什么时候自己创建工具类
如果一个功能经常用到 我们建议把这个功能做成工具类
创建JdbcUtils包含三个方法
1: 把几个字符串 定义为常量
2：得到数据库连接getConnection();
3 关闭和打开资源 package JdbcUtils; import java.sql.*; public class JdbcUtilsDemo {
public static final String USER = "root";
public static final String PSW = "root";
public static final String URL = "jdbc:mysql://localhost:3306/qy97";
public static final String DRIVER = "com.mysql.jdbc.Driver"; static {
try {
Class.forName(DRIVER);
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
} public static Connection getConnection() throws SQLException {
return DriverManager.getConnection(URL,USER,PSW);
}
/*public static void close(Statement st,Connection con){
if (st!=null){
try {
st.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if(con!=null){
try {
con.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
public static void close(Connection con, Statement st, ResultSet rs){
if(rs!=null){
try {
rs.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (st!=null){
try {
st.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (con!=null){
try {
con.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}*/ public static void close(AutoCloseable... ca){
for (AutoCloseable c:ca){
if(c!=null){
try {
c.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
} } 调用工具类方法进行查询 package cn.lideng.dbc; import JdbcUtils.JdbcUtilsDemo; import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement; public class JdbcDemo5 { private static Connection connection;
private static Statement statement;
private static ResultSet rs; public static void main(String[] args){
try {
connection = JdbcUtilsDemo.getConnection();
String sql="select * from users";
statement = connection.createStatement();
rs = statement.executeQuery(sql);
while(rs.next()){
int id = rs.getInt(1);
String name = rs.getString(2);
String address = rs.getString(3);
System.out.println(id+" "+name+" "+address);
}
} catch (SQLException e) {
e.printStackTrace();
}
finally {
JdbcUtilsDemo.close(rs,statement,connection);
} }
}