所需的数据库数据要导入到自己的数据库库中
三：使用PreparedStatement实现CRUD操作
- 数据库连接被用于向数据库服务器发送命令和 SQL 语句，并接受数据库服务器返回的结果。其实一个数据库连接就是一个Socket连接。
- CRUD操作：根据返回值的有无可分为两类
- 删除，添加，修改
- 查询
- 在 java.sql 包中有 3 个接口分别定义了对数据库的调用的不同方式：
- Statement：用于执行静态 SQL 语句并返回它所生成结果的对象。
- PrepatedStatement：SQL 语句被预编译并存储在此对象中，可以使用此对象多次高效地执行该语句。
- CallableStatement：用于执行 SQL 存储过程
1.Statement类（可略过）
示例代码
public class User {private String user;private String password; public User() {}public User(String user, String password) {super();this.user = user;this.password = password;}@Overridepublic String toString() {return "User [user=" + user + ", password=" + password + "]";}public String getUser() {return user;}public void setUser(String user) {this.user = user;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}
}
import java.io.InputStream;
import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;
import java.util.Scanner;import org.junit.Test;public class StatementTest {@Testpublic void testLogin() {Scanner scan = new Scanner(System.in);System.out.print("用户名：");String userName = scan.nextLine();System.out.print("密 码：");String password = scan.nextLine();// SELECT user,password FROM user_table WHERE USER = '1' or ' AND PASSWORD = '// ='1' or '1' = '1';String sql = "SELECT user,password FROM user_table WHERE user = ? and password = ?";User user = get(sql, User.class);if (user != null) {System.out.println("登陆成功!");} else {System.out.println("用户名或密码错误！");}}// 使用Statement实现对数据表的查询操作public <T> T get(String sql, Class<T> clazz) {T t = null;Connection conn = null;Statement st = null;ResultSet rs = null;try {// 1.加载配置文件InputStream is = StatementTest.class.getClassLoader().getResourceAsStream("jdbc.properties");Properties pros = new Properties();pros.load(is);// 2.读取配置信息String user = pros.getProperty("user");String password = pros.getProperty("password");String url = pros.getProperty("url");String driverClass = pros.getProperty("driverClass");// 3.加载驱动Class.forName(driverClass);// 4.获取连接conn = DriverManager.getConnection(url, user, password);st = conn.createStatement();rs = st.executeQuery(sql);// 获取结果集的元数据ResultSetMetaData rsmd = rs.getMetaData();// 获取结果集的列数int columnCount = rsmd.getColumnCount();if (rs.next()) {t = clazz.newInstance();for (int i = 0; i < columnCount; i++) {// //1. 获取列的名称// String columnName = rsmd.getColumnName(i+1);// 1. 获取列的别名String columnName = rsmd.getColumnLabel(i + 1);// 2. 根据列名获取对应数据表中的数据Object columnVal = rs.getObject(columnName);// 3. 将数据表中得到的数据，封装进对象Field field = clazz.getDeclaredField(columnName);field.setAccessible(true);field.set(t, columnVal);}return t;}} catch (Exception e) {e.printStackTrace();} finally {// 关闭资源if (rs != null) {try {rs.close();} catch (SQLException e) {e.printStackTrace();}}if (st != null) {try {st.close();} catch (SQLException e) {e.printStackTrace();}}if (conn != null) {try {conn.close();} catch (SQLException e) {e.printStackTrace();}}}return null;}}
- 上面的代码有两个问题
- 问题一：存在拼串操作
在SQL语句的编写中存在拼串的操作 - 问题二：存在SQL注入问题
在用户输入数据中注入非法的 SQL 语句段或命令
(如：SELECT user, password FROM user_table WHERE user='a' OR 1 = ' AND password = ' OR '1' = '1')
- 问题一：存在拼串操作
使用PreparedStatement(从Statement扩展而来) 取代 Statement 就可以防范 SQL 注入
代码优化见8.user查询的优化
2.PreparedStatement类
-
可以通过调用
Connection对象的 preparedStatement(String sql) 方法获取PreparedStatement对象 -
PreparedStatement 接口是 Statement 的子接口，它表示一条预编译过的 SQL 语句
-
PreparedStatement 对象所代表的 SQL 语句中的参数用问号(
?)来表示，调用 PreparedStatement 对象的 setXxx() 方法来设置这些参数. setXxx() 方法有两个参数，第一个参数是要设置的 SQL 语句中的参数的索引(从 1 开始)，第二个是设置的 SQL 语句中的参数的值
3.Java与SQL对应数据类型转换表
| Java类型 | SQL类型 |
|---|---|
| boolean | BIT |
| byte | TINYINT |
| short | SMALLINT |
| int | INTEGER |
| long | BIGINT |
| String | CHAR,VARCHAR,LONGVARCHAR |
| byte array | BINARY , VAR BINARY |
| java.sql.Date | DATE |
| java.sql.Time | TIME |
| java.sql.Timestamp | TIMESTAMP |
4.使用PreparedStatement类完成Customers表的增删改操作
增删改操作类似下面的案例都是以增数据为例
向customers表中添加一条记录
**例：此处以添加为例
@Testpublic void testInsert() {Connection conn = null; PreparedStatement ps = null;try {//1.读取配置文件中的配置信息InputStream is = ClassLoader.getSystemClassLoader().getResourceAsStream("jdbc.properties");//获取系统类加载器Properties pros = new Properties();pros.load(is);String user = pros.getProperty("user");String password = pros.getProperty("password");String url = pros.getProperty("url");String driverClass = pros.getProperty("driverClass");//2.加载驱动Class.forName(driverClass);//3.获取连接conn = DriverManager.getConnection(url,user,password);//4.预编译sql语句，返回PreparedStatement的实例String sql = "insert into customers(name,email,birth)values(?,?,?)";//?:占位符ps = conn.prepareStatement(sql);//5.填充占位符ps.setString(1, "邓紫棋");ps.setString(2, "GM@gmail.com");SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");java.util.Date date = sdf.parse("2001-09-15");ps.setDate(3, new Date(date.getTime()));//6.执行SQL操作ps.execute();} catch (Exception e) {e.printStackTrace();}finally {//7.资源关闭try {if(ps != null) {ps.close();}} catch (SQLException e) {e.printStackTrace();}try {if(conn != null) {conn.close();}} catch(Exception e) {e.printStackTrace();}}}
5.使用PreparedStatement类完成Customers表的增删改操作（上一步的优化）
将通用的连接与关闭资源写成一个工具类
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;
//操作数据库的工具类
public class JDBC_Utils {//获取数据库连接public static Connection getConnection() throws Exception {InputStream is = ClassLoader.getSystemClassLoader().getResourceAsStream("jdbc.properties");Properties pros = new Properties();pros.load(is);String user = pros.getProperty("user");String password = pros.getProperty("password");String url = pros.getProperty("url");String driverClass = pros.getProperty("driverClass");Class.forName(driverClass);Connection conn = DriverManager.getConnection(url,user,password);return conn;}//关闭连接与Statement资源的操作public static void closeResource(Connection conn,Statement ps) {try {if(ps != null) {ps.close();}} catch (SQLException e) {e.printStackTrace();}try {if(conn != null) {conn.close();}} catch(Exception e) {e.printStackTrace();}}
}
上面的类命名时最好不要带下滑线，对测试向customers表中添加一条记录
@Testpublic void testUpdate(){ Connection conn = null; PreparedStatement ps = null;try {//1.连接数据库conn = JDBC_Utils.getConnection();//2.预编译sql语句，返回PreparedStatement的实例String sql = "update customers set name = ? where id = ?";ps = conn.prepareStatement(sql);//3.填充占位符ps.setObject(1, "李响");ps.setObject(2, 18);//4.执行SQL语言ps.execute();} catch (Exception e) {e.printStackTrace();}finally {//5.资源关闭JDBC_Utils.closeResource(conn, ps);}
}
6.使用PreparedStatement类完成Customers表的增删改通用操作
public class UpdateTest {//通用的增删改操作@Testpublic void testCommonUpdate() {
// String sql = "delete from customers where id = ?";
// update(sql,3);String sql = "update `order` set order_name = ? where order_id = ?";//当表名与关键字重合，可以用` `在SQL语句中加以区分update(sql,"DD","2");}public void update(String sql,Object ...args) {Connection conn = null;PreparedStatement ps = null;try {//1.获取数据库的连接conn = JDBC_Utils.getConnection();//2.预编译SQL语句ps = conn.prepareStatement(sql);//3.填充占位符（可变形参长度与SQL占位符数量一致）for(int i = 0;i < args.length;i++) {ps.setObject(i + 1,args[i]);//小心参数声明错误（从1开始）}//4.执行ps.execute();} catch (Exception e) {e.printStackTrace();}finally {//5.关闭资源JDBC_Utils.closeResource(conn, ps);}}
}
7.使用PreparedStatement类完成Customers表查询操作(单条数据)
import java.sql.Date;/*** ORM编程思想（object relational mapping）对象关系映射* 一个数据表对应一个Java类* 表中的一条记录对应Java类的一个对象* 表中的一个字段对应Java类的一个属性*/
public class Customer {private int id; private String name;private String email;private Date birth;public Customer() {super();}public Customer(int id, String name, String email, Date birth) {super();this.id = id;this.name = name;this.email = email;this.birth = birth;}public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getEmail() {return email;}public void setEmail(String email) {this.email = email;}public Date getBirth() {return birth;}public void setBirth(Date birth) {this.birth = birth;}@Overridepublic String toString() {return "Customer [id=" + id + ", name=" + name + ", email=" + email + ", birth=" + birth + "]";}
}
例：对customers表进行单条查询操作
@Testpublic void testQuery1() {Connection conn = null; PreparedStatement ps = null;ResultSet resultSet = null;try {conn = JDBC_Utils.getConnection();String sql = "select id,name,email,birth from customers where id = ?";ps = conn.prepareStatement(sql);ps.setObject(1, 1);//执行并返回结果集resultSet = ps.executeQuery();//处理结果集if(resultSet.next()) {//next()：判断结果集下一条是否有数据；有，true并指针下移；没有，false,指针不下移；//获取当条数据的各个字段值int id = resultSet.getInt(1);String name = resultSet.getString(2);String email = resultSet.getString(3);Date birth = resultSet.getDate(4);//方式一
// System.out.println("id = " + id + " ,name = " + name + " ,email = " + email + " ,birth = " + birth );//方式二
// Object[] data = new Object[] {id,name,email,birth};//方式三：将数据封装为一个对象（推荐）Customer customer = new Customer(id,name,email,birth);System.out.println(customer); }} catch (Exception e) {e.printStackTrace();}finally {//关闭资源JDBC_Utils.closeResource(conn, ps,resultSet);}}
8.使用PreparedStatement类完成Customers表查询通用操作(单条数据)
针对表的字段名与类的属性名不同的情况（如：针对Order表的通用的查询操作）
- 1.必须在声明SQL时，使用类的属性名来命名表中字段的别名
- 2.使用
ResultSetMetaData时，需要使用getColumnLabel()来替换getColumnName()获得列的列名 - 3.如果sql中没有给字段起别名时，查询的就是列的列名
例：针对Customers表的查询操作
public class CustomersQuery {@Testpublic void testQueryForCustomers() {
// String sql = "select id,name,email,birth from customers where id = ?";
// Customer customer = queryForCustomers(sql,13);
// System.out.println(customer);String sql = "select id,name,email,birth from customers where name = ?";Customer customer = queryForCustomers(sql,"周杰伦");System.out.println(customer);}/**针对customers表的通用操作 */public Customer queryForCustomers(String sql,Object ...args) {Connection conn = null;PreparedStatement ps = null;ResultSet rs = null;try {conn = JDBC_Utils.getConnection();ps = conn.prepareStatement(sql);for(int i = 0;i < args.length;i++) {ps.setObject(i + 1, args[i]);}rs = ps.executeQuery();//获取结果集的元数据ResultSetMetaData rsmd = rs.getMetaData();//通过ResultSetMetaData获取结果集中的列数int columnCount = rsmd.getColumnCount();if(rs.next()) {Customer cust = new Customer();for(int i = 0;i < columnCount;i++) {//获取列值：结果集Object columnvalue = rs.getObject(i +1);//获取每个列的列名：结果集元数据
// String columnName = rsmd.getColumnName(i + 1);//获取每个列的别名（无别名就获取表的列名）：结果集元数据String columnLabel = rsmd.getColumnLabel(i + 1);//给cust指定columnName属性赋值为columnvalue，通过反射Field field = Customer.class.getDeclaredField(columnLabel);field.setAccessible(true);field.set(cust, columnvalue);}return cust;}}catch (Exception e) {e.printStackTrace();}finally {JDBC_Utils.closeResource(conn, ps, rs);}return null;}
例：针对Order表的通用的查询操作
order类
import java.sql.Date;public class Order {private int orderId; private String orderName;private Date orderDate;public Order() {super();}public Order(int orderId, String orderName, Date orderDate) {super();this.orderId = orderId;this.orderName = orderName;this.orderDate = orderDate;}public int getOrderId() {return orderId;}public void setOrderId(int orderId) {this.orderId = orderId;}public String getOrderName() {return orderName;}public void setOrderName(String orderName) {this.orderName = orderName;}public Date getOrderDate() {return orderDate;}public void setOrderDate(Date orderDate) {this.orderDate = orderDate;}@Overridepublic String toString() {return "Order [orderId=" + orderId + ", orderName=" + orderName + ", orderDate=" + orderDate + "]";}}查询操作
import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.Date;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;import org.junit.Test;import com.jdbc.util.JDBC_Utils;/*** 针对于Order表的通用的查询操作*/
public class OrderForQuery {@Testpublic void testOrderForQuery(){String sql = "select order_id orderId,order_name orderName,order_date orderDate from `order` where order_id = ?";Order order = orderForQuery(sql,1);System.out.println(order);}/*** 通用的针对于order表的查询操作*/public Order orderForQuery(String sql,Object...args){Connection conn = null;PreparedStatement ps = null;ResultSet rs = null;try {conn = JDBC_Utils.getConnection();ps = conn.prepareStatement(sql);for(int i = 0;i < args.length;i++){ps.setObject(i + 1, args[i]);}//执行，获取结果集rs = ps.executeQuery();//获取结果集的元数据ResultSetMetaData rsmd = rs.getMetaData();//获取列数int columnCount = rsmd.getColumnCount();if(rs.next()){Order order = new Order();for(int i = 0;i < columnCount;i++){//获取每个列的列值:通过ResultSetObject columnValue = rs.getObject(i + 1);//通过ResultSetMetaData//获取列的列名：getColumnName() --不推荐使用//获取列的别名：getColumnLabel()
// String columnName = rsmd.getColumnName(i + 1);String columnLabel = rsmd.getColumnLabel(i + 1);//通过反射，将对象指定名columnName的属性赋值为指定的值columnValueField field = Order.class.getDeclaredField(columnLabel);field.setAccessible(true);field.set(order, columnValue);}return order;}} catch (Exception e) {e.printStackTrace();}finally{JDBC_Utils.closeResource(conn, ps, rs);}return null;}@Testpublic void testQuery1(){Connection conn = null;PreparedStatement ps = null;ResultSet rs = null;try {conn = JDBC_Utils.getConnection();String sql = "select order_id,order_name,order_date from `order` where order_id = ?";ps = conn.prepareStatement(sql);ps.setObject(1, 1);rs = ps.executeQuery();if(rs.next()){int id = (int) rs.getObject(1);String name = (String) rs.getObject(2);Date date = (Date) rs.getObject(3);Order order = new Order(id, name, date);System.out.println(order);}} catch (Exception e) {e.printStackTrace();}finally{JDBC_Utils.closeResource(conn, ps, rs);}}}
9.针对不同表不同字段的查询通用操作
针对不同表不同字段的查询通用操作,此时返回表中的一条记录
@Testpublic void test1() {String sql = "select id,name,email from customers where id = ?"; Customer customer = getInstance(Customer.class,sql,12);System.out.println(customer);String sql1 = "select order_id orderId,order_name orderName from `order` where order_id = ?";Order order = getInstance(Order.class,sql1,1);System.out.println(order);}public <T> T getInstance(Class<T> clazz,String sql,Object ...args) {Connection conn = null;PreparedStatement ps = null;ResultSet rs = null;try {conn = JDBC_Utils.getConnection();ps = conn.prepareStatement(sql);for(int i = 0;i < args.length;i++) {ps.setObject(i + 1, args[i]);}rs = ps.executeQuery();//获取结果集的元数据ResultSetMetaData rsmd = rs.getMetaData();//通过ResultSetMetaData获取结果集中的列数int columnCount = rsmd.getColumnCount();if(rs.next()) {T t = clazz.newInstance();for(int i = 0;i < columnCount;i++) {//获取列值：结果集Object columnvalue = rs.getObject(i +1);//获取每个列的列名：结果集元数据
// String columnName = rsmd.getColumnName(i + 1);//获取每个列的别名（无别名就获取表的列名）：结果集元数据String columnLabel = rsmd.getColumnLabel(i + 1);//给cust指定columnName属性赋值为columnvalue，通过反射Field field = clazz.getDeclaredField(columnLabel);field.setAccessible(true);field.set(t, columnvalue);}return t;}}catch (Exception e) {e.printStackTrace();}finally {JDBC_Utils.closeResource(conn, ps, rs);}return null;}
针对不同表不同字段的查询通用操作,返回多条数据
public class PreparedStatementQeryTest {@Testpublic void testGetForList() {String sql = "select id,name,email from customers where id > ?"; List<Customer> list = getForList(Customer.class,sql,12);//集合遍历list.forEach(System.out::println);String sql1 = "select order_id orderId,order_name orderName from `order`";List<Order> list1 = getForList(Order.class,sql1);list1.forEach(System.out::println);}public <T> List<T> getForList(Class<T> clazz,String sql,Object ...args){Connection conn = null;PreparedStatement ps = null;ResultSet rs = null;try {conn = JDBC_Utils.getConnection();ps = conn.prepareStatement(sql);for(int i = 0;i < args.length;i++) {ps.setObject(i + 1, args[i]);}rs = ps.executeQuery();//获取结果集的元数据ResultSetMetaData rsmd = rs.getMetaData();//通过ResultSetMetaData获取结果集中的列数int columnCount = rsmd.getColumnCount();//创建集合对象ArrayList<T> list = new ArrayList<T>();while(rs.next()) {T t = clazz.newInstance();//给t对象指定的属性赋值for(int i = 0;i < columnCount;i++) {//获取列值：结果集Object columnvalue = rs.getObject(i +1);//获取每个列的列名：结果集元数据
// String columnName = rsmd.getColumnName(i + 1);//获取每个列的别名（无别名就获取表的列名）：结果集元数据String columnLabel = rsmd.getColumnLabel(i + 1);//给cust指定columnName属性赋值为columnvalue，通过反射Field field = clazz.getDeclaredField(columnLabel);field.setAccessible(true);field.set(t, columnvalue);}list.add(t);}return list;}catch (Exception e) {e.printStackTrace();}finally {JDBC_Utils.closeResource(conn, ps, rs);}return null;}
}
增删改类似
10.user查询的优化
import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.util.Scanner;import org.junit.Test;import com.jdbc.util.JDBC_Utils;
public class PreparedStatementTest {@Testpublic void testLogin() {Scanner scan = new Scanner(System.in);System.out.print("用户名：");String userName = scan.nextLine();System.out.print("密 码：");String password = scan.nextLine();// SELECT user,password FROM user_table WHERE USER = '1' or ' AND PASSWORD = '// ='1' or '1' = '1';String sql = "SELECT user,password FROM user_table WHERE USER = ? and password = ?";User user = getInstance(User.class, sql,userName,password);if (user != null) {System.out.println("登陆成功!");} else {System.out.println("用户名或密码错误！");}}//使用PreparedStatement针对不同表不同字段的查询通用操作,此时返回表中的一条记录public <T> T getInstance(Class<T> clazz,String sql,Object ...args) {Connection conn = null;PreparedStatement ps = null;ResultSet rs = null;try {conn = JDBC_Utils.getConnection();ps = conn.prepareStatement(sql);for(int i = 0;i < args.length;i++) {ps.setObject(i + 1, args[i]);}rs = ps.executeQuery();//获取结果集的元数据ResultSetMetaData rsmd = rs.getMetaData();//通过ResultSetMetaData获取结果集中的列数int columnCount = rsmd.getColumnCount();if(rs.next()) {T t = clazz.newInstance();for(int i = 0;i < columnCount;i++) {//获取列值：结果集Object columnvalue = rs.getObject(i +1);//获取每个列的列名：结果集元数据
// String columnName = rsmd.getColumnName(i + 1);//获取每个列的别名（无别名就获取表的列名）：结果集元数据String columnLabel = rsmd.getColumnLabel(i + 1);//给cust指定columnName属性赋值为columnvalue，通过反射Field field = clazz.getDeclaredField(columnLabel);field.setAccessible(true);field.set(t, columnvalue);}return t;}}catch (Exception e) {e.printStackTrace();}finally {JDBC_Utils.closeResource(conn, ps, rs);}return null;}
}11.练习
练习一
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.util.Scanner;import org.junit.Test;import com.jdbc.util.JDBC_Utils;
public class Exer1Test {@Testpublic void testInsert() {Scanner scanner = new Scanner(System.in);System.out.print("请输入用户名： ");String name = scanner.next();System.out.print("请输入邮箱： ");String email = scanner.next();System.out.print("请输入生日： ");String birthday = scanner.next();String sql = "insert into customers(name,email,birth)values(?,?,?)";int insertCount = update(sql,name,email,birthday);if(insertCount > 0) {System.out.println("添加成功");}else {System.out.println("添加失败");}}//通用的增删改操作public int update(String sql,Object ...args) {Connection conn = null;PreparedStatement ps = null;try {//1.获取数据库的连接conn = JDBC_Utils.getConnection();//2.预编译SQL语句ps = conn.prepareStatement(sql);//3.填充占位符（可变形参长度与SQL占位符数量一致）for(int i = 0;i < args.length;i++) {ps.setObject(i + 1,args[i]);//小心参数声明错误（从1开始）}//4.执行/*** ps.execute()：* false:执行的是增，删改操作，无返回值* ture:执行的是查询操作，有返回值*///方式一：
// return ps.execute();//方式二：return ps.executeUpdate();//返回的是影响的行数} catch (Exception e) {e.printStackTrace();}finally {//5.关闭资源JDBC_Utils.closeResource(conn, ps);}return 0;}
}
练习二
Student类
public class Student {private int flowID;//流水号 private int type;//考试类型private String IDCard;//身份证号private String examCard;//准考证号private String name;//学生姓名private String location;//学生所在城市private int grade;//考试成绩public Student() {super();}public Student(int flowID, int type, String iDCard, String examCard, String name, String location, int grade) {super();this.flowID = flowID;this.type = type;IDCard = iDCard;this.examCard = examCard;this.name = name;this.location = location;this.grade = grade;}public int getType() {return type;}public void setType(int type) {this.type = type;}public String getIDCard() {return IDCard;}public void setIDCard(String iDCard) {IDCard = iDCard;}public String getExamCard() {return examCard;}public void setExamCard(String examCard) {this.examCard = examCard;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getLocation() {return location;}public void setLocation(String location) {this.location = location;}public int getGrade() {return grade;}public void setGrade(int grade) {this.grade = grade;}public int getFlowID() {return flowID;}@Overridepublic String toString() {System.out.println("===============查询结果===================");return info();}private String info() {return "流水号：" + flowID + "\n四级/六级：" + type + "\n身份证号：" + IDCard + "\n准考证号：" + examCard + "\n学生姓名：" + name + "\n区域：" + location + "\n成绩：" + grade;}}
三个小问题写在一起
mport java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.util.Scanner;import org.junit.Test;import com.jdbc.util.JDBC_Utils;
public class Exer1Test2 {//问题1：向examstudent表中添加一条记录@Testpublic void testInsert() {Scanner scanner = new Scanner(System.in);System.out.print("四级/六级：");int type = scanner.nextInt();System.out.print("身份证号：");String IDCard = scanner.next();System.out.print("准考证号：");String examCard = scanner.next();System.out.print("学生姓名：");String studentName = scanner.next();System.out.print("所在城市：");String location = scanner.next();System.out.print("考试成绩：");int grade = scanner.nextInt();String sql = "insert into examstudent(type,IDCard,examCard,studentName,location,grade)values(?,?,?,?,?,?)";int insertCount = update(sql,type,IDCard,examCard,studentName,location,grade);if(insertCount > 0) {System.out.println("添加成功");}else {System.out.println("添加失败");}}//通用的增删改操作public int update(String sql,Object ...args) {Connection conn = null;PreparedStatement ps = null;try {//1.获取数据库的连接conn = JDBC_Utils.getConnection();//2.预编译SQL语句ps = conn.prepareStatement(sql);//3.填充占位符（可变形参长度与SQL占位符数量一致）for(int i = 0;i < args.length;i++) {ps.setObject(i + 1,args[i]);//小心参数声明错误（从1开始）}//4.执行/*** ps.execute()：* false:执行的是增，删改操作，无返回值* ture:执行的是查询操作，有返回值*///方式一：
// return ps.execute();//方式二：return ps.executeUpdate();//返回的是影响的行数} catch (Exception e) {e.printStackTrace();}finally {//5.关闭资源JDBC_Utils.closeResource(conn, ps);}return 0;}//问题2:根据身份证号或者准考证号查询学生成绩@Testpublic void queryWithID() {System.out.println("请选择你要输入的查询类型：");System.out.println("a.准考证号");System.out.println("b.身份证号");Scanner scanner = new Scanner(System.in);String selection = scanner.next();if("a".equalsIgnoreCase(selection)) {System.out.println("请输入准考证号：");String examCard = scanner.next();String sql = "select FlowID flowID,Type type,IDCard,ExamCard examCard,StudentName name,Location location,Grade grade from examstudent where ExamCard = ?";Student student = getInstance(Student.class,sql,examCard);if(student != null) {System.out.println(student);}else { System.out.println("输入准考证号有误");}}else if("b".equalsIgnoreCase(selection)) {System.out.println("请输入身份证号：");String IDCard = scanner.next();String sql = "select FlowID flowID,Type type,IDCard,ExamCard examCard,StudentName name,Location location,Grade grade from examstudent where IDCard = ?";Student student = getInstance(Student.class,sql,IDCard);if(student != null) {System.out.println(student);}else { System.out.println("输入身份证号有误");}}else {System.out.println("您的输入有误，请重新进入程序");}}public <T> T getInstance(Class<T> clazz,String sql,Object ...args) {Connection conn = null;PreparedStatement ps = null;ResultSet rs = null;try {conn = JDBC_Utils.getConnection();ps = conn.prepareStatement(sql);for(int i = 0;i < args.length;i++) {ps.setObject(i + 1, args[i]);}rs = ps.executeQuery();//获取结果集的元数据ResultSetMetaData rsmd = rs.getMetaData();//通过ResultSetMetaData获取结果集中的列数int columnCount = rsmd.getColumnCount();if(rs.next()) {T t = clazz.newInstance();for(int i = 0;i < columnCount;i++) {//获取列值：结果集Object columnvalue = rs.getObject(i +1);//获取每个列的列名：结果集元数据
// String columnName = rsmd.getColumnName(i + 1);//获取每个列的别名（无别名就获取表的列名）：结果集元数据String columnLabel = rsmd.getColumnLabel(i + 1);//给cust指定columnName属性赋值为columnvalue，通过反射Field field = clazz.getDeclaredField(columnLabel);field.setAccessible(true);field.set(t, columnvalue);}return t;}}catch (Exception e) {e.printStackTrace();}finally {JDBC_Utils.closeResource(conn, ps, rs);}return null;}//问题三：删除指定的学生信息@Testpublic void testDeletByExamCard() {System.out.println("请输入学生的考号：");Scanner scanner = new Scanner(System.in);String examCard = scanner.next();//查询指定准考证号的学生String sql = "select FlowID flowID,Type type,IDCard,ExamCard examCard,StudentName name,Location location,Grade grade from examstudent where ExamCard = ?";Student student = getInstance(Student.class,sql,examCard);if(student == null) {System.out.println("查无此人，请重新输入");}else {String sql1 = "delete from examstudent where examCard = ?";int updateCount = update(sql1,examCard);if(updateCount > 0) {System.out.println("删除成功");}else {System.out.println("删除失败，请重新操作");}}}//上一步的优化操作@Testpublic void testdelete() {System.out.println("请输入学生的考号：");Scanner scanner = new Scanner(System.in);String examCard = scanner.next();String sql = "delete from examstudent where examCard = ?";int updateCount = update(sql,examCard);if(updateCount > 0) {System.out.println("删除成功");}else {System.out.println("查无此人，请重新输入");}}
}
其中可能会出现不少的小问题，请多多包含
感谢大家的支持，关注，评论，点赞！
参考资料：尚硅谷_宋红康_JDBC核心技术
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