How to implement data persistence and serialization in Java

How to implement data persistence and serialization in Java

In Java, data persistence and serialization are very important concepts. Data persistence refers to saving data in a program to disk or other persistent media so that it can be read again after the program is closed. Serialization refers to the process of converting the state of an object in memory into a stream of bytes so that it can be stored in a file or transmitted over the network.

The following will introduce how to implement data persistence and serialization in Java and provide specific code examples.

1. Data persistence

1. Use files for data persistence

   import java.io.*;
   
   public class FilePersistence {
    public static void main(String[] args) {
        String data = "Hello, world!";
   
        try {
            // 创建一个文件对象
            File file = new File("data.txt");
   
            // 创建一个字符输出流
            FileWriter writer = new FileWriter(file);
   
            // 将数据写入文件
            writer.write(data);
   
            // 关闭流
            writer.close();
   
            System.out.println("数据已成功写入文件。");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
   }

2. Use database for data persistence

   import java.sql.*;
   
   public class DatabasePersistence {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/test";
        String username = "root";
        String password = "password";
   
        try {
            // 连接数据库
            Connection conn = DriverManager.getConnection(url, username, password);
   
            // 创建一个Statement对象
            Statement stmt = conn.createStatement();
   
            // 创建表
            stmt.executeUpdate("CREATE TABLE IF NOT EXISTS data (id INT, value VARCHAR(20))");
   
            // 插入数据
            stmt.executeUpdate("INSERT INTO data VALUES (1, 'Hello, world!')");
   
            // 查询数据
            ResultSet rs = stmt.executeQuery("SELECT * FROM data");
            while (rs.next()) {
                System.out.println("ID: " + rs.getInt("id") + ", Value: " + rs.getString("value"));
            }
   
            // 关闭连接
            stmt.close();
            conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
   }

2. Serialization

import java.io.*;

public class Serialization {
    public static void main(String[] args) {
        // 创建一个TestClass对象
        TestClass obj = new TestClass("Hello, world!", 123);

        try {
            // 创建一个文件输出流
            FileOutputStream fileOut = new FileOutputStream("data.ser");

            // 创建一个对象输出流
            ObjectOutputStream out = new ObjectOutputStream(fileOut);

            // 将对象进行序列化
            out.writeObject(obj);

            // 关闭流
            out.close();
            fileOut.close();

            System.out.println("对象已成功序列化。");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

class TestClass implements Serializable {
    // 序列化ID
    private static final long serialVersionUID = 1L;

    private String str;
    private int num;

    public TestClass(String str, int num) {
        this.str = str;
        this.num = num;
    }

    public String getStr() {
        return str;
    }

    public int getNum() {
        return num;
    }
}

The above code example demonstrates how to implement data persistence and serialization in Java. For data persistence, files or databases can be used for storage. For serialization, the object to be serialized needs to implement the Serializable interface and write the object to the object output stream. In this way, the object can be converted into a byte stream for storage or transmission.

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