使用 Spring RestTemplate 调用 rest 服务时自定义请求头（custom HTTP headers）

在 Spring 3.0 中可以通过 HttpEntity 对象自定义请求头信息，如：

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);
}

在 Spring 3.1 中有了一个更强大的替代接口 ClientHttpRequestInterceptor，这个接口只有一个方法： intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution)，下面是一个例子：

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);
}
}

原文：http://svenfila.wordpress.com/2012/01/05/resttemplate-with-custom-http-headers/