Java实战（二）读取mysql数据并以特定分隔符写入到本地文件

一、创建一个maven项目Demp,构建结构如下图所示：
1、pom文件设置
因为是连接eimysql，首先肯定要有mysql驱动，这里用的maven管理的，所以添加对应依赖即可

 <!--mysql驱动包-->
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.35</version>
    </dependency>

代码部分

2、读取mysql数据库的数据，封装为User对象。
重新toString()方法，用特定分隔符进行组装。

package example.dao;

import java.util.ArrayList;
import java.util.List;

public class User {
    private String id;
    private String name;
    private String password;

    public User() {
        this.id = id;
        this.name = name;
        this.password = password;
    }

    public String getId() {
        return id;
    }

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

    /**
     * 生成具有特定分割符的to_string方法
     * @return
     * @param serp
     */
    public String toStringNew(String serp) {
//        System.out.println("分割符是"+serp);
        String message = null;
        message=String.join(serp,id,name,password);
//        System.out.println("message:"+ message);
        return message;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPassword() {
        return password;
    }

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


}

3、执行读取数据库操作，并写入本地txt文件

package example.Operation;

import example.dao.User;

import java.io.*;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;

/**
 * note:测试读取数据库文件，并以特定分割符serp，输出到dat文件中
 *
 */
public class serpTest {
    static Connection conn =null;
    static PreparedStatement ps=null;
    static ResultSet rst=null;
    private static ArrayList<User> userList=null;

    /**
     * 获得数据库的连接
     * @return 数据库的数据对象
     */
    public static ArrayList<User> getConnection(){
        ArrayList<User> userList = new ArrayList<User>();
        try {
            System.out.println("Data base connection test:");
            Class.forName("com.mysql.jdbc.Driver");
            String url="jdbc:mysql://127.0.0.1:3306/test?characterEncoding=utf8";  //访问test库
            conn= DriverManager.getConnection(url,"root","root");
            System.out.print(conn);
            if(!conn.isClosed())
                System.out.println("Succeeded connecting to the Database!");
            Statement statement =conn.createStatement();//操作数据库
            String sql ="select * from user";//要执行的sql语句
            ResultSet rs=statement.executeQuery(sql);
            System.out.println("id"+"\t"+"姓名"+"\t"+"密码");
            while(rs.next()){
                User user = new User();
                user.setId(rs.getString("id"));
                user.setName(rs.getString("name"));
                user.setPassword(rs.getString("password"));
                userList.add(user);
//                System.out.println(userList);
//                System.out.println(rs.getString("id")+"\t"+rs.getString("name")+"\t"+rs.getString("password"));

            }

        } catch (Exception e) {
            System.out.println("数据库连接失败!");
        }
        System.out.println(userList);
        return userList;
    }

    /**
     * 根据输出的路径和文件名称创建file对象
     * @param path 写入文件的路径
     * @param fileName 写入文件的路径
     * @throws SQLException
     */


    public String createFile(String path, String fileName ){

        File f = new File(path);
        if (!f.exists()) {
            f.mkdirs(); //创建目录
        }
        File file = new File(path, fileName);
        if (!file.exists()) {
            try {
                file.createNewFile();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return file.getAbsolutePath();

    }

    /**
     * 根据某个路径读取文件
     * @param userList  把数据库的用户数组读取到文件中
     * @throws SQLException
     */
    private  void writeFile(List<User> userList,String filePath,String serp){
        System.out.println("分割符"+serp);
        BufferedWriter bufferedWriter=null;
        FileOutputStream fileOutputStream = null;
        try {
            fileOutputStream = new FileOutputStream(filePath);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        bufferedWriter  = new BufferedWriter(new OutputStreamWriter(fileOutputStream));
        for(int i = 0; i < userList.size(); i++ ) {

            try {
                System.out.print("输出list的数据:"+userList.get(i).toStringNew(serp));
                bufferedWriter.write(userList.get(i).toStringNew(serp));

            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                bufferedWriter.newLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        try {
            bufferedWriter.close();
        } catch (IOException e) {
            e.printStackTrace();
        }


    }
 
    public static void main(String[] args){
        String path="C:\\Users\\migu\\Desktop\\test";
        String fileName="test.dat";
        serpTest serpTest = new serpTest();
        String filePath=serpTest.createFile(path,fileName);
        System.out.println("文件的全路径是："+filePath); //输出文件的绝对路径
        ArrayList<User> userList= serpTest.getConnection();
        System.out.println(userList);
//        serpTest.writeFile(userList,filePath, "|");
        int splitChar = 31;  //找到特定分割符对应的十进制数字
        String splitString = String.valueOf((char)splitChar);
        serpTest.writeFile(userList,filePath,splitString); //特殊十进制=31的对应分隔符
    }


}

3、验证测试数据

1）数据库的数据

2）本地文件的数据，并验证对应的十六进制是否是‘0x1f’，
特定分隔符分割的文件生成验证成功