使用HttpClient發送請求、接收響應

使用HttpClient發送請求、接收響應很簡單，一般需要如下幾步即可：

1. 創建HttpClient對象。

2. 創建請求方法的實例，並指定請求URL。如果需要發送GET請求，創建HttpGet對象；如果需要發送POST請求，創建HttpPost對象。

3. 如果需要發送請求參數，可調用HttpGet、HttpPost共同的setParams(HetpParams params)方法來添加請求參數；對於HttpPost對象而言，也可調用setEntity(HttpEntity entity)方法來設置請求參數。

4. 調用HttpClient對象的execute(HttpUriRequest request)發送請求，該方法返回一個HttpResponse。

5. 調用HttpResponse的getAllHeaders()、getHeaders(String name)等方法可獲取服務器的響應頭；調用HttpResponse的getEntity()方法可獲取HttpEntity對象，該對象包裝了服務器的響應內容。程序可通過該對象獲取服務器的響應內容。

6. 釋放連接。無論執行方法是否成功，都必須釋放連接

 

后台代碼：

import java.io.IOException;
import java.net.URI;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

import org.apache.http.NameValuePair;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.utils.URIBuilder;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;


　　public static String doGet(String url, Map<String, String> param) {

        // 創建Httpclient對象
        CloseableHttpClient httpclient = HttpClients.createDefault();

        String resultString = "";
        CloseableHttpResponse response = null;
        try {
            // 創建uri
            URIBuilder builder = new URIBuilder(url);
            if (param != null) {
                for (String key : param.keySet()) {
                    builder.addParameter(key, param.get(key));
                }
            }
            URI uri = builder.build();

            // 創建http GET請求
            HttpGet httpGet = new HttpGet(uri);

            // 執行請求
            response = httpclient.execute(httpGet);
            // 判斷返回狀態是否為200
            if (response.getStatusLine().getStatusCode() == 200) {
                resultString = EntityUtils.toString(response.getEntity(), "UTF-8");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (response != null) {
                    response.close();
                }
                httpclient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return resultString;
    }

    public static String doGet(String url) {
        return doGet(url, null);
    }

    public static String doPost(String url, Map<String, String> param) {
        // 創建Httpclient對象
        CloseableHttpClient httpClient = HttpClients.createDefault();
        CloseableHttpResponse response = null;
        String resultString = "";
        try {
            // 創建Http Post請求
            HttpPost httpPost = new HttpPost(url);
            // 創建參數列表
            if (param != null) {
                List<NameValuePair> paramList = new ArrayList<>();
                for (String key : param.keySet()) {
                    paramList.add(new BasicNameValuePair(key, param.get(key)));
                }
                // 模擬表單
                UrlEncodedFormEntity entity = new UrlEncodedFormEntity(paramList);
                httpPost.setEntity(entity);
            }
            // 執行http請求
            response = httpClient.execute(httpPost);
            resultString = EntityUtils.toString(response.getEntity(), "utf-8");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                response.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

        return resultString;
    }

    public static String doPost(String url) {
        return doPost(url, null);
    }
    
    public static String doPostJson(String url, String json) {
        // 創建Httpclient對象
        CloseableHttpClient httpClient = HttpClients.createDefault();
        CloseableHttpResponse response = null;
        String resultString = "";
        try {
            // 創建Http Post請求
            HttpPost httpPost = new HttpPost(url);
            // 創建請求內容
            StringEntity entity = new StringEntity(json, ContentType.APPLICATION_JSON);
            httpPost.setEntity(entity);
            // 執行http請求
            response = httpClient.execute(httpPost);
            resultString = EntityUtils.toString(response.getEntity(), "utf-8");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                response.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

        return resultString;
    }

用Httpclient對象對接學習記錄，此文參考和轉載自https://www.cnblogs.com/guxiong/p/6661272.html;

http協議POST請求application/json格式：

package com.xxx.util;

import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.protocol.HTTP;
import org.apache.http.util.EntityUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;

public class HttpUtil {

    private static Logger logger = LoggerFactory.getLogger(HttpUtil.class.getName());

    private static HttpClient httpClient = HttpClientBuilder.create().build();
    private final static String CHARSET = "UTF-8";

    public static String post(String url, String json) {
        HttpPost post = new HttpPost(url);
        post.addHeader(HTTP.CONTENT_TYPE, "application/json");
        StringEntity entity = new StringEntity(json, CHARSET);
        post.setEntity(entity);
        try {
            HttpResponse response = httpClient.execute(post);
            if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
                if (response.getEntity() != null) {
                    return EntityUtils.toString(response.getEntity(), CHARSET);
                }
            }
            throw new IOException("請求出錯");
        } catch (IOException e) {
            e.printStackTrace();
            logger.error(e.getMessage());
        }
        return null;
    }

}