Java learning JDBC connection mysql

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One, JDBC connection process

1. Download the corresponding jar package or use Maven to inject dependencies
2. Register to load a driver
3. Create a database connection (Connection)
4. Construct SQL statement
5. Create statement, send sql statement
6. Execute sql statement
7. Process sql results
8. Close statement and connection

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2. Corresponding dependencies and database preparation

1. The creation of the database

#可以将本代码放入一个create,sql文件，执行下面的操作。（sql脚本的执行）

 # 创建数据库
create database managelibrary;
user managelibrary;
# 创建表
create table if not exists `user`(
    `id` int unsigned auto_increment,
    `name` varchar(11) not null,
    `sid` varchar(11) not null,
    `num` varchar(11) not null,
    `password` varchar(11) not null,
    `telphone` varchar(11),
    primary key(`id`)
)engine=InnoDB Default charset=utf8;

使用 \. D:create.sql 或者 source \D:create.sql 可以直接创建

2.maven dependency

    <!--mysql包括c3p0和mysql的java连接器-->
 <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.47</version>
    </dependency>
    <dependency>
			<groupId>c3p0</groupId>
			<artifactId>c3p0</artifactId>
			<version>0.9.1.2</version>
		</dependency>
		

Three, specific sentences

1. Register to load the driver

Class.forName("com.mysql.jdbc.Driver");	//使用mysql的驱动;

2. Create a connection

Connection connection = DriverManager.getConnection("jdbc://ip地址:端口号/数据库名称“，“用户名”,"密码");

3. Construct sql statement basic sql statement

例如
//插入
insert into user(name, sid, password, telphone, num) values(?,?,?,?,?);//问号表示位置参数
//删除
delete from user where name = '';
//查找
select * from user where name = '';

4. Preparation of prepareStatement
5. carried out

//执行查找
stmt.executeQuery();
//执行更新
stmt.executeUpdate();

6. Processing the search results

ResultSet resultset = statement.executeQuery();

Four, examples

1. Entity file
   basic attributes + constructor + set, get + toString methods

	private int id;
	private String name;
	private String password;
	private String Sid;
	private String telphone;
	private String num;

2. Configuration file jdbc.properties

需要放在classpath路径下

driver=com.mysql.jdbc.Driver         #如果版本较高可以使用com.cj.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/managelibrary?useUnicode=true&characterEncoding=utf8&serverTimezone=GMT%2B8&useSSL=false
#这里指定了字符编码和解码格式，时区，是否加密传输
username=root
password=roto

3. JdbcUtil file

//如果从properties中获取配置信息可以这么写,第一次尝试可以直接下面的写法
	private Properties properties;
	public Connection getCon() throws ClassNotFoundException, SQLException, IOException {
		properties = new Properties();
		InputStream in = JdbcUtil.class.getClassLoader().getResourceAsStream("jdbc.properties");//获取配置文件中的内容
		properties.load(in);
   	    String driver = properties.getProperty("driver");
   	    String url = properties.getProperty("url");
   	    String username = properties.getProperty("username");
   	    String password = properties.getProperty("password");
		Class.forName("com.mysql.jdbc.Driver");
   	 	Connection connection = DriverManager.getConnection(url,username , password);
   	 	return connection;
    }
    

public class JdbcUtil {
     // 1.驱动获取 2.连接数据库 
	public Connection getCon() throws ClassNotFoundException, SQLException {
   	 Class.forName("com.mysql.jdbc.Driver");
   	 Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/ManageLibrary", "root", "1230");
   	 return connection;
    }
    
    //根据姓名查找
    public ResultSet findByName(String username) throws SQLException, ClassNotFoundException {
      	 String sql = "select * from user where name = ?"; //3.构造查找的sql
       	 Connection connection = getCon();					  
       	 PreparedStatement statement = (PreparedStatement) connection.prepareStatement(sql);
       	 statement.setString(1, username);              //4.statement的准备
       	 ResultSet resultset = statement.executeQuery();//5.执行sql的语句

       	 return resultset;
    }
    
    //插入用户
    public boolean insertUser(user user) throws ClassNotFoundException, SQLException {
   	 Connection connection =getCon();
   	 String sql = "insert into user(name, sid, password, telphone, num) values(?,?,?,?,?)";
  
	 PreparedStatement psmt = (PreparedStatement) connection.prepareStatement(sql);
	   psmt.setString(1, user.getName());
       psmt.setString(2, user.getSid());
       psmt.setString(3,user.getPassword());
       psmt.setString(4, user.getTelphone());
       psmt.setInt(5, user.getNum());
       psmt.executeUpdate();
       //用来判断是否插入成功，成功可以从数据库中找到
       ResultSet resultSet = findByName(user.getName());
       boolean flag = false;
       while(resultSet.next()) {
    	  flag = true;
       }
       return flag;
    }
   
    
    //判断用户名和密码是否匹配，这个应该放在service层
    public boolean checkUser(String username,String password) throws Exception {
			
    	Connection connection = getCon();
    	String sql = "select * from user where name = ? and password = ?";
    	PreparedStatement psmt = connection.prepareStatement(sql);
    	psmt.setString(1, username);
    	psmt.setString(2, password);
    	ResultSet resultSet = psmt.executeQuery();
		boolean flag = false;
		while(resultSet.next()) {
			flag = true;
		}
		return flag;
    }
    
    //根据姓名进行删除
    public boolean delete(String username,String Sid) throws SQLException, ClassNotFoundException {
		Connection connection = getCon();
		String sql =  "delete from user where name = ?";
		PreparedStatement pmst = connection.prepareStatement(sql);
		pmst.setString(1, username);
		pmst.executeUpdate();
		//判断删除是否成功
		ResultSet resultSet = findByName(username);
		boolean flag = true;
		while(resultSet.next()) {
			flag = false;
		}
		return flag;
    }
}

3. Test file

public class Main {
	public static void main(String[] args) throws ClassNotFoundException, SQLException {
		//testInser();
		//testDelete();
		testFindByName("kk");
	}
	//检测插入
	static void testInser() throws ClassNotFoundException, SQLException {
		JdbcUtil jdbcdemo = new JdbcUtil();
		user user = new user("","","","","");
        if(jdbcdemo.insertUser(user)) {
        	System.out.println("插入成功");
        }
        else System.out.println("无效注册");
	}
	
	//检测根据姓名查找
	static void testFindByName(String name) throws SQLException, ClassNotFoundException {
		
		JdbcUtil jdbcUtil = new JdbcUtil();
        ResultSet resultSet = jdbcUtil.findByName(name);
        boolean flag = true;
		while(resultSet.next()){
			flag = false;
    		System.out.println("查找信息如下");
    		user user2 = new user(resultSet.getInt(1),
    				resultSet.getString(2),
    		   resultSet.getString(3),
			   resultSet.getString(4),
			   resultSet.getString(5),
					resultSet.getString(6));
    		System.out.println(user2.toString());
    	}
		if(flag) System.out.println("没有此人！");
	}
	
	//检测姓名和密码是否对应
	static void testCheck() throws Exception {
		JdbcUtil jdbcUtil = new JdbcUtil();
		if(jdbcUtil.checkUser("zk", "1234")) {
			testFindByName("zk");
		}
		else System.out.println("账号或密码错误");
		
	}
	
	//检测删除
	static void testDelete() throws ClassNotFoundException, SQLException {
		JdbcUtil jdbcUtil = new JdbcUtil();
		String[] username = {""};
		String[] userpassword = {""};
		for(int i = 0;i < username.length;i++) {
			if(jdbcUtil.delete(username[i],userpassword[i])){
				System.out.println("成功删除" + username[i]);
			}
			else {
				System.out.println( username[i]+"删除失败");
			}
		}
	}
}

V. Summary of specific categories

Concrete class	effect
DriverManager	The driver manager, used to register the driver, is the entry point to get the Connection object
Driver	Database driver, used to obtain the Connection object
Statement	sql executor, used to execute sql
ResultSet	Result set, used to encapsulate and manipulate query results
prepareCall	Used to call stored procedures

1. PreparedStatement

2. statement

3.Connector

4.Driver

5.ResultSet

6. Optimize the sample code

1. After optimization, you can avoid forgetting to close the connect.
2. JbcbUtil is designed to statically use singleton mode.
3. The singleton problem under multithreading should be considered.

1.jdbcUtil

//使用单例模式进行设计JDBC，没有考虑是否多线程问题
//设计成静态的链接可以避免close的问题
public class JdbcUtil {
	static private Properties properties;

	static public Connection getConnection() throws ClassNotFoundException, SQLException {
		properties = new Properties();
		InputStream in = JdbcUtil.class.getClassLoader().getResourceAsStream("jdbc.properties");//获取配置文件中的内容
   	    try{
			properties.load(in);
		}catch (Exception e){
   	    	e.printStackTrace();
		}
   	    String driver = properties.getProperty("driver");
   	    String url = properties.getProperty("url");
   	    String username = properties.getProperty("username");
   	    String password = properties.getProperty("password");
		Class.forName(driver);
   	 	Connection connection = DriverManager.getConnection(url,username , password);
   	 	return connection;
    }
}

2.userDao

public class UserDao {
    private Connection connection;
    public UserDao(Connection connection){
        this.connection = connection;
    }
    public ResultSet findByName(String username) throws SQLException, ClassNotFoundException {
        String sql = "select * from user where name = ?";
        PreparedStatement statement = (PreparedStatement) connection.prepareStatement(sql);
        statement.setString(1, username);
        ResultSet resultset = statement.executeQuery();
        return resultset;
    }

    public boolean insertUser(user user) throws ClassNotFoundException, SQLException {
        String sql = "insert into user(name, sid, password, telphone, num) values(?,?,?,?,?)";

        PreparedStatement psmt = (PreparedStatement) connection.prepareStatement(sql);
        psmt.setString(1, user.getName());
        psmt.setString(2, user.getSid());
        psmt.setString(3,user.getPassword());
        psmt.setString(4, user.getTelphone());
        psmt.setString(5, user.getNum());
        psmt.executeUpdate();
        ResultSet resultSet = findByName(user.getName());
        boolean flag = false;
        while(resultSet.next()) {
            flag = true;
        }
        return flag;
    }


    public boolean checkUser(String username,String password) throws Exception {
        String sql = "select * from user where name = ? and password = ?";
        PreparedStatement psmt = connection.prepareStatement(sql);
        psmt.setString(1, username);
        psmt.setString(2, password);
        ResultSet resultSet = psmt.executeQuery();
        connection.close();
        boolean flag = false;
        while(resultSet.next()) {
            flag = true;
        }
        return flag;
    }

    public boolean delete(String username,String Sid) throws SQLException, ClassNotFoundException {
        String sql =  "delete from user where name = ?";
        PreparedStatement pmst = connection.prepareStatement(sql);
        pmst.setString(1, username);
        pmst.executeUpdate();
        ResultSet resultSet = findByName(username);
        boolean flag = true;
        while(resultSet.next()) {
            flag = false;
        }
        return flag;
    }
}

3.Main

public class Main {
	static private UserDao userDao;					     //包含了dao和service层的部分实现
	public static void main(String[] args) throws ClassNotFoundException, SQLException {
		userDao = new UserDao(JdbcUtil.getConnection());  //开启连接
		testInser();
		testFindByName("zk");
		testDelete();

	}

	//检测插入
	static void testInser() throws ClassNotFoundException, SQLException {
		user user = new user("zk","1525475","2017","17861401461","46");
        if(userDao.insertUser(user)) {
        	System.out.println("插入成功");
        }
        else System.out.println("无效注册");
	}
	
	//检测根据姓名查找
	static void testFindByName(String name) throws SQLException, ClassNotFoundException {

        ResultSet resultSet = userDao.findByName(name);
        boolean flag = true;
		while(resultSet.next()){
			flag = false;
    		System.out.println("查找信息如下");
    		user user2 = new user(resultSet.getInt(1),
    				resultSet.getString(2),
    		   resultSet.getString(3),
			   resultSet.getString(4),
			   resultSet.getString(5),
					resultSet.getString(6));
    		System.out.println(user2.toString());
    	}
		if(flag) System.out.println("没有此人！");
	}
	
	//检测姓名和密码是否对应
	static void testCheck() throws Exception {
		if(userDao.checkUser("zk", "1234")) {
			testFindByName("zk");
		}
		else System.out.println("账号或密码错误");
		
	}
	
	//检测删除
	static void testDelete() throws ClassNotFoundException, SQLException {
		String[] username = {"zk"};
		String[] userpassword = {"201711010416"};
		for(int i = 0;i < username.length;i++) {
			if(userDao.delete(username[i],userpassword[i])){
				System.out.println("成功删除" + username[i]);
			}
			else {
				System.out.println( username[i]+"删除失败");
			}
		}
	}
}

Seven, the realization of JDBC bottom layer

8. Some problems

1. About mysql

2. About JDBC#

Nine, related information

1. Code link
2. This article is original, please enter and indicate if reprinted.