java csv

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package com;

import java.lang.Class;
import java.io.FileWriter;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;

import antlr.collections.List;

public class DbConecter {
public static void main(String[] args) {
  ArrayList li = new ArrayList();
  try {
   Class.forName("com.mysql.jdbc.Driver");
   String url = "jdbc:mysql://localhost:3306/knowledge";
   String user = "root";
   String password = "root";
   Connection conn = DriverManager.getConnection(url, user, password);
   Statement stmt = conn.createStatement();
   if (!conn.isClosed()) {
    int i = 0;
    System.out.println("已连接！ ");
    ResultSet rs = stmt.executeQuery("select * from sample");
    ResultSetMetaData rsmd = rs.getMetaData();
    int columnCount = rsmd.getColumnCount();
    String a = rsmd.getColumnName(2);
    System.out.println(a);
    FileWriter fw = new FileWriter("d://helloCsv.csv");
    fw.write("www,www,www,www,www,www,www,www/r/n");
    while (rs.next()) {
     // rs.gets
     fw.write(rs.getString("ID") + "," + rs.getString("aveidf")
       + "," + rs.getString("categoryID") + "/r/n");

    }
    fw.close();
    System.out.println(li.size());
   }

   else {
    System.out.println("未连接！ ");
   }

  } catch (Exception e) {
   System.out.println("出错啊 ");
   e.printStackTrace();
  }
}
}