Spring Cloud(7.2)：配置Producer Server

我们首先创建一个生产者服务。这里以一个商品价格服务为例，这个微服务可以对商品-价格信息进行增删改查，当有商品-价格信息被更新或删除，则该微服务发送消息，告诉其他调用它的系统这条信息已经被修改。

配置pom.xml

首先，在pom.xml中添加spring-cloud-stream和spring-cloud-starter-stream-kafka两个依赖

<!-- Spring cloud: stream -->
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-stream</artifactId>
</dependency>
<!-- Spring cloud starter: kafka -->
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-stream-kafka</artifactId>
</dependency>

此外，它还是一个Eureka Client和Config Client，如何配置Eureka Client和Config Client请看前面章节。

配置发射器（source），通道（channel），绑定器（binder）及Application

public interface ProductPriceSource {
    @Output("productPriceOutput")
    MessageChannel productPriceOutput();
}

[注] 这里创建了一个叫“productPriceOutput”的自定义发射通道，如果不使用自定义，可以直接使用org.springframework.cloud.stream.messaging.Source接口及叫output的发射通道（下面的yml文件会讲如何配置）。

@Component
public class ProductPriceMessageSender {

    @Autowired
    private ProductPriceSource source;

    private static final Logger logger = LoggerFactory.getLogger(ProductPriceMessageSender.class);

    /**
     * The product is expired and need to send kafka message to consumer service to remove it from cache(redis).
     * 
     * @param productId
     */
    public void sendMessage(Long productId) {
        logger.info(String.format(">>>>> Sending Kafka message: [productId = %s].", productId.toString()));
        source.productPriceOutput().send(MessageBuilder.withPayload(productId).build());
    }
}

[注] 这里配置了一个发射器bean,当有商品-价格信息被更新或删除，则调用该bean，把消息发布到消息队列。

@SpringBootApplication
@EnableBinding({ ProductPriceSource.class })
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }
}

[注] Application中加入@EnableBinding注解，并把定义好的发射通道（output）或接收通道（input）绑定到该服务中。可以绑定多个。

配置application.yml

## Spring info
spring:
  # Stream/Kafka info
  cloud:
    stream:
      bindings:
        # output -> productPriceOutput (自定义通道)
        productPriceOutput:
          # 要写入消息的消息队列的名称
          destination:  productPriceTopic
          # 发送和接收消息类型
          content-type: application/json
      # 使用kafka作为消息总线
      kafka:
        binder:
          # 运行着kafka服务器的网络地址
          brokers: www.mytools.com

API及其他业务逻辑

@Controller
@RequestMapping("pp")
public class ProductPriceController {

    @Autowired
    private ProductPriceService productPriceService;

    @GetMapping(value = "find/all")
    @ResponseBody
    public List<ProductPriceEntity> findAll() {
        return productPriceService.findAll();
    }

    @GetMapping(value = "find/productId/{productId}")
    @ResponseBody
    public ProductPriceEntity find(@PathVariable String productId) {
        return productPriceService.findById(Long.valueOf(productId));
    }

    @GetMapping(value = "add/productId/{productId}/product/{product}/price/{price}")
    @ResponseBody
    public String save(@PathVariable String productId, @PathVariable String product, @PathVariable String price) {
        return productPriceService.save(Long.valueOf(productId), product, new BigDecimal(price));
    }

    @GetMapping(value = "update/productId/{productId}/product/{product}/price/{price}")
    @ResponseBody
    public String update(@PathVariable String productId, @PathVariable String product, @PathVariable String price) {
        return productPriceService.update(Long.valueOf(productId), product, new BigDecimal(price));
    }

    @GetMapping(value = "delete/productId/{productId}")
    @ResponseBody
    public String delete(@PathVariable String productId) {
        return productPriceService.delete(Long.valueOf(productId));
    }
}

[注] 这里创建了几个常规的，包括增删改查的API。

@Service
public class ProductPriceService {

    private static final Map<Long, ProductPriceEntity> db = new ConcurrentHashMap<>();

    static {
        ProductPriceEntity row1 = new ProductPriceEntity(1L, "Apple", new BigDecimal("8.5"));
        ProductPriceEntity row2 = new ProductPriceEntity(2L, "Watermelon", new BigDecimal("2.2"));
        ProductPriceEntity row3 = new ProductPriceEntity(3L, "Grape", new BigDecimal("6.8"));
        db.put(1L, row1);
        db.put(2L, row2);
        db.put(3L, row3);
    }

    @Autowired
    private ProductPriceMessageSender sender;

    public List<ProductPriceEntity> findAll() {

        List<ProductPriceEntity> results = new ArrayList<>();
        results.addAll(db.values());

        return results;
    }

    public ProductPriceEntity findById(Long productId) {
        return db.get(productId);
    }

    public String save(Long productId, String product, BigDecimal price) {
        if (db.containsKey(productId)) {
            return String.format("[WARN] Product which productId = %s already exists in DB.", productId.toString());
        } else {
            ProductPriceEntity param = new ProductPriceEntity(productId, product, price);
            db.put(productId, param);
            return String.format("Save %s completed.", param);
        }
    }

    public String update(Long productId, String product, BigDecimal price) {
        if (db.containsKey(productId)) {
            ProductPriceEntity param = new ProductPriceEntity(productId, product, price);
            db.put(productId, param);
            // [UPDATE] send to kafka
            sender.sendMessage(productId);
            return String.format("Update %s completed.", param);
        } else {
            return String.format("[WARN] No product which productId = %s in DB.", productId.toString());
        }
    }

    public String delete(Long productId) {
        if (db.containsKey(productId)) {
            ProductPriceEntity result = db.remove(productId);
            // [DELETE] send to kafka
            sender.sendMessage(productId);
            return String.format("Delete %s completed.", result.toString());
        } else {
            return String.format("[WARN] No product which productId = %s in DB.", productId.toString());
        }
    }
}

[注] 这里使用一个Map来模拟DB。并且当有商品-价格信息被更新或删除时，才调用ProductPriceMessageSender发送消息。ProductPriceEntity的代码如下：

public class ProductPriceEntity implements Serializable {

    private static final long serialVersionUID = 1L;

    private Long productId;

    private String product;

    private BigDecimal price;

    public ProductPriceEntity() {
    }

    public ProductPriceEntity(Long productId, String product, BigDecimal price) {
        super();
        this.productId = productId;
        this.product = product;
        this.price = price;
    }

    public Long getProductId() {
        return productId;
    }

    public void setProductId(Long productId) {
        this.productId = productId;
    }

    public String getProduct() {
        return product;
    }

    public void setProduct(String product) {
        this.product = product;
    }

    public BigDecimal getPrice() {
        return price;
    }

    public void setPrice(BigDecimal price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "ProductPriceEntity [productId=" + productId + ", product=" + product + ", price=" + price + "]";
    }
}

Input and Output to a broker,