# Bootstrap

graph LR
    A[开始] --> B[中间步骤]
    B --> C[结束]

sequenceDiagram
    loop Daily query
        Alice->>Bob: Hello Bob, how are you?
        alt is sick
            Bob->>Alice: Not so good :(
        else is well
            Bob->>Alice: Feeling fresh like a daisy
        end
        opt Extra response
            Bob->>Alice: Thanks for asking
        end
    end

# 8.mysql

# handing problems

# MySQL JDBC driver was not found at runtime:

it’s easy for Maven but what i used was java EE. So i need

download the mysql-connector-java-xxx.jar from the MySQL official website.
add it to project classpath:
lib -> add Framework Support -> Library -> From Disk -> the download file
modify project structure and classpath:
File -> Project Structure -> Modules -> Dependencies -> + -> JARs or directories -> the download file

# throw exception

problem basic functionality of form submission and database insertion is normal, but an attempt to use a closed PreparedStatement after the insertion operation is completed result in an exception being thrown.

solution modify index.java.

make sure no further operations are performed on the PreparedStatement before closing it. Additionally, it’s a good idea to also do some defensive programming when closing resources to ensure that even if an exception occurs, the connection is closed properly.

	catch (SQLException e) {
	System.out.println("SQL Exception: " + e.getMessage());
	e.printStackTrace();
	} finally { try { if (ps != null && !ps.isClosed()) {
	ps.close();
	} if (conn != null && !conn.isClosed()) {
	conn.close();
	}
	} catch (SQLException e) {
	e.printStackTrace();
	}

add this code after try