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缘由：

之前在学习Java的时候就说要整理一篇如何进行HTTP操作的文章，不过一直都没有写好，这两天刚好想到了验证的方法，所以整个过程很快就OK了，在此记录一下，方便以后参考。

正文：

参考解答：

1、使用 HttpURLConnection

package com.ixyzero.learn.utils;

import javax.net.ssl.HttpsURLConnection;
import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

/**
 * Created by ixyzero on 2019/5/11.
 */
public class HttpURLConnectionExample {

    private final String USER_AGENT = "Mozilla/5.0";

    public static void main(String[] args) throws Exception {

        HttpURLConnectionExample http = new HttpURLConnectionExample();

        System.out.println("Testing 1 - Send Http GET request");
        http.sendGet();

        System.out.println("\nTesting 2 - Send Http POST request");
        http.sendPost();

    }

    // HTTP GET request
    private void sendGet() throws Exception {

        String url = "https://httpbin.org/get?q=test";

        URL obj = new URL(url);
        HttpURLConnection con = (HttpURLConnection) obj.openConnection();

        // optional default is GET
        con.setRequestMethod("GET");

        //add request header
        con.setRequestProperty("User-Agent", USER_AGENT);

        int responseCode = con.getResponseCode();
        System.out.println("\nSending 'GET' request to URL : " + url);
        System.out.println("Response Code : " + responseCode);

        BufferedReader in = new BufferedReader(
                new InputStreamReader(con.getInputStream()));
        String inputLine;
        StringBuffer response = new StringBuffer();

        while ((inputLine = in.readLine()) != null) {
            response.append(inputLine);
        }
        in.close();

        System.out.println(response.toString());
    }

    // HTTP POST request
    private void sendPost() throws Exception {

        String url = "https://httpbin.org/post";
        URL obj = new URL(url);
        HttpsURLConnection con = (HttpsURLConnection) obj.openConnection();

        //add reuqest header
        con.setRequestMethod("POST");
        con.setRequestProperty("User-Agent", USER_AGENT);
        con.setRequestProperty("Accept-Language", "en-US,en;q=0.5");

        String urlParameters = "sn=123&id=12345";

        // Send post request
        con.setDoOutput(true);
        DataOutputStream wr = new DataOutputStream(con.getOutputStream());
        wr.writeBytes(urlParameters);
        wr.flush();
        wr.close();

        int responseCode = con.getResponseCode();
        System.out.println("\nSending 'POST' request to URL : " + url);
        System.out.println("Post parameters : " + urlParameters);
        System.out.println("Response Code : " + responseCode);

        BufferedReader in = new BufferedReader(
                new InputStreamReader(con.getInputStream()));
        String inputLine;
        StringBuffer response = new StringBuffer();

        while ((inputLine = in.readLine()) != null) {
            response.append(inputLine);
        }
        in.close();

        System.out.println(response.toString());
    }

}

2、使用 HttpClient

package com.ixyzero.learn.utils;

import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.message.BasicNameValuePair;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * Created by ixyzero.com on 2019/5/11.
 */
public class HttpUtils {

    private static String getURL = "http://httpbin.org/get?q=test";
    private static String postURL = "https://httpbin.org/post";
    private static String USER_AGENT = "Mozilla/5.0";
    private static int TIMEOUT = 50;

    public String httpGet(String url) {
        HttpClient client = HttpClientBuilder.create().build();
        HttpGet request = new HttpGet(url);
        request.addHeader("User-Agent", USER_AGENT);
        StringBuffer result = new StringBuffer();

        try {
            HttpResponse response = client.execute(request);
            System.out.println("Response Code : "
                    + response.getStatusLine().getStatusCode());

            BufferedReader rd = new BufferedReader(
                    new InputStreamReader(response.getEntity().getContent()));

            String line;
            while ((line = rd.readLine()) != null) {
                result.append(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        return result.toString();
    }

    public String httpPost(String url, Map<String, String> mapParam) {
        StringBuffer result = new StringBuffer();

        HttpClient client = HttpClientBuilder.create().build();
        HttpPost post = new HttpPost(url);
        post.setHeader("User-Agent", USER_AGENT);

        List<NameValuePair> urlParameters = new ArrayList<>();
        for (Map.Entry<String, String> entry : mapParam.entrySet()) {
            urlParameters.add(new BasicNameValuePair(entry.getKey(), entry.getValue()));
        }

        try {
            post.setEntity(new UrlEncodedFormEntity(urlParameters));

            HttpResponse response = client.execute(post);
            System.out.println("Response Code : "
                    + response.getStatusLine().getStatusCode());

            BufferedReader rd = new BufferedReader(
                    new InputStreamReader(response.getEntity().getContent()));
            String line;
            while ((line = rd.readLine()) != null) {
                result.append(line);
            }
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        return result.toString();
    }

    public static void main(String[] args) {
        HttpUtils httpUtils = new HttpUtils();
        String response;

        response = httpUtils.httpGet(getURL);
        System.out.println(String.format("URL: %s\nResponse:\n%s\n", getURL, response));

        Map<String, String> map = new HashMap<String, String>() {
            {
                put("name", "test");
                put("age", "20");
            }
        };
        System.out.println(map);
        response = httpUtils.httpPost(postURL, map);
        System.out.println(String.format("URL: %s\nResponse:\n%s\n", postURL, response));

    }
}

&

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.4.1</version>
</dependency>

3、借助 https://httpbin.org/验证效果

该网站会把你给它发出的请求信息打出来，方便你验证参数和设置是否正确，上面的POST信息如下（包含请求内容、请求头信息、外网IP等）：

{
  "args": {},
  "data": "",
  "files": {},
  "form": {
    "age": "20",
    "name": "test"
  },
  "headers": {
    "Accept-Encoding": "gzip,deflate",
    "Content-Length": "16",
    "Content-Type": "application/x-www-form-urlencoded",
    "Host": "httpbin.org",
    "User-Agent": "Mozilla/5.0"
  },
  "json": null,
  "origin": "x1.x2.x3.x4, x1.x2.x3.x4",
  "url": "https://httpbin.org/post"
}

4、如何解析返回的json数据

在Java中处理json数据时，我一般用的是Alibaba的fastjson库，所以这里也用这个库的相关方法进行说明：

// 当response为json格式的字符串时，直接将其传给JSONObject.parseObject方法进行解析即可得到对应的json对象
JSONObject jsonObj = JSONObject.parseObject(response);

参考链接：

• Java的HTTP GET和POST 请求 #全面、详细
• How to send HTTP request in java?
• How to use java.net.URLConnection to fire and handle HTTP requests#非常详细！
  http://zetcode.com/java/getpostrequest/
• HttpClient Tutorial& Examples
  http://hc.apache.org/httpcomponents-client-ga/tutorial/html/statemgmt.html#d5e576
• 用Java发起GET/POST请求并解析返回的json数据
  https://stackoverflow.com/questions/22816335/java-httprequest-json-response-handling

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