JDBC核心API详解
时间：20180310
Statement对象：可以类比于一艘货船，1.现在java程序中将sql装入Statement对象中，2.Statement对象货船漂洋过海到mysql数据库，3.在数据库中执行Statement对象中sql语句，4.将sql执行的结果放入Statement中，5.Statement再次飘洋过海回到java程序中，6.将Statement对象中结果集ResultSet返回给java程序。
例1：通过Statement去执行sql
使用Statement接口执行DDL语句(Create/drop/alter)
/**
* 使用Statement接口执行DDL语句(Create/drop/alter)
* @author mengjie
*
*/
public class Demo1 {
//url==jdbc协议：mysql协议+ip地址+端口+数据库
private static String url = "jdbc:mysql://localhost:3306/day16";
//user
private static String user = "root";
//password
private static String password = "root";
public static void main(String[] args) throws Exception {
//1.注册驱动程序
Class.forName("com.mysql.jdbc.Driver");
//2.获取连接
Connection conn = DriverManager.getConnection(url,user,password);
//3.准备sql语句
String sql = "CREATE TABLE student(id INT, NAME VARCHAR(20),age INT)";
//Statement对象：可以类比于一艘货轮
//4.在连接基础上，创建Statement
Statement stmt = conn.createStatement();
//5.执行sql,返回结果
int count = stmt.executeUpdate(sql);
System.out.println("影响了"+count+"行！");
//6关闭资源：后打开先关闭
stmt.close();
conn.close();
}
}
例2： 通过Statement去执行sql
使用Statement接口执行DML语句（insert/update/delete）
/**
* 使用Statement对象执行DML语句（insert/update/delete）
* @author mengjie
*
*/
public class Demo2 {
private static String url = "jdbc:mysql://localhost:3306/day16";
private static String username = "root";
private static String password = "root";
public static void main(String[] args) throws Exception {
//1.注册驱动
Class.forName("com.mysql.jdbc.Driver");
//2.创建连接
Connection conn = DriverManager.getConnection(url,username,password);
//3.创建sql
String sql = "INSERT INTO student (id,NAME,age) VALUES(1,'小花',22)";
//4.创建statement
Statement statement = conn.createStatement();
//5.执行sql
int n = statement.executeUpdate(sql);
System.out.println("影响了" + n + "行");
statement.close();
conn.close();
}
}
总结
jdbc操作步骤
- 注册驱动程序
- 获取连接对象
- 准备sql语句
- 创建Statement对象
- 执行sql
- 关闭资源
标准的jdbc，并利用工具类的写法
/**
* jdbc通用方法
* @author mengjie
*
*/
public class JdbcUtil {
//url
private static String url = "jdbc:mysql://localhost:3306/day16";
//user
private static String user = "root";
//password
private static String password = "root";
/**
*z只注册一次驱动，静态代码块
*/
static {
//注册驱动程序
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
* 获取连接的方法
* @throws SQLException
*/
public static Connection getConnection() {
try {
Connection conn = DriverManager.getConnection(url, user, password);
return conn;
} catch (SQLException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
/**
* 释放资源的方法
*/
public static void close(Statement stmt, Connection conn) {
if(stmt != null) {
try {
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
if(conn != null) {
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
}
}
public class Demo3 {
public static void main(String[] args) throws Exception {
Connection conn = null;
Statement stmt = null;
try {
//1)获取连接
conn = JdbcUtil.getConnection();
//2)准备sql
String sql = "CREATE TABLE employee(" +
"id INT PRIMARY KEY AUTO_INCREMENT, "+
"NAME VARCHAR(20),"+
"gender VARCHAR(2), "+
"age INT, "+
"title VARCHAR(20),"+
"email VARCHAR(50),"+
"phone VARCHAR(11))";
//3）创建一个Statement对象
stmt = conn.createStatement();
//4) 执行sql
int n = stmt.executeUpdate(sql);
System.out.println("影响了"+n+"行");
} catch (Exception e) {
e.printStackTrace();
} finally {
//5)关闭资源
JdbcUtil.close(stmt, conn);
}
}
}
重载通用类方法
/**
* jdbc通用方法
* @author mengjie
*
*/
public class JdbcUtil {
//url
private static String url = "jdbc:mysql://localhost:3306/day16";
//user
private static String user = "root";
//password
private static String password = "root";
/**
*z只注册一次驱动，静态代码块
*/
static {
//注册驱动程序
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
* 获取连接的方法
* @throws SQLException
*/
public static Connection getConnection() {
try {
Connection conn = DriverManager.getConnection(url, user, password);
return conn;
} catch (SQLException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
/**
* 释放资源的方法
*/
public static void close(Statement stmt, Connection conn) {
if(stmt != null) {
try {
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
if(conn != null) {
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
}
/**
* 释放资源的方法
*/
public static void close(ResultSet rs, Statement stmt, Connection conn) {
if(rs!=null) {
try {
rs.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if(stmt != null) {
try {
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
if(conn != null) {
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
}
}
public class Demo4 {
public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
ResultSet res = null;
try{
//1)获取连接
conn = JdbcUtil.getConnection();
//2)准备sql
String sql = "select * from student";
//3)创建statement
stmt = conn.createStatement();
//4)执行sql
res = stmt.executeQuery(sql);
//取数据
//int id = res.getInt(1);//java.sql.SQLException: Before start of result set
//上面报错的原因在于 光标指向第一行之前
//System.out.println(res.next());//true
//System.out.println(res.next());//true
//System.out.println(res.next());//true
//System.out.println(res.next());//true
//System.out.println(res.next());//false //java.sql.SQLException: After end of result set
//s上面报错的原因在于光标指向最后一行的之后
//next()方法返回值如果是true代表当前行有数据，那么就可以使用getXX()方法获取列的值，如果是false，则没有数据，这时
//如果调用getXX()就会报错！
//int id = res.getInt(1);
while(res.next()) {
//1)根据列索引来获取
// int id = res.getInt(1);
// String name = res.getString(2);
// int age = rs.getInt(3);
// System.out.println(id+"\t" + name +"\t" + age);
//2)根据列名称来获取
int id = res.getInt("id");
String name = res.getString("name");
int age = res.getInt("age");
System.out.println(id+"\t" + name + "\t" + age);
}
}catch(Exception e){
e.printStackTrace();
}finally {
JdbcUtil.close(res, stmt, conn);
}
}
}
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