JDBC操作MySQL Lob字段记实

虽然Java的持久化框架多如牛毛，但都离不开JDBC技术，JDBC在某些时候是其他框架难以取代的。也是java操作数据库最根本的技术。

上文写了JDBC操作DB2 Lob字段bug问题，为此，我还特意写了MySQL平台下的Lob字段操作，以便能得出更为准确的结论。

本文通过一个简单的Java类，就能增删改查MySQL的Lob字段。google一下，JDBC操作数据库Lob字段的完整代码一个也没找到。因此把这个测试代码也放在blog上，希望给正在用JDBC做MySQL开发的朋友们一点参考。

环境：

MySQL-5.0.45

mysql-connector-java-5.1.5.zip

测试的SQL脚本：

CREATE TABLE t_lob ( 
  NAME varchar(24) DEFAULT NULL, 
  TXT text, 
  IMG blob 
) ENGINE=InnoDB DEFAULT CHARSET=gbk;

测试代码：

package lob;

import java.sql.*; 
import java.io.*;

/** 
* JDBC 读取MySQL lob字段测试 
* File: TestLob4MySQL.java 
* User: leizhimin 
* Date: 2008-3-3 14:44:30 
*/ 
public class TestLob4MySQL { 
    public static final String url = "jdbc:mysql://localhost/testdb"; 
    public static final String username = "root"; 
    public static final String password = "leizhimin"; 
    public static final String driverClassName = "com.mysql.jdbc.Driver";

/** 
     * 数据库连接获取器 
     * 
     * @return 数据库连接 
     */ 
    public static Connection makeConnection() { 
        Connection conn = null; 
        try { 
            Class.forName(driverClassName); 
        } catch (ClassNotFoundException e) { 
            e.printStackTrace(); 
        } 
        try { 
            conn = DriverManager.getConnection(url, username, password); 
        } catch (SQLException e) { 
            e.printStackTrace(); 
        } 
        return conn; 
    }

/** 
     * 测试数据库连接 
     */ 
    public static void testConnection() { 
        Connection conn = makeConnection(); 
        try { 
            Statement stmt = conn.createStatement(); 
            ResultSet rs = stmt.executeQuery("SELECT * FROM mysql.user"); 
            while (rs.next()) { 
                String s1 = rs.getString(1); 
                System.out.println(s1); 
            } 
            rs.close(); 
            stmt.close(); 
        } catch (SQLException e) { 
            e.printStackTrace(); 
        } finally { 
            try { 
                conn.close(); 
            } catch (SQLException e) { 
                e.printStackTrace(); 
            } 
        } 
    }

/** 
     * 插入Lob字段 
     */ 
    public static void testInsertlob() { 
        Connection conn = makeConnection(); 
        try { 
            conn.setAutoCommit(false); 
            File txtFile = new File("C:\\txt.txt"); 
            File imgFile = new File("C:\\img.png"); 
            int txt_len = (int) txtFile.length(); 
            int img_len = (int) imgFile.length(); 
            try { 
                InputStream fis1 = new FileInputStream(txtFile); 
                InputStream fis2 = new FileInputStream(imgFile); 
                PreparedStatement pstmt = conn.prepareStatement("INSERT INTO T_LOB(NAME,TXT,IMG) VALUES('G',?,?)"); 
                pstmt.setAsciiStream(1, fis1, txt_len); 
                pstmt.setBinaryStream(2, fis2, img_len); 
                pstmt.executeUpdate(); 
                conn.commit(); 
            } catch (FileNotFoundException e) { 
                e.printStackTrace(); 
            } 
        } catch (SQLException e) { 
            e.printStackTrace(); 
        } finally { 
            try { 
                conn.close(); 
            } catch (SQLException e) { 
                e.printStackTrace(); 
            } 
        } 
    }

/** 
     * 读取lob字段 
     */ 
    public static void testQueryLob() { 
        Connection conn = makeConnection(); 
        try { 
            conn.setAutoCommit(false); 
            Statement stmt = conn.createStatement(); 
            ResultSet rs = stmt.executeQuery("SELECT TXT,IMG FROM T_LOB"); 
            int i = 1; 
            while (rs.next()) { 
                Clob clob = rs.getClob("TXT"); 
                Blob blob = rs.getBlob("IMG"); 
                InputStream txtIs = rs.getAsciiStream("TXT"); 
                InputStream imgIs = rs.getBinaryStream("IMG");

InputStreamReader txtIsr = new InputStreamReader(txtIs); 
                InputStreamReader imgIsr = new InputStreamReader(imgIs);

BufferedReader buff_txtIsr = new BufferedReader(txtIsr); 
                BufferedReader buff_imgIsr = new BufferedReader(imgIsr);

String line = null; 
                while (null != (line = buff_txtIsr.readLine())) { 
                    System.out.println(line); //将其输出至屏幕，实际你可以按照需要处理 
                }

File fileOutput = new File("c:\\img_x" + i + ".png"); 
                FileOutputStream fo = new FileOutputStream(fileOutput); 
                int c; 
                while ((c = imgIs.read()) != -1) 
                    fo.write(c); 
                fo.close(); 
                System.out.println("img " + i + " retrieved!"); 
                i++; 
            } 
            conn.commit(); 
        } catch (SQLException e) { 
            e.printStackTrace(); 
        } catch (Exception e) { 
            e.printStackTrace(); 
        } finally { 
            try { 
                conn.close(); 
            } catch (SQLException e) { 
                e.printStackTrace(); 
            } 
        }

}

/** 
     * 读取lob字段 
     */ 
    public static void testQueryLob1() { 
        Connection conn = makeConnection(); 
        try { 
            conn.setAutoCommit(false); 
            Statement stmt = conn.createStatement(); 
            ResultSet rs = stmt.executeQuery("SELECT TXT,IMG FROM T_LOB"); 
            while (rs.next()) { 
                Clob clob = rs.getClob("TXT"); 
                Blob blob = rs.getBlob("IMG"); 
                InputStream txtIs = clob.getAsciiStream(); 
                InputStream imgIs = blob.getBinaryStream();

InputStreamReader txtIsr = new InputStreamReader(txtIs); 
                InputStreamReader imgIsr = new InputStreamReader(imgIs);

BufferedReader buff_txtIsr = new BufferedReader(txtIsr); 
                BufferedReader buff_imgIsr = new BufferedReader(imgIsr);

String line = null; 
                while (null != (line = buff_txtIsr.readLine())) { 
                    System.out.println(line); //将其输出至屏幕，实际你可以按照需要处理 
                } 
            } 
            conn.commit(); 
        } catch (SQLException e) { 
            e.printStackTrace(); 
        } catch (Exception e) { 
            e.printStackTrace(); 
        } finally { 
            try { 
                conn.close(); 
            } catch (SQLException e) { 
                e.printStackTrace(); 
            } 
        } 
    }

/** 
     * 删除lob字段 
     */ 
    public static void testDeleteLob() { 
        Connection conn = makeConnection(); 
        try { 
            conn.setAutoCommit(false); 
            Statement stmt = conn.createStatement(); 
            int row = stmt.executeUpdate("DELETE FROM T_LOB"); 
            conn.commit(); 
            System.out.println("删除 " + row + " 行数据！"); 
        } catch (SQLException e) { 
            e.printStackTrace(); 
        } finally { 
            try { 
                conn.close(); 
            } catch (SQLException e) { 
                e.printStackTrace(); 
            } 
        } 
    }

/** 
     * 读取lob字段 
     */ 
    public static void testUpdateLob() { 
        Connection conn = makeConnection();

try { 
            String in_str="HAHAHAHAHAHA!!!"; 
            File in_file=new File("c:\\img_haha.png"); 
            InputStream txt_is = string2InputStream(in_str); 
            InputStream img_is =new FileInputStream(in_file);

conn.setAutoCommit(false); 
            PreparedStatement pstmt = conn.prepareStatement("UPDATE T_LOB SET TXT=?, IMG=? WHERE NAME='G'"); 
            pstmt.setAsciiStream(1,txt_is,in_str.getBytes().length); 
            pstmt.setBinaryStream(2,img_is,(int)in_file.length());

int row = pstmt.executeUpdate();

conn.commit(); 
            txt_is.close(); 
            img_is.close();

//            System.out.println("更新 " + row + " 行数据！"); 
        } catch (SQLException e) { 
            e.printStackTrace(); 
        } catch (FileNotFoundException e) { 
            e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates. 
        } catch (IOException e) { 
            e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates. 
        } finally { 
            try { 
                conn.close(); 
            } catch (SQLException e) { 
                e.printStackTrace(); 
            } 
        } 
    }

public static void main(String args[]) { 
//        testInsertlob(); 
//        testQueryLob(); 
//        testQueryLob1(); 
//        testDeleteLob(); 
        testUpdateLob(); 
    }

public static InputStream string2InputStream(String str) { 
        if (str == null) return null; 
        return new ByteArrayInputStream(str.getBytes()); 
    }

public static String inputStream2String(InputStream is) { 
        StringBuffer sb = new StringBuffer(); 
        BufferedReader br = new BufferedReader(new InputStreamReader(is)); 
        String inputLine; 
        try { 
            while ((inputLine = br.readLine()) != null) { 
                sb.append(inputLine).append("\n"); 
            } 
        } catch (IOException e) { 
            e.printStackTrace(); 
        } 
        return sb.toString(); 
    } 
}

一一运行各个测试方法，都没有问题。

本文转自 leizhimin 51CTO博客，原文链接：http://blog.51cto.com/lavasoft/64963，如需转载请自行联系原作者