Oracle数据库BLOB字段的存取

时间 2019-11-29

原文原文链接

述】
Oracle的Blob字段比较特殊，他比long字段的性能要好不少，能够用来保存例如图片之类的二进制数据。
写入Blob字段和写入其它类型字段的方式很是不一样，由于Blob自身有一个cursor，你必须使用cursor对
blob进行操做，于是你在写入Blob以前，必须得到cursor才能进行写入，那么如何得到Blob的cursor呢？
这须要你先插入一个empty的blob，这将建立一个blob的cursor，而后你再把这个empty的blob的cursor
用select查询出来，这样经过两步操做，你就得到了blob的cursor，能够真正地写入blob数据了。
【处理流程】java

[sql] view plain copy print ?

--Oracle中的Lob类型示例表
create table user_info
(
user_id number(10) primary key,
name varchar2(20),
image blob
);
--1. 插入空blob: (若是在数据库中采用默认值方式对Blob字段赋值, 此步可省略)
insert into user_info values (1, 'Jacky', empty_blob());
--2. 得到blob的cursor:
select image from user_info where user_id = ? for update;
--3. 用cursor往数据库写数据:
update user_info set image = ? where user_id = ?;

--Oracle中的Lob类型示例表

create table user_info 
(
  user_id number(10) primary key,
  name varchar2(20),
  image blob
);

--1. 插入空blob: (若是在数据库中采用默认值方式对Blob字段赋值, 此步可省略)

   insert into user_info values (1, 'Jacky', empty_blob());

--2. 得到blob的cursor:
  
   select image from user_info where user_id = ? for update;

--3. 用cursor往数据库写数据:

   update user_info set image = ? where user_id = ?;

//读取Blob数据

package demo;
import java.sql.*;
import java.io.*;
public class ReadBlob
{
//加载驱动程序
static
{

[java] view plain copy print ?

//读取Blob数据
package demo;
import java.sql.*;
import java.io.*;
public class ReadBlob
{
//加载驱动程序
static
{
try
{
Class.forName("oracle.jdbc.driver.OracleDriver");
} catch (ClassNotFoundException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static void main(String[] args)
{
try
{
//1. 创建链接
String url = "jdbc:oracle:thin:@localhost:1521:OracleDB";
Connection conn = DriverManager.getConnection(url,"scott","tiger");
conn.setAutoCommit(false);
//2. 查询数据
String sql = "select image from user_info where user_id = 1";
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery(sql);
//3. 读取Blob类型数据
Blob blob = null;
if(rs.next())
{
blob = rs.getBlob(1);
}
byte[] temp = new byte[(int)blob.length()];
InputStream in = blob.getBinaryStream();
in.read(temp)s

//读取Blob数据
package demo;

import java.sql.*;
import java.io.*;

public class ReadBlob
{
	//加载驱动程序
	static 
	{
		
		try
		{
			Class.forName("oracle.jdbc.driver.OracleDriver");
		} catch (ClassNotFoundException e)
		{
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	
	public static void main(String[] args)
	{
		try
		{
			//1. 创建链接
			String url = "jdbc:oracle:thin:@localhost:1521:OracleDB";
			Connection conn = DriverManager.getConnection(url,"scott","tiger");
			conn.setAutoCommit(false);
			
			//2. 查询数据
			String sql = "select image from user_info where user_id = 1";
			Statement stmt = conn.createStatement();
			ResultSet rs = stmt.executeQuery(sql);
			
			//3. 读取Blob类型数据
			Blob blob = null;
			if(rs.next())
			{
				blob = rs.getBlob(1);
			}
			byte[] temp = new byte[(int)blob.length()];
			InputStream in = blob.getBinaryStream();
			in.read(temp)s

[java] view plain copy print ?

<strong>//保证文件名惟一,你能够用主键+时间啊等等方法</strong>
File file = new File("D://img.bmp");
FileOutputStream fout = new FileOutputStream(file);
fout.write(temp);
in.close();
fout.close();
} catch (Exception e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

			//保证文件名惟一,你能够用主键+时间啊等等方法				
			File file = new File("D://img.bmp");
			FileOutputStream fout = new FileOutputStream(file);
			fout.write(temp);
			in.close();
			fout.close();
		} catch (Exception e)
		{
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

//写Blob数据

package demo;
import java.sql.*;
import oracle.sql.BLOB;//▲此处的BLOB类全大写, 而java.sql.Blob中的Blob非全大写
import java.io.*;
public class WriteBlob
{
//加载驱动程序
static
{
try
{
Class.forName("oracle.jdbc.driver.OracleDriver");
}
catch(Exception e)
{
e.printStackTrace();
}
}
public static void main(String[] args)
{
try
{
//1. 创建与数据库服务器的链接
String url = "jdbc:oracle:thin:@localhost:1521:OracleDB";
Connection conn = DriverManager.getConnection(url,"scott","tiger");
conn.setAutoCommit(false);
//2. 首先向表中插入空的Blob
//★注意: 对于empty_blob()应放在SQL语句中直接赋值, 使用预置语句的方式赋值没法实现.
String sql = "insert into user_info values(?,?,empty_blob())";
PreparedStatement ps = conn.prepareStatement(sql);
ps.setInt(1, 1);
ps.setString(2, "Lucy");
ps.executeUpdate();
//3. 查询Blob, 得到Blob的Cursor
sql = "select image from user_info where user_id = ?";
ps = conn.prepareStatement(sql);
ps.setInt(1, 1);
ResultSet rs = ps.executeQuery();
BLOB blob = null;
if(rs.next())
{
blob = (BLOB)rs.getBlob(1);
}
//4. 使用字节流将待入库的文件写入到blob中
File file = new File("D://iriver//sample1.bmp");
FileInputStream fin = new FileInputStream(file);
byte[] temp = new byte[fin.available()];
fin.read(temp);
OutputStream out = blob.getBinaryOutputStream();
out.write(temp);
fin.close();
out.close();
//5. 向数据库中写入数据
sql = "update user_info set image = ? where user_id = ?";
ps = conn.prepareStatement(sql);
ps.setBlob(1, blob);
ps.setInt(2, 1);
ps.executeUpdate();
conn.commit();
} catch (Exception e)
{
e.printStackTrace();
}
}
}