Java implements the method of exporting a large number of data records from a database and saving them to a file
- 2020-04-01 04:18:02
- OfStack
This article illustrates how a Java implementation can export a large number of data records from a database and save them to a file. Share with you for your reference, as follows:
Database script:
-- Table "t_test" DDL
CREATE TABLE `t_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`title` varchar(255) DEFAULT NULL,
`createTime` bigint(20) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
Code:
package com.yanek.test;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class TestDB {
public static void main(String[] args) {
Test(); //Generating test data
//Exp();
//Exp(0);
//System.out.println(readText("/opt/id.txt"));
}
public static void Exp() {
Connection Conn=null;
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
String jdbcUrl = "jdbc:mysql://127.0.0.1:3306/testcms?characterEncoding=GBK";
String jdbcUsername = "root";
String jdbcPassword = "root";
Conn = DriverManager.getConnection(jdbcUrl, jdbcUsername, jdbcPassword);
System.out.println("conn"+Conn);
Exp(Conn);
} catch (SQLException e) {
e.printStackTrace();
}
catch (InstantiationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
finally
{
try {
Conn.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public static void Exp(int startid) {
Connection Conn=null;
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
String jdbcUrl = "jdbc:mysql://127.0.0.1:3306/testcms?characterEncoding=GBK";
String jdbcUsername = "root";
String jdbcPassword = "root";
Conn = DriverManager.getConnection(jdbcUrl, jdbcUsername, jdbcPassword);
System.out.println("conn"+Conn);
Exp(Conn,startid);
} catch (SQLException e) {
e.printStackTrace();
}
catch (InstantiationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
finally
{
try {
Conn.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public static void Exp(Connection conn,int start_id) {
int counter = 0;
int startid=start_id;
boolean flag = true;
while (flag) {
flag = false;
String Sql = "SELECT * FROM t_test WHERE id>"
+ startid + " order by id asc LIMIT 50";
System.out.println("sql===" + Sql);
try {
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery(Sql);
while (rs.next()) {
flag = true;
int id = rs.getInt("id");
String title = rs.getString("title");
startid = id ;
counter++;
writeContent(counter+"--id--"+id+"--title-"+title+"rn", "/opt/","log.txt",true);
System.out.println("i="+counter+"--id--"+id+"--title-"+title);
}
rs.close();
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
writeContent(""+startid, "/opt/","id.txt",false);
}
public static void Exp(Connection conn) {
int counter = 0;
//An hour's worth of data
Long timestamp = System.currentTimeMillis() - (60 * 60 * 1000);
boolean flag = true;
while (flag) {
flag = false;
String Sql = "SELECT * FROM t_test WHERE createTime>"
+ timestamp + " LIMIT 50";
System.out.println("sql===" + Sql);
try {
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery(Sql);
while (rs.next()) {
flag = true;
int id = rs.getInt("id");
String title = rs.getString("title");
Long lastmodifytime = rs.getLong("createTime");
timestamp = lastmodifytime;
counter++;
System.out.println("i="+counter+"--id--"+id+"--title-"+title);
}
rs.close();
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
public static void Test() {
Connection Conn=null;
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
String jdbcUrl = "jdbc:mysql://127.0.0.1:3306/testcms?characterEncoding=GBK";
String jdbcUsername = "root";
String jdbcPassword = "root";
Conn = DriverManager.getConnection(jdbcUrl, jdbcUsername, jdbcPassword);
System.out.println("conn"+Conn);
for(int i=1;i<=10000;i++)
{
add(Conn,"testTitle"+i+"-"+System.currentTimeMillis());
}
} catch (SQLException e) {
e.printStackTrace();
}
catch (InstantiationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
finally
{
try {
Conn.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public static void add(Connection conn,String title)
{
PreparedStatement pstmt = null;
String insert_sql = "insert into t_test(title,createTime) values (?,?)";
System.out.println("sql="+insert_sql);
try {
pstmt = conn.prepareStatement(insert_sql);
pstmt.setString(1,title);
pstmt.setLong(2,System.currentTimeMillis());
int ret = pstmt.executeUpdate();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
finally{
try {
pstmt.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public static boolean writeContent(String c, String dirname,String filename,boolean isAppend) {
File f=new File(dirname);
if (!f.exists())
{
f.mkdirs();
}
try {
FileOutputStream fos = new FileOutputStream( dirname+File.separator+filename,isAppend);
OutputStreamWriter writer = new OutputStreamWriter(fos);
writer.write(c);
writer.close();
fos.close();
} catch (IOException e) {
e.printStackTrace();
return false;
}
return true;
}
public static String readText(String filename) {
String content = "";
try {
File file = new File(filename);
if (file.exists()) {
FileReader fr = new FileReader(file);
BufferedReader br = new BufferedReader(fr);
String str = "";
String newline = "";
while ((str = br.readLine()) != null) {
content += newline + str;
newline = "n";
}
br.close();
fr.close();
}
} catch (IOException e) {
e.printStackTrace();
}
return content;
}
}
Basic idea: start recording id by recording and execute SQL for many times. Due to the large amount of data, you can't use a single SQL statement to output. Otherwise, you will run out of memory and cause errors.
Main purpose: you can use the scenario of providing incremental output of data to a third party while doing interface development.
I hope this article has been helpful to you in Java programming.