Spring Cloud Ribbon：负载均衡的服务调用

Spring Cloud Ribbon 是Spring Cloud Netflix 子项目的核心组件之一，主要给服务间调用及API网关转发提供负载均衡的功能，本文将对其用法进行详细介绍。

在微服务架构中，很多服务都会部署多个，其他服务去调用该服务的时候，如何保证负载均衡是个不得不去考虑的问题。负载均衡可以增加系统的可用性和扩展性，当我们使用RestTemplate来调用其他服务时，Ribbon可以很方便的实现负载均衡功能。

RestTemplate是一个HTTP客户端，使用它我们可以方便的调用HTTP接口，支持GET、POST、PUT、DELETE等方法。

<T>TgetForObject(Stringurl,Class<T>responseType,Object...uriVariables);<T>TgetForObject(Stringurl,Class<T>responseType,Map<String,?>uriVariables);<T>TgetForObject(URIurl,Class<T>responseType);<T>ResponseEntity<T>getForEntity(Stringurl,Class<T>responseType,Object...uriVariables);<T>ResponseEntity<T>getForEntity(Stringurl,Class<T>responseType,Map<String,?>uriVariables);<T>ResponseEntity<T>getForEntity(URIvar1,Class<T>responseType);Copy to clipboardErrorCopied

getForObject方法

返回对象为响应体中数据转化成的对象，举例如下：

@GetMapping("/{id}")publicCommonResultgetUser(@PathVariableLongid){returnrestTemplate.getForObject(userServiceUrl+"/user/{1}",CommonResult.class,id);}Copy to clipboardErrorCopied

getForEntity方法

返回对象为ResponseEntity对象，包含了响应中的一些重要信息，比如响应头、响应状态码、响应体等，举例如下：

@GetMapping("/getEntityByUsername")publicCommonResultgetEntityByUsername(@RequestParamStringusername){ResponseEntity<CommonResult>entity=restTemplate.getForEntity(userServiceUrl+"/user/getByUsername?username={1}",CommonResult.class,username);if(entity.getStatusCode().is2xxSuccessful()){returnentity.getBody();}else{returnnewCommonResult("操作失败",500);}}Copy to clipboardErrorCopied

POST请求方法

<T>TpostForObject(Stringurl,@NullableObjectrequest,Class<T>responseType,Object...uriVariables);<T>TpostForObject(Stringurl,@NullableObjectrequest,Class<T>responseType,Map<String,?>uriVariables);<T>TpostForObject(URIurl,@NullableObjectrequest,Class<T>responseType);<T>ResponseEntity<T>postForEntity(Stringurl,@NullableObjectrequest,Class<T>responseType,Object...uriVariables);<T>ResponseEntity<T>postForEntity(Stringurl,@NullableObjectrequest,Class<T>responseType,Map<String,?>uriVariables);<T>ResponseEntity<T>postForEntity(URIurl,@NullableObjectrequest,Class<T>responseType);Copy to clipboardErrorCopied

postForObject示例

@PostMapping("/create")publicCommonResultcreate(@RequestBodyUseruser){returnrestTemplate.postForObject(userServiceUrl+"/user/create",user,CommonResult.class);}Copy to clipboardErrorCopied

postForEntity示例

@PostMapping("/create")publicCommonResultcreate(@RequestBodyUseruser){returnrestTemplate.postForEntity(userServiceUrl+"/user/create",user,CommonResult.class).getBody();}Copy to clipboardErrorCopied

PUT请求方法

voidput(Stringurl,@NullableObjectrequest,Object...uriVariables);voidput(Stringurl,@NullableObjectrequest,Map<String,?>uriVariables);voidput(URIurl,@NullableObjectrequest);Copy to clipboardErrorCopied

PUT请求示例

@PutMapping("/update")publicCommonResultupdate(@RequestBodyUseruser){restTemplate.put(userServiceUrl+"/user/update",user);returnnewCommonResult("操作成功",200);}Copy to clipboardErrorCopied

DELETE请求方法

voiddelete(Stringurl,Object...uriVariables);voiddelete(Stringurl,Map<String,?>uriVariables);voiddelete(URIurl);Copy to clipboardErrorCopied

DELETE请求示例

@DeleteMapping("/delete/{id}")publicCommonResultdelete(@PathVariableLongid){restTemplate.delete(userServiceUrl+"/user/delete/{1}",null,id);returnnewCommonResult("操作成功",200);}Copy to clipboardErrorCopied

创建一个user-service模块

首先我们创建一个user-service，用于给Ribbon提供服务调用。

在pom.xml中添加相关依赖

<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-web</artifactId></dependency>Copy to clipboardErrorCopied

在application.yml进行配置

主要是配置了端口和注册中心地址。

server:

port: 8201

spring:

application:

name: user-service

eureka:

client:

fetch-registry: true

service-url:

defaultZone: http://localhost:8001/eureka/Copy to clipboardErrorCopied

添加UserController用于提供调用接口

UserController类定义了对User对象常见的CRUD接口。

/**

* Created by macro on 2019/8/29.

*/@RestController@RequestMapping("/user")publicclassUserController{privateLoggerLOGGER=LoggerFactory.getLogger(this.getClass());@AutowiredprivateUserServiceuserService;@PostMapping("/create")publicCommonResultcreate(@RequestBodyUseruser){userService.create(user);returnnewCommonResult("操作成功",200);}@GetMapping("/{id}")publicCommonResult<User>getUser(@PathVariableLongid){Useruser=userService.getUser(id);LOGGER.info("根据id获取用户信息，用户名称为：{}",user.getUsername());returnnewCommonResult<>(user);}@GetMapping("/getUserByIds")publicCommonResult<List<User>>getUserByIds(@RequestParamList<Long>ids){List<User>userList=userService.getUserByIds(ids);LOGGER.info("根据ids获取用户信息，用户列表为：{}",userList);returnnewCommonResult<>(userList);}@GetMapping("/getByUsername")publicCommonResult<User>getByUsername(@RequestParamStringusername){Useruser=userService.getByUsername(username);returnnewCommonResult<>(user);}@PostMapping("/update")publicCommonResultupdate(@RequestBodyUseruser){userService.update(user);returnnewCommonResult("操作成功",200);}@PostMapping("/delete/{id}")publicCommonResultdelete(@PathVariableLongid){userService.delete(id);returnnewCommonResult("操作成功",200);}}Copy to clipboardErrorCopied

创建一个ribbon-service模块

这里我们创建一个ribbon-service模块来调用user-service模块演示负载均衡的服务调用。

在pom.xml中添加相关依赖

<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.cloud</groupId><artifactId>spring-cloud-starter-netflix-ribbon</artifactId></dependency>Copy to clipboardErrorCopied

在application.yml进行配置

主要是配置了端口、注册中心地址及user-service的调用路径。

server:

port: 8301

spring:

application:

name: ribbon-service

eureka:

client:

fetch-registry: true

service-url:

defaultZone: http://localhost:8001/eureka/

service-url:

user-service: http://user-serviceCopy to clipboardErrorCopied

使用@LoadBalanced注解赋予RestTemplate负载均衡的能力

可以看出使用Ribbon的负载均衡功能非常简单，和直接使用RestTemplate没什么两样，只需给RestTemplate添加一个@LoadBalanced即可。

/**

* Created by macro on 2019/8/29.

*/@ConfigurationpublicclassRibbonConfig{@Bean@LoadBalancedpublicRestTemplaterestTemplate(){returnnewRestTemplate();}}Copy to clipboardErrorCopied

添加UserRibbonController类

注入RestTemplate，使用其调用user-service中提供的相关接口，这里对GET和POST调用进行了演示，其他方法调用均可参考。

/**

* Created by macro on 2019/8/29.

*/@RestController@RequestMapping("/user")publicclassUserRibbonController{@AutowiredprivateRestTemplaterestTemplate;@Value("${service-url.user-service}")privateStringuserServiceUrl;@GetMapping("/{id}")publicCommonResultgetUser(@PathVariableLongid){returnrestTemplate.getForObject(userServiceUrl+"/user/{1}",CommonResult.class,id);}@GetMapping("/getByUsername")publicCommonResultgetByUsername(@RequestParamStringusername){returnrestTemplate.getForObject(userServiceUrl+"/user/getByUsername?username={1}",CommonResult.class,username);}@GetMapping("/getEntityByUsername")publicCommonResultgetEntityByUsername(@RequestParamStringusername){ResponseEntity<CommonResult>entity=restTemplate.getForEntity(userServiceUrl+"/user/getByUsername?username={1}",CommonResult.class,username);if(entity.getStatusCode().is2xxSuccessful()){returnentity.getBody();}else{returnnewCommonResult("操作失败",500);}}@PostMapping("/create")publicCommonResultcreate(@RequestBodyUseruser){returnrestTemplate.postForObject(userServiceUrl+"/user/create",user,CommonResult.class);}@PostMapping("/update")publicCommonResultupdate(@RequestBodyUseruser){returnrestTemplate.postForObject(userServiceUrl+"/user/update",user,CommonResult.class);}@PostMapping("/delete/{id}")publicCommonResultdelete(@PathVariableLongid){returnrestTemplate.postForObject(userServiceUrl+"/user/delete/{1}",null,CommonResult.class,id);}}Copy to clipboardErrorCopied

负载均衡功能演示

启动eureka-server于8001端口；

启动user-service于8201端口；

启动另一个user-service于8202端口，可以通过修改IDEA中的SpringBoot的启动配置实现：