http://www.cnblogs.com/mengrennwpu/p/6418114.html

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基於項目需求，想要實現Post消息推送，故采用HttpClient組件進行實現，相關代碼如下(註：程序采用的httpclient和httpcore依賴包的版本為4.2.5)：

import org.apache.http.Header;
import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.client.HttpClient;
 
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.params.CoreConnectionPNames;
import java.util.UUID;
import net.sf.json.JSONObject;
import java.nio.charset.Charset;

public static boolean
 
 httpPostWithJson(JSONObject jsonObj,String url,String appId){
    boolean isSuccess = false;
    
    HttpPost post = null;
    try {
        HttpClient httpClient = new DefaultHttpClient();

        // 設置超時時間
        httpClient.getParams().setParameter(CoreConnectionPNames.CONNECTION_TIMEOUT, 2000);
        httpClient.getParams().setParameter(CoreConnectionPNames.SO_TIMEOUT, 
 
2000);
            
        post = new HttpPost(url);
        // 構造消息頭
        post.setHeader("Content-type", "application/json; charset=utf-8");
        post.setHeader("Connection", "Close");
        String sessionId = getSessionId();
        post.setHeader("SessionId", sessionId);
        post.setHeader("appid", appid);
                    
        // 構建消息實體
        StringEntity entity = new StringEntity(jsonObj.toString(), Charset.forName("UTF-8"));
        entity.setContentEncoding("UTF-8");
        // 發送Json格式的數據請求
        entity.setContentType("application/json");
        post.setEntity(entity);
            
        HttpResponse response = httpClient.execute(post);
            
        // 檢驗返回碼
        int statusCode = response.getStatusLine().getStatusCode();
        if(statusCode != HttpStatus.SC_OK){
            LogUtil.info("請求出錯: "+statusCode);
            isSuccess = false;
        }else{
            int retCode = 0;
            String sessendId = "";
            // 返回碼中包含retCode及會話Id
            for(Header header : response.getAllHeaders()){
                if(header.getName().equals("retcode")){
                    retCode = Integer.parseInt(header.getValue());
                }
                if(header.getName().equals("SessionId")){
                    sessendId = header.getValue();
                }
            }
            
            if(ErrorCodeHelper.IAS_SUCCESS != retCode ){
                // 日誌打印
                LogUtil.info("error return code,  sessionId: "sessendId"\t"+"retCode: "+retCode);
                isSuccess = false;
            }else{
                isSuccess = true;
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
        isSuccess = false;
    }finally{
        if(post != null){
            try {
                post.releaseConnection();
                Thread.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    return isSuccess;
}

// 構建唯一會話Id
public static String getSessionId(){
    UUID uuid = UUID.randomUUID();
    String str = uuid.toString();
    return str.substring(0, 8) + str.substring(9, 13) + str.substring(14, 18) + str.substring(19, 23) + str.substring(24);
}

Ps: 在使用Hadoop集群進行發送POST請求時，遇到"java.lang.NoSuchFieldError: INSTANCE"的問題，此類問題一般是"jar包沖突"的問題所致，但奇怪的是本地的pom.xml設置的依賴包中有該字段，相關的httpclient依賴包如下：

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.4.1</version>
</dependency>
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpcore</artifactId>
    <version>4.4.1</version>
</dependency>      

隨後在網上查找了一翻，找到問題的緣由，原因在於Hadoop集群運行程序時，首先會加載自己相關目錄下的jar包，在自己目錄下如果未找到，才會加載程序運行時指定的jar包(具體參見：http://bbs.umeng.com/thread-12187-1-1.html)，隨查找了Hadoop集群中相關Jar包路徑，發現httpclient的相關依賴包為4.2.5，因此將pom.xml配置文件也更新為該版本，程序則運行通過.

Java使用HttpClient實現Post請求