Statement对象与PreparedStatement对象

一、Statement对象

Jdbc中的statement对象用于向数据库发送SQL语句，想完成对数据库的增删改查，只需要通过这个对象 向数据库发送增删改查语句即可。

Statement对象的executeUpdate方法，用于向数据库发送增、删、改的sql语句，executeUpdate执行 完后，将会返回一个整数（即增删改语句导致了数据库几行数据发生了变化）。

Statement.executeQuery方法用于向数据库发送查询语句，executeQuery方法返回代表查询结果的 ResultSet对象。

CRUD操作-create

使用executeUpdate(String sql)方法完成数据添加操作，示例操作：

?
1
2
3
4
5
6
7
Statement st = conn.createStatement();
String sql = "insert into users(id,name,password,email,birthday)" +
                    "values(4,'fubai','123','24736743@qq.com','2020-01-01')";
int num = st.executeUpdate(sql);
if(num>0){
    System.out.println("插入成功！！！");
}

 

CRUD操作-delete

使用executeUpdate(String sql)方法完成数据删除操作，示例操作：

?
1
2
3
4
5
6
Statement st = conn.createStatement();
String sql = "delete from user where id=1";
int num = st.executeUpdate(sql);
if(num>0){
    System.out.println(“删除成功！！！");
}

　　

CRUD操作-update

使用executeUpdate(String sql)方法完成数据修改操作，示例操作：

?
1
2
3
4
5
6
Statement st = conn.createStatement();
String sql = "update users set name='fubai',email='24736743@qq.com' where id=3";
int num = st.executeUpdate(sql);
if(num>0){
    System.out.println(“修改成功！！！");
}

　　

CRUD操作-read

使用executeQuery(String sql)方法完成数据查询操作，示例操作：

?
1
2
3
4
5
Statement st = conn.createStatement();
String sql = "select * from user where id=1";
ResultSet rs = st.executeQuery(sql);
while(rs.next()){
    //根据获取列的数据类型，分别调用rs的相应方法映射到java对象中,如：<br>　　System.out.println("name:" + rs.getString("name"));<br><em id="__mceDel">　　System.out.println("email:" + rs.getString("email"));</em>}

　　

自定义工具类和配置文件对数据库增删改查

1、新建一个 lesson02 的包

2、在src目录下创建一个db.properties文件，如下所示：

?
1
2
3
4
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/jdbcStudy?useUnicode=true&characterEncoding=utf8&useSSL=false
username=root
password=123456

3、在lesson02 下新建一个 utils 包，新建一个类 JdbcUtils

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
package com.fubai.lesson02.utils;
 
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;
 
public class JdbcUtils {
    private static String driver = null;
    private static String url = null;
    private static String username = null;
    private static String password = null;
 
    static {
        try {
            //读取db.properties文件中的数据库连接信息
            InputStream in =
                    JdbcUtils.class.getClassLoader().getResourceAsStream("db.properties");
            Properties prop = new Properties();
            prop.load(in);
            //获取数据库连接驱动
            driver = prop.getProperty("driver");
            //获取数据库连接URL地址
            url = prop.getProperty("url");
            //获取数据库连接用户名
            username = prop.getProperty("username");
            //获取数据库连接密码
            password = prop.getProperty("password");
            //加载数据库驱动
            Class.forName(driver);
        } catch (Exception e) {
            throw new ExceptionInInitializerError(e);
        }
    }
 
    // 获取数据库连接对象
    public static Connection getConnection() throws SQLException {
        return DriverManager.getConnection(url, username, password);
    }
 
    // 释放资源，要释放的资源包括Connection数据库连接对象，负责执行SQL命令的Statement对象，存储查询结果的ResultSet对象
    public static void release(Connection conn, Statement st, ResultSet rs) {
        if (rs != null) {
            try {
                //关闭存储查询结果的ResultSet对象
                rs.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
            rs = null;
        }
        if (st != null) {
            try {
                //关闭负责执行SQL命令的Statement对象
                st.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        if (conn != null) {
            try {
                //关闭Connection数据库连接对象
                conn.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

　　

使用statement对象完成对数据库的CRUD操作

1、插入一条数据

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
package com.fubai.lesson02.utils;
 
import com.fubai.lesson02.utils.JdbcUtils;
 
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
 
public class TestInsert {
    public static void main(String[] args) {
        Connection conn = null;
        Statement st = null;
        ResultSet rs = null;
        try {
            //获取一个数据库连接
            conn = JdbcUtils.getConnection();
            //通过conn对象获取负责执行SQL命令的Statement对象
            st = conn.createStatement();
            //要执行的SQL命令
            String sql = "insert into users(id,name,password,email,birthday) " +
                    "values(4,'fubai','123','2584@qq.com','2020-01-01')";
            //执行插入操作，executeUpdate方法返回成功的条数
            int num = st.executeUpdate(sql);
            if (num > 0) {
                System.out.println("插入成功！！");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            //SQL执行完成之后释放相关资源
            JdbcUtils.release(conn, st, rs);
        }
    }
}

　　

2、删除一条数据

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
package com.fubai.lesson02;
 
import com.fubai.lesson02.utils.JdbcUtils;
 
import java.sql.*;
 
public class TestDelete {
    public static void main(String[] args) {
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
 
        try {
            connection = JdbcUtils.getConnection();
            statement = connection.createStatement();
 
            String sql = "delete from users where id=4";
            int i = statement.executeUpdate(sql);
 
            if (i > 0) {
                System.out.println("删除成功");
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            JdbcUtils.release(connection, statement, resultSet);
        }
    }
}

　　

3、更新一条数据

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
package com.fubai.lesson02;
 
import com.fubai.lesson02.utils.JdbcUtils;
 
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
 
public class TestUpdate {
    public static void main(String[] args) {
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
 
        try {
            connection = JdbcUtils.getConnection();
            statement = connection.createStatement();
 
            String sql = "update users set name='fubai',email='24736743@qq.com' where id=3";
            int i = statement.executeUpdate(sql);
 
            if (i > 0) {
                System.out.println("更改成功");
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            JdbcUtils.release(connection, statement, resultSet);
        }
    }
}

　　

4、查询数据

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
package com.fubai.lesson02;
 
import com.fubai.lesson02.utils.JdbcUtils;
 
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
 
public class TestSelect {
    public static void main(String[] args) {
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
 
        try {
            connection = JdbcUtils.getConnection();
            statement = connection.createStatement();
 
            String sql = "select * from users where id=3";
            resultSet = statement.executeQuery(sql);
 
            while (resultSet.next()) {
                System.out.println("name:" + resultSet.getString("name"));
                System.out.println("email:" + resultSet.getString("email"));
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            JdbcUtils.release(connection, statement, resultSet);
        }
    }
}

　　

SQL 注入问题

通过巧妙的技巧来拼接字符串，造成SQL短路，从而获取数据库数据

 

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
package com.fubai.lesson02;
 
import com.fubai.lesson02.utils.JdbcUtils;
 
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
 
public class SqlInject {
    public static void main(String[] args) {
        // login("zhangsan","123456"); // 正常登陆
        login("'or '1=1", "123456"); // SQL 注入
    }
 
    public static void login(String username, String password) {
        Connection conn = null;
        Statement st = null;
        ResultSet rs = null;
        try {
            conn = JdbcUtils.getConnection();
            // select * from users where name='' or '1=1' and password ='123456'
            String sql = "select * from users where name='" + username + "' and password = '" + password + "' ";
            st = conn.createStatement();
            rs = st.executeQuery(sql);
            while (rs.next()) {
                System.out.println(rs.getString("name"));
                System.out.println(rs.getString("password"));
                System.out.println("==============");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcUtils.release(conn, st, rs);
        }
    }
}

　　

二、PreparedStatement对象

PreperedStatement是Statement的子类，它的实例对象可以通过调用

Connection.preparedStatement()方法获得，相对于Statement对象而言：PreperedStatement可以避 免SQL注入的问题。

Statement会使数据库频繁编译SQL，可能造成数据库缓冲区溢出。

PreparedStatement可对SQL进行预编译，从而提高数据库的执行效率。并且PreperedStatement对于 sql中的参数，允许使用占位符的形式进行替换，简化sql语句的编写。

 

使用PreparedStatement对象完成对数据库的CRUD操作

1、插入数据

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
package com.fubai.lesson03;
 
import com.fubai.lesson03.utils.JdbcUtils;
 
import java.sql.Connection;
import java.util.Date;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
 
public class TestInsert {
    public static void main(String[] args) {
        Connection conn = null;
        PreparedStatement st = null;
        ResultSet rs = null;
        try {
            //获取一个数据库连接
            conn = JdbcUtils.getConnection();
            //要执行的SQL命令，SQL中的参数使用?作为占位符
            String sql = "insert into users(id,name,password,email,birthday) values(?,?,?,?,?)";
            //通过conn对象获取负责执行SQL命令的prepareStatement对象
            st = conn.prepareStatement(sql);
            //为SQL语句中的参数赋值，注意，索引是从1开始的
            st.setInt(1, 4);//id是int类型的
            st.setString(2, "kuangshen");//name是varchar(字符串类型)
            st.setString(3, "123");//password是varchar(字符串类型)
            st.setString(4, "24736743@qq.com");//email是varchar(字符串类型)
            st.setDate(5, new java.sql.Date(new Date().getTime()));//birthday是date类型
            //执行插入操作，executeUpdate方法返回成功的条数
            int num = st.executeUpdate();
            if (num > 0) {
                System.out.println("插入成功！！");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            //SQL执行完成之后释放相关资源
            JdbcUtils.release(conn, st, rs);
        }
    }
}

　　

2、删除一条数据

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
package com.fubai.lesson03;
 
import com.fubai.lesson03.utils.JdbcUtils;
 
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
 
public class TestDelete {
    public static void main(String[] args) {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
 
        try {
            connection = JdbcUtils.getConnection();
 
            String sql = "delete from users where id=?";
            preparedStatement = connection.prepareStatement(sql);
 
            preparedStatement.setInt(1, 4);
 
            int i = preparedStatement.executeUpdate();
            if (i > 0) {
                System.out.println("删除成功");
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            JdbcUtils.release(connection, preparedStatement, null);
        }
    }
}

　　

3、更新一条数据

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
package com.fubai.lesson03;
 
import com.fubai.lesson03.utils.JdbcUtils;
 
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
 
public class TestUpdate {
    public static void main(String[] args) {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
 
        try {
            connection = JdbcUtils.getConnection();
 
            String sql = "update users set name=?,email=? where id=?";
            preparedStatement = connection.prepareStatement(sql);
 
            preparedStatement.setString(1, "wyh");
            preparedStatement.setString(2, "2584@qq.com");
            preparedStatement.setInt(3, 3);
 
            int i = preparedStatement.executeUpdate();
            if (i > 0) {
                System.out.println("修改成功");
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            JdbcUtils.release(connection, preparedStatement, null);
        }
    }
}

　　

4、查询一条数据

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
package com.fubai.lesson03;
 
import com.fubai.lesson03.utils.JdbcUtils;
 
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
 
public class TestSelect {
    public static void main(String[] args) {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
 
        try {
            connection = JdbcUtils.getConnection();
 
            String sql = "select * from users where id = ?";
            preparedStatement = connection.prepareStatement(sql);
 
            preparedStatement.setInt(1, 1);
            resultSet = preparedStatement.executeQuery();
 
            while (resultSet.next()) {
                System.out.println("name:" + resultSet.getString("name"));
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            JdbcUtils.release(connection, preparedStatement, resultSet);
        }
    }
}

　　

避免SQL 注入

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
package com.fubai.lesson03;
 
import com.fubai.lesson03.utils.JdbcUtils;
 
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
 
public class SqlInject {
    public static void main(String[] args) {
// login("zhangsan","123456"); // 正常登陆
        login("'or '1=1", "123456"); // SQL 注入
    }
 
    public static void login(String username, String password) {
        Connection conn = null;
        PreparedStatement st = null;
        ResultSet rs = null;
        try {
            conn = JdbcUtils.getConnection();
            // select * from users where name='' or '1=1' and password ='123456'
            String sql = "select * from users where name=? and password=?";
            st = conn.prepareStatement(sql);
            st.setString(1, username);
            st.setString(2, password);
            rs = st.executeQuery();
            while (rs.next()) {
                System.out.println(rs.getString("name"));
                System.out.println(rs.getString("password"));
                System.out.println("==============");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcUtils.release(conn, st, rs);
        }
    }
}

原理：执行的时候参数会用引号包起来，并把参数中的引号作为转义字符，从而避免了参数也作为条件 的一部分

 

posted @   腹白  阅读(102)  评论(0)  编辑  收藏  举报
相关博文：
· JDBC的对象说明
· Spring的配置、依赖注入、Bean的自动装配及注解开发
· statement对象
· JDBC学习日志三，Statement和SQL注入
· JDBC学习
阅读排行：
· DeepSeek 开源周回顾「GitHub 热点速览」
· 物流快递公司核心技术能力-地址解析分单基础技术分享
· .NET 10首个预览版发布：重大改进与新特性概览！
· AI与.NET技术实操系列（二）：开始使用ML.NET
· 单线程的Redis速度为什么快？
点击右上角即可分享
微信分享提示
AI FOR CODE 大赛