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Java实现从数据库导出大量数据记录并保存到文件的方法

2019年07月22日  | 移动技术网IT编程  | 我要评论

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。

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