越来越多的 Java 应用程序需要直接通过 HTTP 协议来访问网络资源。虽然在 JDK 的 java.net 包中已经提供了访问 HTTP 协议的基本功能，但是对于大部分应用程序来说，JDK 库本身提供的功能还不够丰富和灵活。

HttpClient 是 Apache Jakarta Common 下的子项目，用来提供高效的、最新的、功能丰富的支持 HTTP 协议的客户端编程工具包，并且它支持 HTTP 协议最新的版本和建议。

新建一个 SpringBoot 工程，引入 httpclient 的 POM 依赖：

<dependency>	<groupId>org.apache.httpcomponents</groupId>	<artifactId>httpclient</artifactId>	<version>4.5.6</version></dependency>

详细使用示例

GET 无参

调用接口：

没有入参。

HttpClientController#doGetNoParams() ：GET请求接口不带参数

@RestController@RequestMapping("/httpClient")public class HttpClientController {     @Autowired    private HttpClientService httpClientService;    // GET请求接口不带参数    @GetMapping("/doGetNoParams")    public String doGetNoParams() {         return httpClientService.doGetNoParams();    }}

HttpClientServiceImpl#doGetNoParams() ：GET 请求接口不带参数

@Slf4j@Servicepublic class HttpClientServiceImpl implements HttpClientService {     // GET请求接口不带参数    @Override    public String doGetNoParams() {         String result = HttpClientUtil.doGetNoParams();        log.info("【发送GET请求】返回结果为：{}", result);        if (!StringUtil.isBlank(result)) {             TaskCenterUtil taskCenterUtil = TaskCenterUtil.getTaskCenterUtil();            taskCenterUtil.submitTask(() -> {                 log.info("【子线程】开启了一个新线程，当前线程名为：{}", Thread.currentThread().getName());                return null;            });        }        log.info("【主线程】当前线程名为：{}", Thread.currentThread().getName());        return result;    }}

说明：

当 HTTP 调用成功后，通过线程池开一个子线程，去异步执行任务；主线程继续向下执行

HttpClientUtil#doGetNoParams() ：GET请求接口不带参数

@Slf4jpublic class HttpClientUtil {     // 服务器ip    public static final String IP = ";;    // 端口    public static final String PORT = ":8080";    // GET请求接口不带参数    public static final String GET_URL_NO_PARAMS = IP + PORT + "/http/listUsers";    // GET请求接口不带参数    public static String doGetNoParams() {         CloseableHttpClient httpClient = HttpClientBuilder.create().build();        // 创建 GET 请求        HttpGet httpGet = new HttpGet(GET_URL_NO_PARAMS);        httpGet.setHeader("Accept-Encoding", "identity");        log.info("【发送GET请求】请求地址为：{}", GET_URL_NO_PARAMS);        CloseableHttpResponse httpResponse = null;        try {             httpResponse = httpClient.execute(httpGet);            HttpEntity httpEntity = httpResponse.getEntity();            log.info("【发送GET请求】成功，相应状态为：{}", httpResponse.getStatusLine());            if (HttpStatus.SC_OK == httpResponse.getStatusLine().getStatusCode() && null != httpEntity) {                 String result = EntityUtils.toString(httpEntity);                log.info("【发送GET请求】成功，响应内容为：{}", result);                return result;            }        } catch (IOException e) {             log.error("【发送GET请求】失败，执行发送请求时，出现IO异常，异常信息为：{}", e);            return null;        } finally {             try {                 close(httpClient, httpResponse);            } catch (IOException e) {                 log.error("【发送GET请求】失败，关闭流时，出现IO异常，异常信息为：{}", e);            }        }        return null;    }}

说明：

通过类 HttpGet 发起 GET 请求。

HttpGet ：有 3 个构造方法

public class HttpGet extends HttpRequestBase {     public HttpGet() {     }    public HttpGet(URI uri) {         this.setURI(uri);    }    public HttpGet(String uri) {         this.setURI(URI.create(uri));    }    ...}

这里使用了 public HttpGet(String uri); 方式来构造 HttpGet 实例。

HttpClientUtil#close() ：关闭流

// 关闭流public static void close(CloseableHttpClient httpClient, CloseableHttpResponse httpResponse) throws IOException{     if (null != httpClient) {         httpClient.close();    }    if (null != httpResponse) {         httpResponse.close();    }}

TaskCenterUtil ：线程池工具类

public class TaskCenterUtil {     public static Integer CORE_POOL_SIZE = 10;    public static Integer MAX_NUM_POOL_SIZE = 10;    public static Integer MAX_MESSAGE_SIZE = 100;    public static Long KEEP_ALIVE_TIME = 60L;    private ThreadPoolExecutor poolExecutor = new ThreadPoolExecutor(CORE_POOL_SIZE, MAX_NUM_POOL_SIZE, KEEP_ALIVE_TIME,            TimeUnit.SECONDS, new LinkedBlockingQueue<>(MAX_MESSAGE_SIZE), new ThreadPoolExecutor.CallerRunsPolicy());    private TaskCenterUtil() { }    private static TaskCenterUtil taskCenterUtil = new TaskCenterUtil();    public static TaskCenterUtil getTaskCenterUtil() {         return taskCenterUtil;    }    // 提交任务    public void submitTask(Callable task) {         poolExecutor.submit(task);    }}

POSTMAN 调用：

控制台打印日志：

GET 有参

方式一：使用 public HttpGet(String uri); 方式来构造 HttpGet 实例。即：使用 url 字符串来拼接参数。

方式二：使用 public HttpGet(URI uri); 方式来构造 HttpGet 实例。

调用接口：

入参：

id=1

HttpClientController#doGetParams() ：GET请求接口带参数

@GetMapping("/doGetParams")public String doGetParams(String id) {     return httpClientService.doGetParams(id);}

HttpClientServiceImpl ：

@Overridepublic String doGetParams(String id) {     String result = HttpClientUtil.doGetParams(id);    log.info("【发送GET请求】返回结果为：{}", result);    return result;}

HttpClientUtil#doGetParams() ：GET请求接口带参数

@Slf4jpublic class HttpClientUtil {     // GET请求接口带参数    public static final String GET_URL_PARAMS = IP + PORT + "/http/getUserById";    // 入参名称    public static final String URL_PARAMS_ID = "id";		// http 协议    public static final String SCHEME_HTTP = "http";    // 主机    public static final String LOCAL_HOST = "localhost";    // 请求接口路径    public static final String GET_URL_PARAMS_PATH = "/http/getUserById";    // 端口    public static final Integer LOCAL_PORT = 8080;    // GET请求接口带参数    public static String doGetParams(String id) {         CloseableHttpClient httpClient = HttpClientBuilder.create().build();        // 不同方式获取 HttpGet        // 方式一：        HttpGet httpGet = getStrHttpGet(GET_URL_PARAMS, id);        // 方式二：        //HttpGet httpGet = getUrlHttpGet(id);        // 获取请求头配置信息        RequestConfig requestConfig = HttpClientConfig.getRequestConfig();        httpGet.setConfig(requestConfig);        CloseableHttpResponse response = null;        try {             response = httpClient.execute(httpGet);            HttpEntity httpEntity = response.getEntity();            log.info("【发送GET请求】成功，相应状态为：{}", response.getStatusLine());            if (HttpStatus.SC_OK == response.getStatusLine().getStatusCode() && null != httpEntity) {                 String result = EntityUtils.toString(httpEntity);                log.info("【发送GET请求】成功，响应内容为：{}", result);                return result;            }        } catch (IOException e) {             log.error("【发送GET请求】失败，执行发送请求时，出现IO异常，异常信息为：{}", e);            return null;        } finally {             try {                 close(httpClient, response);            } catch (IOException e) {                 log.error("【发送GET请求】失败，关闭流时，出现IO异常，异常信息为：{}", e);            }        }        return null;    }}

getStrHttpGet() ：方式一：url拼接参数

public static HttpGet getStrHttpGet(String url, String id) {     StringBuilder builder = new StringBuilder();    // url 拼接参数  /http/getUserById?id=1    String strUrl = builder.append(url).append("?").append(URL_PARAMS_ID).append("=").append(id).toString();    log.info("【发送GET请求】请求地址为：{}", strUrl);    HttpGet httpGet = new HttpGet(strUrl);    return httpGet;}

getUrlHttpGet() ：方式二：URI对象

public static HttpGet getUrlHttpGet(String id) {     // 将参数键值对放入集合中    List<NameValuePair> params = new ArrayList<>();    params.add(new BasicNameValuePair(URL_PARAMS_ID, id));    try {         URI uri = new URIBuilder()                .setScheme(SCHEME_HTTP)                .setHost(LOCAL_HOST)                .setPort(LOCAL_PORT)                .setPath(GET_URL_PARAMS_PATH)                .setParameters(params).build();        return new HttpGet(uri);    } catch (URISyntaxException e) {         log.error("【发送GET请求】构建URI失败，失败信息为：{}", e);    }    return null;}

说明：

方式一是使用 public HttpGet(String uri); 方式来构造 HttpGet 实例方式二是使用 public HttpGet(String uri); 方式来构造 HttpGet 实例。即：使用 url 字符串来拼接参数。

POSTMAN 调用：

POST 无参

调用接口：

入参：无

HttpClientController#doPostNoParams() ：POST请求接口不带参数

@PostMapping("/doPostNoParams")public String doPostNoParams() {     return httpClientService.doPostNoParams();}

HttpClientServiceImpl#doPostNoParams() ：

@Overridepublic String doPostNoParams() {     String result = HttpClientUtil.doPostNoParams();    log.info("【发送POST请求】返回结果为：{}", result);    return result;}

HttpClientUtil ：

public class HttpClientUtil {     // POST请求接口不带参数    public static final String POST_URL_NO_PARAMS = IP + PORT + "/http/listUserList";		// POST请求接口带参数    public static final String POST_URL_PARAMS = IP + PORT + "/http/getUserVoById";    // POST请求接口带参数 -- 对象参数    public static final String POST_URL_PARAMS_OBJECT = IP + PORT + "/http/listUsers";    // POST请求接口不带参数    public static String doPostNoParams() {         CloseableHttpClient httpClient = HttpClientBuilder.create().build();        HttpPost httpPost = new HttpPost(POST_URL_NO_PARAMS);        log.info("【发送POST请求】请求地址为：{}", POST_URL_NO_PARAMS);        CloseableHttpResponse response = null;        try {             response = httpClient.execute(httpPost);            HttpEntity httpEntity = response.getEntity();            log.info("【发送POST请求】成功，相应状态为：{}", response.getStatusLine());            if (HttpStatus.SC_OK == response.getStatusLine().getStatusCode() && null != httpEntity) {                 String result = EntityUtils.toString(httpEntity);                log.info("【发送POST请求】成功，响应内容为：{}", result);                return result;            }        } catch (IOException e) {             log.error("【发送POST请求】失败，执行发送请求时，出现IO异常，异常信息为：{}", e);            return null;        } finally {             try {                 close(httpClient, response);            } catch (IOException e) {                 log.error("【发送POST请求】失败，关闭流时，出现IO异常，异常信息为：{}", e);            }        }        return null;    }}

POST 有参

参数是：普通参数。方式与GET一样即可，直接在 url 后缀上拼接参数

参数是：对象。将参数以请求体的方式进行请求

普通参数

请求接口：

请求接口：

入参 UserVo：

{ 	"id": 1}

即：这个接口可以随便写

@PostMapping("/listUsers")public List<UserVo> listUsers(@RequestBody UserVo userVo) {     return httpService.listUsers();}

HttpClientController#doPostParams() ：POST请求接口带参数

@PostMapping("/doPostParams")public String doPostParams(String id) {     return httpClientService.doPostParams(id);}

HttpClientServiceImpl#doPostParams() ：

@Overridepublic String doPostParams(String id) {     String result = HttpClientUtil.doPostParams(id);    log.info("【发送POST请求】返回结果为：{}", result);    return result;}

HttpClientUtil#doPostParams() ：

public static String doPostParams(String id) {     CloseableHttpClient httpClient = HttpClientBuilder.create().build();    // 参数是普通参数    HttpPost httpPost = getStrHttpPost(POST_URL_PARAMS, id);    // 参数是对象    //HttpPost httpPost = getObjectHttpPost(id);    // 设置ContentType(注:如果只是传普通参数的话,ContentType不一定非要用application/json)    httpPost.setHeader("Content-Type", "application/json;charset=utf8");    CloseableHttpResponse response = null;    try {         response = httpClient.execute(httpPost);        HttpEntity httpEntity = response.getEntity();        log.info("【发送POST请求】成功，相应状态为：{}", response.getStatusLine());        if (HttpStatus.SC_OK == response.getStatusLine().getStatusCode() && null != httpEntity) {             String result = EntityUtils.toString(httpEntity);            log.info("【发送POST请求】成功，响应内容为：{}", result);            return result;        }    } catch (IOException e) {         log.error("【发送POST请求】失败，执行发送请求时，出现IO异常，异常信息为：{}", e);        return null;    } finally {         try {             close(httpClient, response);        } catch (IOException e) {             log.error("【发送POST请求】失败，关闭流时，出现IO异常，异常信息为：{}", e);        }    }    return null;}

getStrHttpPost() ：POST请求有参：普通参数

public static HttpPost getStrHttpPost(String url, String id) {     StringBuilder builder = new StringBuilder();    // url 拼接参数  /http/getUserVoById?id=1    String strUrl = builder.append(url).append("?").append(URL_PARAMS_ID).append("=").append(id).toString();    log.info("【发送POST请求】请求地址为：{}", strUrl);    HttpPost httpPost = new HttpPost(strUrl);    return httpPost;}

getObjectHttpPost() ：POST请求有参：对象参数

public static HttpPost getObjectHttpPost(String id) {     HttpPost httpPost = new HttpPost(POST_URL_PARAMS_OBJECT);    log.info("【发送POST请求】请求地址为：{}", POST_URL_PARAMS_OBJECT);    UserVo userVo = new UserVo();    userVo.setId(id);    // 将JAVA对象转换为Json字符串    String jsonString = JSON.toJSONString(userVo);    StringEntity stringEntity = new StringEntity(jsonString, "UTF-8");    // post请求是将参数放在请求体里面传过去的    httpPost.setEntity(stringEntity);    return httpPost;}

原文地址：