1. RestTemplate
首先引入依赖
<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency>编写配置类
@Configuration
public class RestTemplateConfig {@Beanpublic RestTemplate restTemplate(ClientHttpRequestFactory factory){return new RestTemplate(factory);}@Beanpublic ClientHttpRequestFactory simpleClientHttpRequestFactory(){SimpleClientHttpRequestFactory factory = new SimpleClientHttpRequestFactory();factory.setReadTimeout(5000);//单位为msfactory.setConnectTimeout(5000);//单位为msreturn factory;}
}SimpleClientHttpRequestFactory类对应的HTTP库是JDK自带的HttpUrlConnection，也可以修改使用其他的HTTP库，例如HttpComponentsAsyncClientHttpRequestFactory。
这样就可以注入使用了
@Resourceprivate RestTemplate restTemplate; String url = "http://127.0.0.1/test";// 请求参数Map map = new HashMap<>();map.put("key", "111");// 设置请求头属性HttpHeaders httpHeaders = new HttpHeaders();httpHeaders.setContentType(MediaType.APPLICATION_JSON);HttpEntity httpEntity = new HttpEntity(map, httpHeaders);String results = restTemplate.postForObject(url, httpEntity, String.class);2. WebClient
Spring3.0引入了RestTemplate，WebClient是Spring Framework的一部分，但是在后来的官方源码中介绍，RestTemplate有可能在未来的版本中被弃用，所谓替代RestTemplate，在Spring5中引入了WebClient作为异步的非阻塞、响应式的HTTP客户端。
依赖
<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-webflux</artifactId>
</dependency>使用
public class TestWebClient {@Testpublic void doGet() {String userId = "郭郭";String url = "http://127.0.0.1:8094/masterdata/sysUser/getSysUserById?userId={userId}";Mono<String> mono = WebClient//创建WebClient实例.create()//方法调用，WebClient中提供了多种方法.get()//请求url.uri(url, userId)//获取响应结果.retrieve()//将结果转换为指定类型.bodyToMono(String.class);//返回最终结果：block是阻塞的/subscribe()非阻塞式获取响应结果System.out.println("响应结果：" + mono.block());}@Testpublic void doPost() {Map map = new HashMap<>();map.put("name", "郭郭");String requestBody = JSON.toJSONString(map);String url = "http://127.0.0.1:8094/masterdata/sysUser/saveUser";Mono<String> mono = WebClient//创建WebClient实例.create()//方法调用，WebClient中提供了多种方法.post()//请求url.uri(url)//指定请求的Content-Type为JSON.contentType(MediaType.APPLICATION_JSON)//使用bodyValue方法传递请求体.bodyValue(requestBody)//获取响应结果.retrieve()//将结果转换为指定类型.bodyToMono(String.class);//返回最终结果：block是阻塞的/subscribe()非阻塞式获取响应结果System.out.println("响应结果：" + mono.block());}
}在上述doPost请求中，我们的请求接口入参是一个Map，但是需要转换为JSON格式传递，这是因为WebClient默认是使用JSON序列化的。
3.Apache HttpClient
引入依赖
<!-- 此处使用的是 5.x 版本，可以根据自身情况引入版本 --><dependency><groupId>org.apache.httpcomponents.client5</groupId><artifactId>httpclient5</artifactId><version>5.1.1</version></dependency>//步骤一：方式1获取默认配置的httpClient实例
CloseableHttpClient httpClient = HttpClients.createDefault();
// 方式2根据系统配置创建 HttpClient
// CloseableHttpClient httpClient = HttpClients.createSystem();
// 在项目启动时可以通过设置如下JVM启动参数：
// http.agent 配置 userAgent
// http.keepAlive 配置 keepAlive 数据
// 方式3自定义创建全局配置
// CloseableHttpClient httpClient = HttpClients.custom()
// .setDefaultHeaders(Collections.emptyList()) // 设置默认请求头
// .setDefaultRequestConfig(RequestConfig.DEFAULT) // 设置默认配置
// .build();// 设置默认请求头
List<Header> headers = new ArrayList<>();
headers.add(new BasicHeader(HttpHeaders.CONTENT_TYPE, ContentType.APPLICATION_JSON));
headers.add(new BasicHeader(HttpHeaders.ACCEPT_ENCODING, "gzip, x-gzip, deflate"));
headers.add(new BasicHeader(HttpHeaders.CONNECTION, "keep-alive"));
httpClient .setDefaultHeaders(headers) //步骤二：创建HTTP请求
HttpGet httpGet = new HttpGet("http://127.0.0.1:8080/masterdata/sysUser/getSysUserById?userId=张三");// 创建请求配置信息
RequestConfig requestConfig = RequestConfig.custom()
// 设置连接超时时间
.setConnectTimeout(Timeout.of(3000, TimeUnit.MILLISECONDS))
// 设置响应超时时间
.setResponseTimeout(3000, TimeUnit.MILLISECONDS)
// 设置从连接池获取链接的超时时间
.setConnectionRequestTimeout(3000, TimeUnit.MILLISECONDS)
.build();
// 设置请求参数
httpGet.setConfig(requestConfig);// 添加 Content-Type 请求头
httpPost.addHeader(HttpHeaders.CONTENT_TYPE, ContentType.APPLICATION_FORM_URLENCODED);
// 添加 accept 请求头
httpPost.addHeader(new BasicHeader(HttpHeaders.ACCEPT, "*/*"));//步骤三：发送请求并获取响应数据
CloseableHttpResponse response = httpClient.execute(httpGet);
// 获取请求状态
int code = response.getCode();
//步骤四：处理响应数据
HttpEntity entity = response.getEntity();
String result = EntityUtils.toString(entity);
//步骤五：关闭httpClient和response
response.close();
httpClient.close();通过 URIBuilder 构建请求路径
// 构建请求路径，及参数
URL url = new URL("http://localhost:10010/user/params");
URI uri = new URIBuilder()
.setScheme(url.getProtocol())
.setHost(url.getHost())
.setPort(url.getPort())
.setPath(url.getPath())
// 构建参数
.setParameters(
new BasicNameValuePair("name", "张三"),
new BasicNameValuePair("age", "20")
).build();
// 创建 GET 请求对象
HttpGet httpGet = new HttpGet(uri);
// 调用 HttpClient 的 execute 方法执行请求
CloseableHttpResponse response = httpClient.execute(httpGet);
// 获取请求状态
int code = response.getCode();
// 如果请求成功
if(code == HttpStatus.SC_OK){
http://LOGGER.info("响应结果为：{}", EntityUtils.toString(response.getEntity()));
}发送 JSON 数据
HttpClient 中发送 JSON 数据可以使用 StringHttpEntity 类实现，如下所示：
// 请求参数
String url = "http://localhost:10010/user/body";
// 创建 GET 请求对象
HttpPost httpPost = new HttpPost(url);
// 构建对象
User user = new User();
user.setName("张三")
.setAge(20)
.setAddress(new Address()
.setCounty("中国")
.setCity("北京"))
.setAihao(Arrays.asList("跑步", "爬山", "看书"));
// 创建 字符串实体对象
HttpEntity httpEntity = new StringEntity(JSON.toJSONString(user));
httpPost.setEntity(httpEntity);
// 发送 POST 请求
httpClient.execute(httpPost);模拟form表单数据
// 修改 contentType
// 创建 ContentType 对象为 form 表单模式
ContentType contentType = ContentType.create("application/x-www-form-urlencoded", StandardCharsets.UTF_8);
// 添加到 HttpPost 头中
httpPost.setHeader(HttpHeaders.CONTENT_TYPE, contentType);
创建请求数据 HttpEntity
// 方式一、自己拼接请求数据，并且创建 StringEntity 对象
String query = "name="+ URLEncoder.encode("张三", "utf-8") +"&age=20";
HttpEntity httpEntity = new StringEntity(query);
// 方式二、通过UrlEncodedFormEntity 创建 HttpEntity
HttpEntity httpEntity = new UrlEncodedFormEntity(
Arrays.asList(new BasicNameValuePair("name", "张三"),
new BasicNameValuePair("age", "20")),
StandardCharsets.UTF_8
);
// 把 HttpEntity 设置到 HttpPost 中
httpPost.setEntity(httpEntity);上传
//要上传的文件File file = new File("F:/20150703212056_Yxi4L.jpeg");// 创建对象MultipartEntityBuilder builder = MultipartEntityBuilder.create();// 添加二进制消息体builder.addBinaryBody("file", file);// 也可以添加文本消息ContentType contentType = ContentType.TEXT_PLAIN.withCharset(StandardCharsets.UTF_8);builder.addTextBody("name", "张三", contentType);// 通过 MultipartEntityBuilder 构建消息体HttpEntity httpEntity = builder.build();HttpPost httpPost = new HttpPost("http://localhost:10010/user/upload");httpPost.setEntity(httpEntity);CloseableHttpResponse response = httpClient.execute(httpPost);// 获取请求状态int code = response.getCode();// 如果请求成功if(code == HttpStatus.SC_OK){LOGGER.info("响应结果为：{}", EntityUtils.toString(response.getEntity()));}下载
// 请求下载路径HttpGet httpGet = new HttpGet("http://localhost:10010/user/downLoad");CloseableHttpResponse response = httpClient.execute(httpGet);// 如果请求成功if (response.getCode() == HttpStatus.SC_OK){// 获取下载文件的文件名，此处的 File-Name 头信息，需要在服务端进行自定义Header header = response.getFirstHeader("File-Name");String value = header.getValue();// 读取数据byte[] bytes = EntityUtils.toByteArray(response.getEntity());try (OutputStream outputStream = new FileOutputStream("F:/" + value);){outputStream.write(bytes);outputStream.flush();}}响应处理
// 转换为字符串EntityUtils.toString(response.getEntity());// 转换为字节数组EntityUtils.toByteArray(response.getEntity());自定义响应对象
@Data@Accessors(chain = true)class Response {// 响应状态private int code;// 响应描述private String msg;// 响应体private String body;}// 调用 execute 时自定义 响应处理类Response execute = httpClient.execute(httpGet, response -> {return new Response().setCode(response.getCode()).setMsg(response.getReasonPhrase()).setBody(EntityUtils.toString(response.getEntity(), StandardCharsets.UTF_8));});会话保持
// 创建 HttpClientContext对象HttpContext httpContext = new BasicHttpContext();httpContext.setAttribute("name", "zhangsan");HttpClientContext httpClientContext = HttpClientContext.adapt(httpContext);// 登录httpClient.execute(new HttpPost(""), httpClientContext);// 获取数据httpClient.execute(new HttpGet(""), httpClientContext);4. OkHttp
具有低内存占有和出色的性能
引入依赖
<dependency><groupId>com.squareup.okhttp3</groupId><artifactId>okhttp</artifactId><version>4.0.0</version></dependency>5. HttpURLConnection
Java 自带的一个 HTTP 客户端工具
示例：
@Testpublic void doGet() throws IOException {String userId = "张三"; // 参数值userId = URLEncoder.encode(userId, "UTF-8"); // 对参数值进行URL编码//步骤一：创建URL对象URL url = new URL("http://127.0.0.1:8094/masterdata/sysUser/getSysUserById?userId=" + userId);//步骤二：打开连接 HttpURLConnection继承自URLConnection，是它的一个子类，//而HttpURLConnection专门用于处理HTTP协议的连接，如果需要处理其他协议使用通用的URLConnection。HttpURLConnection conn = (HttpURLConnection) url.openConnection();//步骤三：设置请求方式conn.setRequestMethod("GET");//步骤四：读取响应内容BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));StringBuilder sb = new StringBuilder();String line;while ((line = reader.readLine()) != null) {sb.append(line);}reader.close();System.out.println(sb.toString());} @Testpublic void doPost() throws IOException {//创建URL对象URL url = new URL("http://127.0.0.1:8094/masterdata/sysUser/saveUser");//打开连接HttpURLConnection conn = (HttpURLConnection) url.openConnection();//设置请求方式conn.setRequestMethod("POST");// 设置请求头conn.setRequestProperty("Content-Type", "application/json");//启用输出流//告诉连接对象您将使用输出流来发送数据，这样它会准备好接受输出流，并将数据发送到服务器。//这是发送POST请求体数据所必需的步骤。get没有请求体不需要conn.setDoOutput(true);//设置请求体数据Map map = new HashMap<>();map.put("name", "张三");String requestBody = JSON.toJSONString(map);//发送请求体数据try (DataOutputStream outputStream = new DataOutputStream(conn.getOutputStream())) {outputStream.write(requestBody.getBytes(StandardCharsets.UTF_8));}//读取响应内容BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));StringBuilder sb = new StringBuilder();String line;while ((line = reader.readLine()) != null) {sb.append(line);}reader.close();System.out.println(sb.toString());} 6. FeignClient
引入依赖
<dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>在 spring boot 启动类加上@EnableFeignClients注解
// name：指定Feign的名称，如果使用了注册中心，name属性会作为微服务的名称，用于服务发现
// url：Feign调用的跳转路径，可以在配置文件中设置，多用于代码调试
@FeignClient(name = "masterdata",url = "${masterdata-service-url}")
public interface ISysUserClient {@GetMapping(value = "/masterdata/getSysUserById")public Map getSysUserById(@RequestParam("userId") String userId);
}默认是连接超时10s，读超时60s ，feign 集成了 ribbon 和 hystrix，feign 本身不带超时限制，其超时是由 ribbon 和 hystrix 控制的。
## 方法一：设置在ribbon上
ribbon:OkToRetryOnAllOperations: false #对所有操作请求都进行重试,默认falseReadTimeout: 5000 #负载均衡超时时间，默认值5000ConnectTimeout: 3000 #ribbon请求连接的超时时间，默认值2000MaxAutoRetries: 0 #对当前实例的重试次数，默认0MaxAutoRetriesNextServer: 1 #对切换实例的重试次数，默认1## 方法二：设置在feign client上
feign:client:config:default:connectTimeout: 5000readTimeout: 30007. AsyncHttpClient
AsyncHttpClient是一个独立的开源库，它不依赖于任何的框架或者技术栈
依赖：
<dependency><groupId>org.asynchttpclient</groupId><artifactId>async-http-client</artifactId><version>2.12.3</version>
</dependency>示例：
public class TestAsyncHttpClient {@Testpublic void doGet() throws IOException {try (AsyncHttpClient client = new DefaultAsyncHttpClient();) {BoundRequestBuilder requestBuilder = client.prepareGet("http://127.0.0.1:8094/masterdata/sysUser/getSysUserById?userId=郭郭");CompletableFuture<String> future = requestBuilder.execute().toCompletableFuture().thenApply(Response::getResponseBody);//使用join等待响应完成String responseBody = future.join();System.out.println(responseBody);}}@Testpublic void doPost() throws IOException {try (AsyncHttpClient client = new DefaultAsyncHttpClient();) {BoundRequestBuilder requestBuilder = client.preparePost("http://127.0.0.1:8094/masterdata/sysUser/saveUser");//requestBody请求入参Map map = new HashMap<>();map.put("name", "郭郭");String requestBody = JSON.toJSONString(map);requestBuilder.addHeader("Content-Type", "application/json");requestBuilder.setBody(requestBody);CompletableFuture<String> future = requestBuilder.execute().toCompletableFuture().thenApply(Response::getResponseBody);//使用join等待响应完成String responseBody = future.join();System.out.println(responseBody);}}}
