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版主，您好，

我想用httpclient4來存取SSL的網頁，但又不想匯入對方憑証，有什麼好方法嗎?感謝!

下載函式庫: HttpClient 4.1.1 (GA)
http://hc.apache.org/downloads.cgi

預先安裝函式庫:commons-logging-1.1.1.jar, httpcore-4.1.jar, httpclient-4.1.1.jar

這裡我以Servlet 3.0標準來當做練習，請在Tomcat 7.0以上版本執行：
HttpClientServlet.java:

package com.andowson.httpclient;



import java.io.IOException;

import java.io.PrintWriter;

import java.security.KeyManagementException;

import java.security.NoSuchAlgorithmException;

import java.security.cert.CertificateException;

import java.security.cert.X509Certificate;



import javax.net.ssl.SSLContext;

import javax.net.ssl.TrustManager;

import javax.net.ssl.X509TrustManager;

import javax.servlet.Servlet;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;



import org.apache.http.HttpEntity;

import org.apache.http.HttpHost;

import org.apache.http.HttpResponse;

import org.apache.http.client.ResponseHandler;

import org.apache.http.client.methods.HttpGet;

import org.apache.http.conn.params.ConnRoutePNames;

import org.apache.http.conn.scheme.Scheme;

import org.apache.http.conn.ssl.SSLSocketFactory;

import org.apache.http.impl.client.BasicResponseHandler;

import org.apache.http.impl.client.DefaultHttpClient;

import org.apache.http.util.EntityUtils;



/**

 * Servlet implementation class HttpClientServlet

 */

@WebServlet("/HttpClientServlet")

public class HttpClientServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;



	/**

	 * @see HttpServlet#HttpServlet()

	 */

	public HttpClientServlet() {

		super();

	}



	/**

	 * @see Servlet#getServletInfo()

	 */

	public String getServletInfo() {

		return "HttpClient Servlet";

	}



	/**

	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)

	 */

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {	

		String url = request.getParameter("url");

		if (url == null) {

			url = "https://ups.moe.edu.tw/";

		}



		DefaultHttpClient httpclient = new DefaultHttpClient();

		HttpHost proxy = new HttpHost("10.160.3.88", 8080);

		httpclient.getParams().setParameter(ConnRoutePNames.DEFAULT_PROXY, proxy);

		try {

			TrustManager easyTrustManager = new X509TrustManager() {



				@Override

				public void checkClientTrusted(

						X509Certificate[] chain,

						String authType) throws CertificateException {

					// Oh, I am easy!

				}



				@Override

				public void checkServerTrusted(

						X509Certificate[] chain,

						String authType) throws CertificateException {

					// Oh, I am easy!

				}



				@Override

				public X509Certificate[] getAcceptedIssuers() {

					return null;

				}                

			};



			SSLContext sslcontext = SSLContext.getInstance("TLS");

			sslcontext.init(null, new TrustManager[] { easyTrustManager }, null);



			SSLSocketFactory socketFactory = new SSLSocketFactory(sslcontext,

					SSLSocketFactory.ALLOW_ALL_HOSTNAME_VERIFIER);

			Scheme sch = new Scheme("https", 443, socketFactory);

			httpclient.getConnectionManager().getSchemeRegistry().register(sch);



			HttpGet httpget = new HttpGet(url);



			System.out.println("executing request " + httpget.getRequestLine());



			HttpResponse resp = httpclient.execute(httpget);

			HttpEntity entity = resp.getEntity();

			System.out.println("----------------------------------------");	             

			System.out.println(resp.getStatusLine());

			if (entity != null) {

				System.out.println("Response content length: " + entity.getContentLength());

			}

			EntityUtils.consume(entity);



			response.setContentType(entity.getContentType().toString());				

			PrintWriter out = response.getWriter();



			ResponseHandler<String> responseHandler = new BasicResponseHandler();

			String responseBody = httpclient.execute(httpget, responseHandler);

			System.out.println("----------------------------------------");

			System.out.println(responseBody);

			out.println(responseBody);

			System.out.println("----------------------------------------");

		} catch (NoSuchAlgorithmException e) {

			e.printStackTrace();

		} catch (KeyManagementException e) {

			e.printStackTrace();

		} finally {

			httpclient.getConnectionManager().shutdown();

		}

	}



	/**

	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)

	 */

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

		doGet(request, response);

	}



}

修改web.xml，加入下列項目:

	<servlet>

		<servlet-name>HttpClientServlet</servlet-name>

		<servlet-class>com.andowson.httpclient.HttpClientServlet</servlet-class>

	</servlet>

	<servlet-mapping>

		<servlet-name>HttpClientServlet</servlet-name>

		<url-pattern>/servlet/httpclient</url-pattern>

	</servlet-mapping>

說明：
63-64行是如果伺服器需要透過Proxy才能連到Internet(例如公司內部網站）執行時需透過Proxy的設定方式，如果伺服器可以直接連接到Internet時這兩行需要mark為註解掉。

參考資料：
http://hc.apache.org/httpcomponents-client-ga/tutorial/html/connmgmt.html#d4e537

如果要輸出檔案的話,也非常簡便,可以使用HttpEntity 提供的方法: writeTo()

比以下常用的寫法節省不少程式, 也避免了特殊字無法正常輸出的情況:

FileOutputStream fos = new FileOutputStream(request.getParameter("path"));

ByteArrayInputStream bais = new ByteArrayInputStream(httpclient.execute(httpget, responseHandler).getBytes());



byte[] bytes = new byte[1024]; 

int count = 0; 



while (bais!=null && (count = bais.read(bytes))!=-1) { 

    fos.write(bytes, 0, count); 

}

可於版主提供的程式105行中,加入以下程式

entity.writeTo(new FileOutputStream(request.getParameter("path")));