本篇内容主要讲解“MySQL、sqlserver和oracle三种数据库的大对象存取方式”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“mysql、sqlserver和oracle三种数据库的大对象存取方式”吧!

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大对象存取:
类型一般应该用mediumblod,
blob只能存2的16次方个byte,
mediumblod是24次方,
一般来说够用了.longblob是32次方有些大.
 
MYSQL默认配置只能存1M大小的文件,要修改配置,WIN版本的在mysql.ini文件中
修改max_allowed_packet,net_buffer_length等几个参数,或直接SET GLOBAL varName=value.
linux版本可以在启动参数后加-max_allowed_packet=xxM等几个参数.
 
MYSQL存大对象最好直接就setBinaryStream,又快又方便.
而不要先插入空再造型成BLOB然后再setBlob
 
例子:
import java.sql.*;
import java.io.*;
public class DBTest {
 
 
  static String driver = "org.gjt.mm.mysql.Driver";
  static String url = "jdbc:mysql://localhost:3306/test";
  static String user = "root";
  static String passwd = "passwd";
  public static void main(String[] args) throws Exception {
    Connection conn = null;
    try {
      Class.forName(driver);
      conn = DriverManager.getConnection(url,user,passwd);
      
      int op = 1;
      //插入
      if (op == 0) {
        PreparedStatement ps = conn.prepareStatement("insert into tb_file values (?,?)");
        ps.setString(1, "aaa.exe");
        InputStream in = new FileInputStream("d:/aaa.exe");
        ps.setBinaryStream(2,in,in.available());
        ps.executeUpdate();
        ps.close();
      }
      else {
        //取出
        PreparedStatement ps = conn.prepareStatement("select * from  tb_file where filename = ?");
        ps.setString(1, "aaa.exe");
        ResultSet rs = ps.executeQuery();
        rs.next();
        InputStream in = rs.getBinaryStream("filecontent");
        System.out.println(in.available());
        FileOutputStream out = new FileOutputStream("d:/bbb.exe");
        byte[] b = new byte[1024];
        int len = 0;
        while ( (len = in.read(b)) != -1) {
          out.write(b, 0, len);
          out.flush();
        }
        out.close();
        in.close();
        rs.close();
        ps.close();
      }
    }
    catch (Exception ex) {
      ex.printStackTrace(System.out);
    }
    finally {
      try {conn.close();}
      catch (Exception ex) { }
    }
  }
}
 
 
sqlserver 大对象存取没有什么多说的,只要是image类型就行了,注意这是column类型,有人以为它只能存
图象.image是文件镜象的意思.
import java.sql.*;
import java.io.*;
public class DBTest {
 
 
  static String driver = "com.microsoft.jdbc.sqlserver.SQLServerDriver";
  static String url = "jdbc:microsoft:sqlserver://192.168.0.202:9999999999;DatabaseName=dddd";
  static String user = "sa";
  static String passwd = "ps";
  public static void main(String[] args) throws Exception {
    Connection conn = null;
    try {
      Class.forName(driver);
      conn = DriverManager.getConnection(url,user,passwd);
      int op = 0;
      //插入
      if (op == 0) {
        PreparedStatement ps = conn.prepareStatement("insert into tb_file values (?,?)");
        ps.setString(1, "aaa.exe");
        InputStream in = new FileInputStream("d:/aaa.exe");
        ps.setBinaryStream(2,in,in.available());
        ps.executeUpdate();
        ps.close();
      }
      else {
        //取出
        PreparedStatement ps = conn.prepareStatement("select * from  tb_file where filename = ?");
        ps.setString(1, "aaa.exe");
        ResultSet rs = ps.executeQuery();
        rs.next();
        InputStream in = rs.getBinaryStream("filecontent");
        System.out.println(in.available());
        FileOutputStream out = new FileOutputStream("d:/bbb.exe");
        byte[] b = new byte[1024];
        int len = 0;
        while ( (len = in.read(b)) != -1) {
          out.write(b, 0, len);
          out.flush();
        }
        out.close();
        in.close();
        rs.close();
        ps.close();
      }
    }
    catch (Exception ex) {
      ex.printStackTrace(System.out);
    }
    finally {
      try {conn.close();}
      catch (Exception ex) { }
    }
  }
}
 
 
 
ORACLE的大对象存储有些变态,要无论是Blob,还是CLOB都要求先插入一个空值,然后
查询并锁定这一条记录,获取对Lob的引用再进行填充,网上有太多的例子.我个人认为
这种方法垃圾得连写都不想写了,你可以自己去搜索一下.
这种特别的操作既增加操作的复杂度,又违反了JDBC接口的规范,所以我极力反对这样
使用,如果你和我有同样的观点.那么我提供另一种通用的方法.就是你不用LOB而用
oracle的LONG RAW来代替它们.这样就可以象其它对象一样操作了:
 
create table tb_file(filename varchar2(255),filecontent LONG RAW);
 
 
import java.sql.*;
import java.io.*;
 
public class BlobTest {
 
  static String driver = "oracle.jdbc.driver.Driver";
  static String url = "jdbc:oracle:thin:@localhost:1521:test";
  static String user = "system";
  static String passwd = "passwd";
  public static void main(String[] args) throws Exception {
    Connection conn = null;
    try {
      Class.forName(driver);
      conn = DriverManager.getConnection(url, user, passwd);
      int op = 1;
      //插入
      if (op == 0) {
        PreparedStatement ps = conn.prepareStatement("insert into tb_file values (?,?)");
        ps.setString(1, "aaa.exe");
        InputStream in = new FileInputStream("d:/aaa.exe");
        ps.setBinaryStream(2,in,in.available());
        ps.executeUpdate();
        ps.close();
      }
      else {
        //取出
        PreparedStatement ps = conn.prepareStatement("select * from  tb_file where filename = ?");
        ps.setString(1, "aaa.exe");
        ResultSet rs = ps.executeQuery();
        rs.next();
        InputStream in = rs.getBinaryStream("filecontent");
        System.out.println(in.available());
        FileOutputStream out = new FileOutputStream("d:/bbb.exe");
        byte[] b = new byte[1024];
        int len = 0;
        while ( (len = in.read(b)) != -1) {
          out.write(b, 0, len);
          out.flush();
        }
        out.close();
        in.close();
        rs.close();
        ps.close();
      }
    }
    catch (Exception ex) {
      ex.printStackTrace(System.out);
    }
    finally {
      try {
        conn.close();
      }
      catch (Exception ex) {}
    }
  }
}

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