JDBC学习总结(四)

JDBC对LOB的读写

在JDBC中提供了java.sql.Blob和java.sql.Clob，两个类分别代表BLOB和CLOB数据。

        · BLOB(Binary Large Object)：用于存储大量的二进制数据；

        · CLOB(Character Large Object)：用于存储大量的文本数据。

    MySQL中的大容量字段类型：

        BLOB、TEXT最大64KB。BLOB是大小敏感的，而TEXT不是大写敏感的。MEDIUMBLOB、MEDIUMTEXT最大16MB。MEBIUMBLOB是大小写敏感的，而MEDIUMTEXT不是大小写敏感的。LONGBLOB、LONGTEXT最大4GB。LONGBLOB是大小写敏感的。

 

1）创建数据库表stuinfo，有id字段，姓名字段，简介字段，头像字段。头像字段设置为LONGBLOB类型。

create table stuinfo(

   id int(11) not null auto_increment,

   name varchar(20) default null,

   content longText,

   image longBlob,

   primary key(id)

)ENGINE=InnoDB default charset=utf8 row_format=redundant;

 

2）LOB写入文本文件和图片文件

注意：过低的mysql.jar版本会导致本案例不能正常运行，因此将mysql.jar包换成/mysql-connector-java-5.1.22-bin.jar

package com.yyq.blob;
import com.yyq.factory.CloseFactory;
import com.yyq.factory.ConnectionFactory;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
/**
 * Created by gao on 16-4-13.
 */
public class BlobInsertTest {
    public static void insert() throws SQLException{
        Connection conn = ConnectionFactory.getConnection();
        PreparedStatement pstmt = null;
        String sql = "insert into stuinfo(name,content,image) values(?,?,?)";
        BufferedReader brtxt = null;
        InputStream isimg = null;
        try {
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1,"test");
            // 从文件中获取输入流--读取文本
            InputStream istxt =  Thread.currentThread().getContextClassLoader()
                    .getResourceAsStream("test.txt");
            brtxt = new BufferedReader(new InputStreamReader(istxt));
            //设置Blob
            pstmt.setCharacterStream(2,brtxt);
            //从文件中获取输入流--读取图片
            isimg = Thread.currentThread().getContextClassLoader()
                    .getResourceAsStream("panda.png");
            pstmt.setBinaryStream(3,isimg);
            if (pstmt.executeUpdate() == 1){
                System.out.println("恭喜成功添加一条记录！");
            }else{
                System.out.println("添加记录失败！");
            }
        }catch (SQLException e){
            e.printStackTrace();
        }finally {
            try {
                brtxt.close();
            }catch (IOException e){
                e.printStackTrace();
            }
            try{
                isimg.close();
            }catch (IOException e){
                e.printStackTrace();
            }
            CloseFactory.close(pstmt,conn);
        }
    }
    public static void main(String[] args) throws SQLException {
        BlobInsertTest.insert();
    }
}

 

3）LOB的读取

package com.yyq.blob;
import com.yyq.factory.CloseFactory;
import com.yyq.factory.ConnectionFactory;
import java.io.*;
import java.net.ConnectException;
import java.sql.*;
/**
 * Created by gao on 16-4-13.
 */
public class BlobSelectTest {
    public static void select() {
        Connection conn = ConnectionFactory.getConnection();
        PreparedStatement pstmt = null;
        String sql = "select id,name,content,image from stuinfo where name=?";
        ResultSet rs = null;
        BufferedReader br = null;
        try {
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, "test");
            rs = pstmt.executeQuery();
            while (rs.next()) {
                Reader rd = rs.getCharacterStream(3);
                br = new BufferedReader(rd);
                String str = null;
                while ((str = br.readLine()) != null) {
                    System.out.println(str);
                }
                Blob blob = rs.getBlob(4);
                BufferedInputStream bis = new BufferedInputStream(blob.getBinaryStream());
                BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("newpanda.png"));
                byte[] bys = new byte[1024];
                int len = 0;
                while ((len = bis.read(bys, 0, 1024)) != -1) {
                    bos.write(bys, 0, len);
                }
                bos.flush();
                bos.close();
                System.out.println("\n-------------图片写好了！");
            }
        }catch (SQLException e){
            e.printStackTrace();
        }catch (IOException e){
            e.printStackTrace();
        }finally {
            CloseFactory.close(pstmt,conn);
        }
    }
    public static void main(String[] args) {
        BlobSelectTest.select();
    }
}