一 . 概述

跨服务器请求数据方式有很多种,本文介绍 OKHttp3 与 httpclient 两种方式,两种方式返回的数据格式是json, json解析请参考https://www.jianshu.com/writer#/notebooks/39950651/notes/54439484/preview

二 . OKHttp3

2.1 步骤一 : 导包

    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
      <!--okhttp3-->
     <dependency>
       <groupId>com.squareup.okhttp3</groupId>
        <artifactId>okhttp</artifactId>
        <version>4.2.0</version>
     </dependency>
    <dependency>
      <groupId>com.alibaba</groupId>
      <artifactId>fastjson</artifactId>
      <version>1.2.60</version>
    </dependency>

2.2 步骤二 : 配置 spring-config(设定超时)

    @Bean
    public OkHttpClient okHttpClient() {
        OkHttpClient.Builder builder = new OkHttpClient.Builder();
        builder.connectTimeout(30, TimeUnit.SECONDS)
                .readTimeout(30, TimeUnit.SECONDS)
                .writeTimeout(30,TimeUnit.SECONDS)
                .retryOnConnectionFailure(true);
        return builder.build();
    }

2.3 步骤三: 在controller层 的get请求

    @RestController
    @RequestMapping("/test")
    public String run(String url) throws IOException {
        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder()
                .url(url)
                .build();
        try (Response response = client.newCall(request).execute()) {
            return response.body().string();
        }
    }

注:这样是原封不动把JSON数据返回给前端

附 post请求

public static final MediaType JSON
    = MediaType.get("application/json; charset=utf-8");

OkHttpClient client = new OkHttpClient();

String post(String url, String json) throws IOException {
  RequestBody body = RequestBody.create(JSON, json);
  Request request = new Request.Builder()
      .url(url)
      .post(body)
      .build();
  try (Response response = client.newCall(request).execute()) {
    return response.body().string();
  }
}

三 . Httpclient

3.1 步骤一导包

    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
      <groupId>org.apache.httpcomponents</groupId>
      <artifactId>httpclient</artifactId>
    </dependency>
    <dependency>
      <groupId>com.alibaba</groupId>
      <artifactId>fastjson</artifactId>
      <version>1.2.60</version>
    </dependency>

3.2 步骤二 : 编写工具类HttpProtocolHandler

public class HttpProtocolHandler {

    /**
     * 请求方式
     */
    public enum Request_method {
        POST, GET
    }

    /**
     * Http连接管理器，该管理器必须是线程安全的
     */
    private static PoolingHttpClientConnectionManager connectionManager;

    /**
     * 最大的连接数量
     */
    private int maxTotal = 100;

    /**
     * 每个路径最大的连接数
     */
    private int maxConnPerRoute = 20;

    private static HttpProtocolHandler httpProtocolHandler = new HttpProtocolHandler();

    public HttpProtocolHandler() {
        /**
         * Http连接池
         */
        connectionManager = new PoolingHttpClientConnectionManager();
        connectionManager.setMaxTotal(maxTotal);
        connectionManager.setDefaultMaxPerRoute(maxConnPerRoute);
    }

    public static HttpProtocolHandler getInstance() {
        return httpProtocolHandler;
    }

    // 具体的调用方法
    public String execute(Request_method requestMethod, String url, Map<String, String> paramsMap) {
        String responseStr = null;
        CloseableHttpClient httpClient = HttpClients.custom().setConnectionManager(connectionManager).build();

        List<NameValuePair> nameValuePair = generatNameValuePair(paramsMap);
        UrlEncodedFormEntity entity = new UrlEncodedFormEntity(nameValuePair, Consts.UTF_8);

        HttpUriRequest uriRequest = Request_method.GET.equals(requestMethod) ? new HttpGet(generatRequestUrl(url, paramsMap)) : new HttpPost(url);

        if (Request_method.POST.equals(requestMethod)) {
            ((HttpPost) uriRequest).setEntity(entity);
        }
        try {
            HttpResponse httpResponse = httpClient.execute(uriRequest);
            responseStr = EntityUtils.toString(httpResponse.getEntity());
        } catch (ClientProtocolException e) {
            e.printStackTrace();
            return null;
        } catch (IOException e) {
            e.printStackTrace();
            return null;
        } finally {
            /**
             try {
             httpClient.close();
             } catch (IOException e) {
             e.printStackTrace();
             }
             */
        }
        return responseStr;
    }

    /**
     * POST请求参数的组装
     */
    public static List<NameValuePair> generatNameValuePair(Map<String, String> paramsMap) {
        List<NameValuePair> nameValuePair = new LinkedList<NameValuePair>();
        for (Map.Entry<String, String> entry : paramsMap.entrySet()) {
            nameValuePair.add(new BasicNameValuePair(entry.getKey(), entry.getValue()));
        }
        return nameValuePair;
    }

    /**
     * GET请求的参数的封装
     *
     * @param url
     * @param paramsMap
     * @return
     */
    public static String generatRequestUrl(String url, Map<String, String> paramsMap) {
        StringBuffer fullUrl = new StringBuffer(url);
        if (paramsMap != null && paramsMap.size() > 0) {
            fullUrl.append("?");
            int i = 0;
            for (Map.Entry<String, String> entry : paramsMap.entrySet()) {
                i++;
                String paramName = entry.getKey();
                String paramValue = entry.getValue();
                fullUrl.append(i == paramsMap.size() ? paramName + "=" + paramValue : paramName + "=" + paramValue + "&");
            }
        }
        return fullUrl.toString();
    }

} 

3.3 在controller层调用

@RestController
@RequestMapping("/remote")
public class RemoteController {
    private HttpProtocolHandler handler = new HttpProtocolHandler();
    @RequestMapping
    public Object getUser() {
        String url = "http://localhost:8080/user";
        Map<String, String> map = new HashMap<>();
        String result = handler.execute(HttpProtocolHandler.Request_method.GET, url, map);
        return result;
    }
}