1 restTemplate — spring 提供
特点：
1、RestOperations 提供了各种封装办法，十分不便间接将返回转成实体类。
2、默认应用JDK 的HttpURLConnection进行通信，然而能够通过RestTemplate.setRequestFactory 切换到不同的HTTP源：如Apache HttpComponents、Netty、OkHttp。
3、反对同步、异步申请；
4、反对更多的定制，比方拦截器等。
ps：反对 get 申请，参数是 body 的模式。
参考：https://www.huaweicloud.com/a...
国外出名博客Baeldung的博客 The Guide to RestTemplate: https://www.baeldung.com/rest...
1.1 底层是java的HttpURLConnection(默认应用，能够定制)
所有的申请都须要执行 doExecute() 办法
@Nullableprotected <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; Object var14; try { // 创立申请 ClientHttpRequest request = this.createRequest(url, method); if (requestCallback != null) { requestCallback.doWithRequest(request); } response = request.execute(); this.handleResponse(url, method, response); var14 = responseExtractor != null ? responseExtractor.extractData(response) : null; } catch (IOException var12) { String resource = url.toString(); String query = url.getRawQuery(); resource = query != null ? resource.substring(0, resource.indexOf(63)) : resource; throw new ResourceAccessException("I/O error on " + method.name() + " request for \"" + resource + "\": " + var12.getMessage(), var12); } finally { if (response != null) { response.close(); } } return var14;}HttpAccessor 创立申请
public abstract class HttpAccessor { ... // 省略代码有数 protected ClientHttpRequest createRequest(URI url, HttpMethod method) throws IOException { // 应用 ClientHttpRequestFactory 创立申请 ClientHttpRequest request = this.getRequestFactory().createRequest(url, method); if (this.logger.isDebugEnabled()) { this.logger.debug("HTTP " + method.name() + " " + url); } return request; }}ClientHttpRequestFactory接口的具体实现，如：SimpleClientHttpRequestFactory 创立申请
public ClientHttpRequest createRequest(URI uri, HttpMethod httpMethod) throws IOException { // 应用 HttpURLConnection 创立申请 HttpURLConnection connection = this.openConnection(uri.toURL(), this.proxy); this.prepareConnection(connection, httpMethod.name()); return (ClientHttpRequest)(this.bufferRequestBody ? new SimpleBufferingClientHttpRequest(connection, this.outputStreaming) : new SimpleStreamingClientHttpRequest(connection, this.chunkSize, this.outputStreaming));}1.2 post 申请，返回间接封装为实体
RestTemplate restTemplate = new RestTemplate();HttpEntity<Foo> request = new HttpEntity<>(new Foo("bar"));Foo foo = restTemplate.postForObject(fooResourceUrl, request, Foo.class);assertThat(foo, notNullValue());assertThat(foo.getName(), is("bar"));1.3 get申请，然而参数是body模式
个别 get 申请，不反对 body 传参。
参考：https://stackoverflow.com/que...
HTTP GET with a body is a somewhat unconventional construct that falls in a gray area of the HTTP specification - the end result is that many older pieces of software either cannot handle such a request at all, or will explicitly reject it because they believe it to be malformed.
带有body参数的HTTP GET是一种非传统的结构，属于HTTP标准的灰色区域。最终的后果是，许多旧的软件要么基本不能解决这样的申请，要么会明确回绝，因为他们认为它是格局谬误的申请。
/** * 留神：get申请，然而参数是body模式 * * @param url * @param paramBody * @return */private String getWithBody(String url, Map<String, Object> paramBody) { HttpHeaders httpHeaders = new HttpHeaders(); httpHeaders.setContentType(MediaType.APPLICATION_JSON); httpHeaders.setAccept(Arrays.asList(MediaType.APPLICATION_JSON)); HttpEntity requestEntity = new HttpEntity(JsonUtil.of(paramBody), httpHeaders); RestTemplate template = getTemplate(); ResponseEntity response = template.exchange(url, HttpMethod.GET, requestEntity, String.class); Object result = response.getBody(); logger.info("/invokeThirdPartyRequest/getWithBody/result/[{}]", result.toString()); return result.toString();}/** * 获取 RestTemplate * * @return */private RestTemplate getTemplate() { RestTemplate restTemplate = new RestTemplate(); //批改restTemplate的RequestFactory使其反对Get携带body参数 restTemplate.setRequestFactory(new HttpComponentsClientRestfulHttpRequestFactory()); return restTemplate;}import org.apache.http.client.methods.HttpEntityEnclosingRequestBase;import org.apache.http.client.methods.HttpUriRequest;import org.springframework.http.HttpMethod;import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;import java.net.URI;public class HttpComponentsClientRestfulHttpRequestFactory extends HttpComponentsClientHttpRequestFactory { @Override protected HttpUriRequest createHttpUriRequest(HttpMethod httpMethod, URI uri) { if (httpMethod == HttpMethod.GET) { return new HttpGetRequestWithEntity(uri); } return super.createHttpUriRequest(httpMethod, uri); } /** * 定义HttpGetRequestWithEntity实现HttpEntityEnclosingRequestBase抽象类，以反对GET申请携带body数据 */ private static final class HttpGetRequestWithEntity extends HttpEntityEnclosingRequestBase { public HttpGetRequestWithEntity(final URI uri) { super.setURI(uri); } @Override public String getMethod() { return HttpMethod.GET.name(); } }}2 HttpUtil — hutool 提供
HttpUtil 其实是 HttpRequest 的封装。
它反对各种封装好的get、post、put申请。
2.1 get 申请
public static String get(String urlString, Charset customCharset) { return ((HttpRequest)HttpRequest.get(urlString).charset(customCharset)).execute().body();}public static String get(String urlString) { return get(urlString, HttpGlobalConfig.timeout);}public static String get(String urlString, int timeout) { return HttpRequest.get(urlString).timeout(timeout).execute().body();}// form 表单格局的入参public static String get(String urlString, Map<String, Object> paramMap) { return HttpRequest.get(urlString).form(paramMap).execute().body();}// form 表单格局的入参，并设置超时工夫public static String get(String urlString, Map<String, Object> paramMap, int timeout) { return HttpRequest.get(urlString).form(paramMap).timeout(timeout).execute().body();}2.2 post 申请
这些申请最终调用的都是 HttpRequest 的 execute() 办法。
// form 表单格局的入参public static String post(String urlString, Map<String, Object> paramMap) { return post(urlString, paramMap, HttpGlobalConfig.timeout);}// form 表单格局的入参，并设置超时工夫public static String post(String urlString, Map<String, Object> paramMap, int timeout) { return HttpRequest.post(urlString).form(paramMap).timeout(timeout).execute().body();}// body 格局入参public static String post(String urlString, String body) { return post(urlString, body, HttpGlobalConfig.timeout);}// body 格局入参，并设置超时工夫public static String post(String urlString, String body, int timeout) { return HttpRequest.post(urlString).timeout(timeout).body(body).execute().body();}2.3 一个例子
Map<String, Object> param = new HashMap<>();param.put("userId", userId);String res = HttpUtil.post(url, JsonUtil.of(param));3 HttpRequest — hutool 提供
HttpRequest 提供了十分不便结构申请的构造函数。当参数比拟多、header比拟多的时候，能够应用这种形式。（这里应用了结构模式）
3.1 底层是Java的HttpURLConnection
HttpRequest 底层又是应用了 java 提供的 HttpURLConnection
上源码：
最终都须要执行这个execute办法，这个办法调用了hutool封装的HttpConnection，这个HttpConnection又应用了java提供的HttpURLConnection。
// hutool 执行办法public HttpResponse execute(boolean isAsync) { this.urlWithParamIfGet(); this.initConnection(); this.send(); HttpResponse httpResponse = this.sendRedirectIfPossible(); if (null == httpResponse) { httpResponse = new HttpResponse(this.httpConnection, this.charset, isAsync, this.isIgnoreResponseBody()); } return httpResponse;}public class HttpConnection { private final URL url; private final Proxy proxy; // 这个连贯 HttpURLConnection ，是java提供的 private HttpURLConnection conn; ...// 省略有数代码}3.2 一个例子
private String invoke(String url, String isMock, Map<String, Object> map) { String result = HttpRequest.post(url).body(JSONUtil.toJsonStr(map)).execute().body(); return result;}