Java 结果集遍历时空指针错误？救救我吧！！！

package com.dong;

import java.io.IOException;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class BuyerOrderServlet extends HttpServlet {

private static final long serialVersionUID = -3855206432313787833L;
String[] order_id = null;
String[] new_price = null;
String[] product_number = null;

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

doPost(request, response);
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
HttpSession session = request.getSession(true);
response.setContentType("text/html;charset=utf-8");
String driver = "oracle.jdbc.driver.OracleDriver";
String url = "jdbc:oracle:thin:@127.0.0.1:1521:global";
String username = "scott";
String password = "tiger";
ResultSet rs = null;
Connection conn = null;
PreparedStatement pstmt = null;
String sql = "select order_id,new_price,product_number from lineItem_table where user_id='59'";
try {
Class.forName(driver);
} catch (ClassNotFoundException e) {

e.printStackTrace();
}
try {
conn = DriverManager.getConnection(url, username, password);
} catch (SQLException e) {

e.printStackTrace();
}

try {
pstmt = conn.prepareStatement(sql);
} catch (SQLException e) {

e.printStackTrace();
}
try {
rs = pstmt.executeQuery();
} catch (SQLException e) {

e.printStackTrace();
}
int i = 0;
try {
while (rs.next()) {
order_id[i] = rs.getString("order_id");--------------------------这行提示有错，但是不知什么原因
new_price[i] = rs.getString("new_price");
product_number[i] = rs.getString("product_number");

i++;
}
} catch (SQLException e) {

e.printStackTrace();
}

for (int j = 0; j < order_id.length; j++) {

session.setAttribute("order_id[j]", order_id[j]);

session.setAttribute("new_price[j]", new_price[j]);
session.setAttribute("product_number[j]", product_number[j]);

}
response.sendRedirect("/task/maijiadingdan.jsp");
session.setAttribute("order_id_length", order_id.length);
}

}