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;

/**
 * Servlet implementation class ManageRequest
 */
@WebServlet("/ManageRequest")
public class ManageRequest extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public ManageRequest() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        PrintWriter printWriter = response.getWriter();
        printWriter.print("doGet method");
        String policy=request.getParameter("policy");

        if (policy.equals("add") ) {
            printWriter.println("<html><body>Redirecting to Add servlet section..."+"<br>");
            RequestDispatcher dispatcher = request.getRequestDispatcher("/AddPolicy");
            dispatcher.forward(request, response);

        } else if (policy.equals("delete")) {
            printWriter.println("<html><body>Redirectin to Delete servlet section..."+"<br>");
            RequestDispatcher dispatcher = request.getRequestDispatcher("/DeletePolicy");
            dispatcher.forward(request, response);

        }
        else{
            printWriter.println("<html><body>A different option..."+"<br>");
        }
        printWriter.println("</body></html>");
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        PrintWriter printWriter = response.getWriter();
        String policy=request.getParameter("policy");
        printWriter.print("doPost method");

        if (policy.equals("add") ) {
            printWriter.println("<html><body>Redirecting to Add servlet section..."+"<br>");
            RequestDispatcher dispatcher = request.getRequestDispatcher("/AddPolicy");
            dispatcher.forward(request, response);

        } else if (policy.equals("delete")) {
            printWriter.println("<html><body>Redirectin to Delete servlet section..."+"<br>");
            RequestDispatcher dispatcher = request.getRequestDispatcher("/DeletePolicy");
            dispatcher.forward(request, response);

        }
        else{
            printWriter.println("<html><body>A different option..."+"<br>");
        }
        printWriter.println("</body></html>");

    }

}

AddPolicy.java：

package PolicyManager;

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 AddPolicy
 */
@WebServlet("/AddPolicy")
public class AddPolicy extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public AddPolicy() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        PrintWriter printWriter = response.getWriter();
        printWriter.println("<h1>Add Policy</h1>");
        printWriter.println("Add Policy");
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
    }

}

DeletePolicy.java：

package PolicyManager;

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 DeletePolicy
 */
@WebServlet("/DeletePolicy")
public class DeletePolicy extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public DeletePolicy() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        PrintWriter printWriter = response.getWriter();
        printWriter.println("<h1>Delete Policy</h1>");
        printWriter.println("Delete Policy");
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
    }

}

web.xml：

<servlet>
    <servlet-name>ManageRequest</servlet-name>
    <servlet-class>PolicyManager</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ManageRequest</servlet-name>
    <url-pattern>/PolicyManager</url-pattern>
  </servlet-mapping>

问题是只有我可以获得必须将请愿重定向到最终servlet的管理器servlet。

感谢您的帮助。

干杯

Answer 1

您应该尝试了解RequestDispatcher.include()和RequestDispatcher.forward().

之间的区别

RequestDispatcher.forward()表示请求处理的完整控制转发到另一个servlet。转发servlet不应该做任何事情，比如写响应或提交响应。如果响应在转发之前在调用servlet中提交，则抛出IllegalStateException。如果响应尚未提交，则响应将被清除。

无论如何，当您转发到另一个servlet时，将某些内容写入响应是无效的。

如果您需要为各种servlet的响应写一些内容，则应使用RequestDispatcher.include().

在你的情况下，你在forward（）之前写的东西可能是问题。

printWriter.println("<html><body>Redirecting to Add servlet section..."+"<br>

Answer 2

您必须添加： response.sendRedirect是（ “http://localhost:8080/clientLibrary/DeletePolicy”）;

而不是： RequestDispatcher dispatcher = request.getRequestDispatcher（“/ DeletePolicy”）; dispatcher.forward（请求，响应）;

AddPolicy也一样。

干杯

如何将请求从jsp重定向到servlet

2 个答案: