app和mysql数据库连接 |gcc mysql

public class MainActivity extends AppCompatActivity {
private EditText userName;
private EditText password;
private Button loginBtn;
private Connection connection;
private String url = "jdbc:mysql://localhost:3306/userinfo?useUnicode=true&characterEncoding=utf8&autoReconnect=true&failOverReadOnly=false&maxReconnects=10";
private String user = "root";
private String pass = "password";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
userName = findViewById(R.id.etUserName);
password = findViewById(R.id.etPassword);
loginBtn = findViewById(R.id.btnLogin);
loginBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String userNameStr = userName.getText().toString();
String passwordStr = password.getText().toString();
try {
Class.forName("com.mysql.jdbc.Driver");
connection = DriverManager.getConnection(url, user, pass);
String sql = "select * from user where userName = ? and password = ?";
PreparedStatement preparedStatement = connection.prepareStatement(sql);
preparedStatement.setString(1, userNameStr);
preparedStatement.setString(2, passwordStr);
ResultSet resultSet = preparedStatement.executeQuery();
if (resultSet.next()) {
Intent intent = new Intent(MainActivity.this, HomePageActivity.class);
startActivity(intent);
} else {
Toast.makeText(MainActivity.this, "登录失败，请重试", Toast.LENGTH_SHORT).show();
}
} catch (ClassNotFoundException | SQLException e) {
e.printStackTrace();
} finally {
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
});
}
}

上面的代码是一个简单的Android App中使用MySQL数据库的示例。在代码中，大家首先定义了数据库连接的url、用户名和密码，然后在登录按钮的点击事件中建立了与数据库的连接。在进行查询操作时，大家使用了预处理语句来防止SQL注入攻击。最后，在操作完成后要记得关闭连接。

MySQL数据库和App的连接可以帮助开发者实现数据的快速读写和查询，提高App的效率和用户体验。当然，在使用这种方式连接数据库时，需要注意数据安全和防止SQL注入攻击等问题。