Spring Cloud 之使用RestTemplate實作微服務之間互相請求的三種方式
RestTemplate 簡介
RestTemplate是由Spring提供的一個HTTP請求工具。RestTemplate是從Spring3.0開始支援的一個HTTP請求工具,它提供了常見的REST請求方案的模版,例如 GET 請求、POST請求、PUT請求、DELETE請求以及一些通用的請求執行方法exchange以及execute。RestTemplate繼承自InterceptingHttpAccessor并且實作了RestOperations 接口,其中RestOperations接口定義了基本的
restful
操作,這些操作在RestTemplate中都得到了實作。
建立第一個Spring Boot項目作為注冊中心。
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">
<modelVersion>4.0.0</modelVersion>
<groupId>com.kaven</groupId>
<artifactId>eureka</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>eureka</name>
<description>Demo project for Spring Boot</description>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.6.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>1.8</java.version>
<spring-cloud.version>Finchley.SR2</spring-cloud.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>${spring-cloud.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
application.yml
如下:
eureka:
client:
service-url:
defaultZone: http://localhost:8761/eureka/
register-with-eureka: false
server:
enable-self-preservation: false
spring:
application:
name: eureka
server:
port: 8761
啟動類:
package com.kaven.eureka;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;
@SpringBootApplication
@EnableEurekaServer
public class EurekaApplication {
public static void main(String[] args) {
SpringApplication.run(EurekaApplication.class, args);
}
}
注解
@EnableEurekaServer
不要忘記加上。
建立第二個Spring Boot項目作為第一個微服務。
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">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.6.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.kaven</groupId>
<artifactId>server</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>server</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
<spring-cloud.version>Finchley.SR2</spring-cloud.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>${spring-cloud.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
application.yml
如下:
spring:
application:
name: server
server:
port: 8001
eureka:
client:
service-url:
defaultZone: http://localhost:8761/eureka/
啟動類:
package com.kaven.server;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
@SpringBootApplication
@EnableDiscoveryClient
public class ServerApplication {
public static void main(String[] args) {
SpringApplication.run(ServerApplication.class, args);
}
}
注解
@EnableDiscoveryClient
不要忘記加上。
再寫一個接口(用于被其他微服務請求):
package com.kaven.server.controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class MessageServerController {
@GetMapping("/getMessage")
public String getMessage(){
return "hello , Jack";
}
}
建立第三個Spring Boot項目作為第二個微服務。
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">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.6.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.kaven</groupId>
<artifactId>client</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>client</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
<spring-cloud.version>Finchley.SR2</spring-cloud.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>${spring-cloud.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
application.yml
如下:
spring:
application:
name: client
server:
port: 8002
eureka:
client:
service-url:
defaultZone: http://localhost:8761/eureka/
啟動類:
package com.kaven.client;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
@SpringBootApplication
@EnableDiscoveryClient
public class ClientApplication {
public static void main(String[] args) {
SpringApplication.run(ClientApplication.class, args);
}
}
注解
@EnableDiscoveryClient
不要忘記加上。
再寫一個接口用來請求第一個微服務的接口:
package com.kaven.client.controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;
@RestController
public class MessageController {
@GetMapping("/getMessage")
public String getMessage(){
RestTemplate restTemplate = new RestTemplate();
String url = "http://127.0.0.1:8001/getMessage";
String message = restTemplate.getForObject(url , String.class);
return "get: "+message;
}
}
通路
http://localhost:8761/
,可以得到如下圖所示的界面:
可以發現兩個微服務已經注冊上去了,發出警告的原因是因為注冊中心關閉了自我保護模式。通路
http://localhost:8001/getMessage
,即第一個微服務的接口,可以得到如下圖所示的界面。
再來通路
http://localhost:8002/getMessage
,即第二個微服務的接口,可以得到如下圖所示的界面。
該接口會通過RestTemplate來請求第一個微服務的接口,以便擷取資料。
這就是使用RestTemplate實作微服務之間互相請求的第一種方式,這種方式把微服務的接口
url
寫死了,代碼不優雅,并且不利于維護。
下面來介紹第二種方式。
修改第二個微服務的接口:
package com.kaven.client.controller;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.loadbalancer.LoadBalancerClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;
@RestController
public class MessageController {
@Autowired
private LoadBalancerClient loadBalancerClient;
@GetMapping("/getMessage")
public String getMessage(){
RestTemplate restTemplate = new RestTemplate();
ServiceInstance serviceInstance = loadBalancerClient.choose("server");
String url = String.format("http://%s:%s//getMessage" , serviceInstance.getHost() , serviceInstance.getPort());
String message = restTemplate.getForObject(url , String.class);
return "get: "+message;
}
}
這裡使用到了
LoadBalancerClient
,這種方式是不是比上一種方式優雅許多,不用寫死
ip
和
port
,隻要寫接口即可。
再來通路
http://localhost:8002/getMessage
,可以得到如下圖所示的界面,是以這種方式也是成功的。
但第二種方式代碼量稍多,并不簡潔,接下來介紹第三種方式。
第三種方式首先需要加一個配置類:
package com.kaven.client.config;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;
import org.springframework.web.client.RestTemplate;
@Component
public class RestTemplateConfig {
@Bean
@LoadBalanced
public RestTemplate restTemplate(){
return new RestTemplate();
}
}
注解
@LoadBalanced
是關鍵。
再來修改第二個微服務的接口:
package com.kaven.client.controller;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.loadbalancer.LoadBalancerClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;
@RestController
public class MessageController {
@Autowired
private RestTemplate restTemplate;
@GetMapping("/getMessage")
public String getMessage(){
String message = restTemplate.getForObject("http://server/getMessage" , String.class);
return "get: "+message;
}
}
除了配置類,接口主要代碼就一行,是不是很簡潔,
server
是第一個微服務的名稱,這種方式直接使用服務名稱即可,可以知道這肯定是注解
@LoadBalanced
的功勞,其實這種方式和第二種方式是一樣的,隻是實作方式不一樣。
再來通路
http://localhost:8002/getMessage
,可以得到如下圖所示的界面,是以第三種方式也是成功的。