二、SpringCloud Alibaba使用RestTemplate

新建模块Producer，pom.xml如下：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <groupId>com.example</groupId>
        <artifactId>SpringCloudAlibabaDemo</artifactId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.example</groupId>
    <artifactId>Producer</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>Producer</name>
    <description>Producer</description>
    <properties>
        <java.version>17</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
        </dependency>
    </dependencies>

</project>

配置application.properties：

server.port=7000

spring.application.name=producer
spring.cloud.nacos.discovery.server-addr=localhost:8848

新建Controller：

@RestController
public class HelloProducer {
    @Value("${server.port}")
    private int port;

    @RequestMapping("/hello")
    public String  hello() {
        return "hello,Producer,port:" + port;
    }
}

在SpringCloudAlibabaDemo的pom.xml加入

<modules>
    <module>Consumer</module>
    <module>Producer</module>
</modules>

在Consumer加入：

@Configuration
public class MyConfig {
    @Bean
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

修改HelloConsumer：

@RestController
@RequestMapping("/consumer")
public class HelloConsumer {
    @Autowired
    private RestTemplate restTemplate;

    @Autowired
    private DiscoveryClient discoveryClient;

    @Value("${server.port}")
    private int port;

    @RequestMapping("/hello")
    public String  hello() {
        return "hello,Consumer,port:" + port;
    }


    @RequestMapping("/rpc")
    public String rpc() {
        List<ServiceInstance> producer = discoveryClient.getInstances("producer");
        ServiceInstance serviceInstance = null;
        if (producer != null && !producer.isEmpty()) {
            serviceInstance = producer.get(0);
        }


        if (serviceInstance != null) {
            return restTemplate.getForObject("http://"+serviceInstance.getHost()+":"+serviceInstance.getPort()+"/hello",String.class);
        } else {
            throw new RuntimeException("未找到Producer服务");
        }
    }
}

访问http://localhost:7001/consumer/rpc，看到hello,Producer,port:7000。在这里是通过DiscoveryClient解析出服务的ip和端口后通过RestTemplate调用。

在2021.0.4.0版本的springCloudAlibaba中，spring-cloud-starter-alibaba-nacos-discovery依赖引入了spring-cloud-loadbalancer作为负载均衡，RestTemplate要使用负载均衡，只需添加@LoadBalanced:

@Configuration
public class MyConfig {
    @LoadBalanced
    @Bean
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

同时添加依赖：

   <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-loadbalancer</artifactId>
        <version>3.1.4</version>
    </dependency>

修改HelloConsumer：

@RequestMapping("/rpc1")
public String rpc1() {
    return restTemplate.getForObject("http://producer/hello",String.class);
}

访问http://localhost:7001/consumer/rpc1，看到hello,Producer,port:7000。

在启动一个端口是7002的Producer，访问http://localhost:7001/consumer/rpc1，看到负载均衡成功。