跟汤老师学Java笔记：PreparedStatement接口

跟汤老师学Java笔记：PreparedStatement接口

完成：第一遍

1.什么是PreparedStatement接口？

PreparedStatement接口继承自Statement接口，推荐使用

2.PreparedStatement接口和Statement接口相比有哪些优点？

第一：使用PreparedStatement接口可以使用?占位符，简单易读(也称之为动态SQL语句)

第二：提前预编译SQL语句，效率更高

第三：更安全，避免出现SQL注入的问题

3.创建statement对象和创建preparedStatement的不同之处在哪里？

statement=conn.createStatement();//无参数，方法是：createStatement()

preparedStatement = conn.prepareStatement(sql);//必须有参数sql语句，
方法是：prepareStatement(sql)

package season19;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

/**
 * JDBC工具类
 */
public class JdbcUtil {
	/**
	 * 获取数据库连接
	 */
	public static Connection getConnection() {
		String driverClassName = "com.mysql.jdbc.Driver";
		String url = "jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf8&rewriteBatchedStatements=true";
		String username = "root";
		String password = "123456";

		Connection conn = null;
		try {
			Class.forName(driverClassName);
			conn = DriverManager.getConnection(url, username, password);
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		} catch (SQLException e) {
			e.printStackTrace();
		}
		return conn;
	}

	/**
	 * 关闭资源
	 */
	public static void close(Connection conn, Statement stmt, ResultSet rs) {
		if (rs != null) {
			try {
				rs.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
		if (stmt != null) {
			try {
				stmt.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
		if (conn != null) {
			try {
				conn.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
	}

	public static void close(Connection conn, Statement stmt) {
		close(conn, stmt, null);
	}
}

package season19;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class Test{
	public static void main(String[] args) {
		
	boolean flag = login("admin", "123' or '1=1");
		System.out.println(flag);
		
		User user = new User();
		user.setUsername("ddd");
		user.setPassword("111");
		user.setAge(25);
		
		register(user);
		System.out.println("注册成功");
	}

	/*
	 * 用户登陆
	 */
	public static boolean login(String username, String password) {
		
		String sql001="select id,username,password,age from t_user where username='"+username+"' and password='"+password+"'";
		String sql002 = "select id,username,password,age from t_user where username=? and password=?";
		
		// 建议使用StringBuffer或StringBuilder拼接SQL语句，关键字、表名、列名等独占一行
		String sql=new StringBuilder()
			.append(" select ")
			.append(" 	id,username,password,age ")
			.append(" from  ")
			.append(" 	t_user ")
			.append(" where ")
			.append(" 	username = ? and password = ? ")
			.toString();

		Connection conn = null;
		// Statement stmt=null;
		PreparedStatement ps = null;
		ResultSet rs = null;

		try {
			conn = JdbcUtil.getConnection();
			// stmt=conn.createStatement();
			// rs = stmt.executeQuery(sql);
			
			// 获取PreparedStatement，需要传入sql，进行预编译
			ps = conn.prepareStatement(sql); 
			// 为占符符?赋值，编号从1开始
			//set()方法根据要填的数据类型选择：可以setInt(),setDate()
			ps.setString(1, username); 
			ps.setString(2, password);
			rs = ps.executeQuery();
			
			// 如果返回结果集中最多只有一条记录，可以使用if
			if (rs.next()) { 
				return true;
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}finally{
			JdbcUtil.close(conn, ps, rs);
		}

		return false;
	}

	/*
	 * 用户注册
	 */
	public static void register(User user){
		String sql = new StringBuffer()
			.append(" insert into  ")
			.append(" 	t_user ")
			.append(" 		(username,password,age) ")
			.append(" values ")
			.append("  		(?,?,?) ")
			.toString();
		Connection conn=null;
		PreparedStatement ps = null;
		try {
			conn=JdbcUtil.getConnection();
			ps=conn.prepareStatement(sql);
//			ps.setString(1, user.getUsername());
//			ps.setString(2, user.getPassword());
//			ps.setInt(3, user.getAge());
			// set后的类型只代表第二个参数类型，不代表数据库对应的类型
			ps.setObject(1, user.getUsername()); 
			ps.setObject(2, user.getPassword()); 
			ps.setObject(3, user.getAge());
			ps.executeUpdate();
			
		} catch (SQLException e) {
			e.printStackTrace();
		}finally{
			JdbcUtil.close(conn, ps);
		}
	}
}

class User {
	private Integer id;
	private String username;
	private String password;
	private Integer age;

	public User() {
		super();
	}

	public User(Integer id, String username, String password, Integer age) {
		super();
		this.id = id;
		this.username = username;
		this.password = password;
		this.age = age;
	}

	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getUsername() {
		return username;
	}

	public void setUsername(String username) {
		this.username = username;
	}

	public String getPassword() {
		return password;
	}

	public void setPassword(String password) {
		this.password = password;
	}

	public Integer getAge() {
		return age;
	}

	public void setAge(Integer age) {
		this.age = age;
	}

	@Override
	public String toString() {
		return "User [id=" + id + ", username=" + username + ", password="
				+ password + ", age=" + age + "]\n";
	}

}