【1】sql注入攻击：

/*** SQL 注入.*/@Testpublic void testSQLInjection() {String username = "a' OR PASSWORD = ";String password = " OR '1'='1";String sql = "SELECT * FROM user_tbl WHERE user_name = '" + username+ "' AND " + "password = '" + password + "'";// sql注入攻击使用的sql： SELECT * FROM user_tbl WHERE user_name = 'a' OR PASSWORD = ' AND password = ' OR '1'='1'System.out.println(sql);Connection connection = null;Statement statement = null;ResultSet resultSet = null;try {connection = JdbcUtils.getConnection();statement = connection.createStatement();resultSet = statement.executeQuery(sql);if (resultSet.next()) {System.out.println("登录成功!");} else {System.out.println("用户名和密码不匹配或用户名不存在. ");}} catch (Exception e) {e.printStackTrace();} finally {JdbcUtils.closeStatAndConnAndResultSet(statement, connection, resultSet);}}

【2】PreparedStatement 有效防止sql注入攻击

/*** 使用 PreparedStatement 将有效的解决 SQL 注入问题.*/@Testpublic void testSQLInjection2() {String username = "a' OR PASSWORD = ";String password = " OR '1'='1";String sql = "SELECT * FROM user_tbl WHERE user_name = ? "+ "AND password = ?";Connection connection = null;PreparedStatement preparedStatement = null;ResultSet resultSet = null;try {connection = JdbcUtils.getConnection();preparedStatement = connection.prepareStatement(sql);preparedStatement.setString(1, username);preparedStatement.setString(2, password);resultSet = preparedStatement.executeQuery(); // 这里查询失败if (resultSet.next()) {System.out.println("登录成功!");} else {System.out.println("用户名和密码不匹配或用户名不存在. ");}} catch (Exception e) {e.printStackTrace();} finally {JdbcUtils.closeStatAndConnAndResultSet(preparedStatement, connection, resultSet);}}

【3】代码补充：jdbc工具类 

/*** 操作jdbc的工具类-封装了一些工具方法* @author pacoson*/
public class JdbcUtils {/*** 通用的更新方法：insert, update, delete* 版本1* @param sql*/public static void updateV2ByPreparedStatement(String sql, Object... objs) {Connection conn = null;PreparedStatement stat = null;try {// 1.获取数据库连接conn = JdbcUtils.getConnection();// 4.执行插入// 4.1 获取操作sql语句的statement对象； 
//			调用Connection的  createStatement() 方法来获取stat = conn.prepareStatement(sql);int i = 1;for (Object obj : objs) {stat.setObject(i++, obj);}System.out.println("连接=" + conn + "，语句 = " + stat);// 4.2 调用statement对象的 executeUpdate(sql) 执行sql语句进行插入int updateRows = stat.executeUpdate();System.out.println("更新记录行数：" + updateRows);} catch(Exception e) {e.printStackTrace();} finally {JdbcUtils.closeStatAndConn(stat, conn);}}/*** 通用的更新方法：insert, update, delete* 版本1* @param sql*/public static void updateV1(String sql) {Connection conn = null;Statement stat = null;try {// 1.获取数据库连接conn = JdbcUtils.getConnection();// 4.执行插入// 4.1 获取操作sql语句的statement对象； 
//			调用Connection的  createStatement() 方法来获取stat = conn.createStatement();System.out.println("连接=" + conn + "，语句 = " + stat);// 4.2 调用statement对象的 executeUpdate(sql) 执行sql语句进行插入int updateRows = stat.executeUpdate(sql);System.out.println("更新记录行数：" + updateRows);} catch(Exception e) {e.printStackTrace();} finally {JdbcUtils.closeStatAndConn(stat, conn);}}/*** 获取连接的方法。* 通过读取配置文件从数据库服务器获取一个连接* @return* @throws Exception*/public static Connection getConnection() throws Exception {// 读取类路径下的 jdbc.properties 文件并将其封装到 Properties中：InputStream in = JdbcTest01.class.getClassLoader().getResourceAsStream("jdbc.properties");Properties props = new Properties();props.load(in);/* 通过反射获取驱动器Driver */Driver driver = (Driver) Class.forName(props.getProperty("driver")).newInstance();/* 获取数据库连接  */Connection conn = driver.connect(props.getProperty("url"), props);return conn;}/*** 关闭数据库语句 statement 和 数据库连接 conn 和 结果集 ResultSet* @param stat* @param conn*/public static void closeStatAndConnAndResultSet(Statement stat, Connection conn, ResultSet rs) {if (null != rs) {try {rs.close(); // 关闭ResultSet对象} catch(Exception e) {e.printStackTrace();}}if (null != stat) {try {stat.close(); // 关闭statement对象} catch(Exception e) {e.printStackTrace();}}if (null != conn) {try {conn.close(); // 关闭连接} catch(Exception e) {e.printStackTrace();}}}/*** 关闭数据库语句 statement 和 数据库连接 conn * @param stat* @param conn*/public static void closeStatAndConn(Statement stat, Connection conn) {if (null != stat) {try {stat.close(); // 关闭statement对象} catch(Exception e) {e.printStackTrace();}}if (null != conn) {try {conn.close(); // 关闭连接} catch(Exception e) {e.printStackTrace();}}}}