用struts2的框架编的一个程序，在连接数据库时出错，说是有空指针，但是怎么都找不到错在哪里？？求教！！！
eclipse的错误报告：
Servlet.service() for servlet default threw exception
java.lang.NullPointerException
at sale.persistence.GoodsDAOImpl.addGoods(GoodsDAOImpl.java:37)
at sale.service.GoodsFacadeImpl.addGoods(GoodsFacadeImpl.java:18)
at sale.action.GoodsAction.addGoods(GoodsAction.java:143)

----------------------------------

GoodsDAOImpl.java

package sale.persistence;

import java.sql.SQLException;
import java.util.Date;
import java.sql.*;



import sale.domain.Goods;
import sale.util.DBConnection;
import sale.util.Time;


public class GoodsDAOImpl implements GoodsDAO {

Connection conn=null;

Time now=new Time();

Statement st=null;
PreparedStatement psmt1=null;
ResultSet rs=null;

String time=now.getTime();

public void addGoods(String goodsNam,int warehouseId,String description,double number,double cost)
throws SQLException {
String sql="insert into Goods " +"(goodsNam,warehouseId,Description,Number,cost)"
+"values('"+goodsNam+"','"+warehouseId+"','"+description+"','"+number+"','"+cost+"','"+time+"')";
try{
try {
conn=DBConnection.getDBC();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
conn.setAutoCommit(false);
st=conn.createStatement();
st.executeUpdate(sql);
conn.commit();
}catch(SQLException e){
e.printStackTrace();
conn.rollback();
}
conn.setAutoCommit(true);
st.close();
conn.close();


}

public void changeGoods(int goodsId) throws SQLException {
// TODO Auto-generated method stub

}

public void deleteGoods(int goodsId) throws SQLException {
// TODO Auto-generated method stub

}

public void searchGoods(int goodId) throws SQLException {
// TODO Auto-generated method stub

}

}

----------------------------------

GoodsFacadeImpl.java

package sale.service;

import java.sql.SQLException;
import sale.domain.Goods;
import sale.persistence.GoodsDAO;
import sale.persistence.GoodsDAOImpl;

public class GoodsFacadeImpl implements GoodsFacade {

private GoodsDAO goodsDAO;

public GoodsFacadeImpl(){
goodsDAO=new GoodsDAOImpl();
}

public void addGoods(String goodsNam, int warehouseId, String description,
double number, double cost) throws SQLException {
goodsDAO.addGoods(goodsNam, warehouseId, description, number, cost);

}

public void changeGoods(int goodsId) throws SQLException {
// TODO Auto-generated method stub

}

public void deleteGoods(int goodsId) throws SQLException {
// TODO Auto-generated method stub

}

public void searchGoods(int goodId) throws SQLException {
// TODO Auto-generated method stub

}

}
------------------------------------

GoodsAction.java

package sale.action;

import java.sql.SQLException;
import java.util.List;

import javax.servlet.http.HttpServletReque