一、简介

Apache Commons HttpClient是Apache软件基金会的子项目，它是一个完整的HTTP客户端实现库，提供了最基本的HTTP客户端功能，例如支持请求/响应拦截、状态管理和连接管理等。该库支持HTTP/1.0和HTTP/1.1协议，它被广泛应用于Java开发中。在使用org.apache.commons.httpclient进行HTTP客户端编程时，我们可以轻松地访问Web服务并检索数据，同时也可以发送数据到Web服务。我们可以使用HTTP的不同方法，例如GET、POST、PUT、DELETE等方法，以与Web服务进行交互。

二、核心组件

org.apache.commons.httpclient的核心包括以下几个部分：

1. HttpConnectionManager

HttpConnectionManager管理HttpConnection实例，为HttpClient提供连接管理、复用、释放等功能。

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

2. HttpMethod

HttpMethod是HttpClient请求和响应的核心类。它封装请求的方法（GET、POST、PUT等）、请求的URL、请求头、请求体数据以及响应状态码、响应头、响应体数据等信息。HttpGet、HttpPost、HttpPut、HttpDelete等都是HttpMethod的子类。

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封装了客户端的会话状态信息，例如Cookie和身份验证信息等，以便在一系列HTTP请求之间共享和维护状态。

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可以配置代理服务器信息，以便在进行Http请求时使用代理服务器。

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

三、示例代码

1. 发送GET请求

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. 发送POST请求

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. 设置连接超时和读取超时

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. 使用代理服务器发送请求

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. 设置Cookie和身份验证信息

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、总结

通过本文的介绍，我们了解了org.apache.commons.httpclient库的核心组件以及如何使用这些组件来发送HTTP请求和处理HTTP响应。希望这些内容能够对读者在Java开发中的HTTP客户端编程中有所帮助。

org.apache.commons.httpclient详解