Java实现从数据库导出大量数据记录并保存到文件的方法(转)

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+" ", "/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 = " "; 
     } 
     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.

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原文地址：https://www.cnblogs.com/chenning/p/5030854.html