MySQL - Java 語法

Hello, aspiring programmers! Today, we're going to embark on an exciting journey into the world of MySQL and Java. As your friendly neighborhood computer science teacher, I'm here to guide you through this adventure. Don't worry if you've never written a line of code before – we'll start from the very beginning and work our way up together.

JDBC 安裝

Before we dive into the fun stuff, we need to set up our tools. Think of this as preparing your art supplies before painting a masterpiece!

What is JDBC?

JDBC stands for Java Database Connectivity. It's like a translator that helps Java talk to databases, including MySQL. Imagine you're trying to order food in a foreign country – JDBC is your trusty language interpreter!

Steps to Install JDBC

1. Download the MySQL Connector/J: Visit the official MySQL website and download the latest version of the MySQL Connector/J.

2. Add the JAR file to your project:

• If you're using an IDE like Eclipse: a. Right-click on your project b. Select "Properties" c. Go to "Java Build Path" d. Click on "Add External JARs" e. Select the MySQL Connector/J JAR file you downloaded

3. Verify the installation: Create a simple Java class and try to import the JDBC driver:

import java.sql.*;

public class JDBCTest {
public static void main(String[] args) {
System.out.println("JDBC is ready to go!");
}
}

If this compiles without errors, congratulations! You've successfully installed JDBC.

Java Functions to Access MySQL

Now that we have our translator (JDBC) ready, let's learn how to communicate with MySQL using Java. Here are the key functions you'll be using:

Function	Description
DriverManager.getConnection()	Establishes a connection to the database
Connection.createStatement()	Creates a Statement object for sending SQL queries
Statement.executeQuery()	Executes a SELECT query and returns a ResultSet
Statement.executeUpdate()	Executes an INSERT, UPDATE, or DELETE query
ResultSet.next()	Moves the cursor to the next row in the ResultSet
ResultSet.getString()	Retrieves the value of a column as a String
ResultSet.getInt()	Retrieves the value of a column as an int
Connection.close()	Closes the database connection

Don't worry if these seem overwhelming – we'll see them in action soon!

Basic Example

Let's put everything we've learned into practice with a simple example. We'll create a program that connects to a MySQL database, retrieves some data, and displays it.

import java.sql.*;

public class MySQLExample {
public static void main(String[] args) {
// JDBC URL, username, and password of MySQL server
String url = "jdbc:mysql://localhost:3306/mydb";
String user = "root";
String password = "password";

try {
// Step 1: Establish the connection
Connection connection = DriverManager.getConnection(url, user, password);

// Step 2: Create a statement
Statement statement = connection.createStatement();

// Step 3: Execute a query
String sql = "SELECT * FROM employees";
ResultSet resultSet = statement.executeQuery(sql);

// Step 4: Process the results
while (resultSet.next()) {
int id = resultSet.getInt("id");
String name = resultSet.getString("name");
int age = resultSet.getInt("age");
System.out.println("Employee: " + id + ", " + name + ", " + age);
}

// Step 5: Close the connection
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}

Let's break this down step by step:

1. We start by importing the necessary Java SQL package.

2. We define our database connection details: the URL, username, and password.

3. We establish a connection using DriverManager.getConnection().

4. We create a Statement object to send SQL queries to the database.

5. We execute a SELECT query using executeQuery() and store the results in a ResultSet.

6. We process the results using a while loop and ResultSet.next() to move through each row.

7. For each row, we retrieve the values using getInt() and getString().

8. Finally, we close the connection to free up resources.

Remember, always handle exceptions when working with databases. In this example, we're using a try-catch block to catch any SQLException that might occur.

Conclusion

Congratulations! You've just taken your first steps into the world of Java and MySQL integration. We've covered the basics of JDBC installation, key Java functions for database access, and walked through a practical example.

As you continue your journey, remember that programming is like learning a new language – it takes practice and patience. Don't be afraid to experiment and make mistakes – that's how we learn and grow!

In our next lesson, we'll explore more advanced topics like prepared statements and transactions. Until then, happy coding, and may your queries always return the results you're looking for!

Credits: Image by storyset