20155320 十六周课堂实践
关于数据库的相关课堂实践1，由于课上我没有成功连上数据库。课下全部重新安装了一遍数据库，终于连接上了数据库。
查询world数据库，获得人口超过500万的所有城市的列表。
起初用的是原始的messagedao代码，但是message都是红的，后来导入message的代码，修改增加人口等要素及函数,完善后的MessageDAO如下
import java.sql.*;
import java.util.*;
public class MessageDAO {
private String url;
private String user;
private String passwd;
public MessageDAO(String url, String user, String passwd) {
this.url = url;
this.user = user;
this.passwd = passwd;
}
public void add(Message message) {
try(Connection conn = DriverManager.getConnection(url, user, passwd);
Statement statement = conn.createStatement()) {
String sql = String.format(
"INSERT INTO city( Name, Population) VALUES ('%s', '%d')",
message.getName(),message.getPopulation());
statement.executeUpdate(sql);
} catch(SQLException ex) {
throw new RuntimeException(ex);
}
}
public List<Message> get() {
List<Message> messages = new ArrayList<>();
try(Connection conn = DriverManager.getConnection(url, user, passwd);
Statement statement = conn.createStatement()) {
ResultSet result =
statement.executeQuery(
"SELECT DISTINCT city.Name,city.Population\n" +
"FROM city INNER JOIN\n" +
" country ON country.Capital = city.ID\n" +
"WHERE country.Continent = \"Asia\"");
while (result.next()) {
Message message = toCity(result);
messages.add(message);
}
} catch(SQLException ex) {
throw new RuntimeException(ex);
}
return messages;
}
private Message toCity(ResultSet result) throws SQLException {
Message message = new Message();
message.setName(result.getString(1));
message.setPopulation(result.getLong(2));
return message;
}
}
运行结果为：
