Java中有多种方式模拟浏览器发送http请求，本文简要介绍JDK自带的HttpURLConnection，Apache的HttpClient，以及Square公司的OkHttp三种工具发送get/post请求。说明：本文不展开https请求证书验证绕过的问题
JDK自带的网络请求工具定义在java.net包下，其中最核心的是HttpURLConnection/HttpsURLConnection类。范例如下：
public class HttpUrlConnectionTest { public static void main(String [] args) { HttpUrlConnectionTest testObj = new HttpUrlConnectionTest(); testObj.doGet(); testObj.doPost(); } public void doGet() { try { String url = "https://tcc.taobao.com/cc/json/mobile_tel_segment.htm?tel={xxxx}"; URL obj = new URL(url); HttpURLConnection con = (HttpURLConnection) obj.openConnection(); con.setRequestMethod("GET"); // 设置请求头 con.setRequestProperty("user-agent", "Mozilla/5.0 "); int responseCode = con.getResponseCode(); parseResult(con.getInputStream(), "GB2312"); } catch (Exception e) { e.printStackTrace(); } } public void doPost() { try { String url = "https://tcc.taobao.com/cc/json/mobile_tel_segment.htm"; URL obj = new URL(url); HttpURLConnection con = (HttpURLConnection) obj.openConnection(); con.setRequestMethod("POST"); con.setRequestProperty("User-Agent", "Mozilla/5.0"); String params = "tel={xxxx}"; // 表示有数据输出给服务端 con.setDoOutput(true); DataOutputStream dos = new DataOutputStream(con.getOutputStream()); dos.writeBytes(params); dos.flush(); dos.close(); int responseCode = con.getResponseCode(); parseResult(con.getInputStream(), "GB2312"); } catch (Exception e) { e.printStackTrace(); } } private void parseResult(InputStream inStream, String charSet) { try { InputStreamReader stream = new InputStreamReader(inStream, charSet); BufferedReader br = new BufferedReader(stream); String inputLine; StringBuffer response = new StringBuffer(); while ((inputLine = br.readLine()) != null) { response.append(inputLine); } System.out.println(response.toString()); } catch (IOException e) { e.printStackTrace(); } } }说明：
1.con.setRequestProperty()设置请求头，这对于一些请求来说是必要的，很多网站会对请求头中的Referer进行检查，以此来放爬。部分网站还会对User-Agent进行检查，根据这个字段来过滤一些非浏览器的请求2.HTTP协议定义了很多种HTTP请求方法：GET、POST、PUT、DELETE、OPTIONS等，以上只模拟了最常用的GET、POST请求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。以下是HttpClient提供的主要功能：
实现了所有HTTP的方法（GET、POST、PUT、HEAD等）支持自动转向支持HTTPS协议支持代理服务器 public class HttpClientTest { public static void main(String [] args) { try { HttpClientTest testClient = new HttpClientTest(); testClient.doGet(); testClient.doPost(); } catch (Exception e) { e.printStackTrace(); } } public void doGet() throws IOException { String url = "https://tcc.taobao.com/cc/json/mobile_tel_segment.htm?tel={xxxx}"; HttpClient client = HttpClients.createDefault(); HttpGet request = new HttpGet(url); request.addHeader("user-agent", "Mozilla/5.0"); HttpResponse response = client.execute(request); parseResult(response.getEntity().getContent(), "GB2312"); } public void doPost() throws Exception{ String url = "https://tcc.taobao.com/cc/json/mobile_tel_segment.htm"; HttpClient client = HttpClients.createDefault(); HttpPost post = new HttpPost(url); post.setHeader("user-agent", "Mozilla/5.0"); List<NameValuePair> params = new ArrayList<NameValuePair>(); params.add(new BasicNameValuePair("tel", "{xxxx}")); post.setEntity(new UrlEncodedFormEntity(params)); HttpResponse response = client.execute(post); parseResult(response.getEntity().getContent(), "GB2312"); } private void parseResult(InputStream inStream, String charSet) { try { InputStreamReader stream = new InputStreamReader(inStream, charSet); BufferedReader br = new BufferedReader(stream); String inputLine; StringBuffer response = new StringBuffer(); while ((inputLine = br.readLine()) != null) { response.append(inputLine); } System.out.println(response.toString()); } catch (IOException e) { e.printStackTrace(); } } }OkHttp 是由Square公司开发，专注于性能和易用性的HTTP客户端。OkHttp库的设计和实现的首要目标是高效，这也是选择OkHttp的重要理由之一。OkHttp提供了对GZIP的默认支持来降低传输内容的大小，也提供了对HTTP响应的缓存机制，可以避免不必要的网络请求，当网络出现问题时，OkHttp会自动重试一个主机的多个IP地址。
public class OkHttpTest { public static void main(String [] args) throws Exception{ OkHttpTest testClient = new OkHttpTest(); testClient.doGet(); testClient.doPost(); } public void doGet() throws Exception{ String url = "http://wthrcdn.etouch.cn/weather_mini?citykey=101010100"; OkHttpClient client = new OkHttpClient(); Request requst = new Request.Builder().url(url).build(); Response response = client.newCall(requst).execute(); System.out.println(response.body().string()); } public void doPost() throws Exception { String url = "http://wthrcdn.etouch.cn/weather_mini"; OkHttpClient client = new OkHttpClient(); RequestBody requestBody = new FormBody.Builder() .add("citykey", "101010100").build(); Request requst = new Request.Builder().url(url).post(requestBody).build(); Response response = client.newCall(requst).execute(); System.out.println(response.body().string()); } }