Java实现从数据库导出大量数据记录并保存到文件的方法
作者：5iasp
这篇文章主要介绍了Java实现从数据库导出大量数据记录并保存到文件的方法,涉及Java针对数据库的读取及文件写入等操作技巧,具有一定参考借鉴价值,需要的朋友可以参考下
本文实例讲述了Java实现从数据库导出大量数据记录并保存到文件的方法。分享给大家供大家参考，具体如下：
数据库脚本：
-- 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;
代码:
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(); // 生成测试数据
//Exp();
//Exp(0);
//System.out.println(readText("/opt/id.txt"));
}
/**
* 导出数据
*/
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();
}
}
}
/**
* 导出从startid开始的数据
* @param conn
* @param start_id
*/
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+"\r\n", "/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);
}
/**
* 导出一小时内的数据
* @param conn
*/
public static void Exp(Connection conn) {
int counter = 0;
//一小时内的数据
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();
}
}
}
/**
* 写入内容到文件
*
* @param number
* @param filename
* @return
*/
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;
}
/**
* 从文件读取内容
*
* @param filename
* @return
*/
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;
}
}
基本思想: 就是通过记录开始记录id,执行多次sql来处理. 由于大数据量所以不能使用一条sql语句来输出.否则会内存不足导致错误.
主要用途: 可以使用在做接口开发时,给第三方提供数据增量输出的场景使用.
希望本文所述对大家Java程序设计有所帮助。