Oracle數據庫BLOB字段的存取

述】
    Oracle的Blob字段比較特殊，他比long字段的性能要好不少，能夠用來保存例如圖片之類的二進制數據。
寫入Blob字段和寫入其它類型字段的方式很是不一樣，由於Blob自身有一個cursor，你必須使用cursor對
blob進行操做，於是你在寫入Blob以前，必須得到cursor才能進行寫入，那麼如何得到Blob的cursor呢？
這須要你先插入一個empty的blob，這將建立一個blob的cursor，而後你再把這個empty的blob的cursor
用select查詢出來，這樣經過兩步操做，你就得到了blob的cursor，能夠真正地寫入blob數據了。
【處理流程】

--Oracle中的Lob類型示例表

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

--1. 插入空blob: (若是在數據庫中採用默認值方式對Blob字段賦值, 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往數據庫寫數據:

   update user_info set image = ? where user_id = ?;

--Oracle中的Lob類型示例表

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

--1. 插入空blob: (若是在數據庫中採用默認值方式對Blob字段賦值, 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往數據庫寫數據:

   update user_info set image = ? where user_id = ?;

 

package demo;

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

public class ReadBlob
{
    //加載驅動程序
    static
    {
            
   //讀取Blob數據
package demo;

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

public class ReadBlob
{
    //加載驅動程序
    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. 創建鏈接
            String url = "jdbc:oracle:thin:@localhost:1521:OracleDB";
            Connection conn = DriverManager.getConnection(url,"scott","tiger");
            conn.setAutoCommit(false);

            //2. 查詢數據
            String sql = "select image from user_info where user_id = 1";
            Statement stmt = conn.createStatement();
            ResultSet rs = stmt.executeQuery(sql);

            //3. 讀取Blob類型數據
            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 //讀取Blob數據
package demo;

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

public class ReadBlob
{
	//加載驅動程序
	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. 創建鏈接
			String url = "jdbc:oracle:thin:@localhost:1521:OracleDB";
			Connection conn = DriverManager.getConnection(url,"scott","tiger");
			conn.setAutoCommit(false);
			
			//2. 查詢數據
			String sql = "select image from user_info where user_id = 1";
			Statement stmt = conn.createStatement();
			ResultSet rs = stmt.executeQuery(sql);
			
			//3. 讀取Blob類型數據
			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 
               <strong>//保證文件名惟一,你能夠用主鍵+時間啊等等方法</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();
        }
    }
} 			//保證文件名惟一,你能夠用主鍵+時間啊等等方法				
			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();
		}
	}
}

 

package demo;

import java.sql.*;
import oracle.sql.BLOB;//▲此處的BLOB類全大寫, 而java.sql.Blob中的Blob非全大寫
import java.io.*;

public class WriteBlob
{
    //加載驅動程序
    static
    {
        try
        {
            Class.forName("oracle.jdbc.driver.OracleDriver");
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }
    public static void main(String[] args)
    {
        try
        {
            //1. 創建與數據庫服務器的鏈接
            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: 對於empty_blob()應放在SQL語句中直接賦值, 使用預置語句的方式賦值沒法實現.
            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. 查詢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. 使用字節流將待入庫的文件寫入到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. 向數據庫中寫入數據
            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();
        }
    }
}