java攻城狮之路--复习JDBC(PrepareStatement)
PreparedStatement:
package com.shellway.jdbc; import java.io.IOException; import java.io.InputStream; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; import java.util.Properties; public class JDBCTools { /** * 执行 SQL 语句, 使用 PreparedStatement * @param sql * @param args: 填写 SQL 占位符的可变参数 */ public static void update(String sql, Object ... args){ Connection connection = null; PreparedStatement preparedStatement = null; try { connection = JDBCTools.getConnection(); preparedStatement = connection.prepareStatement(sql); for(int i = 0; i < args.length; i++){ preparedStatement.setObject(i + 1, args[i]); } preparedStatement.executeUpdate(); } catch (Exception e) { e.printStackTrace(); } finally{ JDBCTools.releaseDB(null, preparedStatement, connection); } } /** * 执行 SQL 的方法 * * @param sql: insert, update 或 delete。 而不包含 select */ public static void update(String sql) { Connection connection = null; Statement statement = null; try { // 1. 获取数据库连接 connection = getConnection(); // 2. 调用 Connection 对象的 createStatement() 方法获取 Statement 对象 statement = connection.createStatement(); // 4. 发送 SQL 语句: 调用 Statement 对象的 executeUpdate(sql) 方法 statement.executeUpdate(sql); } catch (Exception e) { e.printStackTrace(); } finally { // 5. 关闭数据库资源: 由里向外关闭. releaseDB(null, statement, connection); } } /** * 释放数据库资源的方法 * * @param resultSet * @param statement * @param connection */ public static void releaseDB(ResultSet resultSet, Statement statement, Connection connection) { if (resultSet != null) { try { resultSet.close(); } catch (SQLException e) { e.printStackTrace(); } } if (statement != null) { try { statement.close(); } catch (SQLException e) { e.printStackTrace(); } } if (connection != null) { try { connection.close(); } catch (SQLException e) { e.printStackTrace(); } } } /** * 获取数据库连接的方法 */ public static Connection getConnection() throws IOException, ClassNotFoundException, SQLException { // 0. 读取 jdbc.properties /** * 1). 属性文件对应 Java 中的 Properties 类 2). 可以使用类加载器加载 bin 目录(类路径下)的文件 */ Properties properties = new Properties(); InputStream inStream = ReviewTest.class.getClassLoader() .getResourceAsStream("jdbc.properties"); properties.load(inStream); // 1. 准备获取连接的 4 个字符串: user, password, jdbcUrl, driverClass String user = properties.getProperty("user"); String password = properties.getProperty("password"); String jdbcUrl = properties.getProperty("jdbcUrl"); String driverClass = properties.getProperty("driverClass"); // 2. 加载驱动: Class.forName(driverClass) Class.forName(driverClass); // 3. 调用 // DriverManager.getConnection(jdbcUrl, user, password) // 获取数据库连接 Connection connection = DriverManager.getConnection(jdbcUrl, user, password); return connection; } }
/** * 使用 PreparedStatement 将有效的解决 SQL 注入问题. */ @Test public void testSQLInjection2() { String username = "a‘ OR PASSWORD = "; String password = " OR ‘1‘=‘1"; String sql = "SELECT * FROM users WHERE username = ? " + "AND password = ?"; Connection connection = null; PreparedStatement preparedStatement = null; ResultSet resultSet = null; try { connection = JDBCTools.getConnection(); preparedStatement = connection.prepareStatement(sql); preparedStatement.setString(1, username); preparedStatement.setString(2, password); resultSet = preparedStatement.executeQuery(); 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 { JDBCTools.releaseDB(resultSet, preparedStatement, connection); } } /** * SQL 注入. */ @Test public void testSQLInjection() { String username = "a‘ OR PASSWORD = "; String password = " OR ‘1‘=‘1"; String sql = "SELECT * FROM users WHERE username = ‘" + username + "‘ AND " + "password = ‘" + password + "‘"; System.out.println(sql); Connection connection = null; Statement statement = null; ResultSet resultSet = null; try { connection = JDBCTools.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 { JDBCTools.releaseDB(resultSet, statement, connection); } }
练习:
1)请输入考生的详细信息
Type:
IDCard:
ExamCard:
StudentName:
Location:
Grade:
提示:信息录入成功!
2).在 eclipse 中建立 java 程序:输入身份证号或准考证号可以查询到学生的基本信息。结果如下:
@Test public void testGetStudent() { // 1. 得到查询的类型 int searchType = getSearchTypeFromConsole(); // 2. 具体查询学生信息 Student student = searchStudent(searchType); // 3. 打印学生信息 printStudent(student); } /** * 打印学生信息: 若学生存在则打印其具体信息. 若不存在: 打印查无此人. * * @param student */ private void printStudent(Student student) { if (student != null) { System.out.println(student); } else { System.out.println("查无此人!"); } } /** * 具体查询学生信息的. 返回一个 Student 对象. 若不存在, 则返回 null * * @param searchType * : 1 或 2. * @return */ private Student searchStudent(int searchType) { String sql = "SELECT flowid, type, idcard, examcard," + "studentname, location, grade " + "FROM examstudent " + "WHERE "; Scanner scanner = new Scanner(System.in); // 1. 根据输入的 searchType, 提示用户输入信息: // 1.1 若 searchType 为 1, 提示: 请输入身份证号. 若为 2 提示: 请输入准考证号 // 2. 根据 searchType 确定 SQL if (searchType == 1) { System.out.print("请输入准考证号:"); String examCard = scanner.next(); sql = sql + "examcard = ‘" + examCard + "‘"; } else { System.out.print("请输入身份证号:"); String examCard = scanner.next(); sql = sql + "idcard = ‘" + examCard + "‘"; } // 3. 执行查询 Student student = getStudent(sql); // 4. 若存在查询结果, 把查询结果封装为一个 Student 对象 return student; } /** * 根据传入的 SQL 返回 Student 对象 * * @param sql * @return */ private Student getStudent(String sql) { Student stu = null; Connection connection = null; Statement statement = null; ResultSet resultSet = null; try { connection = JDBCTools.getConnection(); statement = connection.createStatement(); resultSet = statement.executeQuery(sql); if (resultSet.next()) { stu = new Student(resultSet.getInt(1), resultSet.getInt(2), resultSet.getString(3), resultSet.getString(4), resultSet.getString(5), resultSet.getString(6), resultSet.getInt(7)); } } catch (Exception e) { e.printStackTrace(); } finally { JDBCTools.releaseDB(resultSet, statement, connection); } return stu; } /** * 从控制台读入一个整数, 确定要查询的类型 * * @return: 1. 用身份证查询. 2. 用准考证号查询 其他的无效. 并提示请用户重新输入. */ private int getSearchTypeFromConsole() { System.out.print("请输入查询类型: 1. 用身份证查询. 2. 用准考证号查询 "); Scanner scanner = new Scanner(System.in); int type = scanner.nextInt(); if (type != 1 && type != 2) { System.out.println("输入有误请重新输入!"); throw new RuntimeException(); } return type; } @Test public void testAddNewStudent() { Student student = getStudentFromConsole(); addNewStudent2(student); } /** * 从控制台输入学生的信息 */ private Student getStudentFromConsole() { Scanner scanner = new Scanner(System.in); Student student = new Student(); System.out.print("FlowId:"); student.setFlowId(scanner.nextInt()); System.out.print("Type: "); student.setType(scanner.nextInt()); System.out.print("IdCard:"); student.setIdCard(scanner.next()); System.out.print("ExamCard:"); student.setExamCard(scanner.next()); System.out.print("StudentName:"); student.setStudentName(scanner.next()); System.out.print("Location:"); student.setLocation(scanner.next()); System.out.print("Grade:"); student.setGrade(scanner.nextInt()); return student; } public void addNewStudent2(Student student) { String sql = "INSERT INTO examstudent(flowid, type, idcard, " + "examcard, studentname, location, grade) " + "VALUES(?,?,?,?,?,?,?)"; JDBCTools.update(sql, student.getFlowId(), student.getType(), student.getIdCard(), student.getExamCard(), student.getStudentName(), student.getLocation(), student.getGrade()); } public void addNewStudent(Student student) { // 1. 准备一条 SQL 语句: String sql = "INSERT INTO examstudent VALUES(" + student.getFlowId() + "," + student.getType() + ",‘" + student.getIdCard() + "‘,‘" + student.getExamCard() + "‘,‘" + student.getStudentName() + "‘,‘" + student.getLocation() + "‘," + student.getGrade() + ")"; System.out.println(sql); // 2. 调用 JDBCTools 类的 update(sql) 方法执行插入操作. JDBCTools.update(sql); } }
在练习中要注意的问题:
1、在执行这一语句ps = conn.prepareStatement(sql);的时候,如果提示要强制转换成prepareStatement类型,
则不要转换,只需要把包导入就行:import java.sql.PreparedStatement;
2、遇到插入日期语句的时候,比如:ps.setDate(3, new Date(new java.util.Date().getTime()));
前面的new Date()是要声明为java.sql包中的,里面的new Date()则要声明为java.util包中的。
在使用Preparement的时候,最好在主程序中写函数然后调用工具类JDBCTools.java中的更新方法:
public void addStudent(Student stu) throws Exception { String sql = "insert into examstudent values(?,?,?,?,?,?,?)"; JDBCTools.testUpdate(sql, stu.getFlowID(), stu.getType(), stu.getIdCard(), stu.getExamCard(), stu.getStudentName(), stu.getLocation(), stu.getGrade()); }
在 工具类JDBCTools.java中写更新方法,传入 sql 和 可变参数args
public static void testUpdate(String sql, Object... args) throws Exception { Connection conn = null; PreparedStatement ps = null; try { conn = JDBCTools.getConnection(); ps = conn.prepareStatement(sql); for (int i = 0; i < args.length; i++) { ps.setObject(i + 1, args[i]); } System.out.println(sql); ps.executeUpdate(); } catch (Exception e) { e.printStackTrace(); } finally { JDBCTools.release(null, ps, conn); } }
下面写个简单而小巧的PrepareStatement例子:
@Test public void testPreparedStatement() { Connection connection = null; PreparedStatement preparedStatement = null; try { connection = JDBCTools.getConnection(); String sql = "INSERT INTO customers (name, email, birth) " + "VALUES(?,?,?)"; preparedStatement = connection.prepareStatement(sql); preparedStatement.setString(1, "shellway"); preparedStatement.setString(2, "[email protected]"); preparedStatement.setDate(3, new Date(new java.util.Date().getTime())); preparedStatement.executeUpdate(); } catch (Exception e) { e.printStackTrace(); } finally { JDBCTools.releaseDB(null, preparedStatement, connection); } }
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