Manipulate BLOB type fields

Manipulate BLOB type fields

4.1 MySQL BLOB type

• In MySQL, BLOB is a large binary object, a container that can store a large amount of data, and it can hold data of different sizes.

• Inserting BLOB type data must use PreparedStatement, because BLOB type data cannot be written using string concatenation.

• MySQL's four BLOB types (except for the difference in the maximum amount of information stored, they are equivalent)

• In actual use, different BLOB types are defined according to the size of the data to be stored.
• It should be noted that if the stored file is too large, the performance of the database will decrease.
• If after specifying the relevant Blob type, an error is reported: xxx too large, then in the mysql installation directory, find the my.ini file and add the following configuration parameters: max_allowed_packet=16M . At the same time note: After modifying the my.ini file, you need to restart the mysql service.

4.2 Insert large data types into the data table

//获取连接
Connection conn = JDBCUtils.getConnection();
		
String sql = "insert into customers(name,email,birth,photo)values(?,?,?,?)";
PreparedStatement ps = conn.prepareStatement(sql);

// 填充占位符
ps.setString(1, "徐海强");
ps.setString(2, "[email protected]");
ps.setDate(3, new Date(new java.util.Date().getTime()));
// 操作Blob类型的变量
FileInputStream fis = new FileInputStream("xhq.png");
ps.setBlob(4, fis);
//执行
ps.execute();
		
fis.close();
JDBCUtils.closeResource(conn, ps);

4.3 Modify the Blob type field in the data table

Connection conn = JDBCUtils.getConnection();
String sql = "update customers set photo = ? where id = ?";
PreparedStatement ps = conn.prepareStatement(sql);

// 填充占位符
// 操作Blob类型的变量
FileInputStream fis = new FileInputStream("coffee.png");
ps.setBlob(1, fis);
ps.setInt(2, 25);

ps.execute();

fis.close();
JDBCUtils.closeResource(conn, ps);

4.4 Reading large data types from the data table

String sql = "SELECT id, name, email, birth, photo FROM customer WHERE id = ?";
conn = getConnection();
ps = conn.prepareStatement(sql);
ps.setInt(1, 8);
rs = ps.executeQuery();
if(rs.next()){
    
    
	Integer id = rs.getInt(1);
    String name = rs.getString(2);
	String email = rs.getString(3);
    Date birth = rs.getDate(4);
	Customer cust = new Customer(id, name, email, birth);
    System.out.println(cust); 
    //读取Blob类型的字段
	Blob photo = rs.getBlob(5);
	InputStream is = photo.getBinaryStream();
	OutputStream os = new FileOutputStream("c.jpg");
	byte [] buffer = new byte[1024];
	int len = 0;
	while((len = is.read(buffer)) != -1){
    
    
		os.write(buffer, 0, len);
	}
    JDBCUtils.closeResource(conn, ps, rs);
		
	if(is != null){
    
    
		is.close();
	}
		
	if(os !=  null){
    
    
		os.close();
	}
    
}