exception:java.lang.NullPointerException怎么解决？

<%@ page contentType="text/html;charset=gb2312"%>
<%@ page import="java.util.*,java.sql.*"%>
<%@ page import="myBean.SubmitBean.*"%>
<html>
<head>
<title>输入提交</title>
</head>
<body>
<h1>请输入要提交的内容</h1>
<form name="forml" method="post" action="submit.jsp">
<input type="text" name="content"> 
<input type="submit" name="submit"value="提交"></form>
content:
<%
Connection con;
Class.forName("com.mysql.jdbc.Driver");
con = DriverManager.getConnection("jdbc:mysql://31.0.23.6:3306/test","root","panshi");
PreparedStatement stmt = con.prepareStatement("Select * From Content");
ResultSet rs = stmt.executeQuery();
String content = new String(request.getParameter("content").getBytes("iso8859-1"),"gb2312");
String sql = "INSERT INTO Content(content) VALUES(?)";
PreparedStatement stmt2 = con.prepareStatement(sql);
stmt2.setString(1,content);
stmt2.executeUpdate();
ResultSet rs1 = stmt2.executeQuery("Select * From Content where id='"+content+"'");
try {
while(rs1.next())
{
out.println(rs1.getString("content"));
}
}
catch (Exception ex){
out.println(ex.getMessage());
ex.printStackTrace();
}
finally{
rs1.close();
rs.close();
stmt.close();
con.close();
}
 %>
</body>
</html>error:
org.apache.jasper.JasperException: An exception occurred processing JSP page /submit.jsp at line 2219: con = DriverManager.getConnection("jdbc:mysql://31.0.23.6:3306/test","root","panshi");
20: PreparedStatement stmt = con.prepareStatement("Select * From Content");
21: ResultSet rs = stmt.executeQuery();
22: String content = new String(request.getParameter("content").getBytes("iso8859-1"),"gb2312");
23: String sql = "INSERT INTO Content(content) VALUES(?)";
24: PreparedStatement stmt2 = con.prepareStatement(sql);
25: stmt2.setString(1,content);
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:510)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:419)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
root cause java.lang.NullPointerException
org.apache.jsp.submit_jsp._jspService(submit_jsp.java:77)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:377)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)什么问题 应该怎么解决··？

解决方案 »

  1.   

    19、20行：Statement stmt = con.createStatement();
    ResultSet rs = stmt.executeQuery("Select * From Content");
      

  2.   

    请将这一行改成String content = request.getParameter("content");
    if (content==null) content="";
    content = new String(content.getBytes("iso8859-1"),"gb2312");
      

  3.   

    String content = new String(request.getParameter("content").getBytes("iso8859-1"),"gb2312");
    request.getParameter("content")你打印下看下 这句取到值没
      

  4.   

    改成这样
    String content = request.getParameter("content");
    if(content != null){
    content = new String(request.getParameter("content").getBytes("iso8859-1"),"gb2312");
    Connection con;
    Class.forName("com.mysql.jdbc.Driver");
    con = DriverManager.getConnection("jdbc:mysql://31.0.23.6:3306/test","root","panshi");
    PreparedStatement stmt = con.prepareStatement("Select * From Content");
    ResultSet rs = stmt.executeQuery();
    String sql = "INSERT INTO Content(content) VALUES(?)";
    PreparedStatement stmt2 = con.prepareStatement(sql);
    stmt2.setString(1,content);
    stmt2.executeUpdate();
    ResultSet rs1 = stmt2.executeQuery("Select * From Content where id='"+content+"'");
    try {
    while(rs1.next()){
    out.println(rs1.getString("content"));
    }
    }catch (Exception ex){
    out.println(ex.getMessage());
    ex.printStackTrace();
    }finally{
    rs1.close();
    rs.close();
    stmt.close();
    con.close();
    }
    }