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初学者的servlet问题

摘要: 初学者的servlet问题

我用servlet在连接数据库的时候老是出错。代码如下：

package servlet;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;

public class mysev extends HttpServlet
{
public void doGet( HttpServletRequest rq,
HttpServletResponse rp )
throws IOException,ServletException
{
rp.setContentType("text/html;charset=gb2312");
PrintWriter out=rp.getWriter();
out.println("");
out.println("<form method=/"post/" action=/"mysev/">");
out.println("<input type=text name=t1>
");
out.println("<input type=submit value=确定>
");
out.println("</form>");
out.println("");
}

public void doPost( HttpServletRequest rq,
HttpServletResponse rp )
throws IOException,ServletException
{
rp.setHeader("Cache-Control","no-cache");
rp.setContentType("text/html;charset=gb2312");
PrintWriter out=rp.getWriter();
String t = rq.getParameter("t1");
t = new String(t.getBytes("iso8859-1"), "gb2312");
out.println("欢迎你：");
DBconn DBconn1=new DBconn();
out.print("<table border=1>");
try
{
ResultSet RS = DBconn1.executeQuery("SELECT * FROM news where id=13");while (RS.next())
{
out.print("<tr><td>"+RS.getString("id")+"</td><td>" + RS.getString("wzbt")+"</td></tr>");
}
RS.close();
out.print("</table>");
//out.println(t);
out.println("");
}
catch(Exception e)
{
out.print("Sql error
"+e);
e.printStackTrace();
}

}
public class DBconn
{
String DBDriver="org.gjt.mm.mysql.Driver";
String ConnStr="jdbc:mysql://localhost/nlmywyk";
String MyUser="root";
String MyPassword="useUnicode=true&characterEncoding=gb2312";
Connection conn = null;
ResultSet rs = null;

public DBconn()
{
try
{
Class.forName(DBDriver);
}
catch(java.lang.ClassNotFoundException e)
{
System.err.println("DBconn (): " + e.getMessage());
}
}
public ResultSet executeQuery(String sql)
{
rs = null;
try
{
conn = DriverManager.getConnection(ConnStr,MyUser,MyPassword);
Statement stmt = conn.createStatement();
rs = stmt.executeQuery(sql);
}
catch(SQLException ex)
{
System.err.println("aq.executeQuery:"+ex.getMessage());
}
return rs;
}
}

}

提示的错误为：
Sql error
java.lang.NullPointerException

我是想实现用servlet来实现一个简单的查询。把数据库连接写为一个单独的类。
希望有高手修改一下这个程序，或者提供一个实现上述功能的简单代码也行。

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先自己顶一下

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怎么没人解决呢？

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单步调试一下

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jdbc:mysql://localhost/nlmywyk 这里改成：jdbc:mysql://localhost:3306/nlmywyk

数据库连接不上，没有初始化成功，所以抛出了空指针的错误。

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已经搞定。就是没连上数据库。

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d

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