java.net.SocketException： 没有可用的缓冲区空间（已达到最大连接数？）： 连接

嗨，我正在使用Apache HTTP Client 4.0在基于HTTPS协议的服务器上上传一些文件。上传的应用程序正在全天候运行。今天突然它开始抛出这个异常——

java.net.SocketException: No buffer space available (maximum connections reached?): connect
    at java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.net.PlainSocketImpl.doConnect(Unknown Source)
    at java.net.PlainSocketImpl.connectToAddress(Unknown Source)
    at java.net.PlainSocketImpl.connect(Unknown Source)
    at java.net.SocksSocketImpl.connect(Unknown Source)
    at java.net.Socket.connect(Unknown Source)
    at com.sun.net.ssl.internal.ssl.SSLSocketImpl.connect(Unknown Source)
    at org.apache.http.conn.ssl.SSLSocketFactory.connectSocket(SSLSocketFactory.java:333)
    at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:123)
    at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:147)
    at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:101)
    at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:381)
    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:641)
    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:576)
    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:554)

任何人都可以帮我吗？我对发生了什么一无所知？

这是上传文件的源代码 -

public File call() throws Exception {           
            HttpClient httpclient = new DefaultHttpClient();
        try{            
            httpclient.getParams().setParameter(CoreProtocolPNames.PROTOCOL_VERSION, HttpVersion.HTTP_1_1);         
            /*
             * Create POST REQUEST
             */
            HttpPost httpPost = new HttpPost(this.URL);
            /*
             * Create MultipartRequestEntity
             */
            MultipartEntity multipartEntity = new MultipartEntity( HttpMultipartMode.BROWSER_COMPATIBLE );
            /*
             * Add POST Parameters
             */
            multipartEntity.addPart(parameters[0], this.fileBody);
            multipartEntity.addPart(parameters[1], new StringBody(this.TYPE));
            multipartEntity.addPart(parameters[2], new StringBody(this.MAAID));
            /*
             * Add this POST Method
             */
            httpPost.setEntity(multipartEntity);
            /*
             * Upload the file
             */
            HttpResponse response = httpclient.execute(httpPost);
            int responseCode = response.getStatusLine().getStatusCode();
            logger.info("Response Code of HTTP Connectivity ["+ responseCode + "], " +
                                                            "it means ["+ response.getStatusLine().getReasonPhrase()+"]");
            /*
             * Check the server Response
             */
            HttpEntity entity = response.getEntity();
            if(entity != null){
                String status = EntityUtils.toString(entity);
                logger.info("Status of file upload from Server >>"+ status+"<<");
                entity.consumeContent();
                if(status.equalsIgnoreCase("OK")){
                    return this.fileBody.getFile();
                }
            }else{
                logger.error("Unable to retrieve status of file upload from server");
            }           
        }catch(NoRouteToHostException e){
            logger.error("Internet connection to ["+ this.URL + "] is not available", e);
        }catch(SocketException e){
            logger.error("Unable to connect to "+ this.URL, e);
        }catch (Exception e) {          
            logger.error("Exception while uploading the file["+ this.fileBody.getFilename()+ "] on ["+ this.URL+"]", e);
        }finally{
            try{
                httpclient.getConnectionManager().shutdown();
            }catch(Exception e){
                // Ignore this exception
            }
        }
        return null;
    }