数据库的增、删、改、查

实现代码：

package cn.itcast.jdbc;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;

import com.mysql.jdbc.Statement;

public class Crud {
public static void main(String[] args) throws SQLException{
create();
read();
update();
delete();
}

static void delete() throws SQLException{         //删除操作
Connection conn = null;
Statement st = null;
ResultSet rs = null;
try {
conn = JdbcUtils.getConnection();
st = (Statement) conn.createStatement();

String sql = "delete from user where id>4";

int i = st.executeUpdate(sql);           
System.out.println("i = " + i);
} finally {
JdbcUtils.free(rs, st, conn);
}
}

static void update() throws SQLException{            //修改操作
Connection conn = null;
Statement st = null;
ResultSet rs = null;
try {
conn = JdbcUtils.getConnection();
st = (Statement) conn.createStatement();

String sql = "update user set money=money+10";

int i = st.executeUpdate(sql);           
System.out.println("i = " + i);
} finally {
JdbcUtils.free(rs, st, conn);
}
}

static void create() throws SQLException{                  //添加操作
Connection conn = null;
Statement st = null;
ResultSet rs = null;
try {
conn = JdbcUtils.getConnection();
st = (Statement) conn.createStatement();

String sql = "insert into user(name, birthday, money) value('name1', '1978-02-01', 400)";

int i = st.executeUpdate(sql);           
System.out.println("i = " + i);
} finally {
JdbcUtils.free(rs, st, conn);
}
}

static void read() throws SQLException{                         //查询操作
Connection conn = null;
Statement st = null;
ResultSet rs = null;
try {
conn = JdbcUtils.getConnection();
st = (Statement) conn.createStatement();
rs = st.executeQuery("select id, name, birthday, money from user");
while(rs.next()){
System.out.println(rs.getObject("id") + "\t" 
+ rs.getObject("name") + "\t" 
+ rs.getObject("birthday") + "\t" 
+ rs.getObject("money"));
}                            //getObject("");取哪列
} finally {
JdbcUtils.free(rs, st, conn);
}
}

}

工具类代码：

package cn.itcast.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;

import com.mysql.jdbc.Statement;

//将驱动注册优化掉
public final class JdbcUtils {
private static String url = "jdbc:mysql://localhost:3306/jdbc";
private static String user = "root";
private static String password = "123";
private JdbcUtils(){

}
static{
try{                                 //注册驱动
Class.forName("com.mysql.jdbc.Driver");
} catch(ClassNotFoundException e) {
throw new ExceptionInInitializerError(e);
}
}

public static Connection getConnection() throws SQLException {   //建立连接方法
return DriverManager.getConnection(url, user, password);
}

public static void free(ResultSet rs, Statement st, Connection conn){   //释放资源
try{
if(rs != null)
rs.close();
} catch(Exception e){
e.printStackTrace();
}finally{
try{
if(st != null)
st.close();
} catch(Exception e){
e.printStackTrace();
}finally{
if(conn != null)
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
}