不停的实例化对象导致OOM

使用axis调用webService，系统运行一段时间后，出现了 OOM，还好日志中 记下了错误信息。

Exception in thread "Thread-1301" java.lang.OutOfMemoryError: Java heap space
	at org.apache.xerces.dom.DeferredDocumentImpl.createChunk(Unknown Source)
	at org.apache.xerces.dom.DeferredDocumentImpl.ensureCapacity(Unknown Source)
	at org.apache.xerces.dom.DeferredDocumentImpl.createNode(Unknown Source)
	at org.apache.xerces.dom.DeferredDocumentImpl.createDeferredDocument(Unknown Source)
	at org.apache.xerces.parsers.AbstractDOMParser.startDocument(Unknown Source)
	at org.apache.xerces.impl.dtd.XMLDTDValidator.startDocument(Unknown Source)
	at org.apache.xerces.impl.XMLDocumentScannerImpl.startEntity(Unknown Source)
	at org.apache.xerces.impl.XMLVersionDetector.startDocumentParsing(Unknown Source)
	at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
	at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
	at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
	at org.apache.xerces.parsers.DOMParser.parse(Unknown Source)
	at org.apache.xerces.jaxp.DocumentBuilderImpl.parse(Unknown Source)
	at org.apache.axis.utils.XMLUtils.newDocument(XMLUtils.java:369)
	at org.apache.axis.utils.XMLUtils.newDocument(XMLUtils.java:388)
	at org.apache.axis.configuration.FileProvider.configureEngine(FileProvider.java:179)
	at org.apache.axis.AxisEngine.init(AxisEngine.java:172)
	at org.apache.axis.AxisEngine.<init>(AxisEngine.java:156)
	at org.apache.axis.client.AxisClient.<init>(AxisClient.java:52)
	at org.apache.axis.client.Service.getAxisClient(Service.java:104)
	at org.apache.axis.client.Service.<init>(Service.java:113)
	at catic.hotel.server.webservice.PmsServiceData.<init>(PmsServiceData.java:26)
	at catic.hotel.server.task.SendCmdTask.<init>(SendCmdTask.java:200)
	at catic.hotel.server.task.TaskFactory.getTask(TaskFactory.java:155)
	at catic.hotel.server.server.ReadData.read(ReadData.java:82)
	at catic.hotel.server.server.ReadData.run(ReadData.java:57)

　　由于系统会频繁的进入到 SendCmdTask，而我又在此构造方法中不停的new PmsServiceData()，而PmsService的无参构造方法中又new Service()，相当于导致了Service对象不停的被实例化，时间久了，则出现OOM。

解决方法：

　　对PmsServiceData使用单例模式，即：

    private static PmsServiceData pmsServiceData = null;

    // 单例
    public static synchronized PmsServiceData getInstance(){
        if(null == pmsServiceData){
            pmsServiceData = new PmsServiceData();
        }
        return pmsServiceData;
    }

问题解决。