如何使用JDBC连接数据库并执行SQL语句
1. JDBC入门
JDBC（Java Database Connectivity）是Java程序与数据库进行交互的一种标准接口，它提供了一种简单的方式来连接和操作数据库。在使用JDBC之前，需要先了解以下几个概念：
- JDBC Driver：JDBC驱动程序是一个Java类，用于将Java应用程序与特定数据库管理系统（DBMS）连接。JDBC驱动程序分为四种类型：JDBC-ODBC桥接驱动程序、本地api驱动程序、网络协议驱动程序和本地协议驱动程序。
- Connection：Connection是一个JDBC接口，用于连接到数据库。在Java程序中，通过Connection接口的实现类来实现与数据库的连接。
- Statement：Statement是一个JDBC接口，用于向数据库发送sql语句并执行它们。在Java程序中，通过Connection对象创建Statement对象。
- ResultSet：ResultSet是一个JDBC接口，用于表示从数据库中检索到的结果集。ResultSet对象通过Statement对象的executeQuery()方法返回。
下面是一个简单的JDBC连接示例：
import java.sql.*;
public class JDBCDemo {
public static void main(String[] args) {
try {
// 加载JDBC驱动程序
Class.forName("com.Mysql.cj.jdbc.Driver");
// 建立数据库连接
Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb", "root", "passWord");
// 执行SQL查询
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("SELECT * FROM users");
while (rs.next()) {
System.out.println(rs.getInt(1) + ", " + rs.getString(2) + ", " + rs.getString(3));
}
// 关闭数据库连接
rs.close();
stmt.close();
conn.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
2. 抽取工具类
在实际开发中，我们通常会抽取出一个JDBC工具类来封装JDBC相关操作，以方便代码的重用和维护。下面是一个简单的JDBC工具类示例：
import java.sql.*;
public class JDBCUtils {
private static final String URL = "jdbc:mysql://localhost:3306/mydb";
private static final String USER = "root";
private static final String PASSWORD = "password";
static {
try {
// 加载JDBC驱动程序
Class.forName("com.mysql.cj.jdbc.Driver");
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
public static Connection getConnection() {
Connection conn = null;
try {
// 建立数据库连接
conn = DriverManager.getConnection(URL, USER, PASSWORD);
} catch (SQLException e) {
e.printStackTrace();
}
return conn;
}
public static void release(ResultSet rs, Statement stmt, Connection conn) {
try {
if (rs != null) rs.close();
if (stmt != null) stmt.close();
if (conn != null) conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}3. Statement CRUD
Statement是JDBC中最基本的操作方式，它用于向数据库发送SQL语句并执行它们。下面是一个使用Statement进行CRUD操作的示例：
import java.sql.*;
public class StatementCRUD {
public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
try {
conn = JDBCUtils.getConnection();
stmt = conn.createStatement();
// 插入数据
String sql = "INSERT INTO users (name, age) VALUES ('Tom', 18)";
stmt.executeUpdate(sql);
// 更新数据
sql = "UPDATE users SET age = 20 WHERE name = 'Tom'";
stmt.executeUpdate(sql);
// 删除数据
sql = "DELETE FROM users WHERE age = 20";
stmt.executeUpdate(sql);
// 查询数据
sql = "SELECT * FROM users";
rs = stmt.executeQuery(sql);
while (rs.next()) {
System.out.println(rs.getInt(1) + ", " + rs.getString(2) + ", " + rs.getInt(3));
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
JDBCUtils.release(rs, stmt, conn);
}
}
}4. 演练CRUD
下面是一个使用PreparedStatement进行CRUD操作的示例：
import java.sql.*;
public class PreparedStatementCRUD {
public static void main(String[] args) {
Connection conn = null;
PreparedStatement pstmt = null;
ResultSet rs = null;
try {
conn = JDBCUtils.getConnection();
// 插入数据
String sql = "INSERT INTO users (name, age) VALUES (?, ?)";
pstmt = conn.prepareStatement(sql);
pstmt.setString(1, "Tom");
pstmt.setInt(2, 18);
pstmt.executeUpdate();
// 更新数据
sql = "UPDATE users SET age = ? WHERE name = ?";
pstmt = conn.prepareStatement(sql);
pstmt.setInt(1, 20);
pstmt.setString(2, "Tom");
pstmt.executeUpdate();
// 删除数据
sql = "DELETE FROM users WHERE age = ?";
pstmt = conn.prepareStatement(sql);
pstmt.setInt(1, 20);
pstmt.executeUpdate();
// 查询数据
sql = "SELECT * FROM users";
pstmt = conn.prepareStatement(sql);
rs = pstmt.executeQuery();
while (rs.next()) {
System.out.println(rs.getInt(1) + ", " + rs.getString(2) + ", " + rs.getInt(3));
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
JDBCUtils.release(rs, pstmt, conn);
}
}
}5. Dao模式(声明与实现分开)
Dao（Data Access Object）模式是一种用于封装数据访问逻辑的设计模式。它将数据访问逻辑与业务逻辑分离开来，使得代码更易于维护和扩展。下面是一个使用Dao模式进行CRUD操作的示例：
import java.sql.*;
public class UserDAO {
private static final String INSERT_SQL = "INSERT INTO users (name, age) VALUES (?, ?)";
private static final String UPDATE_SQL = "UPDATE users SET age = ? WHERE name = ?";
private static final String DELETE_SQL = "DELETE FROM users WHERE age = ?";
private static final String SELECT_SQL = "SELECT * FROM users";
public void insert(User user) {
Connection conn = null;
PreparedStatement pstmt = null;
try {
conn = JDBCUtils.getConnection();
pstmt = conn.prepareStatement(INSERT_SQL);
pstmt.setString(1, user.getName());
pstmt.setInt(2, user.getAge());
pstmt.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
} finally {
JDBCUtils.release(null, pstmt, conn);
}
}
public void update(User user) {
Connection conn = null;
PreparedStatement pstmt = null;
try {
conn = JDBCUtils.getConnection();
pstmt = conn.prepareStatement(UPDATE_SQL);
pstmt.setInt(1, user.getAge());
pstmt.setString(2, user.getName());
pstmt.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
} finally {
JDBCUtils.release(null, pstmt, conn);
}
}
public void delete(int age) {
Connection conn = null;
PreparedStatement pstmt = null;
try {
conn = JDBCUtils.getConnection();
pstmt = conn.prepareStatement(DELETE_SQL);
pstmt.setInt(1, age);
pstmt.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
} finally {
JDBCUtils.release(null, pstmt, conn);
}
}
public List<User> selectAll() {
Connection conn = null;
PreparedStatement pstmt = null;
ResultSet rs = null;
List<User> userList = new ArrayList<>();
try {
conn = JDBCUtils.getConnection();
pstmt = conn.prepareStatement(SELECT_SQL);
rs = pstmt.executeQuery();
while (rs.next()) {
User user = new User();
user.setId(rs.getInt(1));
user.setName(rs.getString(2));
user.setAge(rs.getInt(3));
userList.add(user);
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
JDBCUtils.release(rs, pstmt, conn);
}
return userList;
}
}
public class User {
private int id;
private String name;
private int age;
// 省略getter、setter方法
}6. PrepareStatement CRUD
PreparedStatement是一种预编译的Statement，它可以通过占位符的方式来替换SQL语句中的参数，避免了SQL注入的危险。下面是一个使用PreparedStatement进行CRUD操作的示例：
import java.sql.*;
public class PrepareStatementCRUD {
public static void main(String[] args) {
Connection conn = null;
PreparedStatement pstmt = null;
ResultSet rs = null;
try {
conn = JDBCUtils.getConnection();
// 插入数据
String sql = "INSERT INTO users (name, age) VALUES (?, ?)";
pstmt = conn.prepareStatement(sql);
pstmt.setString(1, "Tom");
pstmt.setInt(2, 18);
pstmt.executeUpdate();
// 更新数据
sql = "UPDATE users SET age = ? WHERE name = ?";
pstmt = conn.prepareStatement(sql);
pstmt.setInt(1, 20);
pstmt.setString(2, "Tom");
pstmt.executeUpdate();
// 删除数据
sql = "DELETE FROM users WHERE age = ?";
pstmt = conn.prepareStatement(sql);
pstmt.setInt(1, 20);
pstmt.executeUpdate();
// 查询数据
sql = "SELECT * FROM users";
pstmt = conn.prepareStatement(sql);
rs = pstmt.executeQuery();
while (rs.next()) {
System.out.println(rs.getInt(1) + ", " + rs.getString(2) + ", " + rs.getInt(3));
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
JDBCUtils.release(rs, pstmt, conn);
}
}
}以上就是关于JDBC入门、抽取工具类、Statement CRUD、演练CRUD、Dao模式（声明与实现分开）、PrepareStatement CRUD的详细介绍和代码示例。通过学习这些内容，可以让我们更好地掌握JDBC的使用和开发技巧，从而更好地应用到实际的项目中。
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