風行天下

SECTION 01 HttpClient 總覽

Hyper-Text Transfer Protocol (HTTP) 是現在網絡上最通行的通訊協議, 隨著 Webservice 的技術快速發展, 也讓許多的應用程序結合 HTTP 擴展更大的功能, 或許你會說 java.net 不是已經有基本的存取 HTTP 的 method 了, 為何還要有這個 commons 的項目呢, 請容許我慢慢說明 ~~


binary 下載處 http://jakarta.apache.org/builds/jakarta-commons/release/commons-httpclient/v2.0/

source 下載處 http://www.apache.org/dist/jakarta/commons/httpclient/source/


SECTION 02 特色

是因為他的特色..... 有許多是 java.net.* 沒有提供的, 或者自己要實現的. 不如就直接采用 commons-httpclient.

• 使用 Pure Java 開發標準的 HTTP v1.0 及 v1.1
• 實現所有的 HTTP methods (GET, POST, PUT, DELETE,HEAD, OPTIONS, and TRACE)
• 支持 HTTPS 的協議
• 支持 proxies 的各種情況
• 利用 Multi Form 上傳文件
• 支持認證機制
• 可以設置最大連結數量
• 自動的 cookie 處理模式
• Request 及 Response 最佳化處理
• 支持 HTTP 1.0 KeepAlive 聯機模式及 1.1 的 persistance 保存狀態
• 直接存取服務器送來的 response code 及 header
• 能夠設置連結超時
• 實現 Command Pattern 允許去平行處理及有效重復使用連結.
• 這個是開放源碼的

SECTION 03 依循自

Commons-HttpClient 是遵循了下面的 spec ( Internet Engineering Task Force (IETF) )

• RFC1945Hypertext Transfer Protocol -- HTTP/1.0
• RFC2616Hypertext Transfer Protocol -- HTTP/1.1
• RFC2617HTTP Authentication: Basic and Digest Access Authentication
• RFC2109HTTP State Management Mechanism (Cookies)
• RFC2396Uniform Resource Identifiers (URI): Generic Syntax
• RFC1867Form-based File Upload in HTML

SECTION 04 與其它的 HttpClient 比較

此來源出自 http://www.nogoop.com/product_16.html#compare

	nogoop	Sun	innovation	Jakarta
Features
cookies			X	X
plug compatible	X	X	X	[partial]
true request output stream			X	X
true response input stream	X		X	X
connection keep alive	X	X	X	X
connection pool throttling	X			X
connection/request timeout	X		X	X
idle connection timeout	X
pipelining of requests			X
SSL	X	X	X	X
basic authentication	X	X	X	X
digest authentication	X	X	X	X
NTLM authentication	X			X
proxy authentication	X	X	X	X
Support
minimum JRE version	1.2	1.0	1.2	1.2
price	$399	free	free	free
source available	X		X	X
diagnostic tracing	X		X	X
actively supported	X	X		X
fix turnaround	fast	slow	none	medium
license	purchase	Sun JRE	LGPL	Apache

SECTION 05 簡單范例

基本上 HttpClient 需要 commons-logging, 所以你要在 classpath 設置這兩個 jar 文件, 接著你要了解 HTTP 通訊的方式, 標準步驟如下..

1. 建立 HttpClient 的 instance ( HttpClient client = new HttpClient(); )
2. 建立 HttpClient instance 要使用的 method ( 例如 GET/POST 等等 連結到一個 URL , HttpMethod method = new GetMethod("http://www.apache.org/"); )
3. 告訴 HttpClient 去執行這個訊息 ( statusCode = client.executeMethod(method); )
4. 得到 Server 端的響應 ( byte[] responseBody = method.getResponseBody(); )
5. 結束這個連結 ( method.releaseConnection(); )
6. 處理這個響應數據 ( System.err.println(new String(responseBody)); )

import org.apache.commons.httpclient.*;
import org.apache.commons.httpclient.methods.*;
import java.io.*;

public class HttpClientTutorial {
  
  private static String url = "http://www.apache.org/";

  public static void main(String[] args) {
	// Create an instance of HttpClient.
	HttpClient client = new HttpClient();

	// Create a method instance.
	HttpMethod method = new GetMethod(url);

	// Execute the method.
	int statusCode = -1;
	int attempt = 0;
	// We will retry up to 3 times.
	while (statusCode == -1 && attempt < 3) {
	  try {
		// execute the method.
		statusCode = client.executeMethod(method);
	  } catch (HttpRecoverableException e) {
		System.err.println(
		  "A recoverable exception occurred, retrying." + 
		  e.getMessage());
	  } catch (IOException e) {
		System.err.println("Failed to download file.");
		e.printStackTrace();
		System.exit(-1);
	  }
	}
	// Check that we didn't run out of retries.
	if (statusCode == -1) {
	  System.err.println("Failed to recover from exception.");
	  System.exit(-2);
	}


	// Read the response body.
	byte[] responseBody = method.getResponseBody();

	// Release the connection.
	method.releaseConnection();

	// Deal with the response.
	// Use caution: ensure correct character encoding and is not binary data
	System.err.println(new String(responseBody));
  }
}