20170607 JDBC课堂实践 任务四

20170607 JDBC课堂实践 任务四

• 题目

查询world数据库，查询哪个国家的平均寿命最长。

• 码云链接

• SQL语句

SELECT Code, Name, LifeExpectancy FROM `country` WHERE LifeExpectancy=(SELECT MAX(LifeExpectancy) FROM country)

• 代码

1. MessageDAO

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 List<Message> get() {
        List<Message> messages = null;

        try(Connection conn = DriverManager.getConnection(url, user, passwd);
            Statement statement = conn.createStatement()) {
            ResultSet result = statement.executeQuery("SELECT Code, Name, LifeExpectancy FROM `country` WHERE LifeExpectancy=(SELECT MAX(LifeExpectancy) FROM country)");
            messages = new ArrayList<>();
            while (result.next()) {
                Message message = new Message();
                message.setCode(result.getString(1));
                message.setNationName(result.getString(2));
                message.setLifeExpectancy(result.getFloat(3));
                messages.add(message);
            }
        } catch(SQLException ex) {
            throw new RuntimeException(ex);
        }
        return messages;
    }
}

2.MessageDAODemo

public class MessageDAODemo {
    public static void main(String[] args) throws Exception {
        MessageDAO dao = new MessageDAO(
                "jdbc:mysql://localhost:3306/world?" +
                        "useUnicode=true&characterEncoding=UTF8",
                "root", "");
        //while (true) {
            for (Message message : dao.get()) {
                System.out.printf("%s\t%s\t%.1f\t%n",
                        message.getCode(),
                        message.getNationName(),
                        message.getLifeExpectancy());
        //    }
        }
    }
}

3.Message

import java.io.Serializable;

public class Message implements Serializable {
    private Long id;
    private String cityName;
    private String code;
    private String nationName;
    private Long population;

    public Float getLifeExpectancy() {
        return LifeExpectancy;
    }

    public void setLifeExpectancy(Float lifeExpectancy) {
        LifeExpectancy = lifeExpectancy;
    }

    private Float LifeExpectancy;

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }


    public String getNationName() {
        return nationName;
    }

    public void setNationName(String nationName) {
        this.nationName = nationName;
    }


    public Long getPopulation() {
        return population;
    }

    public void setPopulation(Long population) {
        this.population = population;
    }


    public Message() {
    }

    public Message(String cityName) {
        this.cityName = cityName;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getCityName() {
        return cityName;
    }

    public void setCityName(String cityName) {
        this.cityName = cityName;
    }

}

• 运行截图

• 数据库截图