我写了一个连接数据库的类,里面封装了一些QUERY操作,但实际使用中,无论是CONN还是调用过程中,均报NULLPOINTEXCEPTION。请帮我看一下哪里出错了。连接数据库并封装QUERY的类DBConn.java源码如下:
public Connection connect() {
try {
Class.forName("org.gjt.mm.mysql.driver").newInstance();
conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/nicoa?user=root&password=&useUnicode=true&characterEncoding=UTF-8");
stmt = conn.createStatement();
} catch (Exception e) {
System.out.println(e.getMessage());
e.printStackTrace();
}
return conn;
}
public ResultSet selectQuery(String SQLQuery) {
this.SQLQuery = SQLQuery;
try {
conn=this.connect();
stmt = conn.createStatement();
rs = stmt.executeQuery(SQLQuery);
} catch (Exception e) {
e.pring........
}
return rs;
}
在调用的时候,我是这么写的:(在servlet中调用)
DBConn dbconn=new DBConn()
mysql.connect();
String sql = "select password from root passport ";
ResultSet rs = dbconn.selectQuery(sql);
rs.next();
谢谢。
public Connection connect() {
try {
Class.forName("org.gjt.mm.mysql.driver").newInstance();
conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/nicoa?user=root&password=&useUnicode=true&characterEncoding=UTF-8");
stmt = conn.createStatement();
} catch (Exception e) {
System.out.println(e.getMessage());
e.printStackTrace();
}
return conn;
}
public ResultSet selectQuery(String SQLQuery) {
this.SQLQuery = SQLQuery;
try {
conn=this.connect();
stmt = conn.createStatement();
rs = stmt.executeQuery(SQLQuery);
} catch (Exception e) {
e.pring........
}
return rs;
}
在调用的时候,我是这么写的:(在servlet中调用)
DBConn dbconn=new DBConn()
mysql.connect();
String sql = "select password from root passport ";
ResultSet rs = dbconn.selectQuery(sql);
rs.next();
谢谢。
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代码如下:message,表是我建的。
//import com.microsoft.jdbc.sqlserver.SQLServerDriver;
import oracle.jdbc.driver.OracleDriver;
import java.sql.*;
import java.util.*;public class MessageBean1
{
//获得数据库连接。
public static void main(String[] args)
{
//连接数据库
Connection con =null;
String CLASSFORNAME="oracle.jdbc.driver.OracleDriver";
String SERVANDDB="jdbc:oracle:thin:@datacenterpc2:1521:phfund";
String USER="phfund";
String PWD="phfund";
try
{
Class.forName(CLASSFORNAME).newInstance();
con = DriverManager.getConnection(SERVANDDB,USER,PWD);
}
catch(Exception e)
{
System.out.println(e.getMessage());
e.printStackTrace();
}
//打印数据
try
{
Statement stm=con.createStatement();
ResultSet result=stm.executeQuery("select count(*) from message");
int message_count=0;
if(result.next())
{
message_count=result.getInt(1);
System.out.println(message_count+" 条数据");
result.close();
}
if(message_count>0)
{
result=stm.executeQuery("select * from message order by ms_date desc");
while(result.next())
{
System.out.print(result.getString("ms_title")+" ");
System.out.print(result.getString("ms_name")+" ");
System.out.print(result.getString("ms_mail")+" ");
System.out.print(result.getString("ms_content")+" ");
System.out.println(result.getDate("ms_date")+" ");
}
result.close();
stm.close();
}
con.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}