Jdbc--具体代码实现
2016-10-16 01:43
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1、获取连接
1) 把jar包复制到项目目录下2) 把jar包加入项目的buildpath环境变量中, 使得classpath也和buildpath一致, 让类加载器便于加载具体子类
3) 反射加载驱动程序类, 会自动注册驱动程序
4) 通过驱动程序管理器获取连接.
在当前工程下创建jdbc.properties文件,其中内容如下(是连接Oracle、MySql数据库所需要的四大参数分别是:加载驱动、获取连接数据库的IP及端口、用户名,密码),目的是方便调用和修改!
#driverClass = oracle.jdbc.driver.OracleDriver
#url = jdbc:oracle:thin:@127.0.0.1:1521:orcl
#user = scott
#password = tiger
driverClass = com.mysql.jdbc.Driver
url = jdbc:mysql://127.0.0.1:3306/company
user = root
password = 123456
获取连接以及关闭连接的具体实现如下:
package com.atguigu.jdbc; import java.io.FileInputStream; import java.sql.Connection; import java.sql.Driver; import java.sql.DriverManager; import java.sql.SQLException; import java.util.Properties; import org.junit.Test; /** * 获取连接 * 1) 把jar包复制到项目目录下 * 2) 把jar包加入项目的buildpath环境变量中, 使得classpath也和buildpath一致, 让类加载器便于加载具体子类 * 3) 反射加载驱动程序类, 会自动注册驱动程序 * 4) 通过驱动程序管理器获取连接. * @author Administrator * */ public class DriverTest { // 使用Properties类对象的getPropety方法与FileInputStream方法获取文件中的内容,从而创建Connection对象 @Test public void test5() throws Exception { Properties properties = new Properties(); properties.load(new FileInputStream("jdbc.properties")); String driverClass = properties.getProperty("driverClass"); String url = properties.getProperty("url"); String user = properties.getProperty("user"); String password = properties.getProperty("password"); Class.forName(driverClass); // 只需要加载类, 类的静态语句块就会被执行, 创建驱动程序对象,并把此对象注册到驱动程序管理器中. Connection connection = DriverManager.getConnection(url, user, password); System.out.println(connection); connection.close(); } }鉴于每一次jdbc的操作都需要建立连接,我们将建立连接的方法、关闭资源的方法作为固定方法放在JdbcUtil类中,方便使用:
package com.atguigu.jdbc; import java.io.FileInputStream; import java.io.IOException; import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; import java.util.Properties; public class JdbcUtil { // 获取建立连接对象 public static Connection getConnection() throws IOException, ClassNotFoundException, SQLException { Properties properties = new Properties(); properties.load(new FileInputStream("jdbc.properties")); String driverClass = properties.getProperty("driverClass"); String url = properties.getProperty("url"); String user = properties.getProperty("user"); String password = properties.getProperty("password"); Class.forName(driverClass); // 只需要加载类, 类的静态语句块就会被执行, 创建驱动程序对象,并把此对象注册到驱动程序管理器中. Connection connection = DriverManager.getConnection(url, user, password); return connection; } // 关闭资源 public static void close(Connection connection) { close(connection, null); } public static void close(Connection connection, Statement statement) { close(connection, statement, null); } public static void close(Connection connection, Statement statement, ResultSet resultSet) { if (resultSet != null) { try { resultSet.close(); } catch (Exception e) { e.printStackTrace(); } } if (statement != null) { try { statement.close(); } catch (Exception e) { e.printStackTrace(); } } if (connection != null) { try { connection.close(); } catch (Exception e) { e.printStackTrace(); } } } }
Statement类
建立连接成功,现在进行与数据库的交流,与数据库交流需要使用到Statement类,首先我们需要建立一个User类以与Statement类中创建的在company数据库中的的user表相对应:package com.atguigu.jdbc; public class User { private String user; private String password; public User() { } public User(String user, String password) { super(); this.user = user; this.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; } @Override public String toString() { return "User [user=" + user + ", password=" + password + "]"; } }
使用Statement执行创建user表,并插入三行数据:
package com.atguigu.jdbc;
import java.sql.Connection;
import java.sql.Statement;
import org.junit.Test;
// 使用Statement执行创建user表,并插入三行数据
public class StatementTest {
@Test
public void test1() {
Connection connection = null;
Statement statement = null;
try {
connection = JdbcUtil.getConnection();
statement = connection.createStatement();// 获取执行体对象
// 执行SQL
// 创建user表
String sql = "create table if not exists user(user varchar(50), password varchar(100))";
int rows = statement.executeUpdate(sql); // 执行的DDL语句, 还可以执行DML
System.out.println(rows + " rows affected..");
rows = statement.executeUpdate("insert into user values('admin','admin')");
System.out.println(rows + " rows affected..");
rows = statement.executeUpdate("insert into user values('user1','user1')");
System.out.println(rows + " rows affected..");
rows = statement.executeUpdate("insert into user values('user2','123456')");
System.out.println(rows + " rows affected..");
} catch (Exception e) {
e.printStackTrace();
} finally {
JdbcUtil.close(connection, statement);
}
}
}然而Statement存在弊端:不仅需要拼写sql语句,并且存在SQL注入的问题,具体问题在下面的小例子中体现
package com.atguigu.jdbc;
import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.util.Scanner;
import org.junit.Test;
import java.sql.Statement;
public class TestStatement {
// 弊端:需要拼写sql语句,并且存在SQL注入的问题
@Test
public 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();
String sql = "select user, password from user where user = '"
+ userName + "' and password = '" + password + "'";
System.out.println(sql);
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!");
}
}
public <T> T get(String sql, Class<T> clazz) {// (sql, Customer.class)
T t = null;
Connection conn = null;
Statement stam = null;
ResultSet rs = null;
try {
conn = JdbcUtil.getConnection();
stam = conn.createStatement();
rs = stam.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); // 注意:
// 获取结果集中(相当于数据表)列的名称(别名)
// 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); // 注意:反射根据Java中类的属性获取Field对象
field.setAccessible(true);
field.set(t, columnVal);
}
}
} catch (Exception e) {
e.printStackTrace();
} finally {
//JDBCUtils.close(rs, stam, conn);
}
return t;
}
}
此程序我们需要使用正确的用户名,和对应的密码才能进入登陆成功,通过上面的程序我们可知用户名和密码分别是:
+-------+----------+
| user | password |
+-------+----------+
| admin | admin |
| user1 | user1 |
| user2 | 123456 |
+-------+----------+
正常情况下我们登陆情况如下图:
但是SQL高手通过如下操作就能登陆成功,这就是SQL注入的问题
PreparedStatement类
为了防止SQL注入问题,于是我们需要使用他的子类PreparedStatement预编译执行体,下面我们进行PreparedStatement的练习:首先先创建Customer类
// 写一个类Customer, 包含属性name, gender, phone
package com.atguigu.jdbc;
public class Customer {
private String name;
private String gender;
private String phone;
public Customer(String name, int age, String gender, String phone,) {
super();
this.name = name;
this.age = age;
this.gender = gender;
this.phone = phone;
}
public Customer() {
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getGender() {
return gender;
}
public void setGender(String gender) {
this.gender = gender;
}
public String getPhone() {
return phone;
}
public void setPhone(String phone) {
this.phone = phone;
}
@Override
public String toString() {
return "Customer [name=" + name + ", gender=" + gender + ", phone=" + phone + "]";
}
}在测试类中使用PreparedStatment执行体对象创建相应的表, 并插入2条数据。
public class PreparedStatementTest { @Test public void exer1() { Connection connection = null; PreparedStatement preparedStatement = null; try { connection = JdbcUtil.getConnection(); String sql = "create table if not exists customer(name varchar(30), gender enum('男','女') default '男', phone varchar(20))"; preparedStatement = connection.prepareStatement(sql); preparedStatement.executeUpdate(); JdbcUtil.close(null, preparedStatement); // 在获取新的预编译对象前,一定要先关闭原来的. String sql2 = "insert into customer(name, gender, phone) values(?, ?, ?)"; preparedStatement = connection.prepareStatement(sql2); // 要想重新执行新的SQL,必须再次预编译 preparedStatement.setString(1, "张三"); preparedStatement.setString(2, "男"); preparedStatement.setString(3, "13343493434"); int rows = preparedStatement.executeUpdate(); System.out.println(rows + " rows affected."); preparedStatement.setString(1, "李四"); preparedStatement.setString(2, "女"); preparedStatement.setString(3, "1322243434"); rows = preparedStatement.executeUpdate(); System.out.println(rows + " rows affected."); } catch (Exception e) { e.printStackTrace(); } finally { JdbcUtil.close(connection, preparedStatement); } // 并通过客户端验证. } }在Customer类中添加属性int age,double weight,给Customer表中添加对应的列,并添加记录
public class PreparedStatementTest {
// 在Customer类中添加属性int age,double weight,给Customer表中添加对应的列,并添加记录
@Test
public void test3() {
Connection connection = null;
PreparedStatement preparedStatement = null;
try {
connection = JdbcUtil.getConnection();
String sql = "alter table customer add age int after name";
preparedStatement = connection.prepareStatement(sql);
preparedStatement.executeUpdate();
JdbcUtil.close(null, preparedStatement);
sql = "alter table customer add weight double";
preparedStatement = connection.prepareStatement(sql);
preparedStatement.executeUpdate();
JdbcUtil.close(null, preparedStatement);
sql = "insert into customer(name, age, gender, phone, weight) values (?, ?, ?, ?, ?)";
preparedStatement = connection.prepareStatement(sql);
preparedStatement.setString(1, "王五");
preparedStatement.setInt(2, 50);
preparedStatement.setString(3, "男");
preparedStatement.setString(4, "134234234234");
preparedStatement.setDouble(5, 98.5);
int rows = preparedStatement.executeUpdate();
System.out.println(rows + " rows affected");
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
} finally {
JdbcUtil.close(connection, preparedStatement);
}
}
// 添加记录
@Test
public void test4() {
Connection connection = null;
PreparedStatement preparedStatement = null;
try {
connection = JdbcUtil.getConnection();
String sql = "alter table customer add birthdate date";
preparedStatement = connection.prepareStatement(sql);
preparedStatement.executeUpdate();
JdbcUtil.close(null, preparedStatement);
sql = "insert into customer(name, age, gender, phone, weight, birthdate) values (?, ?, ?, ?, ?, ?)";
preparedStatement = connection.prepareStatement(sql);
preparedStatement.setString(1, "赵六");
preparedStatement.setInt(2, 60);
preparedStatement.setString(3, "女");
preparedStatement.setString(4, "13882342323");
preparedStatement.setDouble(5, 40);
preparedStatement.setString(6, "1960-2-3");
int rows = preparedStatement.executeUpdate();
System.out.println(rows + " rows affected");
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
} finally {
JdbcUtil.close(connection, preparedStatement);
}
}
// 再添加记录
@Test
public void test5() {
Connection connection = null;
PreparedStatement preparedStatement = null;
try {
connection = JdbcUtil.getConnection();
String sql = "insert into customer(name, age, gender, phone, weight, birthdate) values (?, ?, ?, ?, ?, ?)";
preparedStatement = connection.prepareStatement(sql);
preparedStatement.setObject(1, "张七");
preparedStatement.setObject(2, 20);
preparedStatement.setObject(3, "女");
preparedStatement.setObject(4, "1343434343");
preparedStatement.setObject(5, 58.8);
preparedStatement.setObject(6, "1980-3-8");
int rows = preparedStatement.executeUpdate();
if (rows == 1) {
System.out.println("插入成功");
}
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
} finally {
JdbcUtil.close(connection, preparedStatement);
}
}
}像上面那样添加每次重复同样的代码,我们这里设置通用的更新操作,并存入CommonUtil类中,作为工具类通用更新操作。具体实现如下:
package com.atguigu.jdbc;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
public class CommonUtil {
/**
* 通用更新操作
* @param sql 一个可以包含?的SQL语句
* @param values SQL中有多少个?,可变参数就有多少个具体值
* @return 更新以后影响的记录数
*/
public static int commonUpdate(String sql, Object... values) throws FileNotFoundException, ClassNotFoundException, IOException,
SQLException {
Connection connection = null;
PreparedStatement preparedStatement = null;
try {
connection = JdbcUtil.getConnection(); // 获取连接
preparedStatement = connection.prepareStatement(sql); // 把带有?的SQL编译
for (int i = 0; i < values.length; i++) { // 可变参数的长度就是?的个数
preparedStatement.setObject(i + 1, values[i]); // 统一给所有的?替换成具体的值
}
return preparedStatement.executeUpdate(); // 替换完?或没有?, 执行更新操作
} finally {
JdbcUtil.close(connection, preparedStatement); // 关闭资源
}
}
}
ResultSet类
至此我们实现了数据库数据的建表,插入,更新,删除,下面进行数据库操作中比较难的查询,需要使用到查询结果集ResultSet类,循序渐进的练习实现如下:package com.atguigu.jdbc;
import java.util.List;
import java.sql.Connection;
import java.sql.Date;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.util.ArrayList;
import org.junit.Test;
public class ResultSetTest {
@Test
public void test1() {
// select * from customer; 结果如下
/*
+------+------+--------+------------+--------+------------+
| name | age | gender | phone | weight | birthdate |
+------+------+--------+------------+--------+------------+
| 张七 20 | 女 | 1343434343 | 58.8 | 1980-03-08 |
| 张九 | 40 | 男 | 1349932423 | 78.2 | 1977-08-08 |
| 张三 | 3 | 女 | 1332324234 | 70 | 1979-08-08 |
+------+------+--------+------------+--------+------------+
*/
Connection connection = null;
PreparedStatement prepareStatment = null;
ResultSet resultSet = null;
try {
connection = JdbcUtil.getConnection();
String sql = "select * from customer";
prepareStatment = connection.prepareStatement(sql);
// 调用PreparedStatement对象的executeQuery方法产生ResultSet对象
resultSet = prepareStatment.executeQuery();
System.out.println(resultSet);
while (resultSet.next()) { // 根据列的<span style="color:#ff0000;">序号</span>,先检测当前游标的下一行是否有数据, 如果有数据则移动游标,并返回true, 如果没有数据,直接返回false
String name = resultSet.getString(1); // 获取到的是当前游标指向的行的第1列的值
int age = resultSet.getInt(2);// 获取到的是当前游标指向的行的第2列的值
String gender = resultSet.getString(3);// 获取到的是当前游标指向的行的第3列的值
String phone = resultSet.getString(4);// 获取到的是当前游标指向的行的第4列的值
double weight = resultSet.getDouble(5);// 获取到的是当前游标指向的行的第5列的值
Date birthDate = resultSet.getDate(6);// 获取到的是当前游标指向的行的第6列的值
System.out.println(name + "\t" + age + "\t" + gender + "\t" + phone + "\t" + weight + "\t" + birthDate);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
JdbcUtil.close(connection, prepareStatment, resultSet);
}
}
// 我们改变查询列名的顺序进行查询操作,使用下标不能实现了,我们需要根据虚表中的<span style="color:#ff0000;">列名</span>进行查询,并将查询结果封装成对象,添加到list集合中
@Test
public void test2() {
Connection connection = null;
PreparedStatement prepareStatment = null;
ResultSet resultSet = null;
try {
connection = JdbcUtil.getConnection();
// name | age | gender | phone | weight | birthdate |
String sql = "select name custName, gender, age, weight, phone, birthdate birth from customer";
prepareStatment = connection.prepareStatement(sql);
resultSet = prepareStatment.executeQuery();
List<Customer> list = new ArrayList<Customer>();
// 基于虚表的结果集
while (resultSet.next()) {
String name = resultSet.getString("custName");// 获取到的是当前游标指向的行的虚表中名字为name列的值
int age = resultSet.getInt("age");// 获取到的是当前游标指向的行的虚表中名字为age列的值
String gender = resultSet.getString("gender");// 获取到的是当前游标指向的行的虚表中名字为gender列的值
String phone = resultSet.getString("phone");
double weight = resultSet.getDouble("weight");
Date birthDate = resultSet.getDate("birth");
Customer customer = new Customer(name, age, gender, phone, weight, birthDate); // 封装成对象 O/R mapping
list.add(customer);
}
// 遍历集合
for (Customer cust : list) {
System.out.println(cust);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
JdbcUtil.close(connection, prepareStatment, resultSet);
}
}
// 我们改变查询列名的顺序进行查询年龄大于任意数的操作,使用下标不能实现了,我们需要根据<span style="color:#ff0000;">虚表中的列名</span>进行查询,并将查询结果封装成对象,添加到list集合中
@Test
public void test3() {
Connection connection = null;
PreparedStatement prepareStatment = null;
ResultSet resultSet = null;
try {
connection = JdbcUtil.getConnection();
// name | age | gender | phone | weight | birthdate |
String sql = "select name custName, gender, age, weight, phone, birthdate birth from customer where age > ?";
prepareStatment = connection.prepareStatement(sql);
prepareStatment.setObject(1, 20);
resultSet = prepareStatment.executeQuery();
List<Customer> list = new ArrayList<Customer>();
// <span style="color:#ff0000;">基于虚表的结果集</span>
while (resultSet.next()) {
String name = resultSet.getString("custName");// 获取到的是当前游标指向的行的<span style="color:#ff0000;">虚表</span>中名字为name列的值
int age = resultSet.getInt("age");// 获取到的是当前游标指向的行的虚表中名字为age列的值
String gender = resultSet.getString("gender");// 获取到的是当前游标指向的行的虚表中名字为gender列的值
String phone = resultSet.getString("phone");
double weight = resultSet.getDouble("weight");
Date birthDate = resultSet.getDate("birth");
Customer customer = new Customer(name, age, gender, phone, weight, birthDate); // 封装成对象 O/R mapping
list.add(customer);
}
// 遍历集合
for (Customer cust : list) {
System.out.println(cust);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
JdbcUtil.close(connection, prepareStatment, resultSet);
}
}
// 获取查询结果,若查询结果并没有类与其对应,就需要获取虚表的表结构进行查询操作的打印输出
@Test
public void test4() {
Connection connection = null;
PreparedStatement prepareStatment = null;
ResultSet resultSet = null;
try {
connection = JdbcUtil.getConnection();
// name | age | gender | phone | weight | birthdate |
String sql = "select name custName, gender, age, weight, phone, birthdate birth from customer";
prepareStatment = connection.prepareStatement(sql);
resultSet = prepareStatment.executeQuery();
/*
+----------+--------+------+--------+------------+------------+
| custName | gender | age | weight | phone | birth |
+----------+--------+------+--------+------------+------------+
| 张七 | 女 | 20 | 58.8 | 1343434343 | 1980-03-08 |
| 张九 | 男 | 40 | 78.2 | 1349932423 | 1977-08-08 |
| 张三 | 女 | 30 | 70 | 1332324234 | 1979-08-08 |
+----------+--------+------+--------+------------+------------+
*/
ResultSetMetaData metaData = resultSet.getMetaData(); // 获取虚表的表结构对象
int cols = metaData.getColumnCount(); // 获取虚表共有多少列
//System.out.println(cols);
String colName = metaData.getColumnName(3);// 获取基表的列名, 参数中的是第几列
//System.out.println(colName);
colName = metaData.getColumnName(6);// 获取基表列名, 参数中的是第几列
//System.out.println(colName);
String colLabel = metaData.getColumnLabel(6); // 获取虚表列名, 参数是第6列
//System.out.println(colLabel);
System.out.println("---------------------------------");
for (int i = 0; i < cols; i++) {
String columnLabel = metaData.getColumnLabel(i + 1); // 列的索引总是从1开始
System.out.print(columnLabel + "\t");
}
System.out.println();
while (resultSet.next()) {
for (int i = 0; i < cols; i++) {
String columnLabel = metaData.getColumnLabel(i + 1); // 先获取列的别名
Object value = resultSet.getObject(columnLabel); // 根据列的别名再获取对应的值
System.out.print(value + "\t");
}
System.out.println();
}
} catch (Exception e) {
e.printStackTrace();
} finally {
JdbcUtil.close(connection, prepareStatment, resultSet);
}
}
}
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