数据库的增、删、改、查

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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();}}}}}

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