抛出空指针问题

Question

请各位帮帮忙.这是源码:
package bean.db.common;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;public class dbOpertaion {
    /**
     * ִ��SQL��ѯ���
     */
    public ResultSet executeQuery(String sqlString){
        if(sqlString==null) return null;
        Connection conn=openDB();
        ResultSet rs=null;//����¼��
        Statement sql=null;//SQL������
        try{
            sql=conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_READ_ONLY);
            rs=sql.executeQuery(sqlString);
            return rs;
        } catch (SQLException e) {
            e.printStackTrace();
           rs=null;
        }
        closeDB(conn);
        return rs;
    }
    /**
     * ִ��SQL�������,����Ӱ�������
     */
    public int executeUpdate(String sqlString){
        if(sqlString==null) return 0;
        Connection conn=openDB();
        Statement sql=null;//SQL������
        int i=0;//Ӱ�������
        try{
            sql=conn.createStatement();
            i=sql.executeUpdate(sqlString);
        } catch (SQLException e) {
            e.printStackTrace();
            i=0;
        }
        closeDB(conn);
        return i;
    }
    /**
     * ����ݿ�l��
     */
    public Connection openDB(){
        dbconn dbconnOBject=new dbconn();//��ݿ�l�Ӷ���
        Connection dbconn=dbconnOBject.getDBConn();//�õ���ݿ�l��
        return dbconn;
    }
    /**
     * �ر���ݿ�l��
     */
    public void closeDB(Connection conn){
        if(conn!=null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}
运行之后报错:java.lang.NullPointerException
bean.db.common.dbOpertaion.executeQuery(dbOpertaion.java:17)
bean.db.bookTypeOPBean.<init>(bookTypeOPBean.java:18)
org.apache.jsp.banner_jsp._jspService(banner_jsp.java:105)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:965)
org.apache.jsp.index_jsp._jspService(index_jsp.java:81)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

Answer 1

错误信息很明确bean.db.common.dbOpertaion.executeQuery(dbOpertaion.java:17)
executeQuery（）方法17行出错，应该是你的sql 连接没获取到

Answer 2

rs=sql.executeQuery(sqlString); 看来是没有获取到sqlString,另外你的方法名executeQuery和sql.executeQuery的方法咋一样的，这样的情况应尽量避免。

Answer 3

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在那里看看有无能回答你的,谢谢,LZ,甭忘了给俺分哦,谢谢LZ