Java如何实现调用外部Api

	public static String requestOCRForHttp(String url, Map<String, String> requestParams, String filePathAndName)
			throws Exception {
		String result = null;
		CloseableHttpClient httpClient = HttpClients.createDefault();
		/** HttpPost */
		HttpPost httpPost = new HttpPost(url);
		MultipartEntity reqEntity = new MultipartEntity(); // 建立多文件实例
		FileBody filebody = new FileBody(new File(filePathAndName));
		reqEntity.addPart("pic", filebody);// upload为请求后台的File upload;
		for (String key : requestParams.keySet()) {
			String value = requestParams.get(key);
			reqEntity.addPart(key, new StringBody(value, Charset.forName("utf-8")));
		}
		httpPost.setEntity(reqEntity); // 设置实体
		/** HttpResponse */
		CloseableHttpResponse httpResponse = httpClient.execute(httpPost);
		try {
			HttpEntity httpEntity = httpResponse.getEntity();
			result = EntityUtils.toString(httpEntity, "utf-8");
			EntityUtils.consume(httpEntity);
		} finally {
			try {
				if (httpResponse != null) {
					httpResponse.close();
				}
			} catch (IOException e) {
				logger.info("## release resouce error ##" + e);
			}
		}
		return result;
	}

	public static String sendHttpPost(String url, String JSONBody) throws Exception {
		CloseableHttpClient httpClient = HttpClients.createDefault();
		HttpPost httpPost = new HttpPost(url);
		httpPost.addHeader("Content-Type", "application/json");
		httpPost.setEntity(new StringEntity(JSONBody));
		CloseableHttpResponse response = httpClient.execute(httpPost);
//		System.out.println(response.getStatusLine().getStatusCode() + "\n");
		HttpEntity entity = response.getEntity();
		String responseContent = EntityUtils.toString(entity, "UTF-8"); 
//		System.out.println(responseContent);
		response.close();
		httpClient.close();
		return responseContent;
	}

	public static String requestOCRForHttp(String url, Map<String, String> requestParams) throws Exception {
		String result = null;
		CloseableHttpClient httpClient = HttpClients.createDefault();
		/** HttpPost */
		HttpPost httpPost = new HttpPost(url);
		List<NameValuePair> params = new ArrayList<NameValuePair>();
		Iterator<Entry<String, String>> it = requestParams.entrySet().iterator();
//		System.out.println(params.toString());
		while (it.hasNext()) {
			Entry<String, String> en = it.next();
			String key = en.getKey();
			String value = en.getValue();
			if (value != null) {
				params.add(new BasicNameValuePair(key, value));
			}
		}
		httpPost.setEntity(new UrlEncodedFormEntity(params, "UTF-8"));
		/** HttpResponse */
		CloseableHttpResponse httpResponse = httpClient.execute(httpPost);
		try {
			HttpEntity httpEntity = httpResponse.getEntity();
			result = EntityUtils.toString(httpEntity, "utf-8");
			EntityUtils.consume(httpEntity);
		} finally {
			try {
				if (httpResponse != null) {
					httpResponse.close();
				}
			} catch (IOException e) {
				logger.info("## release resouce error ##" + e);
			}
		}
		return result;
	}

package edu.controller;

import com.alibaba.fastjson.JSONArray;
import com.alibaba.fastjson.JSONObject;
import com.aliyun.oss.HttpMethod;
import edu.entity.EventVo;
import org.springframework.http.ResponseEntity;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * @Author Fujii
 * @Date 2021-10-11 23:12
 * @Version SpringBoot 2.2.2
 * @projectName 调用外部api接口
 */
@RestController
public class BackEndApiDemo {

    @GetMapping("apiList")
    public Map<String,Object> getByApiList(){
        //这里先创建一个map用于返回api格式
        Map<String,Object> mapList = new HashMap<>();
        //1.我们是要去调用外部api，那么肯定要有一个外部api的地址,这里我是拿我的DEMO作为数据传输
        String apiURL = "这里直接放入你的api接口即可，我的api就不展示了，请谅解!";
        //2.这里有几种方式，你们去试了过后会发现不只有GET，这里因为我们是去获取数据，所以是用GET
        HttpMethod method = HttpMethod.GET;
        //用于接口返回的JSONObject（）
        LinkedMultiValueMap map = new LinkedMultiValueMap();
        //json接收数据
        JSONObject  urlMethod = client(apiURL,method,map);
        JSONObject jsonObject = JSONObject.parseObject(urlMethod.toJSONString());
        JSONArray object = JSONObject.parseArray(jsonObject.get("data").toString());
        if (jsonObject!=null){
            List<EventVo> list = JSONArray.parseArray(object.toJSONString(), EventVo.class);
            mapList.put("list",list);
            mapList.put("code",200);
            mapList.put("msg", "获取成功!");

        }else{
            mapList.put("code",500);
            mapList.put("msg", "获取失败!");
            return mapList;
        }
        return mapList;
    }
    
    //注意：因为是测试，所有我所有内容全部写在一个文件内方便展示清晰，正规写法应写在服务层
    private JSONObject client(String url, HttpMethod method, LinkedMultiValueMap params) {
        RestTemplate template = new RestTemplate();
        ResponseEntity<JSONObject> response = template.getForEntity(url, JSONObject.class);
        return response.getBody();
    }
}