连接数据库时的奇怪问题（myeclipse+struts+sqlserver）
我写了一个数据库操作类在用.jsp 中的useBean方法调用做测试时总是提示错误。
description The server encountered an internal error () that prevented it from fulfilling this request.
exception
org.apache.jasper.JasperException
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:372)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
root cause
java.lang.NullPointerException
com.is.struts.action.Database.selectDb(Database.java:57)
org.apache.jsp.index_jsp._jspService(index_jsp.java:103)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
note The full stack trace of the root cause is available in the Apache Tomcat/5.0.28 logs.
数据库的源码如下，请高手支招：
package com.is.struts.action;
import java.sql.*;
//import javax.swing.*;
//import java.util.*;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class Database {
Connection conn=null;
Statement stmt=null;
ResultSet rs=null;
String driverName=null;
String url=null;
/*
public Database() {
try {
jbInit();
}
catch (Exception ex) {
ex.printStackTrace();
}
}
private void jbInit() throws Exception {
}
*/
//连接数据库
public void setConnection(){// throws Exception{
try {
driverName = "com.microsoft.jdbc.sqlserver.SQLServerDriver ";
url = "jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=test ";
Class.forName(driverName);
conn=DriverManager.getConnection(url, "sa ", "yt ");
conn.setAutoCommit(true);
}
catch (ClassNotFoundException ex) {
ex.printStackTrace();
}
catch(SQLException e){
e.printStackTrace();
}
}
//数据库查询的操作
public ResultSet selectDb(String sql){// throws Exception{
try
{
//PreparedStatement stmt = conn.prepareStatement(sql,java.sql.ResultSet.TYPE_SCROLL_INSENSITIVE,java.sql.ResultSet.CONCUR_READ_ONLY);
//rs=stmt.executeQuery();
return stmt.executeQuery(sql);
}catch(SQLException e)
{
e.printStackTrace();
//JOptionPane.showMessageDialog(null, "数据库操作失败！2 ", "警告 ",JOptionPane.WARNING_MESSAGE);
}
catch(NullPointerException ex){
ex.printStackTrace();
}
return null;
}
//关闭数据集
public void closeRs(){
try
{
if (rs!=null) { rs.close(); }
if(stmt!=null) {stmt.close();}
}catch(SQLException e)
{
e.printStackTrace();
}
}
//关闭数据库
public void closeDb(){
try
{
if(conn!=null) { conn.close();}
}catch(SQLException e)
{
e.printStackTrace();
}
}
}
在调用setConnection时没问题，调用selectDb时就出错。
[解决办法]
java.lang.NullPointerException
搞了老半天，你return的还是null啊
public ResultSet selectDb(String sql){// throws Exception{
try
{
//PreparedStatement stmt = conn.prepareStatement(sql,java.sql.ResultSet.TYPE_SCROLL_INSENSITIVE,java.sql.ResultSet.CONCUR_READ_ONLY);
//rs=stmt.executeQuery();
return stmt.executeQuery(sql);
}catch(SQLException e)
{
e.printStackTrace();
//JOptionPane.showMessageDialog(null, "数据库操作失败！2 ", "警告 ",JOptionPane.WARNING_MESSAGE);
}
catch(NullPointerException ex){
ex.printStackTrace();
}
return null;//这行你写了白做了，return的还是null
}
程序代码可以改成：
public ResultSet selectDb(String sql){// throws Exception{
try
{
//PreparedStatement stmt = conn.prepareStatement(sql,java.sql.ResultSet.TYPE_SCROLL_INSENSITIVE,java.sql.ResultSet.CONCUR_READ_ONLY);
//rs=stmt.executeQuery();
return stmt.executeQuery(sql);
}catch(SQLException e)
{
e.printStackTrace();
//JOptionPane.showMessageDialog(null, "数据库操作失败！2 ", "警告 ",JOptionPane.WARNING_MESSAGE);
return null;
}
catch(NullPointerException ex){
ex.printStackTrace();
return null;
}
}
在使用的时候最好判断一下null可能出现的解决办法
我的异常网推荐解决方案：The server encountered an internal error () that prevented it from fulfilling this request.,http://www.myexception.cn/java-web/317.html
