RestTemplate with custom HTTP headers

Spring Framework’s RestTemplate provides simple ways to make requests to RESTful services. When you want to set additional HTTP headers to such requests, then a tiny bit of more work is needed.

Starting from Spring Framework version 3.0.2 it is possible to utilise HttpEntity class. An example of querying a PDF file from a server:

private static final String APPLICATION_PDF = "application/pdf";

RestTemplate restTemplate = new RestTemplate();

@Test
public void acceptHeaderUsingHttpEntity() throws Exception {
  HttpHeaders headers = new HttpHeaders();
  headers.setAccept(singletonList(MediaType.valueOf(APPLICATION_PDF)));

  ResponseEntity<byte[]> response = restTemplate.exchange("http://example.com/file/123",
      GET,
      new HttpEntity<byte[]>(headers),
      byte[].class);

  String responseText = PdfTextExtractor.getTextFromPage(new PdfReader(response.getBody()), 1);
  assertEquals("Some text in PDF file", responseText);
}

(I’m using iText here for PDF file manipulation.)

Starting from Spring Framework version 3.1 there is a more powerful alternative — ClientHttpRequestInterceptor. ClientHttpRequestInterceptor.intercept() enables more control over the HTTP request that will be sent. Here’s the simple example again, using the interceptor concept:

private static final String APPLICATION_PDF = "application/pdf";

RestTemplate restTemplate = new RestTemplate();

@Test
public void acceptHeaderUsingHttpRequestInterceptors() throws Exception {
  ClientHttpRequestInterceptor acceptHeaderPdf = new AcceptHeaderHttpRequestInterceptor(
      APPLICATION_PDF);

  restTemplate.setInterceptors(singletonList(acceptHeaderPdf));

  byte[] response = restTemplate.getForObject("http://example.com/file/123", byte[].class);

  String responseText = PdfTextExtractor.getTextFromPage(new PdfReader(response), 1);
  assertEquals("Some text in PDF file", responseText);
}

class AcceptHeaderHttpRequestInterceptor implements ClientHttpRequestInterceptor {
  private final String headerValue;

  public AcceptHeaderHttpRequestInterceptor(String headerValue) {
    this.headerValue = headerValue;
  }

  @Override
  public ClientHttpResponse intercept(HttpRequest request, byte[] body,
      ClientHttpRequestExecution execution) throws IOException {

    HttpRequestWrapper requestWrapper = new HttpRequestWrapper(request);
    requestWrapper.getHeaders().setAccept(singletonList(MediaType.valueOf(headerValue)));

    return execution.execute(requestWrapper, body);
  }
}