eclipse Paho MQTT Utility连接mysql数据库

要在 Eclipse Paho MQTT Utility 中连接 MySQL 数据库，需要进行以下步骤：

1.下载并安装 JDBC 驱动程序，比如 MySQL Connector/J。

2.在 Eclipse Paho MQTT Utility 中编写 Java 代码，使用 JDBC 连接 MySQL 数据库。可以使用以下代码示例：

import java.sql.*;

public class MqttToMySQL {
    static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
    static final String DB_URL = "jdbc:mysql://localhost/mydatabase";

    static final String USER = "username";
    static final String PASS = "password";

    public static void main(String[] args) {
        Connection conn = null;
        Statement stmt = null;
        try{
            Class.forName("com.mysql.jdbc.Driver");

            System.out.println("Connecting to database...");
            conn = DriverManager.getConnection(DB_URL,USER,PASS);

            System.out.println("Creating statement...");
            stmt = conn.createStatement();
            String sql;
            sql = "SELECT id, name, age FROM employees";
            ResultSet rs = stmt.executeQuery(sql);

            while(rs.next()){
                int id  = rs.getInt("id");
                String name = rs.getString("name");
                int age = rs.getInt("age");

                System.out.println("ID: " + id);
                System.out.println("Name: " + name);
                System.out.println("Age: " + age);
            }
            rs.close();
            stmt.close();
            conn.close();
        }catch(SQLException se){
            se.printStackTrace();
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            try{
                if(stmt!=null) stmt.close();
            }catch(SQLException se2){
            }
            try{
                if(conn!=null) conn.close();
            }catch(SQLException se){
                se.printStackTrace();
            }
        }
        System.out.println("Goodbye!");
    }
}

这段代码连接了名为“mydatabase”的 MySQL 数据库，并从中读取了“employees”表中的数据。

3.将 MQTT 客户端代码与上面的数据库连接代码结合起来。可以在 MQTT 客户端接收到消息时，将消息写入 MySQL 数据库中。可以使用以下代码示例：

import org.eclipse.paho.client.mqttv3.*;
import java.sql.*;

public class MqttToMySQL implements MqttCallback {
    static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
    static final String DB_URL = "jdbc:mysql://localhost/mydatabase";

    static final String USER = "username";
    static final String PASS = "password";

    public static void main(String[] args) {
        String topic        = "MQTT Examples";
        int qos             = 2;
        String broker       = "tcp://localhost:1883";
        String clientId     = "JavaSample";
        MemoryPersistence persistence = new MemoryPersistence();

        try {
            Class.forName("com.mysql.jdbc.Driver");

            System.out.println("Connecting to database...");
            Connection conn = DriverManager.getConnection(DB_URL,USER,PASS);

            MqttClient sampleClient = new MqttClient(broker, clientId, persistence);
            MqttConnectOptions connOpts = new MqttConnectOptions();
            connOpts.setCleanSession(true);
            System.out.println("Connecting to broker: "+broker);
            sampleClient.connect(connOpts);
            System.out.println("Connected");
            sampleClient.setCallback(new MqttToMySQL());

            sampleClient.subscribe(topic, qos);

            // Wait for messages
            while(true) {
                Thread.sleep(1000);
            }

            //sampleClient.disconnect();
            //System.out.println("Disconnected");
            //System.exit(0);
        } catch(MqttException me) {
            System.out.println("reason "+me.getReasonCode());
            System.out.println("msg "+me.getMessage());
            System.out.println("loc "+me.getLocalizedMessage());
            System.out.println("cause "+me.getCause());
            System.out.println("excep "+me);
            me.printStackTrace();
        } catch(SQLException se) {
            se.printStackTrace();
        } catch(Exception e) {
            e.printStackTrace();
        }
    }

    public void connectionLost(Throwable cause) {
        System.out.println("Connection lost: "+cause);
    }

    public void messageArrived(String topic, MqttMessage message) throws Exception {
        String content = new String(message.getPayload());
        System.out.println("Message arrived: "+content);

        Connection conn = DriverManager.getConnection(DB_URL,USER,PASS);

        String sql = "INSERT INTO messages (content) VALUES (?)";
        PreparedStatement pstmt = conn.prepareStatement(sql);
        pstmt.setString(1, content);
        pstmt.executeUpdate();

        pstmt.close();
        conn.close();
    }

    public void deliveryComplete(IMqttDeliveryToken token) {
        System.out.println("Delivery complete");
    }
}

这段代码连接到名为“mydatabase”的 MySQL 数据库，并在接收到 MQTT 消息时，将消息写入名为“messages”的表中。

需要注意的是，在将 MQTT 客户端代码与数据库连接代码结合时，需要考虑线程安全和数据库连接池等问题，以提高应用程序的性能和稳定性。