/*
 * Copyright 2002-2012 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.client;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.URI;
import java.net.URISyntaxException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.http.client.ClientHttpRequest;
import org.springframework.http.client.ClientHttpRequestFactory;
import org.springframework.http.client.ClientHttpResponse;
import org.springframework.http.client.support.InterceptingHttpAccessor;
import org.springframework.http.converter.ByteArrayHttpMessageConverter;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.ResourceHttpMessageConverter;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.http.converter.feed.AtomFeedHttpMessageConverter;
import org.springframework.http.converter.feed.RssChannelHttpMessageConverter;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.http.converter.json.MappingJacksonHttpMessageConverter;
import org.springframework.http.converter.xml.Jaxb2RootElementHttpMessageConverter;
import org.springframework.http.converter.xml.SourceHttpMessageConverter;
import org.springframework.http.converter.xml.XmlAwareFormHttpMessageConverter;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.web.util.UriTemplate;
import org.springframework.web.util.UriUtils;

/**
 * <strong>The central class for client-side HTTP access.</strong> It simplifies communication with HTTP servers, and
 * enforces RESTful principles. It handles HTTP connections, leaving application code to provide URLs (with possible
 * template variables) and extract results.
 *
 * <p>The main entry points of this template are the methods named after the six main HTTP methods:
 * <table>
 * <tr><th>HTTP method</th><th>RestTemplate methods</th></tr>
 * <tr><td>DELETE</td><td>{@link #delete}</td></tr>
 * <tr><td>GET</td><td>{@link #getForObject}</td></tr>
 * <tr><td></td><td>{@link #getForEntity}</td></tr>
 * <tr><td>HEAD</td><td>{@link #headForHeaders}</td></tr>
 * <tr><td>OPTIONS</td><td>{@link #optionsForAllow}</td></tr>
 * <tr><td>POST</td><td>{@link #postForLocation}</td></tr>
 * <tr><td></td><td>{@link #postForObject}</td></tr>
 * <tr><td>PUT</td><td>{@link #put}</td></tr>
 * <tr><td>any</td><td>{@link #exchange}</td></tr>
 * <tr><td></td><td>{@link #execute}</td></tr> </table>
 *
 * <p>The {@code exchange} and {@code execute} methods are generalized versions of the more specific methods listed
 * above them. They support additional, less frequently used combinations including support for requests using the
 * HTTP PATCH method. However, note that the underlying HTTP library must also support the desired combination.</p>
 *
 * <p>For each of these HTTP methods, there are three corresponding Java methods in the {@code RestTemplate}. Two
 * variant take a {@code String} URI as first argument (eg. {@link #getForObject(String, Class, Object[])}, {@link
 * #getForObject(String, Class, Map)}), and are capable of substituting any {@linkplain UriTemplate URI templates} in
 * that URL using either a {@code String} variable arguments array, or a {@code Map<String, String>}. The string varargs
 * variant expands the given template variables in order, so that
 * <pre>
 * String result = restTemplate.getForObject("http://example.com/hotels/{hotel}/bookings/{booking}", String.class,"42",
 * "21");
 * </pre>
 * will perform a GET on {@code http://example.com/hotels/42/bookings/21}. The map variant expands the template based on
 * variable name, and is therefore more useful when using many variables, or when a single variable is used multiple
 * times. For example:
 * <pre>
 * Map&lt;String, String&gt; vars = Collections.singletonMap("hotel", "42");
 * String result = restTemplate.getForObject("http://example.com/hotels/{hotel}/rooms/{hotel}", String.class, vars);
 * </pre>
 * will perform a GET on {@code http://example.com/hotels/42/rooms/42}. Alternatively, there are {@link URI} variant
 * methods ({@link #getForObject(URI, Class)}), which do not allow for URI templates, but allow you to reuse a single,
 * expanded URI multiple times.
 *
 * <p>Furthermore, the {@code String}-argument methods assume that the URL String is unencoded. This means that
 * <pre>
 * restTemplate.getForObject("http://example.com/hotel list");
 * </pre>
 * will perform a GET on {@code http://example.com/hotel%20list}. As a result, any URL passed that is already encoded
 * will be encoded twice (i.e. {@code http://example.com/hotel%20list} will become {@code
 * http://example.com/hotel%2520list}). If this behavior is undesirable, use the {@code URI}-argument methods, which
 * will not perform any URL encoding.
 *
 * <p>Objects passed to and returned from these methods are converted to and from HTTP messages by {@link
 * HttpMessageConverter} instances. Converters for the main mime types are registered by default, but you can also write
 * your own converter and register it via the {@link #setMessageConverters messageConverters} bean property.
 *
 * <p>This template uses a {@link org.springframework.http.client.SimpleClientHttpRequestFactory} and a {@link
 * DefaultResponseErrorHandler} as default strategies for creating HTTP connections or handling HTTP errors,
 * respectively. These defaults can be overridden through the {@link #setRequestFactory(ClientHttpRequestFactory)
 * requestFactory} and {@link #setErrorHandler(ResponseErrorHandler) errorHandler} bean properties.
 *
 * @author Arjen Poutsma
 * @see HttpMessageConverter
 * @see RequestCallback
 * @see ResponseExtractor
 * @see ResponseErrorHandler
 * @since 3.0
 */
public class RestTemplate extends InterceptingHttpAccessor implements RestOperations {

	private static final boolean jaxb2Present =
			ClassUtils.isPresent("javax.xml.bind.Binder", RestTemplate.class.getClassLoader());

	private static final boolean jackson2Present =
			ClassUtils.isPresent("com.fasterxml.jackson.databind.ObjectMapper", RestTemplate.class.getClassLoader()) &&
					ClassUtils.isPresent("com.fasterxml.jackson.core.JsonGenerator", RestTemplate.class.getClassLoader());

	private static final boolean jacksonPresent =
			ClassUtils.isPresent("org.codehaus.jackson.map.ObjectMapper", RestTemplate.class.getClassLoader()) &&
					ClassUtils.isPresent("org.codehaus.jackson.JsonGenerator", RestTemplate.class.getClassLoader());

	private static boolean romePresent =
			ClassUtils.isPresent("com.sun.syndication.feed.WireFeed", RestTemplate.class.getClassLoader());


	private final ResponseExtractor<HttpHeaders> headersExtractor = new HeadersExtractor();

	private List<HttpMessageConverter<?>> messageConverters = new ArrayList<HttpMessageConverter<?>>();

	private ResponseErrorHandler errorHandler = new DefaultResponseErrorHandler();


	/** Create a new instance of the {@link RestTemplate} using default settings. */
	public RestTemplate() {
		this.messageConverters.add(new ByteArrayHttpMessageConverter());
		this.messageConverters.add(new StringHttpMessageConverter());
		this.messageConverters.add(new ResourceHttpMessageConverter());
		this.messageConverters.add(new SourceHttpMessageConverter());
		this.messageConverters.add(new XmlAwareFormHttpMessageConverter());
		if (romePresent) {
			this.messageConverters.add(new AtomFeedHttpMessageConverter());
			this.messageConverters.add(new RssChannelHttpMessageConverter());
		}
		if (jaxb2Present) {
			this.messageConverters.add(new Jaxb2RootElementHttpMessageConverter());
		}
		if (jackson2Present) {
			this.messageConverters.add(new MappingJackson2HttpMessageConverter());
		}
		else if (jacksonPresent) {
			this.messageConverters.add(new MappingJacksonHttpMessageConverter());
		}
	}

	/**
	 * Create a new instance of the {@link RestTemplate} based on the given {@link ClientHttpRequestFactory}.
	 * @param requestFactory HTTP request factory to use
	 * @see org.springframework.http.client.SimpleClientHttpRequestFactory
	 * @see org.springframework.http.client.CommonsClientHttpRequestFactory
	 */
	public RestTemplate(ClientHttpRequestFactory requestFactory) {
		this();
		setRequestFactory(requestFactory);
	}


	/**
	 * Set the message body converters to use. These converters are used to convert from and to HTTP requests and
	 * responses.
	 */
	public void setMessageConverters(List<HttpMessageConverter<?>> messageConverters) {
		Assert.notEmpty(messageConverters, "'messageConverters' must not be empty");
		this.messageConverters = messageConverters;
	}

	/** Returns the message body converters. These converters are used to convert from and to HTTP requests and responses. */
	public List<HttpMessageConverter<?>> getMessageConverters() {
		return this.messageConverters;
	}

	/** Set the error handler. */
	public void setErrorHandler(ResponseErrorHandler errorHandler) {
		Assert.notNull(errorHandler, "'errorHandler' must not be null");
		this.errorHandler = errorHandler;
	}

	/** Return the error handler. By default, this is the {@link DefaultResponseErrorHandler}. */
	public ResponseErrorHandler getErrorHandler() {
		return this.errorHandler;
	}


	// GET

	public <T> T getForObject(String url, Class<T> responseType, Object... urlVariables) throws RestClientException {
		AcceptHeaderRequestCallback requestCallback = new AcceptHeaderRequestCallback(responseType);
		HttpMessageConverterExtractor<T> responseExtractor =
				new HttpMessageConverterExtractor<T>(responseType, getMessageConverters(), logger);
		return execute(url, HttpMethod.GET, requestCallback, responseExtractor, urlVariables);
	}

	public <T> T getForObject(String url, Class<T> responseType, Map<String, ?> urlVariables) throws RestClientException {
		AcceptHeaderRequestCallback requestCallback = new AcceptHeaderRequestCallback(responseType);
		HttpMessageConverterExtractor<T> responseExtractor =
				new HttpMessageConverterExtractor<T>(responseType, getMessageConverters(), logger);
		return execute(url, HttpMethod.GET, requestCallback, responseExtractor, urlVariables);
	}

	public <T> T getForObject(URI url, Class<T> responseType) throws RestClientException {
		AcceptHeaderRequestCallback requestCallback = new AcceptHeaderRequestCallback(responseType);
		HttpMessageConverterExtractor<T> responseExtractor =
				new HttpMessageConverterExtractor<T>(responseType, getMessageConverters(), logger);
		return execute(url, HttpMethod.GET, requestCallback, responseExtractor);
	}

	public <T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Object... urlVariables)
			throws RestClientException {
		AcceptHeaderRequestCallback requestCallback = new AcceptHeaderRequestCallback(responseType);
		ResponseEntityResponseExtractor<T> responseExtractor =
				new ResponseEntityResponseExtractor<T>(responseType);
		return execute(url, HttpMethod.GET, requestCallback, responseExtractor, urlVariables);
	}

	public <T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Map<String, ?> urlVariables)
			throws RestClientException {
		AcceptHeaderRequestCallback requestCallback = new AcceptHeaderRequestCallback(responseType);
		ResponseEntityResponseExtractor<T> responseExtractor =
				new ResponseEntityResponseExtractor<T>(responseType);
		return execute(url, HttpMethod.GET, requestCallback, responseExtractor, urlVariables);
	}

	public <T> ResponseEntity<T> getForEntity(URI url, Class<T> responseType) throws RestClientException {
		AcceptHeaderRequestCallback requestCallback = new AcceptHeaderRequestCallback(responseType);
		ResponseEntityResponseExtractor<T> responseExtractor =
				new ResponseEntityResponseExtractor<T>(responseType);
		return execute(url, HttpMethod.GET, requestCallback, responseExtractor);
	}

	// HEAD

	public HttpHeaders headForHeaders(String url, Object... urlVariables) throws RestClientException {
		return execute(url, HttpMethod.HEAD, null, this.headersExtractor, urlVariables);
	}

	public HttpHeaders headForHeaders(String url, Map<String, ?> urlVariables) throws RestClientException {
		return execute(url, HttpMethod.HEAD, null, this.headersExtractor, urlVariables);
	}

	public HttpHeaders headForHeaders(URI url) throws RestClientException {
		return execute(url, HttpMethod.HEAD, null, this.headersExtractor);
	}

	// POST

	public URI postForLocation(String url, Object request, Object... urlVariables) throws RestClientException {
		HttpEntityRequestCallback requestCallback = new HttpEntityRequestCallback(request);
		HttpHeaders headers = execute(url, HttpMethod.POST, requestCallback, this.headersExtractor, urlVariables);
		return headers.getLocation();
	}

	public URI postForLocation(String url, Object request, Map<String, ?> urlVariables)
			throws RestClientException {
		HttpEntityRequestCallback requestCallback = new HttpEntityRequestCallback(request);
		HttpHeaders headers = execute(url, HttpMethod.POST, requestCallback, this.headersExtractor, urlVariables);
		return headers.getLocation();
	}

	public URI postForLocation(URI url, Object request) throws RestClientException {
		HttpEntityRequestCallback requestCallback = new HttpEntityRequestCallback(request);
		HttpHeaders headers = execute(url, HttpMethod.POST, requestCallback, this.headersExtractor);
		return headers.getLocation();
	}

	public <T> T postForObject(String url, Object request, Class<T> responseType, Object... uriVariables)
			throws RestClientException {
		HttpEntityRequestCallback requestCallback = new HttpEntityRequestCallback(request, responseType);
		HttpMessageConverterExtractor<T> responseExtractor =
				new HttpMessageConverterExtractor<T>(responseType, getMessageConverters(), logger);
		return execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables);
	}

	public <T> T postForObject(String url, Object request, Class<T> responseType, Map<String, ?> uriVariables)
			throws RestClientException {
		HttpEntityRequestCallback requestCallback = new HttpEntityRequestCallback(request, responseType);
		HttpMessageConverterExtractor<T> responseExtractor =
				new HttpMessageConverterExtractor<T>(responseType, getMessageConverters(), logger);
		return execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables);
	}

	public <T> T postForObject(URI url, Object request, Class<T> responseType) throws RestClientException {
		HttpEntityRequestCallback requestCallback = new HttpEntityRequestCallback(request, responseType);
		HttpMessageConverterExtractor<T> responseExtractor =
				new HttpMessageConverterExtractor<T>(responseType, getMessageConverters());
		return execute(url, HttpMethod.POST, requestCallback, responseExtractor);
	}

	public <T> ResponseEntity<T> postForEntity(String url, Object request, Class<T> responseType, Object... uriVariables)
			throws RestClientException {
		HttpEntityRequestCallback requestCallback = new HttpEntityRequestCallback(request, responseType);
		ResponseEntityResponseExtractor<T> responseExtractor =
				new ResponseEntityResponseExtractor<T>(responseType);
		return execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables);
	}

	public <T> ResponseEntity<T> postForEntity(String url,
										   Object request,
										   Class<T> responseType,
										   Map<String, ?> uriVariables)
			throws RestClientException {
		HttpEntityRequestCallback requestCallback = new HttpEntityRequestCallback(request, responseType);
		ResponseEntityResponseExtractor<T> responseExtractor =
				new ResponseEntityResponseExtractor<T>(responseType);
		return execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables);
	}

	public <T> ResponseEntity<T> postForEntity(URI url, Object request, Class<T> responseType) throws RestClientException {
		HttpEntityRequestCallback requestCallback = new HttpEntityRequestCallback(request, responseType);
		ResponseEntityResponseExtractor<T> responseExtractor =
				new ResponseEntityResponseExtractor<T>(responseType);
		return execute(url, HttpMethod.POST, requestCallback, responseExtractor);
	}

	// PUT

	public void put(String url, Object request, Object... urlVariables) throws RestClientException {
		HttpEntityRequestCallback requestCallback = new HttpEntityRequestCallback(request);
		execute(url, HttpMethod.PUT, requestCallback, null, urlVariables);
	}

	public void put(String url, Object request, Map<String, ?> urlVariables) throws RestClientException {
		HttpEntityRequestCallback requestCallback = new HttpEntityRequestCallback(request);
		execute(url, HttpMethod.PUT, requestCallback, null, urlVariables);
	}

	public void put(URI url, Object request) throws RestClientException {
		HttpEntityRequestCallback requestCallback = new HttpEntityRequestCallback(request);
		execute(url, HttpMethod.PUT, requestCallback, null);
	}

	// DELETE

	public void delete(String url, Object... urlVariables) throws RestClientException {
		execute(url, HttpMethod.DELETE, null, null, urlVariables);
	}

	public void delete(String url, Map<String, ?> urlVariables) throws RestClientException {
		execute(url, HttpMethod.DELETE, null, null, urlVariables);
	}

	public void delete(URI url) throws RestClientException {
		execute(url, HttpMethod.DELETE, null, null);
	}

	// OPTIONS

	public Set<HttpMethod> optionsForAllow(String url, Object... urlVariables) throws RestClientException {
		HttpHeaders headers = execute(url, HttpMethod.OPTIONS, null, this.headersExtractor, urlVariables);
		return headers.getAllow();
	}

	public Set<HttpMethod> optionsForAllow(String url, Map<String, ?> urlVariables) throws RestClientException {
		HttpHeaders headers = execute(url, HttpMethod.OPTIONS, null, this.headersExtractor, urlVariables);
		return headers.getAllow();
	}

	public Set<HttpMethod> optionsForAllow(URI url) throws RestClientException {
		HttpHeaders headers = execute(url, HttpMethod.OPTIONS, null, this.headersExtractor);
		return headers.getAllow();
	}

	// exchange

	public <T> ResponseEntity<T> exchange(String url, HttpMethod method,
			HttpEntity<?> requestEntity, Class<T> responseType, Object... uriVariables) throws RestClientException {
		HttpEntityRequestCallback requestCallback = new HttpEntityRequestCallback(requestEntity, responseType);
		ResponseEntityResponseExtractor<T> responseExtractor = new ResponseEntityResponseExtractor<T>(responseType);
		return execute(url, method, requestCallback, responseExtractor, uriVariables);
	}

	public <T> ResponseEntity<T> exchange(String url, HttpMethod method,
			HttpEntity<?> requestEntity, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException {
		HttpEntityRequestCallback requestCallback = new HttpEntityRequestCallback(requestEntity, responseType);
		ResponseEntityResponseExtractor<T> responseExtractor = new ResponseEntityResponseExtractor<T>(responseType);
		return execute(url, method, requestCallback, responseExtractor, uriVariables);
	}

	public <T> ResponseEntity<T> exchange(URI url, HttpMethod method, HttpEntity<?> requestEntity,
			Class<T> responseType) throws RestClientException {
		HttpEntityRequestCallback requestCallback = new HttpEntityRequestCallback(requestEntity, responseType);
		ResponseEntityResponseExtractor<T> responseExtractor = new ResponseEntityResponseExtractor<T>(responseType);
		return execute(url, method, requestCallback, responseExtractor);
	}

	// general execution

	public <T> T execute(String url, HttpMethod method, RequestCallback requestCallback,
			ResponseExtractor<T> responseExtractor, Object... urlVariables) throws RestClientException {

		UriTemplate uriTemplate = new HttpUrlTemplate(url);
		URI expanded = uriTemplate.expand(urlVariables);
		return doExecute(expanded, method, requestCallback, responseExtractor);
	}

	public <T> T execute(String url, HttpMethod method, RequestCallback requestCallback,
			ResponseExtractor<T> responseExtractor, Map<String, ?> urlVariables) throws RestClientException {

		UriTemplate uriTemplate = new HttpUrlTemplate(url);
		URI expanded = uriTemplate.expand(urlVariables);
		return doExecute(expanded, method, requestCallback, responseExtractor);
	}

	public <T> T execute(URI url, HttpMethod method, RequestCallback requestCallback,
			ResponseExtractor<T> responseExtractor) throws RestClientException {

		return doExecute(url, method, requestCallback, responseExtractor);
	}

	/**
	 * Execute the given method on the provided URI. The {@link ClientHttpRequest} is processed using the {@link
	 * RequestCallback}; the response with the {@link ResponseExtractor}.
	 * @param url the fully-expanded URL to connect to
	 * @param method the HTTP method to execute (GET, POST, etc.)
	 * @param requestCallback object that prepares the request (can be <code>null</code>)
	 * @param responseExtractor object that extracts the return value from the response (can be <code>null</code>)
	 * @return an arbitrary object, as returned by the {@link ResponseExtractor}
	 */
	protected <T> T doExecute(URI url, HttpMethod method, RequestCallback requestCallback,
			ResponseExtractor<T> responseExtractor) throws RestClientException {

		Assert.notNull(url, "'url' must not be null");
		Assert.notNull(method, "'method' must not be null");
		ClientHttpResponse response = null;
		try {
			ClientHttpRequest request = createRequest(url, method);
			if (requestCallback != null) {
				requestCallback.doWithRequest(request);
			}
			response = request.execute();
			if (!getErrorHandler().hasError(response)) {
				logResponseStatus(method, url, response);
			}
			else {
				handleResponseError(method, url, response);
			}
			if (responseExtractor != null) {
				return responseExtractor.extractData(response);
			}
			else {
				return null;
			}
		}
		catch (IOException ex) {
			throw new ResourceAccessException("I/O error: " + ex.getMessage(), ex);
		}
		finally {
			if (response != null) {
				response.close();
			}
		}
	}

	private void logResponseStatus(HttpMethod method, URI url, ClientHttpResponse response) {
		if (logger.isDebugEnabled()) {
			try {
				logger.debug(
						method.name() + " request for \"" + url + "\" resulted in " + response.getStatusCode() + " (" +
								response.getStatusText() + ")");
			}
			catch (IOException e) {
				// ignore
			}
		}
	}

	private void handleResponseError(HttpMethod method, URI url, ClientHttpResponse response) throws IOException {
		if (logger.isWarnEnabled()) {
			try {
				logger.warn(
						method.name() + " request for \"" + url + "\" resulted in " + response.getStatusCode() + " (" +
								response.getStatusText() + "); invoking error handler");
			}
			catch (IOException e) {
				// ignore
			}
		}
		getErrorHandler().handleError(response);
	}


	/**
	 * Request callback implementation that prepares the request's accept headers.
	 */
	private class AcceptHeaderRequestCallback implements RequestCallback {

		private final Class<?> responseType;

		private AcceptHeaderRequestCallback(Class<?> responseType) {
			this.responseType = responseType;
		}

		@SuppressWarnings("unchecked")
		public void doWithRequest(ClientHttpRequest request) throws IOException {
			if (responseType != null) {
				List<MediaType> allSupportedMediaTypes = new ArrayList<MediaType>();
				for (HttpMessageConverter<?> messageConverter : getMessageConverters()) {
					if (messageConverter.canRead(responseType, null)) {
						List<MediaType> supportedMediaTypes = messageConverter.getSupportedMediaTypes();
						for (MediaType supportedMediaType : supportedMediaTypes) {
							if (supportedMediaType.getCharSet() != null) {
								supportedMediaType =
										new MediaType(supportedMediaType.getType(), supportedMediaType.getSubtype());
							}
							allSupportedMediaTypes.add(supportedMediaType);
						}
					}
				}
				if (!allSupportedMediaTypes.isEmpty()) {
					MediaType.sortBySpecificity(allSupportedMediaTypes);
					if (logger.isDebugEnabled()) {
						logger.debug("Setting request Accept header to " + allSupportedMediaTypes);
					}
					request.getHeaders().setAccept(allSupportedMediaTypes);
				}
			}
		}
	}


	/**
	 * Request callback implementation that writes the given object to the request stream.
	 */
	private class HttpEntityRequestCallback extends AcceptHeaderRequestCallback {

		private final HttpEntity requestEntity;

		private HttpEntityRequestCallback(Object requestBody) {
			this(requestBody, null);
		}

		@SuppressWarnings("unchecked")
		private HttpEntityRequestCallback(Object requestBody, Class<?> responseType) {
			super(responseType);
			if (requestBody instanceof HttpEntity) {
				this.requestEntity = (HttpEntity) requestBody;
			}
			else if (requestBody != null) {
				this.requestEntity = new HttpEntity(requestBody);
			}
			else {
				this.requestEntity = HttpEntity.EMPTY;
			}
		}

		@Override
		@SuppressWarnings("unchecked")
		public void doWithRequest(ClientHttpRequest httpRequest) throws IOException {
			super.doWithRequest(httpRequest);
			if (!requestEntity.hasBody()) {
				HttpHeaders httpHeaders = httpRequest.getHeaders();
				HttpHeaders requestHeaders = requestEntity.getHeaders();
				if (!requestHeaders.isEmpty()) {
					httpHeaders.putAll(requestHeaders);
				}
				if (httpHeaders.getContentLength() == -1) {
					httpHeaders.setContentLength(0L);
				}
			}
			else {
				Object requestBody = requestEntity.getBody();
				Class<?> requestType = requestBody.getClass();
				HttpHeaders requestHeaders = requestEntity.getHeaders();
				MediaType requestContentType = requestHeaders.getContentType();
				for (HttpMessageConverter messageConverter : getMessageConverters()) {
					if (messageConverter.canWrite(requestType, requestContentType)) {
						if (!requestHeaders.isEmpty()) {
							httpRequest.getHeaders().putAll(requestHeaders);
						}
						if (logger.isDebugEnabled()) {
							if (requestContentType != null) {
								logger.debug("Writing [" + requestBody + "] as \"" + requestContentType +
										"\" using [" + messageConverter + "]");
							}
							else {
								logger.debug("Writing [" + requestBody + "] using [" + messageConverter + "]");
							}

						}
						messageConverter.write(requestBody, requestContentType, httpRequest);
						return;
					}
				}
				String message = "Could not write request: no suitable HttpMessageConverter found for request type [" +
						requestType.getName() + "]";
				if (requestContentType != null) {
					message += " and content type [" + requestContentType + "]";
				}
				throw new RestClientException(message);
			}
		}
	}

	/**
	 * Response extractor for {@link HttpEntity}.
	 */
	private class ResponseEntityResponseExtractor<T> implements ResponseExtractor<ResponseEntity<T>> {

		private final HttpMessageConverterExtractor<T> delegate;

		public ResponseEntityResponseExtractor(Class<T> responseType) {
			if (responseType != null && !Void.class.equals(responseType)) {
				this.delegate = new HttpMessageConverterExtractor<T>(responseType, getMessageConverters(), logger);
			} else {
				this.delegate = null;
			}
		}

		public ResponseEntity<T> extractData(ClientHttpResponse response) throws IOException {
			if (delegate != null) {
				T body = delegate.extractData(response);
				return new ResponseEntity<T>(body, response.getHeaders(), response.getStatusCode());
			}
			else {
				return new ResponseEntity<T>(response.getHeaders(), response.getStatusCode());
			}
		}
	}


	/**
	 * Response extractor that extracts the response {@link HttpHeaders}.
	 */
	private static class HeadersExtractor implements ResponseExtractor<HttpHeaders> {

		public HttpHeaders extractData(ClientHttpResponse response) throws IOException {
			return response.getHeaders();
		}
	}

	/**
	 * HTTP-specific subclass of UriTemplate, overriding the encode method.
	 */
	private static class HttpUrlTemplate extends UriTemplate {

		public HttpUrlTemplate(String uriTemplate) {
			super(uriTemplate);
		}

		@Override
		protected URI encodeUri(String uri) {
			try {
				String encoded = UriUtils.encodeHttpUrl(uri, "UTF-8");
				return new URI(encoded);
			}
			catch (UnsupportedEncodingException ex) {
				// should not happen, UTF-8 is always supported
				throw new IllegalStateException(ex);
			}
			catch (URISyntaxException ex) {
				throw new IllegalArgumentException("Could not create HTTP URL from [" + uri + "]: " + ex, ex);
			}
		}
	}

}
