Develop RESTful applications with HSF for service registration and discovery - Serverless App Engine - Alibaba Cloud -

Develop RESTful applications in the HSF framework and implement service registration and discovery. Because SAE now supports native Spring Cloud applications, this development method is not recommended for new users.

Background information

To learn how to develop services using the native Spring Cloud framework, see and Host Spring Cloud applications in SAE.

Service registration and discovery

This section walks you through developing a local RESTful application with service registration and discovery.

Download the demo source code:

Create a service provider.

This service provider exposes a simple echo service and registers itself with the service registry.

Create a RESTful application project named sc-vip-server.

Add the required dependencies to the pom.xml file.

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.8.RELEASE</version>
        <relativePath/>
    </parent>
    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-vipclient</artifactId>
            <version>1.3</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-pandora</artifactId>
            <version>1.3</version>
        </dependency>
    </dependencies>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Dalston.SR4</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

If you do not want to set the project's parent to spring-boot-starter-parent, you can add a dependencyManagement section and set scope="import" to manage the dependencies.

<dependencyManagement>
            <dependencies>
                <dependency>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-dependencies</artifactId>
                    <version>1.5.8.RELEASE</version>
                    <type>pom</type>
                    <scope>import</scope>
                </dependency>
            </dependencies>
</dependencyManagement>

Create the service provider application. Use the @EnableDiscoveryClient annotation to enable service registration and discovery.

@SpringBootApplication
    @EnableDiscoveryClient
    public class ServerApplication {
        public static void main(String[] args) {
            PandoraBootstrap.run(args);
            SpringApplication.run(ServerApplication.class, args);
            PandoraBootstrap.markStartupAndWait();
        }
    }

Create an EchoController to provide a simple echo service.

@RestController
    public class EchoController {
        @RequestMapping(value = "/echo/{string}", method = RequestMethod.GET)
        public String echo(@PathVariable String string) {
            return string;
        }
    }

In the application.properties file in the resources directory, configure the application name and listening port.
```
spring.application.name=service-provider
server.port=18081
```

Create a service consumer.

This example creates a service consumer that calls the service provider using RestTemplate, AsyncRestTemplate, and FeignClient.

Create a RESTful application project named sc-vip-client.

Add the required dependencies to the pom.xml file.

<parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.8.RELEASE</version>
        <relativePath/>
    </parent>
    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-vipclient</artifactId>
            <version>1.3</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-pandora</artifactId>
            <version>1.3</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-feign</artifactId>
        </dependency>
    </dependencies>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Dalston.SR4</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

This example uses FeignClient for demonstration. Unlike the service provider (sc-vip-server), the consumer's pom.xml file includes an additional spring-cloud-starter-feign dependency.

To use RestTemplate, AsyncRestTemplate, and FeignClient, you must also enable service registration and discovery (as you did for sc-vip-server) and add the following two configurations.

Add the @LoadBalanced annotation to integrate RestTemplate and AsyncRestTemplate with service discovery.

Add the @EnableFeignClients annotation to activate FeignClient.

@SpringBootApplication
    @EnableDiscoveryClient
    @EnableFeignClients
    public class ConsumerApplication {
        @LoadBalanced
        @Bean
        public RestTemplate restTemplate() {
            return new RestTemplate();
        }
        @LoadBalanced
        @Bean
        public AsyncRestTemplate asyncRestTemplate(){
            return new AsyncRestTemplate();
        }
        public static void main(String[] args) {
            PandoraBootstrap.run(args);
            SpringApplication.run(ConsumerApplication.class, args);
            PandoraBootstrap.markStartupAndWait();
        }
    }

Before you use the FeignClient for EchoService, you must configure the service name and map the method to the corresponding HTTP request. In the sc-vip-server project, the service name is configured as service-provider.
```
@FeignClient(name = "service-provider")
    public interface EchoService {
        @RequestMapping(value = "/echo/{str}", method = RequestMethod.GET)
        String echo(@PathVariable("str") String str);
    }
```

Create a Controller to test the service calls.

@RestController
public class Controller {
   @Autowired
   private RestTemplate restTemplate;
   @Autowired
   private AsyncRestTemplate asyncRestTemplate;
   @Autowired
   private  EchoService echoService;
   @RequestMapping(value = "/echo-rest/{str}", method = RequestMethod.GET)
   public String rest(@PathVariable String str) {
       return restTemplate.getForObject("http://service-provider/echo/" + str, String.class);
   }
   @RequestMapping(value = "/echo-async-rest/{str}", method = RequestMethod.GET)
   public String asyncRest(@PathVariable String str) throws Exception{
       ListenableFuture<ResponseEntity<String>> future = asyncRestTemplate.
               getForEntity("http://service-provider/echo/"+str, String.class);
       return future.get().getBody();
   }
   @RequestMapping(value = "/echo-feign/{str}", method = RequestMethod.GET)
   public String feign(@PathVariable String str) {
       return echoService.echo(str);
   }
}

The code implements three endpoints for testing:

/echo-rest/: Verifies the call to the service provider using RestTemplate.
/echo-async-rest/: Verifies the call to the service provider using AsyncRestTemplate.
/echo-feign/: Verifies the call to the service provider using FeignClient.

Configure the application name and listening port.

spring.application.name=service-consumer
server.port=18082

Develop and debug locally.
1. Start the lightweight configuration center.
  For local development and debugging, use the lightweight configuration center. It provides a lightweight version of the server-side service registration and discovery component used by and SAE. For more information, see Start the lightweight configuration and registration center.
2. Start the application.
  - Start from an IDE
    To start the application from your IDE, add the -Dvipserver.server.port=8080 VM option and then run the main method. Note: This parameter is required only for local development with the lightweight configuration center. You must remove this parameter when you deploy the application to or SAE. Otherwise, the application may fail to publish or subscribe to services.
    
    If the lightweight configuration center and your application are on different machines, configure host bindings. For more information, see Start the lightweight configuration and registration center.
  - Start from a FatJar
    1. Add the FatJar packaging plug-in.
      To package the pandora-boot project into a FatJar using Maven, add the following plug-in to your pom.xml file. To avoid conflicts, do not add other FatJar plug-ins to the <plugins> section of the build configuration.
      <build> <plugin> <groupId>com.taobao.pandora</groupId> <artifactId>pandora-boot-maven-plugin</artifactId> <version>2.1.9.1</version> <executions> <execution> <phase>package</phase> <goals> <goal>repackage</goal> </goals> </execution> </executions> </plugin> </build>
    2. After you add the plug-in, run the mvn clean package command in the project's root directory. The FatJar file is generated in the target directory.
    3. Start the application using a Java command.
      java -Dvipserver.server.port=8080 -Dpandora.location=/Users/{$username}/.m2/repository/com/taobao/pandora/taobao-hsf.sar/dev-SNAPSHOT/taobao-hsf.sar-dev-SNAPSHOT.jar -jar sc-vip-server-0.0.1-SNAPSHOT.jar
      
      Note The path specified by -Dpandora.location must be an absolute path and must be placed before the -jar argument.
  Start the services and call the endpoints. The output shows that all calls are successful.
```
→ ~ curl http://localhost:18082/echo-rest/rest-test
rest-test%
→ ~ curl http://localhost:18082/echo-async-rest/async-rest-test
async-rest-test%
→ ~ curl http://localhost:18082/echo-feign/feign-test
feign-test%
```
Troubleshoot common issues.
- AsyncRestTemplate cannot connect to service discovery.
  Support for service discovery using AsyncRestTemplate was added in Spring Cloud Dalston. You must use this version or a later version. For more information, see this pull request.
- Conflicts with the FatJar packaging plug-in.
  To avoid conflicts, do not add other FatJar plug-ins to the <plugins> section of the build configuration.
- Can I include taobao-hsf.sar in the package?
  Yes, but this is not recommended.
  You can modify the pandora-boot-maven-plugin configuration by setting excludeSar to false. This automatically includes taobao-hsf.sar in the package.
```
<plugin>
    <groupId>com.taobao.pandora</groupId>
    <artifactId>pandora-boot-maven-plugin</artifactId>
    <version>2.1.9.1</version>
    <configuration>
    <excludeSar>false</excludeSar>
    </configuration>
       <executions>
           <execution>
              <phase>package</phase>
              <goals>
                  <goal>repackage</goal>
              </goals>
            </execution>
    </executions>
</plugin>
```
  This way, you can start the application without configuring the Pandora location.
```
java -jar  -Dvipserver.server.port=8080 sc-vip-server-0.0.1-SNAPSHOT.jar
```
  Before deploying the application to or SAE, restore the default configuration to exclude the SAR package.