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我是jsp中的新成員。我正在嘗試使用jsp製作一個網站，但無法弄清楚如何解決此錯誤。我在互聯網上搜索，但無法解決它。這裏是我的代碼：錯誤：變量conn已在方法_jspService（HttpServletRequest，HttpServletResponse）中定義
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Login As</title>
</head>
<body>
<%@ page import = "java.io.*, java.util.*" %>
<%@ page import = "javax.servlet.*" %>
<%@ page import = "java.sql.*, javax.sql.*" %>
<%
String JDBC_DRIVER = "com.mysql.jdbc.Driver";
String DB_URL = "jdbc:mysql://localhost:3306/cvproject";
// Database credentials
String USER = "root";
String PASS = "admin";
Connection conn = null;
PreparedStatement ps1 = null;
String uname=request.getParameter("username");
String uspass=request.getParameter("password");
String t = "";
int a=0;
try
{
//STEP 2: Register JDBC driver
Class.forName("com.mysql.jdbc.Driver");
//STEP 3: Open a connection
System.out.println("Connecting to database...");
conn = DriverManager.getConnection(DB_URL,USER,PASS);
//STEP 4: Execute a query
System.out.println("Creating statement...");
ps1 = conn.prepareStatement("select * from user_record where uid=? and pwd=?");
ps1.setString(1, uname);
ps1.setString(2, uspass);
//ps1.setString(3, type);
ResultSet rs = ps1.executeQuery();
if(rs.next())
{
System.out.println("success");
a=1;
t = rs.getString("type");
System.out.println("type="+t);
}
else
{
System.out.println("Error occurred");
}
if(a==1)
{ if("A".equals(t))
{%>
<%@ include file="admin.jsp" %>
<%}
else if("F".equals(t))
{%>
<%@ include file="faculty.jsp" %>
<%}
else if("S".equals(t))
{%>
<%@ include file="student.jsp" %>
<%}
else
{%>
<%@ include file="error.jsp" %>
<%}
}
rs.close();
ps1.close();
conn.close();
}
catch(SQLException se){
//Handle errors for JDBC
se.printStackTrace();
}catch(Exception e){
//Handle errors for Class.forName
e.printStackTrace();
}finally{
//finally block used to close resources
try{
if(ps1!=null)
ps1.close();
}catch(SQLException se2){
}// nothing we can do
try{
if(conn!=null)
conn.close();
}catch(SQLException se){
se.printStackTrace();
}//end finally try
}//end try
System.out.println("Goodbye!");
%>
</body>
</html>
問題： 此前每當我用任意字符串名稱分配給JDBC_DRIVER，DB_URL，USER和PASS和任何名義向連接變量康恩，我用來獲取變量是在已定義_jsp服務方法。 現在，它甚至沒有編制，這裏的NetBeans的輸出畫面：
ant -f "D:\\4th year project and presentations\\project4th year main\\Mithapton" -Dnb.internal.action.name=compile.single -DforceRedeploy=false -Djavac.jsp.includes=org/apache/jsp/student_jsp.java "-Djsp.includes=D:\\4th year project and presentations\\project4th year main\\Mithapton\\build\\web\\student.jsp" "-Dbrowser.context=D:\\4th year project and presentations\\project4th year main\\Mithapton\\web\\student.jsp" compile-single-jsp
compile-single-jsp:
init:
deps-module-jar:
deps-ear-jar:
deps-jar:
library-inclusion-in-archive:
library-inclusion-in-manifest:
compile:
Compiling 2 source files to D:\4th year project and presentations\project4th year main\Mithapton\build\generated\classes
D:\4th year project and presentations\project4th year main\Mithapton\build\generated\src\org\apache\jsp\login_jsp.java:198: error: variable JDBC_DRIVER is already defined in method _jspService(HttpServletRequest,HttpServletResponse)
String JDBC_DRIVER = "com.mysql.jdbc.Driver";
^
D:\4th year project and presentations\project4th year main\Mithapton\build\generated\src\org\apache\jsp\login_jsp.java:199: error: variable DB_URL is already defined in method _jspService(HttpServletRequest,HttpServletResponse)
String DB_URL = "jdbc:mysql://localhost:3306/cvproject";
^
D:\4th year project and presentations\project4th year main\Mithapton\build\generated\src\org\apache\jsp\login_jsp.java:202: error: variable USER is already defined in method _jspService(HttpServletRequest,HttpServletResponse)
String USER = "root";
^
D:\4th year project and presentations\project4th year main\Mithapton\build\generated\src\org\apache\jsp\login_jsp.java:203: error: variable PASS is already defined in method _jspService(HttpServletRequest,HttpServletResponse)
String PASS = "admin";
^
D:\4th year project and presentations\project4th year main\Mithapton\build\generated\src\org\apache\jsp\login_jsp.java:204: error: variable conn is already defined in method _jspService(HttpServletRequest,HttpServletResponse)
Connection conn = null;
^
D:\4th year project and presentations\project4th year main\Mithapton\build\generated\src\org\apache\jsp\login_jsp.java:221: error: variable rs is already defined in method _jspService(HttpServletRequest,HttpServletResponse)
ResultSet rs = stmt.executeQuery(sql);
^
6 errors
D:\4th year project and presentations\project4th year main\Mithapton\nbproject\build-impl.xml:986: The following error occurred while executing this line:
D:\4th year project and presentations\project4th year main\Mithapton\nbproject\build-impl.xml:978: The following error occurred while executing this line:
D:\4th year project and presentations\project4th year main\Mithapton\nbproject\build-impl.xml:321: Compile failed; see the compiler error output for details.
BUILD FAILED (total time: 1 second)
我試着用很多不同的字符串名稱，但一切都是徒勞。任何幫助將是非常appreciated.Thank你這麼多....