SpringCloud（二）RestTemplate的使用

r囧r小猫 2022-10-02 14:00 156阅读 0赞

## 源码 ##

GitHub：[https://github.com/291685399/springcloud-learning/tree/master/springcloud-eureka01][https_github.com_291685399_springcloud-learning_tree_master_springcloud-eureka01]

## RestTemplate是什么？ ##

RestTemplate是Spring对Http客户端进行封装的一个模板工具类，对常用的Http客户端例如：HttpClient、OKHttp、JDK原生的URLConnection(默认的)都支持。

## RestTemplate能做什么？ ##

基于Restful风格可以对远程服务基于http协议进行远程调用

## RestTemplate的使用 ##

*  新建一个父工程，命名为springcloud-eureka01

目录结构如下图：  
![在这里插入图片描述][20190621204717662.png]  
pom.xml：

<parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.0.RELEASE</version>
        <relativePath/>
    </parent>
    
    <dependencies>
       
       <dependency>
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-starter</artifactId>
       </dependency>
       <dependency>
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-devtools</artifactId>
           <scope>runtime</scope>
           <optional>true</optional>
       </dependency>
       <dependency>
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-starter-test</artifactId>
           <scope>test</scope>
       </dependency>
    </dependencies>
    
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

*  新建模块，命名为eureka-provider01

目录结构如下图：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1NjIwNTAx_size_16_color_FFFFFF_t_70]

pom.xml：

<parent>
        <groupId>com.wyj</groupId>
        <artifactId>springcloud-eureka01</artifactId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>
    
    
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
    
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <scope>runtime</scope>
    </dependency>
    
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <optional>true</optional>
    </dependency>

ProviderController：

@Controller
    public class ProviderController { 
    
        @Autowired
        private UserService userService;
    
        @RequestMapping(value = "/findById/{id}")
        @ResponseBody
        public User findById(@PathVariable int id) { 
            User user = userService.findById(id);
            return user;
        }
    }

UserService：

public interface UserService { 
        public User findById(int id);
    }

UserServiceImpl：

@Service
    public class UserServiceImpl implements UserService { 
    
        @Autowired
        private UserRepository userRepository;
    
        @Override
        public User findById(int id) { 
            Optional<User> userOptional = userRepository.findById(id);
            User user = userOptional.get();
            return user;
        }
    }

UserRepository：

public interface UserRepository extends JpaRepository<User, Integer> { 
    }

User：

@Entity
    @Data
    public class User implements Serializable { 
    
        @Id
        @GeneratedValue
        private int id;
        private String name;
        private String sex;
        private int age;
        private String address;
        private String phone;
    }

application.properties：

server.port=8081
    spring.datasource.url=jdbc:mysql://127.0.0.1:3306/springcloud-eureka01?serverTimezone=UTC&useUnicode=true&characterEncoding=utf-8&useSSL=true
    spring.datasource.driver-class-name=com.mysql.jdbc.Driver
    spring.datasource.username=root
    spring.datasource.password=root
    spring.jpa.show-sql=true
    spring.jpa.hibernate.ddl-auto=update
    spring.jpa.properties.hibernate.format_sql=true
    spring.jpa.properties.hibernate.use_sql_comments=true
    spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL5InnoDBDialect

*  新建模块，命名为eureka-consumer01

目录结构如下图：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1NjIwNTAx_size_16_color_FFFFFF_t_70 1]

pom.xml：

<parent>
        <groupId>com.wyj</groupId>
        <artifactId>springcloud-eureka01</artifactId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>
    
    
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <optional>true</optional>
    </dependency>

ConsumerController：

@Controller
    public class ConsumerController{ 
    
        @Autowired
        private RestTemplate restTemplate;
    
        @RequestMapping(value = "/findById/{id}")
        @ResponseBody
        public User findById(@PathVariable int id) { 
            User user = restTemplate.getForObject("http://127.0.0.1:8081/findById/" + id, User.class);
            return user;
        }
    }

RestConfig：

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

User：

@Data
    public class User implements Serializable { 
    
        private int id;
        private String name;
        private String sex;
        private int age;
        private String address;
        private String phone;
    }

## 测试使用 ##

分别启动eureka-provider01和eureka-consumer01，启动顺序没关系

浏览器访问http://127.0.0.1:8080/findById/1  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1NjIwNTAx_size_16_color_FFFFFF_t_70 2]

## 总结 ##

在ConsumerController中，RestTemplate调用远程服务

User user = restTemplate.getForObject("http://127.0.0.1:8081/findById", User.class);

RestTemplate通过getForObject方法传递url地址及实体类的字节码，自动发起请求，接收响应，并且帮我们对响应结果通过SpringMVC内置的Jackson中的ObjectMapper进行json反序列化，最后返回一个User对象

虽然RestTemplate能够调用远程服务，但是这样还存在着很多问题：  
1、请求地址http://127.0.0.1:8081/findById硬编码了，如果更换环境，那么需要更改大量的代码  
2、并没有一个中心来控制并管理provider和consumer之间的关系与调用  
3、使用RestTemplate调用远程服务代码开发量相对而言大，现在的Demo是业务简单，只需要简单调用getForObject就能获取数据。事实上，RestTemplate还有大量基于Http协议的方法，比如delete()、getForEntity()、getForObject()、put()、headForHeaders()等。但是在后期的SpringCloud学习过程中，Feign作为SpringCloud的核心组件，用于远程服务调用，也是基于Http协议，并且支持注解开发，能够大量减少开发量

[https_github.com_291685399_springcloud-learning_tree_master_springcloud-eureka01]: https://github.com/291685399/springcloud-learning/tree/master/springcloud-eureka01
[20190621204717662.png]: /images/20220109/76bef2f5f3044e2886563354e0ec27fc.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1NjIwNTAx_size_16_color_FFFFFF_t_70]: /images/20220109/e02aa3acd8724c85b23b6ea43995d64a.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1NjIwNTAx_size_16_color_FFFFFF_t_70 1]: /images/20220109/037043b43d4a4375a2aea8d0a87d2707.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1NjIwNTAx_size_16_color_FFFFFF_t_70 2]: /images/20220109/e7bd6a092cab433b9f8704a40e9c3d91.png