Java调用外部REST请求的几种方式 javahttprpc源码分析

1 restTemplate — spring 提供特点：
【Java调用外部REST请求的几种方式】1、RestOperations 提供了各种封装方法，非常方便直接将返回转成实体类。
2、默认使用JDK 的HttpURLConnection进行通信，但是可以通过RestTemplate.setRequestFactory 切换到不同的HTTP源：如Apache HttpComponents、Netty、OkHttp。
3、支持同步、异步请求；
4、支持更多的定制，比如拦截器等。
ps：支持 get 请求，参数是 body 的形式。
参考：https://www.huaweicloud.com/a...
国外知名博客Baeldung的博客 The Guide to RestTemplate: https://www.baeldung.com/rest...
1.1 底层是java的HttpURLConnection(默认使用，可以定制)
所有的请求都需要执行 doExecute() 方法

@Nullable protected T doExecute(URI url, @Nullable HttpMethod method, @Nullable RequestCallback requestCallback, @Nullable ResponseExtractor responseExtractor) throws RestClientException { Assert.notNull(url, "URI is required"); Assert.notNull(method, "HttpMethod is required"); ClientHttpResponse response = null; Object var14; try { // 创建请求 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 创建请求

public abstract class HttpAccessor { ... // 省略代码无数 protected ClientHttpRequest createRequest(URI url, HttpMethod method) throws IOException { // 使用 ClientHttpRequestFactory 创建请求 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 创建请求

public ClientHttpRequest createRequest(URI uri, HttpMethod httpMethod) throws IOException { // 使用 HttpURLConnection 创建请求 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 请求，返回直接封装为实体

RestTemplate restTemplate = new RestTemplate(); HttpEntity 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请求，但是参数是body形式
一般 get 请求，不支持 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是一种非传统的构造，属于HTTP规范的灰色区域。最终的结果是，许多旧的软件要么根本不能处理这样的请求，要么会明确拒绝，因为他们认为它是格式错误的请求。

/** * 注意：get请求，但是参数是body形式 * * @param url * @param paramBody * @return */ private String getWithBody(String url, Map 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(); //修改restTemplate的RequestFactory使其支持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，以支持GET请求携带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。
它支持各种封装好的get、post、put请求。
2.1 get 请求

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 表单格式的入参 public static String get(String urlString, Map paramMap) { return HttpRequest.get(urlString).form(paramMap).execute().body(); }// form 表单格式的入参，并设置超时时间 public static String get(String urlString, Map paramMap, int timeout) { return HttpRequest.get(urlString).form(paramMap).timeout(timeout).execute().body(); }

2.2 post 请求
这些请求最终调用的都是 HttpRequest 的 execute() 方法。

// form 表单格式的入参 public static String post(String urlString, Map paramMap) { return post(urlString, paramMap, HttpGlobalConfig.timeout); }// form 表单格式的入参，并设置超时时间 public static String post(String urlString, Map paramMap, int timeout) { return HttpRequest.post(urlString).form(paramMap).timeout(timeout).execute().body(); }// body 格式入参 public static String post(String urlString, String body) { return post(urlString, body, HttpGlobalConfig.timeout); }// body 格式入参，并设置超时时间 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 param = new HashMap<>(); param.put("userId", userId); String res = HttpUtil.post(url, JsonUtil.of(param));

3 HttpRequest — hutool 提供 HttpRequest 提供了非常方便构造请求的构造函数。当参数比较多、header比较多的时候，可以使用这种方式。（这里使用了构造模式）
3.1 底层是Java的HttpURLConnection
HttpRequest 底层又是使用了 java 提供的 HttpURLConnection
上源码：
最终都需要执行这个execute方法，这个方法调用了hutool封装的HttpConnection，这个HttpConnection又使用了java提供的HttpURLConnection。

// hutool 执行方法 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; // 这个连接 HttpURLConnection ，是java提供的 private HttpURLConnection conn; ...// 省略无数代码 }

3.2 一个例子

private String invoke(String url, String isMock, Map map) { String result = HttpRequest.post(url).body(JSONUtil.toJsonStr(map)).execute().body(); return result; }