PreparedStatement执行sql語句

import com.loaderman.util.JdbcUtil;

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

import org.junit.Test;
/**
 * PreparedStatement執行sql語句
 *
 */
public class Demo1 {

    /**
     * 增加
     */
    @Test
    public void testInsert() {
        Connection conn = null;
        PreparedStatement stmt = null;
        try {
            //1.获取连接
            conn = JdbcUtil.getConnection();
            
            //2.准备预编译的sql
            String sql = "INSERT INTO student(NAME,gender) VALUES(?,?)"; //?表示一个参数的占位符
            
            //3.执行预编译sql语句(检查语法)
            stmt = conn.prepareStatement(sql);
            
            //4.设置参数值
            /**
             * 参数一： 参数位置  从1开始
             */
            stmt.setString(1, "李四");
            stmt.setString(2, "男");
            
            //5.发送参数，执行sql
            int count = stmt.executeUpdate();
            
            System.out.println("影响了"+count+"行");
            
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        } finally {
            JdbcUtil.close(conn, stmt);
        }
    }
    
    /**
     * 修改
     */
    @Test
    public void testUpdate() {
        Connection conn = null;
        PreparedStatement stmt = null;
        try {
            //1.获取连接
            conn = JdbcUtil.getConnection();
            
            //2.准备预编译的sql
            String sql = "UPDATE student SET NAME=? WHERE id=?"; //?表示一个参数的占位符
            
            //3.执行预编译sql语句(检查语法)
            stmt = conn.prepareStatement(sql);
            
            //4.设置参数值
            /**
             * 参数一： 参数位置  从1开始
             */
            stmt.setString(1, "王五");
            stmt.setInt(2, 9);
            
            //5.发送参数，执行sql
            int count = stmt.executeUpdate();
            
            System.out.println("影响了"+count+"行");
            
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        } finally {
            JdbcUtil.close(conn, stmt);
        }
    }
    
    /**
     * 删除
     */
    @Test
    public void testDelete() {
        Connection conn = null;
        PreparedStatement stmt = null;
        try {
            //1.获取连接
            conn = JdbcUtil.getConnection();
            
            //2.准备预编译的sql
            String sql = "DELETE FROM student WHERE id=?"; //?表示一个参数的占位符
            
            //3.执行预编译sql语句(检查语法)
            stmt = conn.prepareStatement(sql);
            
            //4.设置参数值
            /**
             * 参数一： 参数位置  从1开始
             */
            stmt.setInt(1, 9);
            
            //5.发送参数，执行sql
            int count = stmt.executeUpdate();
            
            System.out.println("影响了"+count+"行");
            
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        } finally {
            JdbcUtil.close(conn, stmt);
        }
    }
    
    /**
     * 查询
     */
    @Test
    public void testQuery() {
        Connection conn = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            //1.获取连接
            conn = JdbcUtil.getConnection();
            
            //2.准备预编译的sql
            String sql = "SELECT * FROM student"; 
            
            //3.预编译
            stmt = conn.prepareStatement(sql);
            
            //4.执行sql
            rs = stmt.executeQuery();
            
            //5.遍历rs
            while(rs.next()){
                int id = rs.getInt("id");
                String name = rs.getString("name");
                String gender = rs.getString("gender");
                System.out.println(id+","+name+","+gender);
            }
            
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        } finally {
            //关闭资源
            JdbcUtil.close(conn,stmt,rs);
        }
    }
}

---

import com.loaderman.util.JdbcUtil;

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

import org.junit.Test;

/**
 * 模拟用户登录效果
 * @author APPle
 *
 */
public class Demo2 {
    //模拟用户输入
    //private String name = "ericdfdfdfddfd' OR 1=1 -- ";
    private String name = "eric";
    //private String password = "123456dfdfddfdf";
    private String password = "123456";

    /**
     * Statment存在sql被注入的风险
     */
    @Test
    public void testByStatement(){
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            //获取连接
            conn = JdbcUtil.getConnection();
            
            //创建Statment
            stmt = conn.createStatement();
            
            //准备sql
            String sql = "SELECT * FROM users WHERE NAME='"+name+"' AND PASSWORD='"+password+"'";
            
            //执行sql
            rs = stmt.executeQuery(sql);
            
            if(rs.next()){
                //登录成功
                System.out.println("登录成功");
            }else{
                System.out.println("登录失败");
            }
            
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        } finally {
            JdbcUtil.close(conn, stmt ,rs);
        }
        
    }
    
    /**
     * PreparedStatement可以有效地防止sql被注入
     */
    @Test
    public void testByPreparedStatement(){
        Connection conn = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            //获取连接
            conn = JdbcUtil.getConnection();
            
            String sql = "SELECT * FROM users WHERE NAME=? AND PASSWORD=?";
            
            //预编译
            stmt = conn.prepareStatement(sql);
            
            //设置参数
            stmt.setString(1, name);
            stmt.setString(2, password);
            
            //执行sql
            rs = stmt.executeQuery();
            
            if(rs.next()){
                //登录成功
                System.out.println("登录成功");
            }else{
                System.out.println("登录失败");
            }
            
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        } finally {
            JdbcUtil.close(conn, stmt ,rs);
        }
        
    }
}

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;

/**
 * jdbc工具类
 * @author APPle
 *
 */
public class JdbcUtil {
    private static String url = null;
    private static String user = null;
    private static String password = null;
    private static String driverClass = null;
    
    /**
     * 静态代码块中（只加载一次）
     */
    static{
        try {
            //读取db.properties文件
            Properties props = new Properties();
            /**
             *  . 代表java命令运行的目录
             *  在java项目下，. java命令的运行目录从项目的根目录开始
             *  在web项目下，  . java命令的而运行目录从tomcat/bin目录开始
             *  所以不能使用点.
             */
            //FileInputStream in = new FileInputStream("./src/db.properties");
            
            /**
             * 使用类路径的读取方式
             *  / : 斜杠表示classpath的根目录
             *     在java项目下，classpath的根目录从bin目录开始
             *     在web项目下，classpath的根目录从WEB-INF/classes目录开始
             */
            InputStream in = JdbcUtil.class.getResourceAsStream("/db.properties");
            
            //加载文件
            props.load(in);
            //读取信息
            url = props.getProperty("url");
            user = props.getProperty("user");
            password = props.getProperty("password");
            driverClass = props.getProperty("driverClass");
            
            
            //注册驱动程序
            Class.forName(driverClass);
        } catch (Exception e) {
            e.printStackTrace();
            System.out.println("驱程程序注册出错");
        }
    }

    /**
     * 抽取获取连接对象的方法
     */
    public static Connection getConnection(){
        try {
            Connection conn = DriverManager.getConnection(url, user, password);
            return conn;
        } catch (SQLException e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }
    
    
    /**
     * 释放资源的方法
     */
    public static void close(Connection conn,Statement stmt){
        if(stmt!=null){
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
                throw new RuntimeException(e);
            }
        }
        if(conn!=null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
                throw new RuntimeException(e);
            }
        }
    }
    
    public static void close(Connection conn,Statement stmt,ResultSet rs){
        if(rs!=null)
            try {
                rs.close();
            } catch (SQLException e1) {
                e1.printStackTrace();
                throw new RuntimeException(e1);
            }
        if(stmt!=null){
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
                throw new RuntimeException(e);
            }
        }
        if(conn!=null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
                throw new RuntimeException(e);
            }
        }
    }
}

db.properties

url=jdbc:mysql://localhost:3306/test
user=root
password=root
driverClass=com.mysql.jdbc.Driver