HttpClient的使用

HTTP 协议可能是现在 Internet 上使用得最多、最重要的协议了，越来越多的 Java 应用程序需要直接通过 HTTP 协议来访问网络资源。

http的主要功能包括：

1. 实现了所有 HTTP 的方法（GET,POST,PUT,HEAD 等）

2. 支持自动转向

3. 支持 HTTPS 协议

4. 支持代理服务器等 

使用 HttpClient 需要以下 6 个步骤：

1. 创建 HttpClient 的实例

2. 创建某种连接方法的实例，在这里是 GetMethod。在 GetMethod 的构造函数中传入待连接的地址

3. 调用第一步中创建好的实例的 execute 方法来执行第二步中创建好的 method 实例

4. 读 response

5. 释放连接。无论执行方法是否成功，都必须释放连接

6. 对得到后的内容进行处理

根据以上步骤，我们来编写用GET方法来取得某网页内容的代码。

HttpClient httpClient = new HttpClient();

GetMethod getMethod = new GetMethod(http://www.ibm.com/);

//设置成了默认的恢复策略，在发生异常时候将自动重试3次，在这里你也可以设置成自定义的恢复策略  
getMethod.getParams().setParameter(HttpMethodParams.RETRY_HANDLER,   
        new DefaultHttpMethodRetryHandler());   
//执行getMethod  
int statusCode = client.executeMethod(getMethod);  
if (statusCode != HttpStatus.SC_OK) {  
  System.err.println("Method failed: " + getMethod.getStatusLine());  
}  
//设置成了默认的恢复策略，在发生异常时候将自动重试3次，在这里你也可以设置成自定义的恢复策略
getMethod.getParams().setParameter(HttpMethodParams.RETRY_HANDLER, 
        new DefaultHttpMethodRetryHandler()); 
//执行getMethod
int statusCode = client.executeMethod(getMethod);
if (statusCode != HttpStatus.SC_OK) {
  System.err.println("Method failed: " + getMethod.getStatusLine());
}

method.releaseConnection();

System.out.println(new String(responseBody));

完整的代码示例

public class FeedBackServiceImpl implements FeedBackService, InitializingBean {
    private static final Logger log = LoggerFactory.getLogger(FeedBackServiceImpl.class);

    private static final int    CONNECTION_TIME_OUT      = 1000;
    private static final int    TIME_OUT                 = 2000;
    /**
     * 参数
     */
    private static final String PARAM_ID                 = "id";
    private static final String PARAM_QUESTION_ID        = "questionId";
    private static final String PARAM_ANSWER             = "answer";
    private static final String PARAM_COOKIE_ID          = "cookieId";

    /**
     * 盖娅系统获取调查问卷的url
     */
    private String              feedBackQuestionaireUrl;
    /**
     * 盖娅系统保存用户反馈信息的url
     */
    private String              feedBackAnswerUrl;
    /**
     * 问卷类型与问卷id的映射
     * 
     * <pre>
     * 问卷类型，从前台传递过来。目前有两个取值："1"表示进货单页面的问卷；"2"表示确认订单页面的问卷
     * 问卷id，作为从盖娅系统中获取调查问卷的参数
     * </pre>
     */
    private Map<String, String> questionTypeToQuestionId = new HashMap<String, String>();

    private HttpClient          httpClient;

    public boolean addFeedBack(FeedBackModel feedBackModel) {
        if (feedBackModel == null) {
            return false;
        }
        boolean res = false;
        // 调用盖娅系统的接口，提交反馈
        PostMethod postMethod = new PostMethod(feedBackAnswerUrl);
        postMethod.addParameter(PARAM_QUESTION_ID, feedBackModel.getQuestionId());
        postMethod.addParameter(PARAM_ANSWER, feedBackModel.getAnswer());
        postMethod.addParameter(PARAM_COOKIE_ID, feedBackModel.getCookieId());
        try {
            int statusCode = httpClient.executeMethod(postMethod);
            if (statusCode != HttpStatus.SC_OK) {
                StringBuilder sb = new StringBuilder("fail to add feedback, requestUrl=");
                sb.append(feedBackAnswerUrl).append(", parameter: ").append(feedBackModel.toString()).append(", HTTP StatusCode=").append(statusCode);
                log.error(sb.toString());
                res = false;
            } else {
                res = true;
            }
        } catch (HttpException e) {
            log.error("HttpException occured when addFeedBack, requestUrl=" + feedBackAnswerUrl + ", parameter: " + feedBackModel.toString(), e);
            res = false;
        } catch (IOException e) {
            log.error("IOException occured when addFeedBack, requestUrl=" + feedBackAnswerUrl + ", parameter: " + feedBackModel.toString(), e);
            res = false;
        } finally {
            postMethod.releaseConnection();
            postMethod = null;
        }
        return res;
    }

    public JSONObject getQuestionaire(String questionType) {
        String id = questionTypeToQuestionId.get(questionType);
        if (StringUtil.isBlank(id)) {
            return null;
        }
        
        // 调用盖娅系统的接口，获取调查问卷
        GetMethod getMethod = new GetMethod(feedBackQuestionaireUrl);
        NameValuePair param = new NameValuePair(PARAM_ID, id);
        getMethod.setQueryString(new NameValuePair[]{param});
        String responseText = null;
        try {
            // 执行getMethod
            int statusCode = httpClient.executeMethod(getMethod);
            if (statusCode != HttpStatus.SC_OK) {
                StringBuilder sb = new StringBuilder("fail to getQuestionaire, requestUrl=");
                sb.append(feedBackQuestionaireUrl).append("?id=").append(id).append(", HTTP StatusCode=").append(statusCode);
                log.error(sb.toString());
                return null;
            }
            // 读取内容
            responseText = getMethod.getResponseBodyAsString();
        } catch (HttpException e) {
            StringBuilder sb = new StringBuilder("HttpException occured when getQuestionaire, requestUrl=");
            sb.append(feedBackQuestionaireUrl).append("?id=").append(id);
            log.error(sb.toString(), e);
            return null;
        } catch (IOException e) {
            StringBuilder sb = new StringBuilder("IOException occured when getQuestionaire, requestUrl=");
            sb.append(feedBackQuestionaireUrl).append("?id=").append(id);
            log.error(sb.toString(), e);
            return null;
        } finally {
            getMethod.releaseConnection();
            getMethod = null;
        }
        
        if (StringUtil.isBlank(responseText)) {
            return null;
        }
        
        // 从查询结果中解析出包含问卷的json字符串
        int index = responseText.indexOf("=");
        if (index >= 0) {
            responseText = responseText.substring(index + 1);
        }
        try {
            JSONObject json = JSONObject.fromObject(responseText);
            return json;
        } catch (Exception e) {
            log.error("fail to change from String to JSONObject, string=" + responseText, e);
            return null;
        }
    }
    
    public void afterPropertiesSet() throws Exception {
        HttpConnectionManager connectionManager = new MultiThreadedHttpConnectionManager();
        httpClient = new HttpClient(connectionManager);
        httpClient.setConnectionTimeout(CONNECTION_TIME_OUT);
        httpClient.setTimeout(TIME_OUT);
    }