读取student表的数据内容，将其转为JSON格式，发送给Kafka；再从Kafka中获取到JSON格式数据，打印出来；实现过程

好的，下面我会给出一个简单的Java示例程序，演示如何实现读取student表数据、将其转为JSON格式、发送到Kafka、从Kafka中获取JSON格式数据并打印出来的过程。

首先，需要引入以下依赖：

<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-databind</artifactId>
  <version>2.12.2</version>
</dependency>

<dependency>
  <groupId>org.apache.kafka</groupId>
  <artifactId>kafka-clients</artifactId>
  <version>2.8.0</version>
</dependency>

接下来是代码实现：

import java.sql.*;
import java.util.Properties;

import com.fasterxml.jackson.databind.ObjectMapper;
import org.apache.kafka.clients.producer.*;

public class KafkaProducerExample {

    private final static String TOPIC = "my-topic";
    private final static String BOOTSTRAP_SERVERS = "localhost:9092";

    private static Connection conn = null;
    private static Statement stmt = null;
    private static ResultSet rs = null;

    public static void main(String[] args) throws Exception {

        // 读取student表中的数据
        conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "password");
        stmt = conn.createStatement();
        rs = stmt.executeQuery("SELECT * FROM student");

        // 将结果集转为JSON格式
        ObjectMapper objectMapper = new ObjectMapper();
        while (rs.next()) {
            Student student = new Student(rs.getInt("id"), rs.getString("name"), rs.getInt("age"));
            String json = objectMapper.writeValueAsString(student);

            // 发送JSON格式数据到Kafka
            Properties props = new Properties();
            props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, BOOTSTRAP_SERVERS);
            props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, "org.apache.kafka.common.serialization.StringSerializer");
            props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, "org.apache.kafka.common.serialization.StringSerializer");
            Producer<String, String> producer = new KafkaProducer<>(props);
            ProducerRecord<String, String> record = new ProducerRecord<>(TOPIC, json);
            producer.send(record);

            System.out.println("Sent message successfully: " + json);
            Thread.sleep(1000);
        }
        producer.close();

        // 从Kafka中获取JSON格式数据并打印出来
        Properties consumerProps = new Properties();
        consumerProps.put("bootstrap.servers", BOOTSTRAP_SERVERS);
        consumerProps.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
        consumerProps.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
        consumerProps.put("group.id", "test-group");
        KafkaConsumer<String, String> consumer = new KafkaConsumer<>(consumerProps);
        consumer.subscribe(Arrays.asList(TOPIC));
        while (true) {
            ConsumerRecords<String, String> records = consumer.poll(Duration.ofMillis(100));
            for (ConsumerRecord<String, String> record : records) {
                System.out.printf("offset = %d, key = %s, value = %s%n", record.offset(), record.key(), record.value());
            }
        }
    }

    private static class Student {
        private int id;
        private String name;
        private int age;

        public Student(int id, String name, int age) {
            this.id = id;
            this.name = name;
            this.age = age;
        }

        public int getId() {
            return id;
        }

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

        public String getName() {
            return name;
        }

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

        public int getAge() {
            return age;
        }

        public void setAge(int age) {
            this.age = age;
        }
    }

}

上面的代码中，我们使用了Jackson库来将ResultSet对象转为JSON格式字符串。然后，使用KafkaProducer类将JSON格式数据发送到Kafka中。接下来，使用KafkaConsumer类从Kafka中读取JSON格式数据，并将其打印出来。

需要注意的是，本示例程序中使用了MySQL作为数据库，需要先在本地安装MySQL，并创建名为"test"的数据库，并在其中创建名为"student"的表。同时，需要在本地启动Kafka服务，创建名为"my-topic"的主题。

希望这个示例程序可以帮助到你，如果有任何问题，欢迎随时向我提问。