package com.test.lihongxu;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
public class ConnectMysql { public List<Instance> getTag(int start,int end){ List<Instance> intList=new ArrayList<Instance>(); Connection con=getConnetion(); try { con.setAutoCommit(false);//此处开启事务 Statement stm=con.createStatement(); ResultSet set=stm.executeQuery("select * from tag_feed limit "+start+","+end); while(set.next()){ Instance instance=new Instance(); instance.setFeed_id(set.getInt(2)); instance.setTag_id(set.getInt(3)); intList.add(instance); } con.commit();//事务提交 con.close(); } catch (SQLException e) { try { con.rollback(); System.out.println("not Ok"); } catch (SQLException e1) { // TODO Auto-generated catch block e1.printStackTrace(); } e.printStackTrace(); } return intList; } public Connection getConnetion(){ Connection con=null; try { Class.forName("com.mysql.jdbc.Driver"); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } try { con = DriverManager.getConnection("jdbc:mysql://localhost/minisite?useUnicode=true&characterEncoding=GBK", "root", "admin"); } catch (SQLException e) { e.printStackTrace(); } return con; } }
2,采取算法规则如下:
1)先设定一个无限循环,
2)循环内嵌套一个循环,每次从数据库查500条,查四次 放入List,然后遍历List 写入txt
3)在内层循环设置一个flag ,当查的数据小于500条时,则false.
4)在外层循环判断false的值,若为false 跳出循环
package com.test.lihongxu; import java.io.BufferedWriter; import java.io.FileNotFoundException; import java.io.FileWriter; import java.io.IOException; import java.util.ArrayList; import java.util.List; public class WriteTag implements Runnable { public void run() { //设置标记 boolean flag=true; ConnectMysql cmysql = new ConnectMysql(); //外层循环,每次加4 for (int j = 0;;j += 4) { List<Instance> intList = new ArrayList<Instance>();//储存两千条后清空,重新储存 for (int i = j; i < j + 4; i++) { List<Instance> selectList = new ArrayList<Instance>();//储存五百条后清空,重新储存 int h = i * 500; selectList = cmysql.getTag(h, 500); intList.addAll(selectList); //设置循环终止条件 if(selectList.size()<500){ flag=false; } } //将两千条数据写入txt中 try { FileWriter output = new FileWriter("D:\\tag.txt", true); BufferedWriter bf = new BufferedWriter(output); for (Instance l : intList) { bf.write("http://zhan.renren.com/" + l.getFeed_id() + "?gid=" + l.getTag_id() + "\r\n"); } bf.flush(); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } //若查询终止,则跳出循环,结束查询和写入 if(!flag){ break; } } } public static void main(String[] args) { WriteTag rt = new WriteTag(); Thread demo1 = new Thread(rt); demo1.start(); } }