org.apache.commons.httpclient詳解

一、簡介

Apache Commons HttpClient是Apache軟件基金會的子項目，它是一個完整的HTTP客戶端實現庫，提供了最基本的HTTP客戶端功能，例如支持請求/響應攔截、狀態管理和連接管理等。該庫支持HTTP/1.0和HTTP/1.1協議，它被廣泛應用於Java開發中。

在使用org.apache.commons.httpclient進行HTTP客戶端編程時，我們可以輕鬆地訪問Web服務並檢索數據，同時也可以發送數據到Web服務。我們可以使用HTTP的不同方法，例如GET、POST、PUT、DELETE等方法，以與Web服務進行交互。

二、核心組件

org.apache.commons.httpclient的核心包括以下幾個部分：

1. HttpConnectionManager

HttpConnectionManager管理HttpConnection實例，為HttpClient提供連接管理、復用、釋放等功能。

HttpConnectionManager connectionManager = new MultiThreadedHttpConnectionManager();
HttpClient httpClient = new HttpClient(connectionManager);

2. HttpMethod

HttpMethod是HttpClient請求和響應的核心類。它封裝請求的方法（GET、POST、PUT等）、請求的URL、請求頭、請求體數據以及響應狀態碼、響應頭、響應體數據等信息。HttpGet、HttpPost、HttpPut、HttpDelete等都是HttpMethod的子類。

HttpMethod method = new GetMethod("http://www.example.com/");
int status = httpClient.executeMethod(method);
if (status == HttpStatus.SC_OK) {
    byte[] responseBody = method.getResponseBody();
    // process the response body
}

3. HttpState

HttpState封裝了客戶端的會話狀態信息，例如Cookie和身份驗證信息等，以便在一系列HTTP請求之間共享和維護狀態。

HttpState state = httpClient.getState();
// set cookie
state.addCookie(new Cookie("example.com", "MYCOOKIE", "123"));
// set authentication
state.setCredentials(new AuthScope("example.com", 80),
        new UsernamePasswordCredentials("username", "password"));

4. ProxyHost

ProxyHost可以配置代理服務器信息，以便在進行Http請求時使用代理服務器。

httpClient.getHostConfiguration().setProxy("proxy.example.com", 8080);

三、示例代碼

1. 發送GET請求

HttpClient httpClient = new HttpClient();
GetMethod method = new GetMethod("http://www.example.com/");
int status = httpClient.executeMethod(method);
if (status == HttpStatus.SC_OK) {
    byte[] responseBody = method.getResponseBody();
    // process the response body
}

2. 發送POST請求

HttpClient httpClient = new HttpClient();
PostMethod method = new PostMethod("http://www.example.com/");
method.addParameter("param1", "value1");
method.addParameter("param2", "value2");
int status = httpClient.executeMethod(method);
if (status == HttpStatus.SC_OK) {
    byte[] responseBody = method.getResponseBody();
    // process the response body
}

3. 設置連接超時和讀取超時

HttpClient httpClient = new HttpClient();
httpClient.getHttpConnectionManager().getParams().setConnectionTimeout(5000); // 5 seconds
httpClient.getHttpConnectionManager().getParams().setSoTimeout(10000); // 10 seconds
GetMethod method = new GetMethod("http://www.example.com/");
int status = httpClient.executeMethod(method);
if (status == HttpStatus.SC_OK) {
    byte[] responseBody = method.getResponseBody();
    // process the response body
}

4. 使用代理服務器發送請求

HttpClient httpClient = new HttpClient();
httpClient.getHostConfiguration().setProxy("proxy.example.com", 8080);
GetMethod method = new GetMethod("http://www.example.com/");
int status = httpClient.executeMethod(method);
if (status == HttpStatus.SC_OK) {
    byte[] responseBody = method.getResponseBody();
    // process the response body
}

5. 設置Cookie和身份驗證信息

HttpClient httpClient = new HttpClient();
HttpState state = httpClient.getState();
state.addCookie(new Cookie("example.com", "MYCOOKIE", "123"));
state.setCredentials(new AuthScope("example.com", 80),
        new UsernamePasswordCredentials("username", "password"));
GetMethod method = new GetMethod("http://www.example.com/");
int status = httpClient.executeMethod(method);
if (status == HttpStatus.SC_OK) {
    byte[] responseBody = method.getResponseBody();
    // process the response body
}

四、總結

通過本文的介紹，我們了解了org.apache.commons.httpclient庫的核心組件以及如何使用這些組件來發送HTTP請求和處理HTTP響應。希望這些內容能夠對讀者在Java開發中的HTTP客戶端編程中有所幫助。