java用limit循环读取mysql直到全部读完，并能显示读了多少条

Question

数据库数据很多，每次读5000条左右，用分页的方式循环读完，下面是测试代码，现在需要分页的代码，可以写在我发的测试代码上面，尽量详细，谢谢。
package webtest;
import java.sql.*;
import java.io.BufferedWriter;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.File;

public class test5{

static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";

static final String DB_URL = "jdbc:mysql://localhost:3306/gumysql";

static final String USER = "root";
static final String PASS = "123456";
public static final String FILE_NAME = "again1.txt";//要创建的文件名
public static final String fn = "F:/NEWtest/";//文件指定存放的路径
public static void creatFile(String fn, String fileName) {
File folder = new File(fn);
//文件夹路径不存在
if (!folder.exists() && !folder.isDirectory()) {
System.out.println("文件夹路径不存在，创建路径:" + fn);
folder.mkdirs();
} else {
System.out.println("文件夹路径存在:" + fn);
}

// 如果文件不存在就创建
File file = new File(fn + fileName);
if (!file.exists()) {
    System.out.println("文件不存在，创建文件:" + fn+ fileName);
    try {
        file.createNewFile();
    } catch (IOException e) {
        e.printStackTrace();
    }
} else {
    System.out.println("文件已存在，文件为:" + fn+ fileName);
}

}

public static void wf(String file, String conent) {
BufferedWriter out = null;
try {
out = new BufferedWriter(new OutputStreamWriter(
new FileOutputStream(file, true)));
out.write(conent+"\r\n");
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}

public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
try{
creatFile(fn, FILE_NAME);
Class.forName("com.mysql.jdbc.Driver");

System.out.println("连接数据库...");
conn = DriverManager.getConnection(DB_URL,USER,PASS);


System.out.println(" 实例化Statement对象...");
stmt = conn.createStatement();
String sql;
sql = "SELECT id, name, url ,country FROM websites ";
ResultSet rs = stmt.executeQuery(sql);

String fn = "F://NEWtest//again1.txt";
wf(fn,"ID ,站点名称, 站点,country.");
while(rs.next()){

    int id  = rs.getInt("id");            
    String name = rs.getString("name");
    String url = rs.getString("url");
    String country = rs.getString("country");



    System.out.print("ID: " + id);

    System.out.print(", 站点名称: " + name);

    System.out.print(", 站点 URL: " + url);
    System.out.print(", country: " + country);

    System.out.print("\n");
    wf(fn,id+"," + name+ "," + url+ "," + country);
}

rs.close();
stmt.close();
conn.close();

}catch(SQLException se){

se.printStackTrace();

}catch(Exception e){

e.printStackTrace();

}finally{

try{
    if(stmt!=null) stmt.close();
}catch(SQLException se2){
}
try{
    if(conn!=null) conn.close();
}catch(SQLException se){
    se.printStackTrace();
}

}
System.out.println("Goodbye!");
}

}

Answer 1

可以先查询表里所有数据的总数 sumNum;
SELECT count(*) FROM websites;
System.out.print("共获取到"+sumNum+"条数据")；
再根据得到的总数值去除以5000，再用总数求余，这样获取循环的次数pageSize
int pageSize = 0;
pageSize = sumNum / 5000;
int tmpPage = 0;
tmpPage = sumNum % 5000 == 0 ? 0 : 1;
pageSize = pageSize + tmpPage;
然后循环
for（int i=0;i<=pageSize;i++）{
// 处理逻辑查询
SELECT id, name, url ,country FROM websites limit i*5000，5000；
// 遍历ResultSet 得到数据去处理
}
既然分页查询那就要建立很多连接，注意关闭