java输出。打印方法不起作用？

11 月，3 周 Questions & Answers 522

这是我的密码

登录控制器。爪哇

包mvc。演示。控制

    import java.io.IOException;
    import java.io.PrintWriter;
    import javax.servlet.RequestDispatcher;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;

    import mvc.demo.model.Authenticate;


    public class LoginController extends HttpServlet {
        private static final long SerialVersionUID=1L;

        public LoginController()
        {
            super();
        }

        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp)
                throws ServletException, IOException {
            String s1=req.getParameter("username");
            String s2=req.getParameter("password");
            RequestDispatcher rd=null;
            Authenticate au=new Authenticate();
            String result=au.authorise(s1, s2);
            if(result.equals("success"))
            {
                rd=req.getRequestDispatcher("/success.jsp");    
            }
            else
            {
               //This is the point where i try to print error message on jsp.
                PrintWriter out = resp.getWriter(  );
                out.print("Sorry UserName or Password Error!");
                rd=req.getRequestDispatcher("/login.jsp");  
                rd.include(req, resp);  
            }
            rd.forward(req, resp);
        }   
    }

    <%@ page language="java" contentType="text/html; charset=ISO-8859-1"
        pageEncoding="ISO-8859-1"%>
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <html>
    <head>
    <title>Login Page</title>
    </head>
    <body>
        <form method="post" action="LoginController" >  
        UserName:   <input type="text" name="username"><BR><BR>
        PassWord:   <input type="password" name="password"><BR><BR>
                    <input type="submit" />   
        </form>
    </body>
    </html>

请检查loginController类的else块，我试图在我的jsp文件上打印错误消息，当前“out.print”方法无法反映我的登录。jsp文件。请帮我整理这个问题，提前谢谢

import java.io.IOException; import java.io.PrintWriter; import javax.servlet.RequestDispatcher; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import mvc.demo.model.Authenticate; public class LoginController extends HttpServlet { private static final long SerialVersionUID=1L; public LoginController() { super(); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String s1=req.getParameter("username"); String s2=req.getParameter("password"); RequestDispatcher rd=null; Authenticate au=new Authenticate(); String result=au.authorise(s1, s2); if(result.equals("success")) { rd=req.getRequestDispatcher("/success.jsp"); //The error was with this line rd.forward(req, resp); } else { PrintWriter out = resp.getWriter( ); out.print("Sorry UserName or Password Error!"); rd=req.getRequestDispatcher("/login.html"); rd.include(req, resp); } } }

共 (4) 个答案

# 1 楼答案

# 2 楼答案
如果您想在Jsp中打印错误消息，并首先在请求中设置错误消息
```
        req.setAttribute("msg","error msg configure here");
```
现在，您可以通过使用EL表达式在jsp中获得相同的结果
```
   ${msg} 
```
或者你可以使用脚本语言来实现
```
 <%Object obj=request.getAttribute("msg");%>
```
将Obj键入字符串，然后使用以下命令打印
```
             <%=str%>
```
注意：-建议使用El表达式

# 3 楼答案

您可以在请求属性中设置错误消息，并可以在JSP中获取它

String errorMsg = "UserName or Password is invalid !";
req.setAttribute("errorMsg", errorMsg);
req.getRequestDispatcher("/login.jsp").forward(req, res);

现在在JSP上

<h2>${errorMsg}</h2>  // Print wherever you need it

# 4 楼答案

我看不见外面。在代码中使用close（）。最后必须关闭PrintWriter对象

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java输出。打印方法不起作用？

共 (4) 个答案

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