mysql 百万级数据查找，并写入txt文件

1，建立mysql的查询类，里面包含查询方法（两个参数，为了分页查找）

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();
	}
}