第六周：数据库

String ORACLE_CON_URL = "jdbc:oracle:thin:@localhost:1521/orcl"; //Oracle 数据库连接URL
String MYSQL_CON_URL = "jdbc:mysql://localhost:3306/booklibrary"; //MySQL 数据库连接URL
String POSTGRESQL_CON_URL = "jdbc:postgresql://localhost:5432/testdb"; //PostgreSQL 数据库连接URL

String SQLSERVER2005_CON_URL = "jdbc:sqlserver://localhost:1433;DatabaseName=booklibrary";

和数据库（数据源）建立连接以后，就可以对数据库进行各种操作了。对数据库最经常进行的操作，
就是数据查询。

我们实现一个数据访问对象类CoffeesDAO.java，由其提供对数据表coffees
的查询方法。实现代码如下：

package com.citymango.dao;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class CoffeesDAO{
//查看coffees 表中的记录数据
public void viewTable(){
String query = "select cof_name,sup_id,price,sales,total from coffees";
try(Connection con = JDBCUtilities.getConnection();
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(query) ){
while(rs.next()){
String coffeeName = rs.getString("cof_name");
int supplierID = rs.getInt("sup_id");
float price = rs.getFloat("price");
int sales = rs.getInt("sales");
int total = rs.getInt("total");
System.out.println(coffeeName + "\t\t" + supplierID + "\t" + price +
"\t" + sales + "\t" + total);
}
}catch(SQLException e){
System.out.println("查询coffees 表失败!");
e.printStackTrace();
}
}
}