Java使用HttpClient实现Post请求

    基于项目需求，想要实现Post消息推送，故采用HttpClient组件进行实现，相关代码如下(注：程序采用的httpclient和httpcore依赖包的版本为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();

        // 设置超时时间
        httpClient.getParams().setParameter(CoreConnectionPNames.CONNECTION_TIMEOUT, 2000);
        httpClient.getParams().setParameter(CoreConnectionPNames.SO_TIMEOUT, 2000);
            
        post = new HttpPost(url);
        // 构造消息头
        post.setHeader("Content-type", "application/json; charset=utf-8");
        post.setHeader("Connection", "Close");
        String sessionId = getSessionId();
        post.setHeader("SessionId", sessionId);
        post.setHeader("appid", appid);
                    
        // 构建消息实体
        StringEntity entity = new StringEntity(jsonObj.toString(), Charset.forName("UTF-8"));
        entity.setContentEncoding("UTF-8");
        // 发送Json格式的数据请求
        entity.setContentType("application/json");
        post.setEntity(entity);
            
        HttpResponse response = httpClient.execute(post);
            
        // 检验返回码
        int statusCode = response.getStatusLine().getStatusCode();
        if(statusCode != HttpStatus.SC_OK){
            LogUtil.info("请求出错: "+statusCode);
            isSuccess = false;
        }else{
            int retCode = 0;
            String sessendId = "";
            // 返回码中包含retCode及会话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 ){
                // 日志打印
                LogUtil.info("error return code,  sessionId: "sessendId"	"+"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;
}

// 构建唯一会话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集群进行发送POST请求时，遇到"java.lang.NoSuchFieldError: INSTANCE"的问题，此类问题一般是"jar包冲突"的问题所致，但奇怪的是本地的pom.xml设置的依赖包中有该字段，相关的httpclient依赖包如下：　　

<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>        

随后在网上查找了一翻，找到问题的缘由，原因在于Hadoop集群运行程序时，首先会加载自己相关目录下的jar包，在自己目录下如果未找到，才会加载程序运行时指定的jar包(具体参见：http://bbs.umeng.com/thread-12187-1-1.html)，随查找了Hadoop集群中相关Jar包路径，发现httpclient的相关依赖包为4.2.5，因此将pom.xml配置文件也更新为该版本，程序则运行通过.