一、概述
spring框架提供的RestTemplate類可用於在應用中調用rest服務，它簡化了與http服務的通信方式，統一了RESTful的標准，封裝了http鏈接， 我們只需要傳入url及返回值類型即可。相較於之前常用的HttpClient，RestTemplate是一種更優雅的調用RESTful服務的方式。
在Spring應用程序中訪問第三方REST服務與使用Spring RestTemplate類有關。RestTemplate類的設計原則與許多其他Spring *模板類(例如JdbcTemplate、JmsTemplate)相同，為執行復雜任務提供了一種具有默認行為的簡化方法。
RestTemplate默認依賴JDK提供http連接的能力（HttpURLConnection），如果有需要的話也可以通過setRequestFactory方法替換為例如 Apache HttpComponents、Netty或OkHttp等其它HTTP library。
考慮到RestTemplate類是為調用REST服務而設計的，因此它的主要方法與REST的基礎緊密相連就不足為奇了，后者是HTTP協議的方法:HEAD、GET、POST、PUT、DELETE和OPTIONS。例如，RestTemplate類具有headForHeaders()、getForObject()、postForObject()、put()和delete()等方法。
二、實現
最新api地址：https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/web/client/RestTemplate.html
RestTemplate包含以下幾個部分：
- HttpMessageConverter 對象轉換器
- ClientHttpRequestFactory 默認是JDK的HttpURLConnection
- ResponseErrorHandler 異常處理
- ClientHttpRequestInterceptor 請求攔截器
常規配置
public MyRestClientService(RestTemplateBuilder restTemplateBuilder) {
this.restTemplate = restTemplateBuilder
.basicAuthorization("username", "password")
.setConnectTimeout(3000)
.setReadTimeout(5000)
.rootUri("http://api.example.com/")
.build();
} |
ClientHttpRequestInterceptor
學習使用帶有Spring RestTemplate的ClientHttpRequestInterceptor，以Spring AOP風格記錄請求和響應頭和主體。
攔截器記錄請求和響應
import org.slf4j.Logger;import org.slf4j.LoggerFactory;
import org.springframework.http.HttpRequest;
import org.springframework.http.client.ClientHttpRequestExecution;
import org.springframework.http.client.ClientHttpRequestInterceptor;
import org.springframework.http.client.ClientHttpResponse;
import org.springframework.util.StreamUtils;
import java.io.IOException;
import java.nio.charset.Charset;
public class RequestResponseLoggingInterceptor implements ClientHttpRequestInterceptor {
private final Logger log = LoggerFactory.getLogger(this.getClass());
@Override
public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) throws IOException
{
logRequest(request, body);
ClientHttpResponse response = execution.execute(request, body);
logResponse(response);
//Add optional additional headers
response.getHeaders().add("headerName", "VALUE");
return response;
}
private void logRequest(HttpRequest request, byte[] body) throws IOException
{
if (log.isDebugEnabled())
{
log.debug("===========================request begin================================================");
log.debug("URI : {}", request.getURI());
log.debug("Method : {}", request.getMethod());
log.debug("Headers : {}", request.getHeaders());
log.debug("Request body: {}", new String(body, "UTF-8"));
log.debug("==========================request end================================================");
}
}
private void logResponse(ClientHttpResponse response) throws IOException
{
if (log.isDebugEnabled())
{
log.debug("============================response begin==========================================");
log.debug("Status code : {}", response.getStatusCode());
log.debug("Status text : {}", response.getStatusText());
log.debug("Headers : {}", response.getHeaders());
log.debug("Response body: {}", StreamUtils.copyToString(response.getBody(), Charset.defaultCharset()));
log.debug("=======================response end=================================================");
}
}
} |
注冊ClientHttpRequestInterceptor
@Bean
public RestTemplate restTemplate(){
RestTemplate restTemplate = new RestTemplate();
restTemplate.setRequestFactory(newBufferingClientHttpRequestFactory(clientHttpRequestFactory()));
restTemplate.setMessageConverters(Collections.singletonList(mappingJacksonHttpMessageConverter()));
restTemplate.setInterceptors( Collections.singletonList(newRequestResponseLoggingInterceptor()) );
return restTemplate;
} |
三、請求示例
GET
private static void getEmployees(){
final String uri = "http://localhost:8080/springrestexample/employees";
RestTemplate restTemplate = new RestTemplate();
String result = restTemplate.getForObject(uri, String.class);
System.out.println(result);
} |
使用RestTemplate定制HTTP頭文件
private static void getEmployees(){
final String uri = "http://localhost:8080/springrestexample/employees";
RestTemplate restTemplate = new RestTemplate();
HttpHeaders headers = new HttpHeaders();
headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));
HttpEntity<String> entity = new HttpEntity<String>("parameters", headers);
ResponseEntity<String> result = restTemplate.exchange(uri, HttpMethod.GET, entity, String.class);
System.out.println(result);
} |
Get請求獲取響應為一個對象
private static void getEmployees(){
final String uri = "http://localhost:8080/springrestexample/employees";
RestTemplate restTemplate = new RestTemplate();
EmployeeListVO result = restTemplate.getForObject(uri, EmployeeListVO.class);
System.out.println(result);
} |
URL 參數
private static void getEmployeeById(){
final String uri = "http://localhost:8080/springrestexample/employees/{id}";
Map<String, String> params = new HashMap<String, String>();
params.put("id", "1");
RestTemplate restTemplate = new RestTemplate();
EmployeeVO result = restTemplate.getForObject(uri, EmployeeVO.class, params);
System.out.println(result);
} |
POST
private static void createEmployee(){
final String uri = "http://localhost:8080/springrestexample/employees";
EmployeeVO newEmployee = new EmployeeVO(-1, "Adam", "Gilly", "test@email.com");
RestTemplate restTemplate = new RestTemplate();
EmployeeVO result = restTemplate.postForObject( uri, newEmployee, EmployeeVO.class);
System.out.println(result);
} |
Submit Form Data
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
MultiValueMap<String, String> map= new LinkedMultiValueMap<>();
map.add("id", "1");
HttpEntity<MultiValueMap<String, String>> request = new HttpEntity<>(map, headers);
RestTemplate restTemplate = new RestTemplate();
EmployeeVO result = restTemplate.postForObject( uri, request, EmployeeVO.class);
System.out.println(result); |
PUT
private static void updateEmployee(){
final String uri = "http://localhost:8080/springrestexample/employees/{id}";
Map<String, String> params = new HashMap<String, String>();
params.put("id", "2");
EmployeeVO updatedEmployee = new EmployeeVO(2, "New Name", "Gilly", "test@email.com");
RestTemplate restTemplate = new RestTemplate();
restTemplate.put ( uri, updatedEmployee, params);
} |
Simple PUT
Foo updatedInstance = new Foo("newName");
updatedInstance.setId(createResponse.getBody().getId());
String resourceUrl =
fooResourceUrl + '/' + createResponse.getBody().getId();
HttpEntity<Foo> requestUpdate = new HttpEntity<>(updatedInstance, headers);
template.exchange(resourceUrl, HttpMethod.PUT, requestUpdate, Void.class); |
使用.exchange和請求回調
RequestCallback requestCallback(final Foo updatedInstance) {
return clientHttpRequest -> {
ObjectMapper mapper = new ObjectMapper();
mapper.writeValue(clientHttpRequest.getBody(), updatedInstance);
clientHttpRequest.getHeaders().add(
HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE);
clientHttpRequest.getHeaders().add(
HttpHeaders.AUTHORIZATION, "Basic " + getBase64EncodedLogPass());
};
} |
DELETE
private static void deleteEmployee(){
final String uri = "http://localhost:8080/springrestexample/employees/{id}";
Map<String, String> params = new HashMap<String, String>();
params.put("id", "2");
RestTemplate restTemplate = new RestTemplate();
restTemplate.delete ( uri, params );
} |
參考資料：
https://howtodoinjava.com/spring-restful/spring-restful-client-resttemplate-example/
https://www.xncoding.com/2017/07/06/spring/sb-restclient.html
https://www.baeldung.com/rest-template
