如何用Java(Spring)向Kafka Topic发送JSON格式消息？

Hey there! Let's break down your three questions about sending that specific JSON message to a Kafka topic one by one:

1. How to convert the given JSON to a string? #

You’ve got two practical options here:

• Directly write the escaped string
  In Java, double quotes inside a string literal need to be escaped with backslashes. Your JSON would look like this as a string:

  String jsonStr = "{\"targetFileInfo\":{\"path\":\"2018-05-07-10/row01-small-01.txt.ready\"}}";
  

• Serialize a Java object to JSON string (recommended for dynamic data)
  First, create a POJO that matches your JSON structure:

  public class TargetFileInfo {
      private String path;
  
      // Getters and setters
      public String getPath() { return path; }
      public void setPath(String path) { this.path = path; }
  }
  
  public class KafkaMessage {
      private TargetFileInfo targetFileInfo;
  
      // Getters and setters
      public TargetFileInfo getTargetFileInfo() { return targetFileInfo; }
      public void setTargetFileInfo(TargetFileInfo targetFileInfo) { this.targetFileInfo = targetFileInfo; }
  }
  

  Then use a JSON library like Jackson or Gson to convert the object to a string. For example, with Jackson:

  ObjectMapper objectMapper = new ObjectMapper();
  KafkaMessage message = new KafkaMessage();
  TargetFileInfo fileInfo = new TargetFileInfo();
  fileInfo.setPath("2018-05-07-10/row01-small-01.txt.ready");
  message.setTargetFileInfo(fileInfo);
  
  String jsonStr = objectMapper.writeValueAsString(message);
  

2. Maven dependencies for JSON serialization (similar to JSON.stringify) #

Java doesn’t have a built-in JSON.stringify function, so you’ll need a third-party library. Here are the most common options with their Maven dependencies:

Jackson (industry standard) #

Add this to your pom.xml:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.15.2</version> <!-- Use the latest stable version available -->
</dependency>

Gson (Google’s lightweight library) #

Add this to your pom.xml:

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.10.1</version> <!-- Use the latest stable version available -->
</dependency>

With Gson, serialization is just as simple:

Gson gson = new Gson();
String jsonStr = gson.toJson(message);

3. Can I send the message directly without converting it to a string? #

It depends on your Kafka setup:

• Native Kafka Producer (default configuration)
  The default StringSerializer expects a string input, so you can’t send the JSON object directly. You’ll either need to convert it to a string (as we covered) or serialize it to a byte array manually and use the ByteArraySerializer.

• Using a framework or custom serializer
  If you’re using a framework like Spring Kafka, you can configure a JsonSerializer to handle conversion automatically. This lets you send the Java object directly— the serializer will turn it into a JSON-formatted byte stream behind the scenes.

  For example, in Spring Kafka, set up your producer factory like this:

  @Bean
  public ProducerFactory<String, KafkaMessage> producerFactory() {
      Map<String, Object> configProps = new HashMap<>();
      // Add your Kafka broker connection configs here
      configProps.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
      configProps.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, JsonSerializer.class);
      return new DefaultKafkaProducerFactory<>(configProps);
  }
  

  Then you can send the KafkaMessage object directly via KafkaTemplate without manual string conversion.

内容的提问来源于stack exchange，提问作者guguli