微服务学习系列8：RestTemplate

系列文章目录

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目录

系列文章目录

前言

一、Calling REST Services with RestTemplate

RestTemplateAutoConfiguration 

RestTemplateConfig 

栗子参考

getForObject

getForEntity

postForObject

交换资源 

总结

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前言

在java的http开发中，访问第三方网络接口，通常使用的连接工具为HttpClient和OKHttp。

这两种连接工具，使用起来比较复杂，新手容易出问题。如果我们使用的是spring框架，可以使用RestTemplate来进行http连接请求。

RestTemplate默认的连接方式是java中的HttpConnection，可以使用ClientHttpRequestFactory指定不同的HTTP连接方式。

官方文档：

https://docs.spring.io/spring-boot/docs/2.0.2.RELEASE/reference/htmlsingle/#boot-features-resttemplate

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一、Calling REST Services with RestTemplate

RestTemplateAutoConfiguration 

@Configuration(
    proxyBeanMethods = false
)
@AutoConfigureAfter({HttpMessageConvertersAutoConfiguration.class})
@ConditionalOnClass({RestTemplate.class})
@Conditional({NotReactiveWebApplicationCondition.class})
public class RestTemplateAutoConfiguration {
    public RestTemplateAutoConfiguration() {
    }

    @Bean
    @Lazy
    @ConditionalOnMissingBean
    public RestTemplateBuilder restTemplateBuilder(ObjectProvider messageConverters, ObjectProvider restTemplateCustomizers, ObjectProvider> restTemplateRequestCustomizers) {
        RestTemplateBuilder builder = new RestTemplateBuilder(new RestTemplateCustomizer[0]);
        HttpMessageConverters converters = (HttpMessageConverters)messageConverters.getIfUnique();
        if (converters != null) {
            builder = builder.messageConverters(converters.getConverters());
        }

        builder = this.addCustomizers(builder, restTemplateCustomizers, RestTemplateBuilder::customizers);
        builder = this.addCustomizers(builder, restTemplateRequestCustomizers, RestTemplateBuilder::requestCustomizers);
        return builder;
    }

    private  RestTemplateBuilder addCustomizers(RestTemplateBuilder builder, ObjectProvider objectProvider, BiFunction, RestTemplateBuilder> method) {
        List customizers = (List)objectProvider.orderedStream().collect(Collectors.toList());
        return !customizers.isEmpty() ? (RestTemplateBuilder)method.apply(builder, customizers) : builder;
    }

    static class NotReactiveWebApplicationCondition extends NoneNestedConditions {
        NotReactiveWebApplicationCondition() {
            super(ConfigurationPhase.PARSE_CONFIGURATION);
        }

        @ConditionalOnWebApplication(
            type = Type.REACTIVE
        )
        private static class ReactiveWebApplication {
            private ReactiveWebApplication() {
            }
        }
    }
}

RestTemplateConfig 

还记得RestTemplate吗？它是Spring为开发人员提供的一款访问外部restful api的利器，其针对每个HTTP方法进行了更高级别的抽象。在Spring Boot应用中使用RestTemplate极其简单，只需要像下面这样声明一个配置类，然后通过@Resource或@Autowired注解将RestTemplate实例注入到业务类中即可。 

/**
 * RestTemplate工具类，主要用来提供RestTemplate对象
 *
 *
 * @author yangyanping
 * @date 2023-03-18
 */
@Slf4j
@Configuration
public class RestTemplateConfig {
    @Bean
    public RestTemplate restTemplate(RestTemplateBuilder builder) {
        log.info("RestTemplateConfig create restTemplate start ......");

        builder.setConnectTimeout(Duration.ofSeconds(6000))
                .setReadTimeout(Duration.ofSeconds(6000));
        log.info("RestTemplateConfig create restTemplate end ......");

        return builder.build();
    }
}

栗子参考

@Service
public class MyService {
    private final RestTemplate restTemplate;

    public MyService(RestTemplateBuilder restTemplateBuilder) {
        this.restTemplate = restTemplateBuilder.build();
    }

    public BookDTO someRestCall(Integer bookId) {

        BookDetailQuery query = new BookDetailQuery();
        query.setBookId(bookId);
        return this.restTemplate.postForObject("http://www.test.com/api/author/web/book/getById", query, BookDTO.class);
    }
}

getForObject

    GET资源，返回的请求体将映射为一个对象

• getForObject(URI url, Class responseType)

        栗子：根据书籍ID查询书籍信息请求

    /**
     * 查询书籍明细
     */
    @GetMapping("getById/{bookId}")
    public BookInfoDTO getById(@PathVariable Integer bookId) {
        BookInfoIdQuery query = new BookInfoIdQuery();
        query.setBookId(bookId);

        ApiResult apiResult = new RpcExecutor().invokeMethod(
                "book-api",
                "BookController.getById",
                (param) -> bookService.getById(getProtocol(), param),
                query);

        return apiResult.getData();
    }

@Service
public class MyService {
    private final RestTemplate restTemplate;

    public MyService(RestTemplateBuilder restTemplateBuilder) {
        this.restTemplate = restTemplateBuilder.build();
    }

    public BookDTO getById(Integer bookId) {
        return restTemplate.getForObject("https://www.test.com/api/test/book/getById/21248", BookDTO.class);
    }
}

• getForObject(String url, Class responseType, Map uriVariables) 

    /**
     * 查询章节信息
     */
    public ChapterInfoDTO getChapter() {
        Map map = Maps.newHashMap();
        map.put("bookId", 21248);
        map.put("position", 1);
        return restTemplate.getForObject("https://www.test.com/api/test/book/getChapter?bookId={bookId}&position={position}", ChapterInfoDTO.class, map);
    }

• getForObject(String url, Class responseType, Object... uriVariables) 

    /**
     * 查询章节信息
     */
    public ChapterInfoDTO getChapter() {
        return restTemplate.getForObject("https://www.test.com/api/test/book/getChapter?bookId={bookId}&position={position}", ChapterInfoDTO.class, new Object[]{21248, 1});
    }

getForEntity

发送一个HTTP GET请求，返回的ResponseEntity包含了响应体所映射成的对象

• ResponseEntity getForEntity(URI url, Class responseType)

    public ResponseEntity getById() {
        return restTemplate.getForEntity("http://www.test.com/api/test/book/getById/21248", BookDTO.class);
    }

• ResponseEntity getForEntity(String url, Class responseType, Map uriVariables) 

      /**
       * 查询章节信息
       */
      public ResponseEntity getChapter() {
          Map map = Maps.newHashMap();
          map.put("bookId", 21248);
          map.put("position", 1);
          return restTemplate.getForEntity("http://www.test.com/api/test/book/getChapter?bookId={bookId}&position={position}", ChapterInfoDTO.class, map);
      }

• ResponseEntity getForEntity(String url, Class responseType, Object... uriVariables)
  

    /**
       * 查询章节信息
       */
      public ResponseEntity getChapter() {
          return restTemplate.getForEntity("https://www.test.com/api/test/book/getChapter?bookId={bookId}&position={position}", ChapterInfoDTO.class, new Object[]{21248, 1});
      }

postForObject

POST数据，返回的请求体将匹配为一个对象

参数含义

String url 请求的URL路径
Object request 请求的body,通过@RequestBody接收传过去的值
Class responseType 请求完成之后返回的结果类型
Map< String,?> uriVariables POST请求中要传过去的参数

• postForObject(URI url, @Nullable Object request, Class responseType)

    public String queryBookCategory() {
        BookCategoryListQry query = new BookCategoryListQry();
        query.setParentId(0);

        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.valueOf("application/json;UTF-8"));
        HttpEntity httpEntity = new HttpEntity<>(JSON.toJSONString(query), headers);

        return this.restTemplate.postForObject("http://www.test.com/api/test/book/listBookCategory", httpEntity, String.class);
}

通过RestTemplate发送Http接口调用时，对于请求需要携带请求头时，需要额外再进行配置。

给请求携带请求头，有两种实现的方式：

方式一：在每次发送请求时，构建一个HttpEntity对象，传入请求参数与请求头。

方式二：通过配置RestTemplate，使通过RestTemplate调用的http请求都携带上请求头。

• postForEntity(String url, @Nullable Object request, Class responseType, Object... uriVariables)

    public ResponseEntity queryBookCategory() {
        BookCategoryListQry query = new BookCategoryListQry();
        query.setParentId(0);

        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.valueOf("application/json;UTF-8"));
        HttpEntity httpEntity = new HttpEntity<>(JSON.toJSONString(query), headers);

        return this.restTemplate.postForEntity("https://www.test.com/api/test/book/listBookCategory", httpEntity, String.class);
    }

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交换资源 

在URL上执行特定的HTTP方法，返回包含对象的ResponseEntity，这个对象是从响应体中映射得到的

•  exchange(String url, HttpMethod method, @Nullable HttpEntity requestEntity, Class responseType, Object... uriVariables) 

参数	说明
url	调用的url地址
method	枚举值，HTTP方法：GET、POST、PUT、DELETE等
requestEntity	发起请求时携带的对象：请求头header 和/或 请求体body
responseType	请求响应对象的类型
uriVariables	就是针对url中的@PathVariable参数，可变长度参数列表

    public ResponseEntity queryBookCategory() {
        BookCategoryListQry query = new BookCategoryListQry();
        query.setParentId(0);

        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.valueOf("application/json;UTF-8"));
        HttpEntity httpEntity = new HttpEntity<>(JSON.toJSONString(query), headers);

        return this.restTemplate.exchange("https://www.test.com/api/test/book/listBookCategory", HttpMethod.POST, httpEntity, String.class);
    }

• exchange(String url, HttpMethod method, @Nullable HttpEntity requestEntity, ParameterizedTypeReference responseType, Object... uriVariables)
  
  与上面重载的唯一区别是responseType类型变成了ParameterizedTypeReference，其它参数说明不变.
  设计这个类的目的：是允许传递泛型类型。用法建议是使用匿名类

  ParameterizedTypeReference> parameterized = new ParameterizedTypeReference>() {};

栗子：

    public ResponseEntity> queryBookCategory() {
        BookCategoryListQry query = new BookCategoryListQry();
        query.setParentId(0);

        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.valueOf("application/json;UTF-8"));
        HttpEntity httpEntity = new HttpEntity<>(JSON.toJSONString(query), headers);
        String url = "http://www.test.com/api/test/book/listBookCategory";
        ParameterizedTypeReference> parameterized = new ParameterizedTypeReference>() {
        };
       return restTemplate.exchange(url,HttpMethod.POST,httpEntity,parameterized);
    }

总结