Java Novice Learning Guide [day28]---Introduction to JDBC (2)

1. Use of PreparedStatement

1. Why use PreparedStatement

SQL injection problems will occur when logging in and using Statement

For example: the password is set to 'OR 1=1 OR', you can test the effect of SQL injection

Second, the use of PreparedStatement

You can use SQL statement templates

Corresponding value use? Placeholder

Don't forget? The value in the later needs to be set

Three, PreparedStatement and Statement comparison

PreparedStatement: prepared statement object

1 Allowing us to write SQL templates can avoid the trouble of string splicing. Caution:? Only write in specific places

2 Avoid SQL injection problems (as long as the characters are spliced, there is a danger of SQL injection)

3 PreparedStatement performs better than Statement in some databases

2. Things

Four characteristics of transactions (ACID)

Atomicity (Atomicity) Atomicity means that a transaction is an indivisible unit of work, and the operations in the transaction either all happen or never happen.

**Consistency** The integrity of the data before and after the transaction must be consistent.

**Isolation** Transaction isolation is when multiple users access the database concurrently, the transaction opened by the database for each user cannot be interfered by the operation data of other transactions, and multiple concurrent transactions must be isolated from each other .

**Durability (Durability) **Durability means that once a transaction is committed, its changes to the data in the database are permanent, and then even if the database fails, it should not have any impact on it.

3. Back to the primary key

After adding data, the primary key value of the data will be returned. Function key: Statement.RETURN_GENERATED_KEYS

public class HW3 {
    
    
	@Test
	public void testPK() throws Exception {
    
    
		Connection conn = JDBCUtil.getConnection();
		PreparedStatement pr = conn.prepareStatement("insert into people (name,password) values (?,?)",
				Statement.RETURN_GENERATED_KEYS);
		pr.setString(1, "麦克格雷迪");
		pr.setString(2, "1");
		pr.executeUpdate();
		ResultSet ge = pr.getGeneratedKeys();
		while (ge.next()) {
    
    
			System.out.println(ge.getLong(1));
		}
		JDBCUtil.close(ge, pr, conn);
	}
}

4. Connection pool

It is the container that holds the connection object, which can greatly improve the performance of our database operation

1. Four King Kong (required)

• Drive name driverClassName
• Address path url
• username username
• password password

2. Other common attributes

• Initial connections initialSize
• Maximum number of connections MaxActive
• Maximum waiting time maxWait
• …

3. DBCP function realization

①, guide package:

commons-dbcp-1.4.jar : Function package of data source

commons-pool-1.5.6.jar`: pool package

②, prepare jdbc.properties

③ Use key objects: BasicDataSource/ Use BasicDataSourceFactoryfactory in one step

④、DBCPUtil : Connection pool tools