org/springframework/web/client/RestTemplate.java

package org.oa.main;

/*
 * Copyright 2002-2018 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.lang.reflect.Type;
import java.net.URI;
import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.springframework.core.ParameterizedTypeReference;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.MediaType;
import org.springframework.http.RequestEntity;
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.GenericHttpMessageConverter;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.ResourceHttpMessageConverter;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.http.converter.cbor.MappingJackson2CborHttpMessageConverter;
import org.springframework.http.converter.feed.AtomFeedHttpMessageConverter;
import org.springframework.http.converter.feed.RssChannelHttpMessageConverter;
import org.springframework.http.converter.json.GsonHttpMessageConverter;
import org.springframework.http.converter.json.JsonbHttpMessageConverter;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.http.converter.smile.MappingJackson2SmileHttpMessageConverter;
import org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter;
import org.springframework.http.converter.xml.Jaxb2RootElementHttpMessageConverter;
import org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter;
import org.springframework.http.converter.xml.SourceHttpMessageConverter;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.web.util.DefaultUriBuilderFactory;
import org.springframework.web.util.UriTemplateHandler;

/**
 * <strong>Spring's central class for synchronous 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>
 * <strong>Note:</strong> by default the RestTemplate relies on standard JDK facilities to establish
 * HTTP connections. You can switch to use a different HTTP library such as Apache HttpComponents,
 * Netty, and OkHttp through the {@link #setRequestFactory} property.
 *
 * <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>
 * In addition the {@code exchange} and {@code execute} methods are generalized versions of the
 * above methods and can be used to support additional, less frequent combinations (e.g. HTTP PATCH,
 * HTTP PUT with response body, etc.). Note however that the underlying HTTP library used must also
 * support the desired combination.
 *
 * <p>
 * <strong>Note:</strong> For URI templates it is assumed encoding is necessary, e.g.
 * {@code restTemplate.getForObject("http://example.com/hotel list")} becomes
 * {@code "http://example.com/hotel%20list"}. This also means if the URI template or URI variables
 * are already encoded, double encoding will occur, e.g. {@code http://example.com/hotel%20list}
 * becomes {@code http://example.com/hotel%2520list}). To avoid that use a {@code URI} method
 * variant to provide (or re-use) a previously encoded URI. To prepare such an URI with full control
 * over encoding, consider using {@link org.springframework.web.util.UriComponentsBuilder}.
 *
 * <p>
 * Internally the template uses {@link HttpMessageConverter} instances to convert HTTP messages to
 * and from POJOs. Converters for the main mime types are registered by default but you can also
 * register additional converters via {@link #setMessageConverters}.
 *
 * <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
 * {@link #setRequestFactory} and {@link #setErrorHandler} respectively.
 *
 * @author Arjen Poutsma
 * @author Brian Clozel
 * @author Roy Clarkson
 * @author Juergen Hoeller
 * @since 3.0
 * @see HttpMessageConverter
 * @see RequestCallback
 * @see ResponseExtractor
 * @see ResponseErrorHandler
 * @see AsyncRestTemplate
 */
public class RestTemplate extends InterceptingHttpAccessor implements RestOperations
{

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

	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 jackson2XmlPresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.xml.XmlMapper", RestTemplate.class.getClassLoader());

	private static final boolean jackson2SmilePresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.smile.SmileFactory", RestTemplate.class.getClassLoader());

	private static final boolean jackson2CborPresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.cbor.CBORFactory", RestTemplate.class.getClassLoader());

	private static final boolean gsonPresent = ClassUtils.isPresent("com.google.gson.Gson", RestTemplate.class.getClassLoader());

	private static final boolean jsonbPresent = ClassUtils.isPresent("javax.json.bind.Jsonb", RestTemplate.class.getClassLoader());

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

	private ResponseErrorHandler errorHandler = new DefaultResponseErrorHandler();

	private UriTemplateHandler uriTemplateHandler = new DefaultUriBuilderFactory();

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

	/**
	 * Create a new instance of the {@link RestTemplate} using default settings. Default
	 * {@link HttpMessageConverter}s are initialized.
	 */
	public RestTemplate()
	{
		this.messageConverters.add(new ByteArrayHttpMessageConverter());
		this.messageConverters.add(new StringHttpMessageConverter());
		this.messageConverters.add(new ResourceHttpMessageConverter(false));
		this.messageConverters.add(new SourceHttpMessageConverter<>());
		this.messageConverters.add(new AllEncompassingFormHttpMessageConverter());

		if (romePresent)
		{
			this.messageConverters.add(new AtomFeedHttpMessageConverter());
			this.messageConverters.add(new RssChannelHttpMessageConverter());
		}

		if (jackson2XmlPresent)
		{
			this.messageConverters.add(new MappingJackson2XmlHttpMessageConverter());
		}
		else if (jaxb2Present)
		{
			this.messageConverters.add(new Jaxb2RootElementHttpMessageConverter());
		}

		if (jackson2Present)
		{
			this.messageConverters.add(new MappingJackson2HttpMessageConverter());
		}
		else if (gsonPresent)
		{
			this.messageConverters.add(new GsonHttpMessageConverter());
		}
		else if (jsonbPresent)
		{
			this.messageConverters.add(new JsonbHttpMessageConverter());
		}

		if (jackson2SmilePresent)
		{
			this.messageConverters.add(new MappingJackson2SmileHttpMessageConverter());
		}
		if (jackson2CborPresent)
		{
			this.messageConverters.add(new MappingJackson2CborHttpMessageConverter());
		}
	}

	/**
	 * 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.HttpComponentsClientHttpRequestFactory
	 */
	public RestTemplate(ClientHttpRequestFactory requestFactory)
	{
		this();
		setRequestFactory(requestFactory);
	}

	/**
	 * Create a new instance of the {@link RestTemplate} using the given list of
	 * {@link HttpMessageConverter} to use
	 * 
	 * @param messageConverters the list of {@link HttpMessageConverter} to use
	 * @since 3.2.7
	 */
	public RestTemplate(List<HttpMessageConverter<?>> messageConverters)
	{
		Assert.notEmpty(messageConverters, "At least one HttpMessageConverter required");
		this.messageConverters.addAll(messageConverters);
	}

	/**
	 * Set the message body converters to use.
	 * <p>
	 * These converters are used to convert from and to HTTP requests and responses.
	 */
	public void setMessageConverters(List<HttpMessageConverter<?>> messageConverters)
	{
		Assert.notEmpty(messageConverters, "At least one HttpMessageConverter required");
		// Take getMessageConverters() List as-is when passed in here
		if (this.messageConverters != messageConverters)
		{
			this.messageConverters.clear();
			this.messageConverters.addAll(messageConverters);
		}
	}

	/**
	 * Return the list of message body converters.
	 * <p>
	 * The returned {@link List} is active and may get appended to.
	 */
	public List<HttpMessageConverter<?>> getMessageConverters()
	{
		return this.messageConverters;
	}

	/**
	 * Set the error handler.
	 * <p>
	 * By default, RestTemplate uses a {@link DefaultResponseErrorHandler}.
	 */
	public void setErrorHandler(ResponseErrorHandler errorHandler)
	{
		Assert.notNull(errorHandler, "ResponseErrorHandler must not be null");
		this.errorHandler = errorHandler;
	}

	/**
	 * Return the error handler.
	 */
	public ResponseErrorHandler getErrorHandler()
	{
		return this.errorHandler;
	}

	/**
	 * Configure default URI variable values. This is a shortcut for:
	 * 
	 * <pre class="code">
	 * DefaultUriBuilderFactory factory = new DefaultUriBuilderFactory();
	 * handler.setDefaultUriVariables(...);
	 * 
	 * RestTemplate restTemplate = new RestTemplate();
	 * restTemplate.setUriTemplateHandler(handler);
	 * </pre>
	 * 
	 * @param uriVars the default URI variable values
	 * @since 4.3
	 */
	@SuppressWarnings("deprecation")
	public void setDefaultUriVariables(Map<String, ?> uriVars)
	{
		if (this.uriTemplateHandler instanceof DefaultUriBuilderFactory)
		{
			((DefaultUriBuilderFactory) this.uriTemplateHandler).setDefaultUriVariables(uriVars);
		}
		else if (this.uriTemplateHandler instanceof org.springframework.web.util.AbstractUriTemplateHandler)
		{
			((org.springframework.web.util.AbstractUriTemplateHandler) this.uriTemplateHandler).setDefaultUriVariables(uriVars);
		}
		else
		{
			throw new IllegalArgumentException("This property is not supported with the configured UriTemplateHandler.");
		}
	}

	/**
	 * Customize how URI templates are expanded into URI instances.
	 * <p>
	 * By default {@link DefaultUriBuilderFactory} with default settings is used. You can supply a
	 * {@code DefaultUriBuilderFactory} configured differently, or an entirely different
	 * implementation, for example that plugs in a 3rd party URI template library.
	 * <p>
	 * <strong>Note:</strong> in 5.0 the switch from
	 * {@link org.springframework.web.util.DefaultUriTemplateHandler DefaultUriTemplateHandler}
	 * (deprecated in 4.3), as the default to use, to {@link DefaultUriBuilderFactory} brings in a
	 * different default for the {@code parsePath} property (switching from false to true).
	 * 
	 * @param handler the URI template handler to use
	 */
	public void setUriTemplateHandler(UriTemplateHandler handler)
	{
		Assert.notNull(handler, "UriTemplateHandler must not be null");
		this.uriTemplateHandler = handler;
	}

	/**
	 * Return the configured URI template handler.
	 */
	public UriTemplateHandler getUriTemplateHandler()
	{
		return this.uriTemplateHandler;
	}

	// GET

	@Override
	@Nullable
	public <T> T getForObject(String url, Class<T> responseType, Object... uriVariables) throws RestClientException
	{
		RequestCallback requestCallback = acceptHeaderRequestCallback(responseType);
		HttpMessageConverterExtractor<T> responseExtractor = new HttpMessageConverterExtractor<>(responseType, getMessageConverters(), logger);
		return execute(url, HttpMethod.GET, requestCallback, responseExtractor, uriVariables);
	}

	@Override
	@Nullable
	public <T> T getForObject(String url, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException
	{
		RequestCallback requestCallback = acceptHeaderRequestCallback(responseType);
		HttpMessageConverterExtractor<T> responseExtractor = new HttpMessageConverterExtractor<>(responseType, getMessageConverters(), logger);
		return execute(url, HttpMethod.GET, requestCallback, responseExtractor, uriVariables);
	}

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

	@Override
	public <T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Object... uriVariables) throws RestClientException
	{

		RequestCallback requestCallback = acceptHeaderRequestCallback(responseType);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
		return nonNull(execute(url, HttpMethod.GET, requestCallback, responseExtractor, uriVariables));
	}

	@Override
	public <T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException
	{

		RequestCallback requestCallback = acceptHeaderRequestCallback(responseType);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
		return nonNull(execute(url, HttpMethod.GET, requestCallback, responseExtractor, uriVariables));
	}

	@Override
	public <T> ResponseEntity<T> getForEntity(URI url, Class<T> responseType) throws RestClientException
	{
		RequestCallback requestCallback = acceptHeaderRequestCallback(responseType);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
		return nonNull(execute(url, HttpMethod.GET, requestCallback, responseExtractor));
	}

	// HEAD

	@Override
	public HttpHeaders headForHeaders(String url, Object... uriVariables) throws RestClientException
	{
		return nonNull(execute(url, HttpMethod.HEAD, null, headersExtractor(), uriVariables));
	}

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

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

	// POST

	@Override
	@Nullable
	public URI postForLocation(String url, @Nullable Object request, Object... uriVariables) throws RestClientException
	{

		RequestCallback requestCallback = httpEntityCallback(request);
		HttpHeaders headers = execute(url, HttpMethod.POST, requestCallback, headersExtractor(), uriVariables);
		return (headers != null ? headers.getLocation() : null);
	}

	@Override
	@Nullable
	public URI postForLocation(String url, @Nullable Object request, Map<String, ?> uriVariables) throws RestClientException
	{

		RequestCallback requestCallback = httpEntityCallback(request);
		HttpHeaders headers = execute(url, HttpMethod.POST, requestCallback, headersExtractor(), uriVariables);
		return (headers != null ? headers.getLocation() : null);
	}

	@Override
	@Nullable
	public URI postForLocation(URI url, @Nullable Object request) throws RestClientException
	{
		RequestCallback requestCallback = httpEntityCallback(request);
		HttpHeaders headers = execute(url, HttpMethod.POST, requestCallback, headersExtractor());
		return (headers != null ? headers.getLocation() : null);
	}

	@Override
	@Nullable
	public <T> T postForObject(String url, @Nullable Object request, Class<T> responseType, Object... uriVariables) throws RestClientException
	{

		RequestCallback requestCallback = httpEntityCallback(request, responseType);
		HttpMessageConverterExtractor<T> responseExtractor = new HttpMessageConverterExtractor<>(responseType, getMessageConverters(), logger);
		return execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables);
	}

	@Override
	@Nullable
	public <T> T postForObject(String url, @Nullable Object request, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException
	{

		RequestCallback requestCallback = httpEntityCallback(request, responseType);
		HttpMessageConverterExtractor<T> responseExtractor = new HttpMessageConverterExtractor<>(responseType, getMessageConverters(), logger);
		return execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables);
	}

	@Override
	@Nullable
	public <T> T postForObject(URI url, @Nullable Object request, Class<T> responseType) throws RestClientException
	{

		RequestCallback requestCallback = httpEntityCallback(request, responseType);
		HttpMessageConverterExtractor<T> responseExtractor = new HttpMessageConverterExtractor<>(responseType, getMessageConverters());
		return execute(url, HttpMethod.POST, requestCallback, responseExtractor);
	}

	@Override
	public <T> ResponseEntity<T> postForEntity(String url, @Nullable Object request, Class<T> responseType, Object... uriVariables) throws RestClientException
	{

		RequestCallback requestCallback = httpEntityCallback(request, responseType);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
		return nonNull(execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables));
	}

	@Override
	public <T> ResponseEntity<T> postForEntity(String url, @Nullable Object request, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException
	{

		RequestCallback requestCallback = httpEntityCallback(request, responseType);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
		return nonNull(execute(url, HttpMethod.POST, requestCallback, responseExtractor, uriVariables));
	}

	@Override
	public <T> ResponseEntity<T> postForEntity(URI url, @Nullable Object request, Class<T> responseType) throws RestClientException
	{

		RequestCallback requestCallback = httpEntityCallback(request, responseType);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
		return nonNull(execute(url, HttpMethod.POST, requestCallback, responseExtractor));
	}

	// PUT

	@Override
	public void put(String url, @Nullable Object request, Object... uriVariables) throws RestClientException
	{

		RequestCallback requestCallback = httpEntityCallback(request);
		execute(url, HttpMethod.PUT, requestCallback, null, uriVariables);
	}

	@Override
	public void put(String url, @Nullable Object request, Map<String, ?> uriVariables) throws RestClientException
	{

		RequestCallback requestCallback = httpEntityCallback(request);
		execute(url, HttpMethod.PUT, requestCallback, null, uriVariables);
	}

	@Override
	public void put(URI url, @Nullable Object request) throws RestClientException
	{
		RequestCallback requestCallback = httpEntityCallback(request);
		execute(url, HttpMethod.PUT, requestCallback, null);
	}

	// PATCH

	@Override
	@Nullable
	public <T> T patchForObject(String url, @Nullable Object request, Class<T> responseType, Object... uriVariables) throws RestClientException
	{

		RequestCallback requestCallback = httpEntityCallback(request, responseType);
		HttpMessageConverterExtractor<T> responseExtractor = new HttpMessageConverterExtractor<>(responseType, getMessageConverters(), logger);
		return execute(url, HttpMethod.PATCH, requestCallback, responseExtractor, uriVariables);
	}

	@Override
	@Nullable
	public <T> T patchForObject(String url, @Nullable Object request, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException
	{

		RequestCallback requestCallback = httpEntityCallback(request, responseType);
		HttpMessageConverterExtractor<T> responseExtractor = new HttpMessageConverterExtractor<>(responseType, getMessageConverters(), logger);
		return execute(url, HttpMethod.PATCH, requestCallback, responseExtractor, uriVariables);
	}

	@Override
	@Nullable
	public <T> T patchForObject(URI url, @Nullable Object request, Class<T> responseType) throws RestClientException
	{

		RequestCallback requestCallback = httpEntityCallback(request, responseType);
		HttpMessageConverterExtractor<T> responseExtractor = new HttpMessageConverterExtractor<>(responseType, getMessageConverters());
		return execute(url, HttpMethod.PATCH, requestCallback, responseExtractor);
	}

	// DELETE

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

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

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

	// OPTIONS

	@Override
	public Set<HttpMethod> optionsForAllow(String url, Object... uriVariables) throws RestClientException
	{
		ResponseExtractor<HttpHeaders> headersExtractor = headersExtractor();
		HttpHeaders headers = execute(url, HttpMethod.OPTIONS, null, headersExtractor, uriVariables);
		return (headers != null ? headers.getAllow() : Collections.emptySet());
	}

	@Override
	public Set<HttpMethod> optionsForAllow(String url, Map<String, ?> uriVariables) throws RestClientException
	{
		ResponseExtractor<HttpHeaders> headersExtractor = headersExtractor();
		HttpHeaders headers = execute(url, HttpMethod.OPTIONS, null, headersExtractor, uriVariables);
		return (headers != null ? headers.getAllow() : Collections.emptySet());
	}

	@Override
	public Set<HttpMethod> optionsForAllow(URI url) throws RestClientException
	{
		ResponseExtractor<HttpHeaders> headersExtractor = headersExtractor();
		HttpHeaders headers = execute(url, HttpMethod.OPTIONS, null, headersExtractor);
		return (headers != null ? headers.getAllow() : Collections.emptySet());
	}

	// exchange

	@Override
	public <T> ResponseEntity<T> exchange(String url, HttpMethod method, @Nullable HttpEntity<?> requestEntity, Class<T> responseType, Object... uriVariables) throws RestClientException
	{

		RequestCallback requestCallback = httpEntityCallback(requestEntity, responseType);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
		return nonNull(execute(url, method, requestCallback, responseExtractor, uriVariables));
	}

	@Override
	public <T> ResponseEntity<T> exchange(String url, HttpMethod method, @Nullable HttpEntity<?> requestEntity, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException
	{

		RequestCallback requestCallback = httpEntityCallback(requestEntity, responseType);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
		return nonNull(execute(url, method, requestCallback, responseExtractor, uriVariables));
	}

	@Override
	public <T> ResponseEntity<T> exchange(URI url, HttpMethod method, @Nullable HttpEntity<?> requestEntity, Class<T> responseType) throws RestClientException
	{

		RequestCallback requestCallback = httpEntityCallback(requestEntity, responseType);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
		return nonNull(execute(url, method, requestCallback, responseExtractor));
	}

	@Override
	public <T> ResponseEntity<T> exchange(String url, HttpMethod method, @Nullable HttpEntity<?> requestEntity, ParameterizedTypeReference<T> responseType, Object... uriVariables) throws RestClientException
	{

		Type type = responseType.getType();
		RequestCallback requestCallback = httpEntityCallback(requestEntity, type);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(type);
		return nonNull(execute(url, method, requestCallback, responseExtractor, uriVariables));
	}

	@Override
	public <T> ResponseEntity<T> exchange(String url, HttpMethod method, @Nullable HttpEntity<?> requestEntity, ParameterizedTypeReference<T> responseType, Map<String, ?> uriVariables) throws RestClientException
	{

		Type type = responseType.getType();
		RequestCallback requestCallback = httpEntityCallback(requestEntity, type);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(type);
		return nonNull(execute(url, method, requestCallback, responseExtractor, uriVariables));
	}

	@Override
	public <T> ResponseEntity<T> exchange(URI url, HttpMethod method, @Nullable HttpEntity<?> requestEntity, ParameterizedTypeReference<T> responseType) throws RestClientException
	{

		Type type = responseType.getType();
		RequestCallback requestCallback = httpEntityCallback(requestEntity, type);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(type);
		return nonNull(execute(url, method, requestCallback, responseExtractor));
	}

	@Override
	public <T> ResponseEntity<T> exchange(RequestEntity<?> requestEntity, Class<T> responseType) throws RestClientException
	{

		RequestCallback requestCallback = httpEntityCallback(requestEntity, responseType);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
		return nonNull(doExecute(requestEntity.getUrl(), requestEntity.getMethod(), requestCallback, responseExtractor));
	}

	@Override
	public <T> ResponseEntity<T> exchange(RequestEntity<?> requestEntity, ParameterizedTypeReference<T> responseType) throws RestClientException
	{

		Type type = responseType.getType();
		RequestCallback requestCallback = httpEntityCallback(requestEntity, type);
		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(type);
		return nonNull(doExecute(requestEntity.getUrl(), requestEntity.getMethod(), requestCallback, responseExtractor));
	}

	// general execution

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

		URI expanded = getUriTemplateHandler().expand(url, uriVariables);
		return doExecute(expanded, method, requestCallback, responseExtractor);
	}

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

		URI expanded = getUriTemplateHandler().expand(url, uriVariables);
		return doExecute(expanded, method, requestCallback, responseExtractor);
	}

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

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

	/**
	 * Execute the given method on the provided URI.
	 * <p>
	 * 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})
	 * @param responseExtractor object that extracts the return value from the response (can be
	 *        {@code null})
	 * @return an arbitrary object, as returned by the {@link ResponseExtractor}
	 */
	@Nullable
	protected <T> T doExecute(URI url, @Nullable HttpMethod method, @Nullable RequestCallback requestCallback, @Nullable ResponseExtractor<T> responseExtractor) throws RestClientException
	{

		Assert.notNull(url, "URI is required");
		Assert.notNull(method, "HttpMethod is required");
		ClientHttpResponse response = null;
		try
		{
			ClientHttpRequest request = createRequest(url, method);
			if (requestCallback != null)
			{
				requestCallback.doWithRequest(request);
			}
			response = request.execute();
			handleResponse(url, method, response);
			return (responseExtractor != null ? responseExtractor.extractData(response) : null);
		}
		catch (IOException ex)
		{
			String resource = url.toString();
			String query = url.getRawQuery();
			resource = (query != null ? resource.substring(0, resource.indexOf('?')) : resource);
			throw new ResourceAccessException("I/O error on " + method.name() + " request for \"" + resource + "\": " + ex.getMessage(), ex);
		}
		finally
		{
			if (response != null)
			{
				response.close();
			}
		}
	}

	/**
	 * Handle the given response, performing appropriate logging and invoking the
	 * {@link ResponseErrorHandler} if necessary.
	 * <p>
	 * Can be overridden in subclasses.
	 * 
	 * @param url the fully-expanded URL to connect to
	 * @param method the HTTP method to execute (GET, POST, etc.)
	 * @param response the resulting {@link ClientHttpResponse}
	 * @throws IOException if propagated from {@link ResponseErrorHandler}
	 * @since 4.1.6
	 * @see #setErrorHandler
	 */
	protected void handleResponse(URI url, HttpMethod method, ClientHttpResponse response) throws IOException
	{
		ResponseErrorHandler errorHandler = getErrorHandler();
		boolean hasError = errorHandler.hasError(response);
		if (logger.isDebugEnabled())
		{
			try
			{
				logger.debug(method.name() + " request for \"" + url + "\" resulted in " + response.getRawStatusCode() + " (" + response.getStatusText() + ")" + (hasError ? "; invoking error handler" : ""));
			}
			catch (IOException ex)
			{
				// ignore
			}
		}
		if (hasError)
		{
			errorHandler.handleError(url, method, response);
		}
	}

	/**
	 * Returns a request callback implementation that prepares the request {@code Accept} headers
	 * based on the given response type and configured {@linkplain #getMessageConverters() message
	 * converters}.
	 */
	protected <T> RequestCallback acceptHeaderRequestCallback(Class<T> responseType)
	{
		return new AcceptHeaderRequestCallback(responseType);
	}

	/**
	 * Returns a request callback implementation that writes the given object to the request stream.
	 */
	protected <T> RequestCallback httpEntityCallback(@Nullable Object requestBody)
	{
		return new HttpEntityRequestCallback(requestBody);
	}

	/**
	 * Returns a request callback implementation that writes the given object to the request stream.
	 */
	protected <T> RequestCallback httpEntityCallback(@Nullable Object requestBody, Type responseType)
	{
		return new HttpEntityRequestCallback(requestBody, responseType);
	}

	/**
	 * Returns a response extractor for {@link ResponseEntity}.
	 */
	protected <T> ResponseExtractor<ResponseEntity<T>> responseEntityExtractor(Type responseType)
	{
		return new ResponseEntityResponseExtractor<>(responseType);
	}

	/**
	 * Returns a response extractor for {@link HttpHeaders}.
	 */
	protected ResponseExtractor<HttpHeaders> headersExtractor()
	{
		return this.headersExtractor;
	}

	private static <T> T nonNull(@Nullable T result)
	{
		Assert.state(result != null, "No result");
		return result;
	}

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

		@Nullable
		private final Type responseType;

		public AcceptHeaderRequestCallback(@Nullable Type responseType)
		{
			this.responseType = responseType;
		}

		@Override
		public void doWithRequest(ClientHttpRequest request) throws IOException
		{
			if (this.responseType != null)
			{
				Class<?> responseClass = null;
				if (this.responseType instanceof Class)
				{
					responseClass = (Class<?>) this.responseType;
				}
				List<MediaType> allSupportedMediaTypes = new ArrayList<>();
				for (HttpMessageConverter<?> converter : getMessageConverters())
				{
					if (responseClass != null)
					{
						if (converter.canRead(responseClass, null))
						{
							allSupportedMediaTypes.addAll(getSupportedMediaTypes(converter));
						}
					}
					else if (converter instanceof GenericHttpMessageConverter)
					{
						GenericHttpMessageConverter<?> genericConverter = (GenericHttpMessageConverter<?>) converter;
						if (genericConverter.canRead(this.responseType, null, null))
						{
							allSupportedMediaTypes.addAll(getSupportedMediaTypes(converter));
						}
					}
				}
				if (!allSupportedMediaTypes.isEmpty())
				{
					MediaType.sortBySpecificity(allSupportedMediaTypes);
					if (logger.isDebugEnabled())
					{
						logger.debug("Setting request Accept header to " + allSupportedMediaTypes);
					}
					request.getHeaders().setAccept(allSupportedMediaTypes);
				}
			}
		}

		private List<MediaType> getSupportedMediaTypes(HttpMessageConverter<?> messageConverter)
		{
			List<MediaType> supportedMediaTypes = messageConverter.getSupportedMediaTypes();
			List<MediaType> result = new ArrayList<>(supportedMediaTypes.size());
			for (MediaType supportedMediaType : supportedMediaTypes)
			{
				if (supportedMediaType.getCharset() != null)
				{
					supportedMediaType = new MediaType(supportedMediaType.getType(), supportedMediaType.getSubtype());
				}
				result.add(supportedMediaType);
			}
			return result;
		}
	}

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

		private final HttpEntity<?> requestEntity;

		public HttpEntityRequestCallback(@Nullable Object requestBody)
		{
			this(requestBody, null);
		}

		public HttpEntityRequestCallback(@Nullable Object requestBody, @Nullable Type 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);
			Object requestBody = this.requestEntity.getBody();
			if (requestBody == null) {
				HttpHeaders httpHeaders = httpRequest.getHeaders();
				HttpHeaders requestHeaders = this.requestEntity.getHeaders();
				if (!requestHeaders.isEmpty()) {
					requestHeaders.forEach((key, values) -> httpHeaders.put(key, new LinkedList<>(values)));
				}
				if (httpHeaders.getContentLength() < 0) {
					httpHeaders.setContentLength(0L);
				}
			}
			else {
				Class<?> requestBodyClass = requestBody.getClass();
				Type requestBodyType = (this.requestEntity instanceof RequestEntity ?
						((RequestEntity<?>)this.requestEntity).getType() : requestBodyClass);
				HttpHeaders httpHeaders = httpRequest.getHeaders();
				HttpHeaders requestHeaders = this.requestEntity.getHeaders();
				MediaType requestContentType = requestHeaders.getContentType();
				for (HttpMessageConverter<?> messageConverter : getMessageConverters()) {
					if (messageConverter instanceof GenericHttpMessageConverter) {
						GenericHttpMessageConverter<Object> genericConverter =
								(GenericHttpMessageConverter<Object>) messageConverter;
						if (genericConverter.canWrite(requestBodyType, requestBodyClass, requestContentType)) {
							if (!requestHeaders.isEmpty()) {
								requestHeaders.forEach((key, values) -> httpHeaders.put(key, new LinkedList<>(values)));
							}
							if (logger.isDebugEnabled()) {
								if (requestContentType != null) {
									logger.debug("Writing [" + requestBody + "] as \"" + requestContentType +
											"\" using [" + messageConverter + "]");
								}
								else {
									logger.debug("Writing [" + requestBody + "] using [" + messageConverter + "]");
								}

							}
							genericConverter.write(requestBody, requestBodyType, requestContentType, httpRequest);
							return;
						}
					}
					else if (messageConverter.canWrite(requestBodyClass, requestContentType)) {
						if (!requestHeaders.isEmpty()) {
							requestHeaders.forEach((key, values) -> httpHeaders.put(key, new LinkedList<>(values)));
						}
						if (logger.isDebugEnabled()) {
							if (requestContentType != null) {
								logger.debug("Writing [" + requestBody + "] as \"" + requestContentType +
										"\" using [" + messageConverter + "]");
							}
							else {
								logger.debug("Writing [" + requestBody + "] using [" + messageConverter + "]");
							}

						}
						((HttpMessageConverter<Object>) messageConverter).write(
								requestBody, requestContentType, httpRequest);
						return;
					}
				}
				String message = "Could not write request: no suitable HttpMessageConverter found for request type [" +
						requestBodyClass.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>>
	{

		@Nullable
		private final HttpMessageConverterExtractor<T> delegate;

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

		@Override
		public ResponseEntity<T> extractData(ClientHttpResponse response) throws IOException
		{
			if (this.delegate != null)
			{
				T body = this.delegate.extractData(response);
				return ResponseEntity.status(response.getRawStatusCode()).headers(response.getHeaders()).body(body);
			}
			else
			{
				return ResponseEntity.status(response.getRawStatusCode()).headers(response.getHeaders()).build();
			}
		}
	}

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

		@Override
		public HttpHeaders extractData(ClientHttpResponse response)
		{
			return response.getHeaders();
		}
	}

}