JDBC数据库连接操作

1.建立数据库、表

如图：表结构，数据库名为test

2.建立java项目

建立一个文件夹，找一个mysql驱动jar包丟进去，buildpath

监理User实体类,重写一下toString方便查看。

public class User {
    private int id;
    private String userName;
    private String passWord;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    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 [id=" + id + ", userName=" + userName + ", passWord="
                + passWord + "]";
    }
    

}

dao

public interface IUserDao {
    public int saveUser(User user);
    public void deleteUser(User user);
    public int updateUser(User user);
    public User selectUserById(int id);
}

public class UserDaoImpl implements IUserDao {

    @Override
    public int saveUser(User user) {
        int result=0;
        try {
            Class.forName("com.mysql.jdbc.Driver"); //加载驱动，只加载一次就行
            Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "root"); //获得数据库连接
            String sql="insert into user (userName,passWord)value(?,?)";
            PreparedStatement statement = conn.prepareStatement(sql); //预执行，置换参数，从1开始的
            statement.setString(1, user.getUserName());
            statement.setString(2, user.getPassWord());
            result = statement.executeUpdate();  //修改了数据的使用该方法，没有修改数据的使用execute（）
        } catch (Exception e) {
            e.printStackTrace();
        }
        return result;
    }

    @Override
    public void deleteUser(User user) {
        int result=0;
        try {
            Class.forName("com.mysql.jdbc.Driver"); //加载驱动，只加载一次就行
            Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "root"); //获得数据库连接
            String sql="delete from user where userName=?  and passWord=?";
            PreparedStatement statement = conn.prepareStatement(sql); //预执行，置换参数，从1开始的
            statement.setString(1, user.getUserName());
            statement.setString(2, user.getPassWord());
            result = statement.executeUpdate();  //修改了数据的使用该方法，没有修改数据的使用execute（）
            System.out.println(result);
        } catch (Exception e) {
            e.printStackTrace();
        }
        
        
    }

    @Override
    public int updateUser(User user) {
        return 0;
    }

    @Override
    public User selectUserById(int id) {
        return null;
    }
    public static void main(String[] args) {
        UserDaoImpl userDaoImpl=new UserDaoImpl();
        User user=new User();
        user.setPassWord("123456");
        user.setUserName("帅哥");
         userDaoImpl.deleteUser(user);
    }
}

当然，实现着实际不能这样，起码要搞一个基本的工具类，写静态代码块的加载驱动一次、获取连接、关闭连接等操作方法。

2.研究一下时间日期在sql和java中的关系。

数据库中对应的日期类型格式如图，date是没有时分秒的，timestamp的总体时间区间是没有datetime大的（上限）。在写入数据库的时候可以按照都转换为sql的timestamp类型写入数据库，在数据库会自动变成它们定义的类型。

@Override
    public int saveUser(User user) {
        int result=0;
        try {
            Class.forName("com.mysql.jdbc.Driver"); //加载驱动，只加载一次就行
            Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "root"); //获得数据库连接
            String sql="insert into user (userName,passWord,date,datetime,timestamp)value(?,?,?,?,?)";
            PreparedStatement statement = conn.prepareStatement(sql); //预执行，置换参数，从1开始的
            statement.setString(1, user.getUserName());
            statement.setString(2, user.getPassWord());
            statement.setTimestamp(3, new Timestamp(user.getDate().getTime())); //需要转换一下才行
            statement.setTimestamp(4, new Timestamp(user.getDatetime().getTime()));
            statement.setTimestamp(5, user.getTimestamp());
            result = statement.executeUpdate();  //修改了数据的使用该方法，没有修改数据的使用execute（）
        } catch (Exception e) {
            e.printStackTrace();
        }
        return result;
    }

取出来：要转换一下，否则会丢失了精度。还有后面还有.0，贼麻烦。建议统统使用string记录就好了

public User selectUserById(int id) {
        User user=null;
        try {
            Class.forName("com.mysql.jdbc.Driver"); //加载驱动，只加载一次就行
            Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "root");
            String sql="select * from user where id = 5";
            Statement statement = connection.createStatement();
            ResultSet resultSet = statement.executeQuery(sql);
            while(resultSet.next()){
                user=new User();
                user.setId(resultSet.getInt(1));
                user.setPassWord(resultSet.getString(2));
                user.setUserName(resultSet.getString("userName"));
                user.setDate(resultSet.getDate("date"));
//                user.setDatetime(resultSet.getDate(5)); //这里数据库使用的类型为datetime=YYYY-MM-DD HH:MM:SS,取出来就没了时分秒了
                user.setDatetime(resultSet.getTimestamp(5)); //使用这个timestamp就可以获得全。
                user.setTimestamp(resultSet.getTimestamp("timestamp"));
            }
            
        } catch (Exception e) {
            e.printStackTrace();
        }
        return user;
    }

3.数据库写入图片。正常没什么卵用的东西，还不如直接存在服务器上，搞在数据库压力很大的。

public class TestBlob {
    public static void main(String[] args) {
        //add();
        read();
    }
    
    public static void read(){
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        
        try {
            connection = JDBCUtil.getConnection();
            String sql = "select * from user where id=?";
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setInt(1, 8);
            resultSet = preparedStatement.executeQuery();
            if(resultSet.next()){
                //InputStream inputStream = resultSet.getBinaryStream("pic");
                Blob blob = resultSet.getBlob("pic");
                InputStream inputStream = blob.getBinaryStream();
                OutputStream outputStream = new BufferedOutputStream(new FileOutputStream(new File("d:/bak4.jpg")));
                byte[] buffer = new byte[1024];
                for(int i=0;(i=inputStream.read(buffer))>0;){
                    outputStream.write(buffer, 0, i);
                }
                inputStream.close();
                outputStream.close();
            }
            
        } catch (SQLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally{
            JDBCUtil.free(resultSet, preparedStatement, connection);
        }
    }
    
    

    /**
     * 
     */
    public static void add() {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        try {
            // 在指定的文件上插入读取管道
            File file = new File("d:/4.jpg");
            InputStream inputStream = new BufferedInputStream(new FileInputStream(file));
            connection = JDBCUtil.getConnection();
            String sql = "insert into user (username,password,pic) values (?,?,?)";
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, "root");
            preparedStatement.setString(2, "root");
            preparedStatement.setBinaryStream(3, inputStream, file.length());
            preparedStatement.executeUpdate();
            inputStream.close();
        } catch (SQLException e) {
            e.printStackTrace();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            JDBCUtil.free(null, preparedStatement, connection);
        }
    }
}

4.写入大文本文件。这个有时候还有点用

public class TestText {

    public static void main(String[] args) {

        // add();
        read();
    }

    public static void read() {
        Connection con = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultset = null;

        try {

            Writer writer = new BufferedWriter(new FileWriter(
                    "c:/bak_db_kaoqin.txt"));

            con = JDBCUtil.getConnection();
            String sql = "select * from user where id=?";
            preparedStatement = con.prepareStatement(sql);
            preparedStatement.setInt(1, 12);

            resultset = preparedStatement.executeQuery();
            if (resultset.next()) {
                char[] date = new char[1024];
                int length = 0;
                Reader reader = resultset.getCharacterStream("info");
                while ((length = reader.read(date)) != -1) {
                    writer.write(date, 0, length);

                }

                reader.close();
            }
            writer.close();

        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            JDBCUtil.free(resultset, preparedStatement, con);
        }

    }

    public static void add() {
        Connection con = null;
        PreparedStatement preparestatement = null;

        try {
            File file = new File("c:/db_kaoqin.sql");
            Reader reader = new BufferedReader(new FileReader(file));

            con = JDBCUtil.getConnection();
            String sql = "insert into user (username,info) values(?,?)";
            preparestatement = con.prepareStatement(sql);

            preparestatement.setString(1, "root");
            preparestatement.setCharacterStream(2, reader, file.length());

            preparestatement.executeUpdate();

            try {
                reader.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } finally {
            JDBCUtil.free(null, preparestatement, con);
        }

    }

}

好了，如有不足或者错误请各位指出，虚心请教！

5.批量sql操作

@Override
    public int allExcuse() throws Exception {
        String sql1="insert into user (userName) value(?)";
        
        Class.forName("com.mysql.jdbc.Driver"); //加载驱动，只加载一次就行
        Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "root");
        PreparedStatement statement = connection.prepareStatement(sql1);
        statement.setString(1, "张三");
        statement.addBatch();
        statement.setString(1, "李四");
        statement.addBatch();
        statement.setString(1, "王五");
        statement.addBatch();
        statement.setString(1, "甲");
        statement.addBatch();
        statement.setString(1, "乙");
        statement.addBatch();
        statement.setString(1, "丙");
        statement.addBatch();
        
        int[] batch = statement.executeBatch();
        System.out.println(batch);
        return 0;
    }