JavaEE-博客系统1（数据库和后端的交互）

本部分内容包括网站设计总述，数据库和后端的交互；

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数据库操作代码如下：

-- 编写SQL完成建库建表操作
create database if not exists java_blog_system charset utf8;
use java_blog_system;
-- 建立两张表，一个存储博客信息，一个存储用户信息
drop table if exists user;
drop table if exists blog;

create table blog(
-- 主键必须包含唯一的值    主键列不能包含null值  设置主键进行自增长，默认从1开始，每次+1
blogId int primary key auto_increment,
title varchar(256),
content varchar(4096),
userId int,
postTime datetime
);

create table user(
userId int primary key auto_increment,
username varchar(64) unique,
password varchar(64)
);

-- 构造一些初始数据，方便后续的测试
insert into user values(1,'zhansan','123'),(2,'lisi','123');

insert into blog values(1,'这是第一篇','这里是内容',1,'2023-06-07 18:00:00');
insert into blog values(2,'这是第一篇','这里是内容',1,'2023-06-07 18:00:00');
insert into blog values(3,'这是第一篇','这里是内容',1,'2023-06-07 18:00:00');

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DBUtil.java

package Dao;

import com.mysql.jdbc.jdbc2.optional.MysqlDataSource;

import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: Home-pc
 * Date: 2023-10-28
 * Time: 11:07
 */
//通过这个类将数据库建立连接和断开连接的逻辑进行封装
public class DBUtil {
    //进行连接前的准备工作，初始化数据库地址，用户名，密码
    //单例模式   只需要一个实例
    //volatile 禁止指令重排序
    private  static volatile DataSource dataSource=null;

    //提供一个方法获取datasource
    private static DataSource getDataSource(){
        if(dataSource==null){//此处if的作用在于避免频繁加锁；如果dataSource已经有值，再进行加锁，他会很快的解锁，但是这会导致频繁枷锁，因此一旦发现ataSource已经有值，就直接返回该值
            synchronized (DBUtil.class){//为了保证线程安全(多线程问题)，加锁
                if(dataSource==null){//第二个if判断是否为空，当a线程优先获得锁，执行到此处，b线程没竞争到锁会被阻塞在外面，a线程判断实例是否为空，为空则new实例，a线程释放锁之后，b线程拿到锁进来后先判断instance是否为null，此时可能因上一个线程导致此处不为null，则释放锁往下或者为null
                    dataSource=new MysqlDataSource();
                    ((MysqlDataSource)dataSource).setUrl("jdbc:mysql://127.0.0.1:3306/java_blog_system?useSSL=false&characterEncoding=utf8");
                    ((MysqlDataSource)dataSource).setUser("root");
                    ((MysqlDataSource)dataSource).setPassword("1111");
                }
            }
        }
        return dataSource;
    }

    //提供一个方法和数据库建立连接
    public static Connection getConnection(){
        try {
            return getDataSource().getConnection();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }

    //提供一个方法和数据库断开连接 PreparedStatement statement用来执行SQL语句   ResultSet resultSet接收执行SQL语句后返回的结果
    public static void close(Connection connection, PreparedStatement statement, ResultSet resultSet){
        //将3个close放置到3个try中，即使前面的close出现问题，也不会影响后续close的执行
        if(resultSet!=null){
            try {
                resultSet.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if(statement!=null){
            try {
                statement.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        if(connection!=null){
            try {
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

blog.java

package Dao;

import java.sql.Timestamp;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: Home-pc
 * Date: 2023-10-28
 * Time: 12:13
 */
//这个类中的属性要和数据库中blog表中的属性相对应
//通过这个类的对象能够表示出一条blog表中的记录
public class Blog {
    private int blogId;
    private String title;
    private String content;
    private int UserId;
    // SQL 里有 timestamp 类型, 还有 datetime 类型.
    // 使用 SQL 时, 推荐使用 datetime, 因为 timestamp 只有 4 字节, 2038 年就不够用了.
    // 但是 Java 代码中的 Timestamp 是可以使用的.
    private Timestamp postTime;

    public int getBlogId() {
        return blogId;
    }

    public void setBlogId(int blogId) {
        this.blogId = blogId;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }

    public int getUserId() {
        return UserId;
    }

    public void setUserId(int userId) {
        this.UserId = userId;
    }

    public Timestamp getPostTime() {
        return postTime;
    }

    public void setPostTime(Timestamp postTime) {
        this.postTime = postTime;
    }

    @Override
    public String toString() {
        return "Blog{" +
                "blogId=" + blogId +
                ", title='" + title + '\'' +
                ", content='" + content + '\'' +
                ", userId=" + UserId +
                ", postTime=" + postTime +
                '}';
    }
}

user.java

package Dao;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: Home-pc
 * Date: 2023-10-28
 * Time: 13:32
 */
//这个类的属性要和user表里的一致
    //通过这个类的对象表示user表中的一条记录
public class User {
    private int userId;
    private String username;
    private String password;

    public int getUserId() {
        return userId;
    }

    public void setUserId(int userId) {
        this.userId = userId;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User{" +
                "userId=" + userId +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

blogDao.java

package Dao;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: Home-pc
 * Date: 2023-10-28
 * Time: 13:36
 */
//通过这个类封装对blog表的增删改查
public class BlogDao {
    //1.新增一个博客,构造一个insert方法
    public void insert(Blog blog){
        Connection connection=null;
        PreparedStatement statement=null;

        try {
            //和数据库建立连接
            connection =DBUtil.getConnection();
            //构造SQL语句
            String sql="insert into blog values(null,?,?,?,now())";
            //准备好sql语句
            statement=connection.prepareStatement(sql);
            statement.setString(1, blog.getTitle());
            statement.setString(2, blog.getContent());
            statement.setInt(3,blog.getUserId());
            //执行SQL语句
            statement.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            //关闭连接，释放资源
            DBUtil.close(connection,statement,null);
        }
    }

    //2.查询blog表中的所有博客
    public List<Blog> getblogs(){
        Connection connection=null;
        PreparedStatement statement=null;
        ResultSet resultSet=null;
        List<Blog> blogs=new ArrayList<>();//此时list为空

        try {
            //和数据库建立连接
            connection=DBUtil.getConnection();
            //构造sql语句
            String sql="select * from blog order by postTime desc";//按时间顺序降序排序
            //准备语句
            statement=connection.prepareStatement(sql);
            //执行sql
            resultSet=statement.executeQuery();
            //遍历结果集合
            while(resultSet.next()){
                Blog blog=new Blog();
                //前面是java类中的属性，后面则是从数据库的表中对应属性的值
                blog.setBlogId(resultSet.getInt("blogId"));
                blog.setTitle(resultSet.getString("title"));
                blog.setContent(resultSet.getString("content"));
                blog.setUserId(resultSet.getInt("userId"));
                blog.setPostTime(resultSet.getTimestamp("postTime"));
                blogs.add(blog);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(connection,statement,resultSet);
        }
        return blogs;
    }

    //指定ID，查询某一个博客
    public Blog getblog(int blogId){
        Connection connection=null;
        PreparedStatement statement=null;
        ResultSet resultSet=null;

        try {
            connection=DBUtil.getConnection();
            String sql="select * from blog where blogId=?";
            statement.setInt(1,blogId);
            resultSet=statement.executeQuery();
            // 由于此处是按照 blogId 来查询, blogId 又是主键.
            // 查询到的结果要么是 1 条记录, 要么是 0 条记录. 不会有别的情况.
            // 因此这里就没必要循环了, 直接条件判定即可.
            if(resultSet.next()){//查询到了，则进入；否则不会进来
                Blog blog=new Blog();
                blog.setBlogId(resultSet.getInt("blogId"));
                blog.setTitle(resultSet.getString("title"));
                blog.setContent(resultSet.getString("content"));
                blog.setUserId(resultSet.getInt("userId"));
                blog.setPostTime(resultSet.getTimestamp("postTime"));
                return blog;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            DBUtil.close(connection,statement,resultSet);
        }
        return null;
    }

    //指定博客进行删除
    public void delete(int blogId){
        Connection connection=null;
        PreparedStatement statement=null;

        try {
            connection=DBUtil.getConnection();
            String sql="delete from blog where blogId=?";
            statement=connection.prepareStatement(sql);
            statement.setInt(1,blogId);
            statement.executeQuery();
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            DBUtil.close(connection, statement,null );
        }
    }

}

userDao.java

package Dao;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: Home-pc
 * Date: 2023-10-28
 * Time: 14:50
 */
//使用这个类封装对user表的增删改查
public class UserDao {
    //根据userId查询用户信息
    public User getUserById(int userId){
        Connection connection=null;
        PreparedStatement statement=null;
        ResultSet resultSet=null;

        try {
            connection=DBUtil.getConnection();
            String sql="select * from user where userId = ?";
            statement=connection.prepareStatement(sql);
            statement.setInt(1,userId);
            resultSet=statement.executeQuery();
            if(resultSet.next()){
                User user=new User();
                user.setUserId(resultSet.getInt("userId"));
                user.setUsername(resultSet.getString("username"));
                user.setPassword(resultSet.getString("password"));
                return user;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            DBUtil.close(connection,statement,resultSet);
        }
        return null;
    }

    //根据username来查询用户信息
    public User getUserByName(String username){
        Connection connection=null;
        PreparedStatement statement=null;
        ResultSet resultSet=null;

        try {
            connection=DBUtil.getConnection();
            String sql="select * from user where username = ?";
            statement=connection.prepareStatement(sql);
            statement.setString(1,username);
            resultSet=statement.executeQuery();
            if(resultSet.next()){
                User user=new User();
                user.setUserId(resultSet.getInt("userId"));
                user.setUsername(resultSet.getString("username"));
                user.setPassword(resultSet.getString("password"));
                return user;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            DBUtil.close(connection,statement,resultSet);
        }
        return null;
    }
}