Spring Boot 入门 - 进阶篇（4）- REST访问(RestTemplate)

经常需要发送一个GET/POST请求到其他系统(REST API)，通过JDK自带的HttpURLConnection、Apache HttpClient、Netty 4、OkHTTP 2/3都可以实现。

HttpClient的使用：http://rensanning.iteye.com/blog/1550436

Spring的RestTemplate封装了这些库的实现，使用起来更简洁。

RestTemplate包含以下几个部分：

• HttpMessageConverter 对象转换器
• ClientHttpRequestFactory 默认是JDK的HttpURLConnection
• ResponseErrorHandler 异常处理
• ClientHttpRequestInterceptor 请求拦截器

@Service
public class AccountService {

    @Autowired
    private RestTemplate restTemplate;

    // ...

}

（1）发送GET请求（getForObject()、getForEntity()、exchange()）

// 1-getForObject()
User user1 = this.restTemplate.getForObject(uri, User.class);

// 2-getForEntity()
ResponseEntity<User> responseEntity1 = this.restTemplate.getForEntity(uri, User.class);
HttpStatus statusCode = responseEntity1.getStatusCode();
HttpHeaders header = responseEntity1.getHeaders();
User user2 = responseEntity1.getBody();

// 3-exchange()
RequestEntity requestEntity = RequestEntity.get(new URI(uri)).build();
ResponseEntity<User> responseEntity2 = this.restTemplate.exchange(requestEntity, User.class);
User user3 = responseEntity2.getBody();

（2）发送POST请求（postForObject()、postForEntity()、exchange()）

// 1-postForObject()
User user1 = this.restTemplate.postForObject(uri, user, User.class);

// 2-postForEntity()
ResponseEntity<User> responseEntity1 = this.restTemplate.postForEntity(uri, user, User.class);

// 3-exchange()
RequestEntity<User> requestEntity = RequestEntity.post(new URI(uri)).body(user);
ResponseEntity<User> responseEntity2 = this.restTemplate.exchange(requestEntity, User.class);

（3）设置HTTP Header信息

// 1-Content-Type
RequestEntity<User> requestEntity = RequestEntity
        .post(new URI(uri))
        .contentType(MediaType.APPLICATION_JSON)
        .body(user);

// 2-Accept
RequestEntity<User> requestEntity = RequestEntity
        .post(new URI(uri))
        .accept(MediaType.APPLICATION_JSON)
        .body(user);

// 3-Other
RequestEntity<User> requestEntity = RequestEntity
        .post(new URI(uri))
        .header("Authorization", "Basic " + base64Credentials)
        .body(user);

（4）异常处理

捕获HttpServerErrorException

int retryCount = 0;
while (true) {
    try {
        responseEntity = restTemplate.exchange(requestEntity, String.class);
        break;
    } catch (HttpServerErrorException e) {
        if (retryCount == 3) {
            throw e;
        }
        retryCount++;
    }
}

自定义异常处理

public class CustomErrorHandler extends DefaultResponseErrorHandler {

    @Override
    public void handleError(ClientHttpResponse response) throws IOException {

    }

}

@Configuration
public class RestClientConfig {

    @Bean
    public RestTemplate restTemplate() {
        RestTemplate restTemplate = new RestTemplate();
        restTemplate.setErrorHandler(new CustomErrorHandler());
        return restTemplate;
    }

}

（5）设置超时时间

@Configuration
public class RestClientConfig {

    @Bean
    public RestTemplate restTemplate() {
        return new RestTemplate(clientHttpRequestFactory());
    }

    private ClientHttpRequestFactory clientHttpRequestFactory() {
        HttpComponentsClientHttpRequestFactory factory = new HttpComponentsClientHttpRequestFactory();
        factory.setReadTimeout(2000);
        factory.setConnectTimeout(2000);
        return factory;
    }
}

（6）设置连接池

@Configuration
public class RestClientConfig {

  @Bean
  public ClientHttpRequestFactory httpRequestFactory() {
    return new HttpComponentsClientHttpRequestFactory(httpClient());
  }

  @Bean
  public RestTemplate restTemplate() {
    return new RestTemplate(httpRequestFactory());
  }

  @Bean
  public HttpClient httpClient() {
    Registry<ConnectionSocketFactory> registry = RegistryBuilder.<ConnectionSocketFactory> create()
		.register("http", PlainConnectionSocketFactory.getSocketFactory())
		.register("https", SSLConnectionSocketFactory.getSocketFactory())
		.build();
    PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager(registry);
    connectionManager.setMaxTotal(5);
    connectionManager.setDefaultMaxPerRoute(5);

    RequestConfig requestConfig = RequestConfig.custom()
		.setSocketTimeout(8000)
		.setConnectTimeout(8000)
		.setConnectionRequestTimeout(8000)
		.build();

    return HttpClientBuilder.create()
		.setDefaultRequestConfig(requestConfig)
		.setConnectionManager(connectionManager)
		.build();
  }

}

（7）发送文件

MultiValueMap<String, Object> multiPartBody = new LinkedMultiValueMap<>();
multiPartBody.add("file", new ClassPathResource("/tmp/user.txt"));
RequestEntity<MultiValueMap<String, Object>> requestEntity = RequestEntity
        .post(uri)
        .contentType(MediaType.MULTIPART_FORM_DATA)
        .body(multiPartBody);

（8）下载文件

// 小文件
RequestEntity requestEntity = RequestEntity.get(uri).build();
ResponseEntity<byte[]> responseEntity = restTemplate.exchange(requestEntity, byte[].class);
byte[] downloadContent = responseEntity.getBody();

// 大文件
ResponseExtractor<ResponseEntity<File>> responseExtractor = new ResponseExtractor<ResponseEntity<File>>() {
    @Override
    public ResponseEntity<File> extractData(ClientHttpResponse response) throws IOException {
        File rcvFile = File.createTempFile("rcvFile", "zip");
        FileCopyUtils.copy(response.getBody(), new FileOutputStream(rcvFile));
        return ResponseEntity.status(response.getStatusCode()).headers(response.getHeaders()).body(rcvFile);
    }
};
File getFile = this.restTemplate.execute(targetUri, HttpMethod.GET, null, responseExtractor);

（9）Spring Boot的RestTemplateBuilder

全局设置

@Component
public class CustomRestTemplateCustomizer implements RestTemplateCustomizer {
    @Override
    public void customize(RestTemplate restTemplate) {
        new RestTemplateBuilder()
                .detectRequestFactory(false)
                .basicAuthorization("username", "password")
                .uriTemplateHandler(new OkHttp3ClientHttpRequestFactory())
                .errorHandler(new CustomResponseErrorHandler())
                .configure(restTemplate);
    }
}

单独设置

@Service
public class MyRestClientService {

    private RestTemplate restTemplate;

    public MyRestClientService(RestTemplateBuilder restTemplateBuilder) {
        this.restTemplate = restTemplateBuilder
            .basicAuthorization("username", "password")
            .setConnectTimeout(3000)
            .setReadTimeout(5000)
            .rootUri("http://api.example.com/")
            .errorHandler(new CustomResponseErrorHandler())
            .additionalMessageConverters(new CustomHttpMessageConverter())
            .uriTemplateHandler(new OkHttp3ClientHttpRequestFactory())
            .build();
    }

    public String site() {
        return this.restTemplate.getForObject("http://rensanning.iteye.com/", String.class);
    }

}

参考：
http://qiita.com/kazuki43zoo/items/7cf3c8ca4f6f2283cefb
http://terasolunaorg.github.io/guideline/5.1.0.RELEASE/ja/ArchitectureInDetail/RestClient.html