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把数据保存到可掉电式存储设备中以供之后使用
。大多数情况下,特别是企业级应用,数据持久化意味着将内存中的数据保存到硬盘上
加以固化
,而持久化的实现过程大多通过各种关系数据库来完成。磁盘文件
、XML数据文件中
。JDBC
直接访问数据库第三方O/R工具
,如Hibernate, Mybatis 等封装了JDBC
。一个独立于特定数据库管理系统
、通用的SQL数据库存取和操作的公共接口(一组API),定义了用来访问数据库的标准Java类库,(java.sql、javax.sql
)使用这些类库可以以一种标准的方法、方便地访问数据库资源。统一的途径
,为开发者屏蔽了一些细节问题。JDBC驱动程序的数据库系统
,这样就使得程序员无需对特定的数据库系统的特点有过多的了解,从而大大简化和加快了开发过程。JDBC接口(API)包括两个层次:
Java API
,抽象接口,供应用程序开发人员使用(连接数据库,执行SQL语句,获得结果)。Java Driver API
,供开发商开发数据库驱动程序用。JDBC是
sun公司
提供的一套用于数据库操作的接口,java程序员只需要面向这套接口编程即可。不同的数据库厂商,需要针对这套接口,提供不同实现。不同的实现的集合,即为不同数据库的驱动。
—面向接口编程
补充:ODBC(
Open Database Connectivity
,开放式数据库连接),是微软在Windows平台下推出的。使用者在程序中只需要调用ODBC API
,由 ODBC 驱动程序将调用转换成为对特定的数据库的调用请求。
java.sql.Driver
接口是所有 JDBC 驱动程序需要实现的接口。这个接口是提供给数据库厂商使用的,不同数据库厂商提供不同的实现。oracle.jdbc.driver.OracleDriver
com.mysql.jdbc.Driver
maven导入mysql的驱动依赖
mysql mysql-connector-java 8.0.20
Class.forName("com.mysql.jdbc.Driver")
;DriverManager.registerDriver(com.mysql.jdbc.Driver)
来注册驱动jdbc
定位数据库
提供足够的信息。包含主机名(对应服务端的ip地址),端口号,数据库名
import org.junit.Test;import java.sql.Connection;import java.sql.Driver;import java.util.Properties;/** * @author xiexu * @create 2020-11-11 9:36 下午 */public class ConnectionTest { @Test public void testConnection1() throws Exception{ //获取Driver的实现类对象 Driver driver = new com.mysql.cj.jdbc.Driver(); //jdbc:mysql 主协议 //localhost ip地址 //3306 mysql默认的端口号 //test test数据库名 String url = "jdbc:mysql://localhost:3306/test"; //将用户名和密码封装在Properties中 Properties info = new Properties(); info.setProperty("user", "root"); info.setProperty("password", "283619"); Connection connect = driver.connect(url, info); System.out.println(connect); }}
说明:上述代码中显式出现了第三方数据库的API
//方式二:对方式一的迭代,在如下的程序中不出现第三方的api,使得程序具有更好的可移植性 @Test public void testConnection2() throws Exception{ //1.获取Driver实现类对象,使用反射 Class clazz = Class.forName("com.mysql.cj.jdbc.Driver"); Driver driver = (Driver) clazz.newInstance(); //2.提供url,指明具体操作的数据 String url = "jdbc:mysql://localhost:3306/test"; //3.提供需要的用户名和密码 Properties info = new Properties(); info.setProperty("user", "root"); info.setProperty("password", "283619"); //4.调用driver的connect(),获取连接 Connection conn = driver.connect(url, info); System.out.println(conn); }
说明:相较于方式一,这里使用反射实例化Driver,不在代码中体现
第三方数据库的API
。体现了面向接口编程思想。
// 方式三:使用DriverManager替换Driver @Test public void testConnection3() throws Exception { // 1.获取Driver实现类的对象 Class clazz = Class.forName("com.mysql.cj.jdbc.Driver"); Driver driver = (Driver) clazz.newInstance(); // 2.提供另外三个连接的基本信息: String url = "jdbc:mysql://localhost:3306/test"; String user = "root"; String password = "283619"; // 注册驱动 DriverManager.registerDriver(driver); // 获取连接 Connection conn = DriverManager.getConnection(url, user, password); System.out.println(conn); }
说明:使用DriverManager实现数据库的连接。体会获取连接必要的4个基本要素。
// 方式四:可以只是加载驱动,不用显示的注册驱动过了。 @Test public void testConnection4() throws Exception { // 1.提供三个连接的基本信息: String url = "jdbc:mysql://localhost:3306/test"; String user = "root"; String password = "283619"; // 2.加载Driver实现类的对象 Class.forName("com.mysql.cj.jdbc.Driver"); /* 相较于方式三:可以省略如下两行操作 Driver driver = (Driver) clazz.newInstance(); DriverManager.registerDriver(driver); 为什么可以省略上述两行操作呢? 在mysql的Driver实现类中,声明了如下的操作: static { try { java.sql.DriverManager.registerDriver(new Driver()); } catch (SQLException E) { throw new RuntimeException("Can't register driver!"); } } */ // 3.获取连接 Connection conn = DriverManager.getConnection(url, user, password); System.out.println(conn); }
说明:不必显式的注册驱动了。因为在DriverManager的源码中已经存在静态代码块,实现了驱动的注册。
resources
下,先新建一个File文件,作为配置文件:其中,配置文件jdbc.properties
内容如下:
user=rootpassword=283619url=jdbc:mysql://localhost:3306/testdriverClass=com.mysql.cj.jdbc.Driver
// 方式五(最终版):将数据库连接需要的4个基本信息声明在配置文件中,通过读取配置文件的方式,获取连接 @Test public void testConnection5() throws Exception { // 1.读取配置文件中的4个基本信息 InputStream is = ConnectionTest.class.getClassLoader().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"); // 2.加载驱动 Class.forName(driverClass); // 3.获取连接 Connection conn = DriverManager.getConnection(url, user, password); System.out.println(conn); }
说明:使用配置文件的方式保存配置信息,在代码中加载配置文件
使用配置文件的好处
:1.实现了代码和数据的分离,如果需要修改配置信息,直接在配置文件中修改,不需要深入代码
2.如果修改了配置信息,省去重新编译的过程。
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。
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:
int excuteUpdate(String sql):执行更新操作INSERT、UPDATE、DELETEResultSet executeQuery(String sql):执行查询操作SELECT
代码示例
User类
public class User { private String user; private String password; public User() { } public User(String user, String password) { super(); this.user = user; this.password = password; } @Override public 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; }}
测试类
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 { // 使用Statement的弊端:需要拼写sql语句,并且存在SQL注入的问题 @Test public void testLogin() { @SuppressWarnings("resource") Scanner scan = new Scanner(System.in); System.out.print("用户名:"); String user = scan.next(); System.out.print("密 码:"); String password = scan.next(); // 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 = '" + user + "' AND password = '" + password + "'"; User resuser = get(sql, User.class); if (resuser != 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 publicT get(String sql, Class 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; }}
代码的可读性和可维护性。
PreparedStatement 能最大可能提高性能:
PreparedStatement 可以防止 SQL 注入
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 |
import org.junit.Test;import java.io.InputStream;import java.sql.*;import java.text.ParseException;import java.text.SimpleDateFormat;import java.util.Properties;/** * 使用PreparedStatement来替换Statement,实现对数据表的增删改查操作 * * @author xiexu * @create 2020-11-30 8:44 下午 */public class PreparedStatementUpdateTest { //向customers表中添加一条记录 @Test public void testInsert() { Connection conn = null; PreparedStatement ps = null; try { // 1.读取配置文件中的4个基本信息 InputStream is = ClassLoader.getSystemClassLoader().getResourceAsStream("jdbc.properties"); Properties pros = new Properties(); pros.load(is); // 2.获取数据库连接的参数 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); //System.out.println(conn); // 5.预编译sql语句,返回PrepareStatement的实例 String sql = "insert into customers(name,email,birth) values (?,?,?)"; //?:占位符 ps = conn.prepareStatement(sql); // 6.填充占位符 ps.setString(1, "哪吒"); ps.setString(2, "nezha@163.com"); SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd"); java.util.Date date = sdf.parse("1000-01-01"); ps.setDate(3, new Date(date.getTime())); // 7.执行操作 ps.execute(); } catch (Exception e) { e.printStackTrace(); } finally { // 8.关闭资源 if (ps != null) { try { ps.close(); } catch (SQLException throwables) { throwables.printStackTrace(); } } if (conn != null) { try { conn.close(); } catch (SQLException throwables) { throwables.printStackTrace(); } } } }}
import java.io.InputStream;import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;import java.sql.SQLException;import java.util.Properties;/** * 操作数据库的工具类 * * @author xiexu * @create 2020-11-30 10:58 下午 */public class JDBCUtils { /** * 获取数据库的连接 * @return * @throws Exception */ public static Connection getConnection() throws Exception{ // 1.读取配置文件中的4个基本信息 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"); // 2.加载驱动 Class.forName(driverClass); // 3.获取连接 Connection conn = DriverManager.getConnection(url, user, password); return conn; } /** * 关闭数据库连接和PreparedStatement的操作 * @param conn * @param ps */ public static void closeResource(Connection conn, PreparedStatement ps) { if (ps != null) { try { ps.close(); } catch (SQLException throwables) { throwables.printStackTrace(); } } if (conn != null) { try { conn.close(); } catch (SQLException throwables) { throwables.printStackTrace(); } } }}
//修改customers表的一条记录 @Test public void testUpdate() { Connection conn = null; PreparedStatement ps = null; try { //1.获取数据库连接 conn = JDBCUtils.getConnection(); //2.预编译sql语句,返回PreparedStatement实例 String sql = "update customers set name = ? where id = ?"; ps = conn.prepareStatement(sql); //3.填充占位符 ps.setObject(1, "莫扎特"); ps.setObject(2, 18); //4.执行操作 ps.execute(); } catch (Exception e) { e.printStackTrace(); } finally { //5.关闭资源 JDBCUtils.closeResource(conn, ps); } }
public class PreparedStatementUpdateTest { //通用的增删改操作 public void update(String sql, Object... args) { Connection conn = null; PreparedStatement ps = null; try { //1.获取数据库连接 conn = JDBCUtils.getConnection(); //2.预编译sql语句,返回PreparedStatement实例 ps = conn.prepareStatement(sql); //3.填充占位符 for (int i = 0; i < args.length; i++) { ps.setObject(i + 1, args[i]); } //4.执行操作 ps.execute(); } catch (Exception e) { e.printStackTrace(); } finally { //5.关闭资源 JDBCUtils.closeResource(conn, ps); } } //测试 @Test public void testCommonUpdate() { String sql = "update `order` set order_name = ? where order_id = ?"; update(sql, "DD", "2"); }}
/** ORM编程思想 (object relational mapping)* 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() { } 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; } @Override public String toString() { return "Customer [id=" + id + ", name=" + name + ", email=" + email + ", birth=" + birth + "]"; }}
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; } @Override public String toString() { return "Order [orderId=" + orderId + ", orderName=" + orderName + ", orderDate=" + orderDate + "]"; }}
/** * 操作数据库的工具类 * * @author xiexu * @create 2020-11-30 10:58 下午 */public class JDBCUtils { /** * 获取数据库的连接 * @return * @throws Exception */ public static Connection getConnection() throws Exception{ // 1.读取配置文件中的4个基本信息 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"); // 2.加载驱动 Class.forName(driverClass); // 3.获取连接 Connection conn = DriverManager.getConnection(url, user, password); return conn; } /** * 关闭数据库连接和PreparedStatement的操作 * @param conn * @param ps */ public static void closeResource(Connection conn, PreparedStatement ps) { if (ps != null) { try { ps.close(); } catch (SQLException throwables) { throwables.printStackTrace(); } } if (conn != null) { try { conn.close(); } catch (SQLException throwables) { throwables.printStackTrace(); } } } public static void closeResource(Connection conn, PreparedStatement ps, ResultSet rs) { if (ps != null) { try { ps.close(); } catch (SQLException throwables) { throwables.printStackTrace(); } } if (conn != null) { try { conn.close(); } catch (SQLException throwables) { throwables.printStackTrace(); } } if (rs != null) { try { rs.close(); } catch (SQLException throwables) { throwables.printStackTrace(); } } }}
/** * 使用PreparedStatement实现针对于不同表的通用的查询操作 * * @author xiexu * @create 2020-11-30 11:37 下午 */public class PreparedStatementQueryTest { @Test public void testGetForList() { String sql = "select id,name,email from customers where id < ?"; Listlist = getForList(Customer.class, sql, 12); list.forEach(System.out::println); } public List getForList(Class clazz, String sql, Object... args) { Connection conn = null; PreparedStatement ps = null; ResultSet rs = null; try { //1.获取数据库的连接 conn = JDBCUtils.getConnection(); //2.预编译sql语句,得到PreparedStatement对象 ps = conn.prepareStatement(sql); //3.填充占位符 for (int i = 0; i < args.length; i++) { ps.setObject(i + 1, args[i]); } //4.执行,并返回结果集 rs = ps.executeQuery(); //5.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 list = new ArrayList<>(); //处理结果集 while (rs.next()) { //next( ):判断结果集的下一条是否有数据,如果有数据则返回true,并且指针下移;如果没有数据则返回false,并且指针不会下移 T t = clazz.newInstance(); //循环处理结果集中每一行数据的每一个列:给t对象指定的属性赋值 for (int i = 0; i < columnCount; i++) { //获取每个列值:通过ResultSet Object value = rs.getObject(i + 1); //获取列的别名:通过ResultSetMetaData的getColumnLabel() String columnLabel = rsmd.getColumnLabel(i + 1); //通过反射,给t对象指定的columnLabel属性,赋值为value Field field = clazz.getDeclaredField(columnLabel); field.setAccessible(true); field.set(t, value); } list.add(t); } return list; } catch (Exception e) { e.printStackTrace(); } finally { //关闭资源 JDBCUtils.closeResource(conn, ps, rs); } return null; } /** * 针对于不同的表的通用的查询操作,返回表中的一条记录 * * @param clazz * @param sql * @param args * @param * @return */ public T getInstance(Class clazz, String sql, Object... args) { Connection conn = null; PreparedStatement ps = null; ResultSet rs = null; try { //1.获取数据库的连接 conn = JDBCUtils.getConnection(); //2.预编译sql语句,得到PreparedStatement对象 ps = conn.prepareStatement(sql); //3.填充占位符 for (int i = 0; i < args.length; i++) { ps.setObject(i + 1, args[i]); } //4.执行,并返回结果集 rs = ps.executeQuery(); //5.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(); //处理结果集 if (rs.next()) { //next( ):判断结果集的下一条是否有数据,如果有数据则返回true,并且指针下移;如果没有数据则返回false,并且指针不会下移 T t = clazz.newInstance(); //处理结果集一行数据的每一个列:给t对象指定的属性赋值 for (int i = 0; i < columnCount; i++) { //获取每个列值:通过ResultSet Object value = rs.getObject(i + 1); //获取列的别名:通过ResultSetMetaData的getColumnLabel() String columnLabel = rsmd.getColumnLabel(i + 1); //通过反射,给t对象指定的columnLabel属性,赋值为value Field field = clazz.getDeclaredField(columnLabel); field.setAccessible(true); field.set(t, value); } return t; } } catch (Exception e) { e.printStackTrace(); } finally { //关闭资源 JDBCUtils.closeResource(conn, ps, rs); } return null; } @Test public void testGetInstance() { String sql = "select id,name,email from customers where id = ?"; Customer customer = getInstance(Customer.class, sql, 12); System.out.println(customer); String sql2 = "select order_id orderId,order_name orderName from `order` where order_id = ?"; Order order = getInstance(Order.class, sql2, 1); System.out.println(order); }}
问题1:得到结果集后, 如何知道该结果集中有哪些列 ? 列名是什么?
需要使用一个描述 ResultSet 的对象, 即 ResultSetMetaData
问题2:关于ResultSetMetaData
两种思想
sql是需要结合列名和表的属性名来写的,需要注意起别名。
两种技术
练习题1:从控制台向数据库的表customers中插入一条数据,表结构如下:
/** * @author xiexu * @create 2020-12-02 4:33 下午 */public class ExerTest1 { //通用的增删改操作 public int update(String sql, Object... args) { Connection conn = null; PreparedStatement ps = null; try { //1.获取数据库连接 conn = JDBCUtils.getConnection(); //2.预编译sql语句,返回PreparedStatement实例 ps = conn.prepareStatement(sql); //3.填充占位符 for (int i = 0; i < args.length; i++) { ps.setObject(i + 1, args[i]); } // 4.执行 /* * ps.execute(): * 如果执行的是查询操作,有返回结果,则此方法返回true; * 如果执行的是增、删、改操作,没有返回结果,则此方法返回false. */ //方式一:// return ps.execute(); //方式二: return ps.executeUpdate(); } catch (Exception e) { e.printStackTrace(); } finally { //5.关闭资源 JDBCUtils.closeResource(conn, ps); } return 0; } @Test public void testInsert() { @SuppressWarnings("resource") 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:"); //1998-08-08,数据库的隐式转换 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!"); } }}
练习题2:创立数据库表 examstudent,表结构如下:
向数据表中添加如下数据:
代码实现1:插入一个新的student 信息
请输入考生的详细信息Type: IDCard:ExamCard:StudentName:Location:Grade:信息录入成功!
public class ExerTest2 { // 通用的增删改操作 public int update(String sql, Object... args) { // sql中占位符的个数与可变形参的长度相同! Connection conn = null; PreparedStatement ps = null; try { // 1.获取数据库的连接 conn = JDBCUtils.getConnection(); // 2.预编译sql语句,返回PreparedStatement的实例 ps = conn.prepareStatement(sql); // 3.填充占位符 for (int i = 0; i < args.length; i++) { ps.setObject(i + 1, args[i]); // 小心参数声明错误!! } // 4.执行 /* * ps.execute(): 如果执行的是查询操作,有返回结果,则此方法返回true; * 如果执行的是增、删、改操作,没有返回结果,则此方法返回false. */ // 方式一: // return ps.execute(); // 方式二: return ps.executeUpdate(); } catch (Exception e) { e.printStackTrace(); } finally { // 5.关闭资源 JDBCUtils.closeResource(conn, ps); } return 0; } // 问题1:向examstudent表中添加一条记录 /** * Type: * IDCard: * ExamCard: * StudentName: * Location: * Grade: */ @Test public void testInsert() { @SuppressWarnings("resource") 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!"); } }}
代码实现2:在 idea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:
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; //所在城市 private int grade; //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 getFlowID() { return flowID; } public void setFlowID(int flowID) { this.flowID = flowID; } 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; } @Override public 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; }}
public class ExerTest2 { //问题2:根据身份证号或者准考证号查询学生成绩信息 @Test public void queryWithIDCardOrExamCard(){ System.out.println("请选择您要输入的类型:"); System.out.println("a.准考证号"); System.out.println("b.身份证号"); @SuppressWarnings("resource") 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("输入的准考证号有误!"); } }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("输入的身份证号有误!"); } }else{ System.out.println("您的输入有误,请重新进入程序。"); } } publicT getInstance(Class clazz, String sql, Object... args) { Connection conn = null; PreparedStatement ps = null; ResultSet rs = null; try { // 1.获取数据库连接 conn = JDBCUtils.getConnection(); // 2.预编译sql语句,得到PreparedStatement对象 ps = conn.prepareStatement(sql); // 3.填充占位符 for (int i = 0; i < args.length; i++) { ps.setObject(i + 1, args[i]); } // 4.执行executeQuery(),得到结果集:ResultSet rs = ps.executeQuery(); // 5.得到结果集的元数据:ResultSetMetaData ResultSetMetaData rsmd = rs.getMetaData(); // 6.1通过ResultSetMetaData得到columnCount,columnLabel;通过ResultSet得到列值 int count = rsmd.getColumnCount(); if (rs.next()) { T t = clazz.newInstance(); for (int i = 0; i < count; i++) { //获取每个列值:通过ResultSet Object value = rs.getObject(i + 1); //获取列的别名:getColumnLabel() String columnLabel = rsmd.getColumnLabel(i + 1); //通过反射,将t对象指定名className的属性赋值为指定的值value Field field = clazz.getDeclaredField(columnLabel); field.setAccessible(true); field.set(t, value); } return t; } } catch (Exception e) { e.printStackTrace(); } finally { JDBCUtils.closeResource(conn, ps, rs); } return null; }}
代码实现3:完成学生信息的删除功能
public class ExerTest2 { // 通用的增删改操作 public int update(String sql, Object... args) { // sql中占位符的个数与可变形参的长度相同! Connection conn = null; PreparedStatement ps = null; try { // 1.获取数据库的连接 conn = JDBCUtils.getConnection(); // 2.预编译sql语句,返回PreparedStatement的实例 ps = conn.prepareStatement(sql); // 3.填充占位符 for (int i = 0; i < args.length; i++) { ps.setObject(i + 1, args[i]); // 小心参数声明错误!! } // 4.执行 /* * ps.execute(): 如果执行的是查询操作,有返回结果,则此方法返回true; * 如果执行的是增、删、改操作,没有返回结果,则此方法返回false. */ // 方式一: // return ps.execute(); // 方式二: return ps.executeUpdate(); } catch (Exception e) { e.printStackTrace(); } finally { // 5.关闭资源 JDBCUtils.closeResource(conn, ps); } return 0; } // 问题1:向examstudent表中添加一条记录 /** * Type: * IDCard: * ExamCard: * StudentName: * Location: * Grade: */ @Test public void testInsert() { @SuppressWarnings("resource") 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!"); } } //问题2:根据身份证号或者准考证号查询学生成绩信息 @Test public void queryWithIDCardOrExamCard(){ System.out.println("请选择您要输入的类型:"); System.out.println("a.准考证号"); System.out.println("b.身份证号"); @SuppressWarnings("resource") 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("输入的准考证号有误!"); } }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("输入的身份证号有误!"); } }else{ System.out.println("您的输入有误,请重新进入程序。"); } } publicT getInstance(Class clazz, String sql, Object... args) { Connection conn = null; PreparedStatement ps = null; ResultSet rs = null; try { // 1.获取数据库连接 conn = JDBCUtils.getConnection(); // 2.预编译sql语句,得到PreparedStatement对象 ps = conn.prepareStatement(sql); // 3.填充占位符 for (int i = 0; i < args.length; i++) { ps.setObject(i + 1, args[i]); } // 4.执行executeQuery(),得到结果集:ResultSet rs = ps.executeQuery(); // 5.得到结果集的元数据:ResultSetMetaData ResultSetMetaData rsmd = rs.getMetaData(); // 6.1通过ResultSetMetaData得到columnCount,columnLabel;通过ResultSet得到列值 int count = rsmd.getColumnCount(); if (rs.next()) { T t = clazz.newInstance(); for (int i = 0; i < count; i++) { //获取每个列值:通过ResultSet Object value = rs.getObject(i + 1); //获取列的别名:getColumnLabel() String columnLabel = rsmd.getColumnLabel(i + 1); //通过反射,将t对象指定名className的属性赋值为指定的值value Field field = clazz.getDeclaredField(columnLabel); field.setAccessible(true); field.set(t, value); } return t; } } catch (Exception e) { e.printStackTrace(); } finally { JDBCUtils.closeResource(conn, ps, rs); } return null; } // 问题3:删除指定的学生信息 @Test public void testDeleteByExamCard() { System.out.println("请输入学生的考号:"); @SuppressWarnings("resource") 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 deleteCount = update(sql1, examCard); if (deleteCount > 0) { System.out.println("删除成功!"); } } } // 优化以后的操作: @Test public void testDeleteByExamCard1() { System.out.println("请输入学生的考号:"); @SuppressWarnings("resource") Scanner scanner = new Scanner(System.in); String examCard = scanner.next(); String sql = "delete from examstudent where examCard = ?"; int deleteCount = update(sql, examCard); if (deleteCount > 0) { System.out.println("删除成功!"); } else { System.out.println("查无此人,请重新输入!"); } }}
/** * 测试使用PreparedStatement操作Blob类型的数据 * @author xiexu * @create 2020-12-02 9:42 下午 */public class BlobTest { // 向数据表customers中插入Blob类型的字段 @Test public void testInsert() throws Exception { Connection conn = JDBCUtils.getConnection(); String sql = "insert into customers(name,email,birth,photo)values(?,?,?,?)"; PreparedStatement ps = conn.prepareStatement(sql); ps.setObject(1,"张宇"); ps.setObject(2, "zhanyu@qq.com"); ps.setObject(3,"1999-04-28"); FileInputStream is = new FileInputStream(new File("n6qx6q.jpg")); ps.setBlob(4, is); ps.execute(); JDBCUtils.closeResource(conn, ps); }}
/** * 测试使用PreparedStatement操作Blob类型的数据 * @author xiexu * @create 2020-12-02 9:42 下午 */public class BlobTest { // 查询数据表customers中Blob类型的字段 @Test public void testQuery(){ Connection conn = null; PreparedStatement ps = null; ResultSet rs = null; InputStream is = null; FileOutputStream fos = null; try { conn = JDBCUtils.getConnection(); String sql = "select id,name,email,birth,photo from customers where id = ?"; ps = conn.prepareStatement(sql); ps.setObject(1,20); rs = ps.executeQuery(); if (rs.next()) { //方式一: // int id = rs.getInt(1); // String name = rs.getString(2); // String email = rs.getString(3); // Date birth = rs.getDate(4); //方式二: int id = rs.getInt("id"); String name = rs.getString("name"); String email = rs.getString("email"); Date birth = rs.getDate("birth"); Customer customer = new Customer(id, name, email, birth); System.out.println(customer); //将Blob类型的字段下载下来,以文件的方式保存在本地 Blob photo = rs.getBlob("photo"); is = photo.getBinaryStream(); fos = new FileOutputStream("github.jpg"); byte[] buffer = new byte[1024]; int len; while((len = is.read(buffer)) != -1){ fos.write(buffer,0,len); } } } catch (Exception e) { e.printStackTrace(); } finally { if (is != null) { try { is.close(); } catch (IOException e) { e.printStackTrace(); } } if (fos != null) { try { fos.close(); } catch (IOException e) { e.printStackTrace(); } } JDBCUtils.closeResource(conn,ps,rs); } } // 向数据表customers中插入Blob类型的字段 @Test public void testInsert() throws Exception { Connection conn = JDBCUtils.getConnection(); String sql = "insert into customers(name,email,birth,photo)values(?,?,?,?)"; PreparedStatement ps = conn.prepareStatement(sql); ps.setObject(1,"张宇"); ps.setObject(2, "zhanyu@qq.com"); ps.setObject(3,"1999-04-28"); FileInputStream is = new FileInputStream(new File("n6qx6q.jpg")); ps.setBlob(4, is); ps.execute(); JDBCUtils.closeResource(conn, ps); }}
当需要成批插入或者更新记录时,可以采用Java的批量更新机制,这一机制允许多条语句一次性提交给数据库批量处理。通常情况下比单独提交处理更有效率
JDBC的批量处理语句包括下面三个方法:
通常我们会遇到两种批量执行SQL语句的情况:
举例:向数据表中插入20000条数据
CREATE TABLE goods(id INT PRIMARY KEY AUTO_INCREMENT,NAME VARCHAR(20));
Connection conn = JDBCUtils.getConnection();Statement st = conn.createStatement();for(int i = 1;i <= 20000;i++){ String sql = "insert into goods(name) values('name_' + "+ i +")"; st.executeUpdate(sql);}
/** * 使用PreparedStatement实现批量数据的操作 * update、delete本身就具有批量操作的效果 * 此时的批量操作主要指的是批量插入。使用PreparedStatement如何实现更高效的批量插入? * * @author xiexu * @create 2020-12-02 10:13 下午 */public class InsertTest { //批量插入的方式二:使用PreparedStatement @Test public void testInsert(){ Connection conn = null; PreparedStatement ps = null; try { long start = System.currentTimeMillis(); conn = JDBCUtils.getConnection(); String sql = "insert into goods(name) values(?)"; ps = conn.prepareStatement(sql); for (int i = 0; i < 20000; i++) { ps.setObject(1,"name_" + i); ps.execute(); } long end = System.currentTimeMillis(); System.out.println("花费的时间为:" + (end - start)); //8760 } catch (Exception e) { e.printStackTrace(); } finally { JDBCUtils.closeResource(conn,ps); } }}
/** * 批量插入的方式三:使用 addBatch() / executeBatch() / clearBatch() * 修改:mysql服务器默认是关闭批处理的,我们需要通过一个参数,让mysql开启批处理的支持。 * ?rewriteBatchedStatements=true 写在配置文件的url后面 */ @Test public void testInsert2() throws Exception{ Connection conn = null; PreparedStatement ps = null; try { long start = System.currentTimeMillis(); conn = JDBCUtils.getConnection(); String sql = "insert into goods(name) values(?)"; ps = conn.prepareStatement(sql); for (int i = 0; i < 1000000; i++) { ps.setObject(1,"name_" + i); //1."攒"sql ps.addBatch(); if(i % 500 == 0){ //"攒"够500执行一次 //2.执行batch ps.executeBatch(); //3.清空batch ps.clearBatch(); } } long end = System.currentTimeMillis(); System.out.println("花费的时间为:" + (end - start)); //7888 } catch (Exception e) { e.printStackTrace(); } finally { JDBCUtils.closeResource(conn,ps); } }
/* * 方式四:设置连接不允许自动提交数据 * 使用Connection 的 setAutoCommit(false) / commit() */ @Test public void testInsert3() { Connection conn = null; PreparedStatement ps = null; try { long start = System.currentTimeMillis(); conn = JDBCUtils.getConnection(); //设置不允许自动提交数据 conn.setAutoCommit(false); String sql = "insert into goods(name)values(?)"; ps = conn.prepareStatement(sql); for (int i = 1; i <= 1000000; i++) { ps.setObject(1, "name_" + i); // 1."攒"sql ps.addBatch(); if (i % 500 == 0) { // 2.执行batch ps.executeBatch(); // 3.清空batch ps.clearBatch(); } } //提交数据 conn.commit(); long end = System.currentTimeMillis(); System.out.println("花费的时间为:" + (end - start));// 6884 } catch (Exception e) { e.printStackTrace(); } finally { JDBCUtils.closeResource(conn, ps); } }
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