java jdbc 连接 mysql 数据库， mysql 实现 查询 指定行

java jdbc 连接数据库是入门级的数据库实验，之所以在这里把代码贴出来 是为了 方便以后阅读。

package com;

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

public class DbStoreHelper {
	private String insert_sql;
	private String connectStr;
	private String username;
	private String password;
	private Connection conn = null;
	private PreparedStatement psts = null;
	private static DbStoreHelper _instance = null;
	private static int count = 0;
	private static int tot = 0;
	private static Object lock = new Object();
	private final static int every_time = 20000;

	public static DbStoreHelper get() {
		if (_instance == null) {
			return _instance = new DbStoreHelper();
		}
		return _instance;
	}

	private DbStoreHelper() {
	}

	public void addPacket(Persons item) throws SQLException {
		synchronized (lock) {
			if (count == 0) {
				try {
					init();
				} catch (Exception e) {
					// TODO: handle exception
					e.printStackTrace();
				}
			}
			count++;
			psts.setString(1,item.id);
			psts.setString(2,item.time);
			psts.setString(3,item.name);
			psts.setString(4,item.gender);
			psts.setString(5,item.sign);
			psts.setDouble(6,item.latitude);
			psts.setDouble(7,item.longitude);
			psts.setInt(8,item.dis);
			psts.addBatch();
			if (count == every_time) {
				tot++;
				System.out.println("commit : " + count * tot);
				//long start = System.currentTimeMillis();
				count = 0;
				commit();
				//long end = System.currentTimeMillis();
				//System.out.println("cost time : " + (end - start) / (1000)
					//	+ "s");
			}
		}
	}

	public void commit() throws SQLException {
		psts.executeBatch(); //批量执行
		conn.commit(); //批量提交
		conn.close();
	}

	private void init() throws ClassNotFoundException, SQLException {
		connectStr = "jdbc:mysql://localhost:3306/"+FinalUtil.database+"?useServerPrepStmts=false&rewriteBatchedStatements=true&useUnicode=true&characterEncoding=utf8mb4&charset=utf8mb4";
		//指定编码方式连接数据库

		insert_sql = "INSERT INTO "+FinalUtil.new_table_name+" VALUES (?,?,?,?,?,?,?,?)";

		username = "root";//用户名
		password = "111111";//密码
		Class.forName("com.mysql.jdbc.Driver");//加载数据驱动

		//初始化连接
		conn = DriverManager.getConnection(connectStr, username, password);

		conn.setAutoCommit(false); //设置手动提交

		//获取操作对象
		psts = conn.prepareStatement(insert_sql);
	}
}

关于mysql 按行查找 数据记录

select * from limit 20 offset 10

意思是 从 第10行开始，查找20行