本篇文章幫大家學習HttpClient基于表單登入，包含了HttpClient基于表單登入使用方法、操作技巧、執行個體示範和注意事項，有一定的學習價值，大家可以用來參考。
使用HttpClient庫，可以發送請求或通過傳遞參數登入表單。
按照以下步驟登入表單。
第1步 - 建立一個HttpClient對象HttpClients類的createDefault()方法傳回類CloseableHttpClient的對象，該對象是HttpClient接口的基本實作。使用此方法建立一個HttpClient對象 -
CloseableHttpClient httpClient = HttpClients.createDefault();
第2步 - 建立RequestBuilder對象
RequestBuilder類用于通過向其添加參數來建構請求。如果請求類型是：PUT或POST，則它将參數作為URL編碼實體添加到請求中
使用post()方法建立RequestBuilder對象(類型為POST)。
//Building the post request object
RequestBuilder reqbuilder = RequestBuilder.post();
第3步 - 将Uri和參數設定為RequestBuilder。使用RequestBuilder類的setUri()和addParameter()方法将URI和參數設定為RequestBuilder對象。
//Set URI and parameters
RequestBuilder reqbuilder = reqbuilder.setUri("http://httpbin.org/post");
reqbuilder = reqbuilder1.addParameter("Name", "username").addParameter("password", "password");
第4步 - 建構HttpUriRequest對象設定所需參數後，使用build()方法建構HttpUriRequest對象。
//Building the HttpUriRequest object
HttpUriRequest httppost = reqbuilder2.build();
第5步 - 執行請求CloseableHttpClient對象的execute()方法接受HttpUriRequest(接口)對象(即：HttpGet，HttpPost，HttpPut，HttpHead等)并傳回響應對象。
通過将它傳遞給execute()方法來執行前面步驟中建立的HttpUriRequest。
//Execute the request
HttpResponse httpresponse = httpclient.execute(httppost);
示例
以下示例示範了如何通過發送登入憑據登入到表單。在這裡，我們向表單發送了兩個參數 - username和password，并嘗試列印消息實體和請求的狀态。
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.client.methods.RequestBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;
import java.io.IOException;
import java.net.URISyntaxException;
public class FormLoginExample {
public static void main(String args[]) throws Exception {
//Creating CloseableHttpClient object
CloseableHttpClient httpclient = HttpClients.createDefault();
//Creating the RequestBuilder object
RequestBuilder reqbuilder = RequestBuilder.post();
//Setting URI and parameters
RequestBuilder reqbuilder1 = reqbuilder.setUri("http://httpbin.org/post");
RequestBuilder reqbuilder2 = reqbuilder1.addParameter("Name",
"username").addParameter("password", "password");
//Building the HttpUriRequest object
HttpUriRequest httppost = reqbuilder2.build();
//Executing the request
HttpResponse httpresponse = httpclient.execute(httppost);
//Printing the status and the contents of the response
System.out.println(EntityUtils.toString(httpresponse.getEntity()));
System.out.println(httpresponse.getStatusLine());
}
}
執行上面示例代碼，得到以下結果:
{
"args": {},
"data": "",
"files": {},
"form": {
"Name": "username",
"password": "password"
},
"headers": {
"Accept-Encoding": "gzip,deflate",
"Connection": "close",
"Content-Length": "31",
"Content-Type": "application/x-www-form-urlencoded; charset = UTF-8",
"Host": "httpbin.org",
"User-Agent": "Apache-HttpClient/4.5.6 (Java/1.8.0_91)"
},
"json": null,
"origin": "217.216.145.180",
"url": "http://httpbin.org/post"
}
HTTP/1.1 200 OK
Cookie表單登入
如果表單存儲cookie，而不是建立預設的CloseableHttpClient對象。通過執行個體化BasicCookieStore類來建立CookieStore對象。
//Creating a BasicCookieStore object
BasicCookieStore cookieStore = new BasicCookieStore();
使用HttpClients類的custom()方法建立HttpClientBuilder。
//Creating an HttpClientBuilder object
HttpClientBuilder clientbuilder = HttpClients.custom();
使用setDefaultCookieStore()方法将cookie存儲設定為用戶端建構器。
//Setting default cookie store to the client builder object
Clientbuilder = clientbuilder.setDefaultCookieStore(cookieStore);
使用build()方法建構CloseableHttpClient對象。
//Building the CloseableHttpClient object
CloseableHttpClient httpclient = clientbuilder1.build();
通過傳遞執行請求來建構上面指定的HttpUriRequest對象。如果頁面存儲cookie，則傳遞的參數将添加到cookie存儲中。
可以列印CookieStore對象的内容，在其中檢視參數(以及以前存儲的頁面)。
要列印cookie，請使用getCookies()方法從CookieStore對象擷取所有cookie。此方法傳回List對象。使用Iterator列印清單對象内容，如下所示 -
//Printing the cookies
List list = cookieStore.getCookies();
System.out.println("list of cookies");
Iterator it = list.iterator();
if(it.hasNext()){
System.out.println(it.next());
}