使用java实现从数据库查出来存redis 查的时候先查redis redis没有再读数据库的代码

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以下是使用Java实现从数据库查出数据存入Redis，并在查询时先查Redis，如果Redis中没有数据再从数据库中读取的示例代码：

首先，确保已经引入了Redis的Java客户端依赖，例如Jedis：

<dependency><groupId>redis.clients</groupId><artifactId>jedis</artifactId><version>3.7.0</version>
</dependency>

接下来，我们需要创建一个RedisUtil类，用于连接Redis并提供操作方法：

import redis.clients.jedis.Jedis;public class RedisUtil {private static final String REDIS_HOST = "localhost";private static final int REDIS_PORT = 6379;private static Jedis jedis;public static Jedis getJedis() {if (jedis == null) {jedis = new Jedis(REDIS_HOST, REDIS_PORT);}return jedis;}public static void set(String key, String value) {getJedis().set(key, value);}public static String get(String key) {return getJedis().get(key);}public static void close() {if (jedis != null) {jedis.close();}}
}

然后，我们需要创建一个Dao类，用于从数据库中读取数据，并将数据存入Redis：

import java.sql.*;public class DataDao {private static final String DB_URL = "jdbc:mysql://localhost:3306/mydatabase";private static final String DB_USER = "root";private static final String DB_PASSWORD = "password";public static String getDataFromDatabase(String key) {String data = RedisUtil.get(key);if (data == null) {data = fetchDataFromDatabase(key);if (data != null) {RedisUtil.set(key, data);}}return data;}private static String fetchDataFromDatabase(String key) {Connection conn = null;Statement stmt = null;ResultSet rs = null;String data = null;try {conn = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);stmt = conn.createStatement();String sql = "SELECT data FROM mytable WHERE key = '" + key + "'";rs = stmt.executeQuery(sql);if (rs.next()) {data = rs.getString("data");}} catch (SQLException e) {e.printStackTrace();} finally {if (rs != null) {try {rs.close();} catch (SQLException e) {e.printStackTrace();}}if (stmt != null) {try {stmt.close();} catch (SQLException e) {e.printStackTrace();}}if (conn != null) {try {conn.close();} catch (SQLException e) {e.printStackTrace();}}}return data;}
}

最后，我们可以在主程序中调用Dao类的方法进行测试：

public class Main {public static void main(String[] args) {String key = "mykey";String data = DataDao.getDataFromDatabase(key);System.out.println(data);RedisUtil.close();}
}