聊聊RestTemplate对HttpClient的适配

/**
 * Factory for {@link ClientHttpRequest} objects.
 * Requests are created by the {@link #createRequest(URI, HttpMethod)} method.
 *
 * @author Arjen Poutsma
 * @since 3.0
 */
@FunctionalInterface
public interface ClientHttpRequestFactory {

	/**
	 * Create a new {@link ClientHttpRequest} for the specified URI and HTTP method.
	 * <p>The returned request can be written to, and then executed by calling
	 * {@link ClientHttpRequest#execute()}.
	 * @param uri the URI to create a request for
	 * @param httpMethod the HTTP method to execute
	 * @return the created request
	 * @throws IOException in case of I/O errors
	 */
	ClientHttpRequest createRequest(URI uri, HttpMethod httpMethod) throws IOException;

}

public class HttpComponentsClientHttpRequestFactory implements ClientHttpRequestFactory, DisposableBean {

	private HttpClient httpClient;

	@Nullable
	private RequestConfig requestConfig;

	private boolean bufferRequestBody = true;

	/**
	 * Create a new instance of the {@code HttpComponentsClientHttpRequestFactory}
	 * with a default {@link HttpClient} based on system properties.
	 */
	public HttpComponentsClientHttpRequestFactory() {
		this.httpClient = HttpClients.createSystem();
	}

	/**
	 * Create a new instance of the {@code HttpComponentsClientHttpRequestFactory}
	 * with the given {@link HttpClient} instance.
	 * @param httpClient the HttpClient instance to use for this request factory
	 */
	public HttpComponentsClientHttpRequestFactory(HttpClient httpClient) {
		this.httpClient = httpClient;
	}

	@Override
	public ClientHttpRequest createRequest(URI uri, HttpMethod httpMethod) throws IOException {
		HttpClient client = getHttpClient();

		HttpUriRequest httpRequest = createHttpUriRequest(httpMethod, uri);
		postProcessHttpRequest(httpRequest);
		HttpContext context = createHttpContext(httpMethod, uri);
		if (context == null) {
			context = HttpClientContext.create();
		}

		// Request configuration not set in the context
		if (context.getAttribute(HttpClientContext.REQUEST_CONFIG) == null) {
			// Use request configuration given by the user, when available
			RequestConfig config = null;
			if (httpRequest instanceof Configurable) {
				config = ((Configurable) httpRequest).getConfig();
			}
			if (config == null) {
				config = createRequestConfig(client);
			}
			if (config != null) {
				context.setAttribute(HttpClientContext.REQUEST_CONFIG, config);
			}
		}

		if (this.bufferRequestBody) {
			return new HttpComponentsClientHttpRequest(client, httpRequest, context);
		}
		else {
			return new HttpComponentsStreamingClientHttpRequest(client, httpRequest, context);
		}
	}

【/**
	 * Shutdown hook that closes the underlying
	 * {@link org.apache.http.conn.HttpClientConnectionManager ClientConnectionManager}'s
	 * connection pool, if any.
	 */
	@Override
	public void destroy() throws Exception {
		HttpClient httpClient = getHttpClient();
		if (httpClient instanceof Closeable) {
			((Closeable) httpClient).close();
		}
	}
	//......
}	

public interface ClientHttpRequest extends HttpRequest, HttpOutputMessage {

	/**
	 * Execute this request, resulting in a {@link ClientHttpResponse} that can be read.
	 * @return the response result of the execution
	 * @throws IOException in case of I/O errors
	 */
	ClientHttpResponse execute() throws IOException;

}

final class HttpComponentsClientHttpRequest extends AbstractBufferingClientHttpRequest {

	private final HttpClient httpClient;

	private final HttpUriRequest httpRequest;

	private final HttpContext httpContext;


	HttpComponentsClientHttpRequest(HttpClient client, HttpUriRequest request, HttpContext context) {
		this.httpClient = client;
		this.httpRequest = request;
		this.httpContext = context;
	}


	@Override
	public String getMethodValue() {
		return this.httpRequest.getMethod();
	}

	@Override
	public URI getURI() {
		return this.httpRequest.getURI();
	}

	HttpContext getHttpContext() {
		return this.httpContext;
	}


	@Override
	protected ClientHttpResponse executeInternal(HttpHeaders headers, byte[] bufferedOutput) throws IOException {
		addHeaders(this.httpRequest, headers);

		if (this.httpRequest instanceof HttpEntityEnclosingRequest) {
			HttpEntityEnclosingRequest entityEnclosingRequest = (HttpEntityEnclosingRequest) this.httpRequest;
			HttpEntity requestEntity = new ByteArrayEntity(bufferedOutput);
			entityEnclosingRequest.setEntity(requestEntity);
		}
		HttpResponse httpResponse = this.httpClient.execute(this.httpRequest, this.httpContext);
		return new HttpComponentsClientHttpResponse(httpResponse);
	}


	/**
	 * Add the given headers to the given HTTP request.
	 * @param httpRequest the request to add the headers to
	 * @param headers the headers to add
	 */
	static void addHeaders(HttpUriRequest httpRequest, HttpHeaders headers) {
		headers.forEach((headerName, headerValues) -> {
			if (HttpHeaders.COOKIE.equalsIgnoreCase(headerName)) {  // RFC 6265
				String headerValue = StringUtils.collectionToDelimitedString(headerValues, "; ");
				httpRequest.addHeader(headerName, headerValue);
			}
			else if (!HTTP.CONTENT_LEN.equalsIgnoreCase(headerName) &&
					!HTTP.TRANSFER_ENCODING.equalsIgnoreCase(headerName)) {
				for (String headerValue : headerValues) {
					httpRequest.addHeader(headerName, headerValue);
				}
			}
		});
	}

}

final class HttpComponentsStreamingClientHttpRequest extends AbstractClientHttpRequest
		implements StreamingHttpOutputMessage {

	private final HttpClient httpClient;

	private final HttpUriRequest httpRequest;

	private final HttpContext httpContext;

	@Nullable
	private Body body;


	HttpComponentsStreamingClientHttpRequest(HttpClient client, HttpUriRequest request, HttpContext context) {
		this.httpClient = client;
		this.httpRequest = request;
		this.httpContext = context;
	}


	@Override
	public String getMethodValue() {
		return this.httpRequest.getMethod();
	}

	@Override
	public URI getURI() {
		return this.httpRequest.getURI();
	}

	@Override
	public void setBody(Body body) {
		assertNotExecuted();
		this.body = body;
	}

	@Override
	protected OutputStream getBodyInternal(HttpHeaders headers) throws IOException {
		throw new UnsupportedOperationException("getBody not supported");
	}

	@Override
	protected ClientHttpResponse executeInternal(HttpHeaders headers) throws IOException {
		HttpComponentsClientHttpRequest.addHeaders(this.httpRequest, headers);

		if (this.httpRequest instanceof HttpEntityEnclosingRequest && this.body != null) {
			HttpEntityEnclosingRequest entityEnclosingRequest = (HttpEntityEnclosingRequest) this.httpRequest;
			HttpEntity requestEntity = new StreamingHttpEntity(getHeaders(), this.body);
			entityEnclosingRequest.setEntity(requestEntity);
		}

		HttpResponse httpResponse = this.httpClient.execute(this.httpRequest, this.httpContext);
		return new HttpComponentsClientHttpResponse(httpResponse);
	}

	//......
}	

/**
 * Represents a client-side HTTP response.
 * Obtained via an calling of the {@link ClientHttpRequest#execute()}.
 *
 * <p>A {@code ClientHttpResponse} must be {@linkplain #close() closed},
 * typically in a {@code finally} block.
 *
 * @author Arjen Poutsma
 * @since 3.0
 */
public interface ClientHttpResponse extends HttpInputMessage, Closeable {

	/**
	 * Return the HTTP status code as an {@link HttpStatus} enum value.
	 * @return the HTTP status as an HttpStatus enum value (never {@code null})
	 * @throws IOException in case of I/O errors
	 * @throws IllegalArgumentException in case of an unknown HTTP status code
	 * @since #getRawStatusCode()
	 * @see HttpStatus#valueOf(int)
	 */
	HttpStatus getStatusCode() throws IOException;

	/**
	 * Return the HTTP status code (potentially non-standard and not
	 * resolvable through the {@link HttpStatus} enum) as an integer.
	 * @return the HTTP status as an integer value
	 * @throws IOException in case of I/O errors
	 * @since 3.1.1
	 * @see #getStatusCode()
	 * @see HttpStatus#resolve(int)
	 */
	int getRawStatusCode() throws IOException;

	/**
	 * Return the HTTP status text of the response.
	 * @return the HTTP status text
	 * @throws IOException in case of I/O errors
	 */
	String getStatusText() throws IOException;

	/**
	 * Close this response, freeing any resources created.
	 */
	@Override
	void close();

}

final class HttpComponentsClientHttpResponse extends AbstractClientHttpResponse {

	private final HttpResponse httpResponse;

	@Nullable
	private HttpHeaders headers;


	HttpComponentsClientHttpResponse(HttpResponse httpResponse) {
		this.httpResponse = httpResponse;
	}


	@Override
	public int getRawStatusCode() throws IOException {
		return this.httpResponse.getStatusLine().getStatusCode();
	}

	@Override
	public String getStatusText() throws IOException {
		return this.httpResponse.getStatusLine().getReasonPhrase();
	}

	@Override
	public HttpHeaders getHeaders() {
		if (this.headers == null) {
			this.headers = new HttpHeaders();
			for (Header header : this.httpResponse.getAllHeaders()) {
				this.headers.add(header.getName(), header.getValue());
			}
		}
		return this.headers;
	}

	@Override
	public InputStream getBody() throws IOException {
		HttpEntity entity = this.httpResponse.getEntity();
		return (entity != null ? entity.getContent() : StreamUtils.emptyInput());
	}

	@Override
	public void close() {
		// Release underlying connection back to the connection manager
		try {
			try {
				// Attempt to keep connection alive by consuming its remaining content
				EntityUtils.consume(this.httpResponse.getEntity());
			}
			finally {
				if (this.httpResponse instanceof Closeable) {
					((Closeable) this.httpResponse).close();
				}
			}
		}
		catch (IOException ex) {
			// Ignore exception on close...
		}
	}

}