rednight

当前，CORBA、DCOM、RMI等RPC中间件技术已广泛应用于各个领域。但是面对规模和复杂度都越来越高的分布式系统，这些技术也显示出其局限性：（1）同步通信：客户发出调用后，必须等待服务对象完成处理并返回结果后才能继续执行；（2）客户和服务对象的生命周期紧密耦合：客户进程和服务对象进程都必须正常运行；如果由于服务对象崩溃或者网络故障导致客户的请求不可达，客户会接收到异常；（3）点对点通信：客户的一次调用只发送给某个单独的目标对象。
   面向消息的中间件（Message Oriented Middleware，MOM）较好的解决了以上问题。发送者将消息发送给消息服务器，消息服务器将消息存放在若干队列中，在合适的时候再将消息转发给接收者。这种模式下，发送和接收是异步的，发送者无需等待；二者的生命周期未必相同：发送消息的时候接收者不一定运行，接收消息的时候发送者也不一定运行；一对多通信：对于一个消息可以有多个接收者。
   已有的MOM系统包括IBM的MQSeries、Microsoft的MSMQ和BEA的MessageQ等。由于没有一个通用的标准，这些系统很难实现互操作和无缝连接。Java Message Service（JMS）是SUN提出的旨在统一各种MOM系统接口的规范，它包含点对点（Point to Point，PTP）和发布/订阅（Publish/Subscribe，pub/sub）两种消息模型，提供可靠消息传输、事务和消息过滤等机制。

1.JMS
   JAVA 消息服务(JMS)定义了Java 中访问消息中间件的接口。JMS 只是接口，并没有给予实现，实现JMS 接口的消息中间件称为JMS Provider，iLink实现了JMS接口，用户可以通过使用JMS接口，在iLink中进行JMS编程。 iLink支持JMS1.0.2版本。

2.JMS接口描述
   JMS 支持两种消息类型PTP 和Pub/Sub，分别称作：PTP Domain 和Pub/Sub Domain，这两种接口都继承统一的JMS父接口，JMS 主要接口如下所示：

MS父接口 PTP Pub/Sub ConnectionFactory QueueConnectionFactory TopicConnectionFactory Connection QueueConnection TopicConnection Destination Queue Topic Session QueueSession TopicSession MessageProducer QueueSender TopicPublisher MessageConsumer QueueReceiver,QueueBrowse r TopicSubscriber

                  
   ConnectionFactory ：连接工厂，JMS 用它创建连接
   Connection ：JMS 客户端到JMS Provider 的连接
   Destination ：消息的目的地
   Session： 一个发送或接收消息的线程
   MessageProducer： 由Session 对象创建的用来发送消息的对象
   MessageConsumer： 由Session 对象创建的用来接收消息的对象

3.JMS消息模型
JMS 消息由以下几部分组成：消息头，属性，消息体。
  
3.1 消息头(Header) - 消息头包含消息的识别信息和路由信息，消息头包含一些标准的属性如：JMSDestination,JMSMessageID 等。

消息头  由谁设置 JMSDestination send 或 publish 方法 JMSDeliveryMode send 或 publish 方法 JMSExpiration send 或 publish 方法 JMSPriority send 或 publish 方法 JMSMessageID send 或 publish 方法 JMSTimestamp send 或 publish 方法 JMSCorrelationID 客户 JMSReplyTo 客户 JMSType 客户 JMSRedelivered JMS Provider

Some XA JDBC drivers do not support local transaction operations, which can cause an error similar to the following when optimistic concurrency is used with such a driver:

SQL operations are not allowed with no global transaction by default for XA drivers.

In other words, the error will occur when SupportsLocalTransactions="true" is specified for the JDBCConnectionPool.

This problem occurs because optimistic concurrency suspends a global transaction and does reads in a local transaction when the database is not Oracle. (When using Oracle, you can avoid this problem by explicitly setting <database-type>Oracle</database-type> in your CMP deployment descriptor.)

Workaround : Use the "RollbackLocalTxUponConnClose" on the JDBCConnection.

If you encountered “ Cannot call Connection.commit in distributed transaction ” error, should check the weblogic connection pool and the datasource

If the connection pool is XA,

you should make sure that when you create the datasource to make it XA by select the check from "Honor Global Transaction" from the weblogic console.(default is selected)

If the connection pool is non-XA

    <[ServletContext(id=18489944,name=EBLGWeb,context-path=/)]: Deployment descriptor "/WEB-INF/bhr-tags-pagination.tld" is malformed. Check against the DTD: Content is not allowed in prolog. (line 1, column 1).>
    <[ServletContext(id=18489944,name=EBLGWeb,context-path=/)]: Error while parsing the Tag Library Descriptor at "/WEB-INF/bhr-tags-pagination.tld".
org.xml.sax.SAXException: [HTTP:101248][ServletContext(id=18489944,name=EBLGWeb,context-path=/)]: Deployment descriptor "/WEB-INF/bhr-tags-pagination.tld" is malformed. Check against the DTD: Content is not allowed in prolog. (line 1, column 1).
        at weblogic.apache.xerces.parsers.DOMParser.parse(DOMParser.java:285)
        at weblogic.apache.xerces.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:201)
        at weblogic.servlet.jsp.dd.JSPEntityResolver.load(JSPEntityResolver.java:81)
        at weblogic.servlet.jsp.dd.JSPEntityResolver.load(JSPEntityResolver.java:96)
        at weblogic.servlet.internal.WebAppHelper.registerTagLibListeners(WebAppHelper.java:293)
        at weblogic.servlet.internal.WebAppServletContext.activateFromDescriptors(WebAppServletContext.java:2530)
        at weblogic.servlet.internal.WebAppServletContext.activate(WebAppServletContext.java:6163)
        at weblogic.servlet.internal.WebAppServletContext.setActive(WebAppServletContext.java:6141)
        at weblogic.servlet.internal.WebAppModule.activate(WebAppModule.java:836)
        at weblogic.j2ee.J2EEApplicationContainer.activateModule(J2EEApplicationContainer.java:3322)
        at weblogic.j2ee.J2EEApplicationContainer.activate(J2EEApplicationContainer.java:2201)
        at weblogic.j2ee.J2EEApplicationContainer.activate(J2EEApplicationContainer.java:2174)
        at weblogic.j2ee.J2EEApplicationContainer.activate(J2EEApplicationContainer.java:2122)
        at weblogic.management.deploy.slave.SlaveDeployer$Application.setActivation(SlaveDeployer.java:3099)
        at weblogic.management.deploy.slave.SlaveDeployer.setActivationStateForAllApplications(SlaveDeployer.java:1768)
        at weblogic.management.deploy.slave.SlaveDeployer.resume(SlaveDeployer.java:351)
        at weblogic.management.deploy.DeploymentManagerServerLifeCycleImpl.resume(DeploymentManagerServerLifeCycleImpl.java:229)
        at weblogic.t3.srvr.SubsystemManager.resume(SubsystemManager.java:136)
        at weblogic.t3.srvr.T3Srvr.resume(T3Srvr.java:965)
        at weblogic.t3.srvr.T3Srvr.run(T3Srvr.java:360)
        at weblogic.Server.main(Server.java:32)
>

是由于某些文本编辑器（UltraEdit）存文本的时候产生的问题。可以使用text pad, word pad编辑XML格式的文件。

通过HTTP提交EDI请求,当EDI处理时间超过了20分钟后,就会看到在另一个weblogic server也接收到了这个EDI请求,重新处理这个报文.
如果报文处理时间更长,比如超过了50分钟,就会发现这个报文被处理了3遍或5遍.

When the Apache HTTP Server Plug-In attempts to connect to WebLogic Server, the plug-in uses several configuration 
parameters to determine how long to wait for connections to the WebLogic Server host and, after a connection is
established, how long the plug-in waits for a response. If the plug-in cannot connect or does not receive a response, 
the plug-in attempts to connect and send the request to other WebLogic Server instances in the cluster. If the 
connection fails or there is no response from any WebLogic Server in the cluster, an error message is sent.


响应等待时间参数WLIOTimeoutSecs (http://e-docs.bea.com/wls/docs81/plugins/plugin_params.html#1149781.
按照BEA 推荐的，这个值应该设得大一些, 这个参数的缺省值为300s. 见下面：
<Location /EDIHandler>
         SetHandler weblogic-handler
         WebLogicCluster apc_app1wls1:7011,apc_app1wls2:7011
         KeepAliveEnabled ON
         WLIOTimeoutSecs 7200
</Location>

有时候使用的mq jar文件的版本不对给出现一些末名奇妙的问题,本文则是能接收消息但不能发送消息的一个问题.碰到这样的问题一定要记得double-check你使用的mq jar文件的版本

MQJMS200713 Oct 2006 16:47:15,484 ERROR MessagingUtilServlet [ExecuteThread: '14' for queue: 'weblogic.kernel.Default'][]: **********EXCEPTION TRACE START*************
13 Oct 2006 16:47:15,484 ERROR MessagingUtilServlet [ExecuteThread: '14' for queue: 'weblogic.kernel.Default'][]: produce error
com.bhr.infra.messaging.exception.PMException: JMSException
        at com.bhr.infra.messaging.PMHandler.send(PMHandler.java:419)
        at com.bhr.epc.infra.messaging.util.MessagingUtilServlet.produce(MessagingUtilServlet.java:312)
        at com.bhr.epc.infra.messaging.util.MessagingUtilServlet.service(MessagingUtilServlet.java:74)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
        at weblogic.servlet.internal.ServletStubImpl$ServletInvocationAction.run(ServletStubImpl.java:1072)
        at weblogic.servlet.internal.ServletStubImpl.invokeServlet(ServletStubImpl.java:465)
        at weblogic.servlet.internal.ServletStubImpl.invokeServlet(ServletStubImpl.java:348)
        at weblogic.servlet.internal.WebAppServletContext$ServletInvocationAction.run(WebAppServletContext.java:6981)
        at weblogic.security.acl.internal.AuthenticatedSubject.doAs(AuthenticatedSubject.java:321)
        at weblogic.security.service.SecurityManager.runAs(SecurityManager.java:121)
        at weblogic.servlet.internal.WebAppServletContext.invokeServlet(WebAppServletContext.java:3892)
        at weblogic.servlet.internal.ServletRequestImpl.execute(ServletRequestImpl.java:2766)
        at weblogic.kernel.ExecuteThread.execute(ExecuteThread.java:224)
        at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:183)
Caused by: javax.jms.JMSException: MQJMS2007: failed to send message to MQ queue
        at com.ibm.mq.jms.services.ConfigEnvironment.newException(ConfigEnvironment.java:553)
        at com.ibm.mq.jms.MQMessageProducer.sendInternal(MQMessageProducer.java:1589)
        at com.ibm.mq.jms.MQMessageProducer.send(MQMessageProducer.java:1012)
        at com.ibm.mq.jms.MQMessageProducer.send(MQMessageProducer.java:1046)
        at com.bhr.infra.messaging.PMQueueSender.send(PMQueueSender.java:57)
        at com.bhr.infra.messaging.PMHandler.send(PMHandler.java:410)
        ... 13 more
13 Oct 2006 16:47:15,486 ERROR MessagingUtilServlet [ExecuteThread: '14' for queue: 'weblogic.kernel.Default'][]: **********EXCEPTION TRACE END**************

It may be caused by use of old version MQ jar. It can receive message, but cannot send message.

如果你碰到"Cannot Forward a Response that is Already Committed"这样的错误信息,一定是应用对一次http请求做了多次页面跳转或对response对象做过close后,又去写响应.

这个问题的根本原因由于响应本次请求的Response对象的状态是已提交状态造成的, 它不允许响应提交多次。

什么时候Response对象的状态变成已提交状态：当你的应用已经实现了页面跳转逻辑。

通常原因：

1． 如果你使用了community的话， community的安全认证和授权如果没有通过，community内部会进行页面跳转。但你的应用(对于workshop应用的话，指的是action)又试图进行页面跳转，就会出现这样的问题。


    /**

     * @jpf:action

     * @jpf:forward name="page" path="page.jsp"

     */

    protected Forward actionMethod()

{

    //如果已经提交了响应，你仍然试图再次进行页面跳转，即再次提交响应，可能出现问题

    //通常可以加一个判断

 

       if (!getResponse().isCommitted()) {

            return new Forward("success");

        } else {

            return null;

        }

    }

 

    protected void beforeAction() {

       SecurityManager.checkAuthorization(getRequest(), getResponse(), config.getString(

                CDConstants.CREATE_TERM_ACTION_NAME, ""));

      //这个调用可能实现了页面跳转，即提交响应

}

 

注意JSP中实现页面跳转后，加return 语句防止继续提交响应:

 

<%

       SecurityManager.checkAuthorization(getRequest(), getResponse(), config.getString(

                CDConstants.CREATE_TERM_ACTION_NAME, ""));

{

     //可能有实现页面跳转逻辑

    ……………forward();

        return;//记得加retrun.

    }

%>

 

2. .如果没有使用community的话，下面情景也会出现这个问题

 

    /**

     * @jpf:action

     * @jpf:forward name="page" path="page.jsp"

     */

    protected Forward actionMethod()

 

//直接操作Response对象写响应

     getResponse().getPrintWriter().println();

    …

/

   // 又执行的页面跳转，也可能出现问题

        return new Forward("index");

    }

一个页面流在第一次使用时,内部属性currentpage并没有指定页面,所以避免在begin方法里使用return-to: current page用法.同时在用的时候注意页面流的工作方式

Error message like below in Web Page is displayed:

Page Flow:
 /com/xxxx/xxx/xxx.jpf
Action:
 update
 
Page Flow Error - No Relevant Page
You have tried to return to a recent page in the current page flow through return-to="currentPage", 
but there is no appropriate page. 


Exception's stack trace:

Exception: No previous page for return-to="currentPage" on action create in page flow
 /com/gems/mt/web/CreateReleaseCntr/CreateReleaseCntrController.jpf.
com.bea.wlw.netui.pageflow.NoPreviousPageException: No relevant page for return-to="currentPage" 
on action create in page flow /com/gems/mt/web/CreateReleaseCntr/CreateReleaseCntrController.jpf.
at com.bea.wlw.netui.pageflow.FlowController.doReturnToPage(FlowController.java:1328)
at com.bea.wlw.netui.pageflow.FlowController.forwardTo(FlowController.java:1023)
at com.bea.wlw.netui.pageflow.PageFlowController.forwardTo(PageFlowController.java:606)
at com.bea.wlw.netui.pageflow.FlowController.internalExecute(FlowController.java:765)

...

When a new page flow is created and its current page is null (it mean you visit at the fist time),
 so such an exception like NoPreviousPageException occur if you use return-to="currentPage".

if a new page flow finish a successful forward, it will treat last page as current page

so that we can use current page to display error message conveniently.

Solution:

ensure page flow finish a successful forward and use current page again.

You can also use path="specificPage.jsp" instead of return-to="currentPage" 
if your original return-to is just one specific page.

We have known, the ListCellRenderer interface has only one method public Component getListCellRendererComponent(), and it returns a Component. When a JList needs to compute its dimension or paint its cell item, this method will be called. So it will be called frequently, and we have a best practice, try to reuse object, avoid time-consumed computation and unnecessary operation in this method.

Recently found, there is a memory leak bug for list cell renderer in both JDK 1.4.x and JDK 5 (don’t know whether has the same bug in earlier JDK). The component returned from getListCellRendererComponent() method could not be GC, and all its referenced objects also could not be GC. Unfortunately, this bug is only fixed in JDK 6.

So currently, if a JList use the ListCellRenderer, but only holds a little resource (eg: the JList only has little items, and the component is returned from ListCellRenderer is a simple JLable), you may not care about the memory leak.

But if a JList use the ListCellRenderer, and holds a large resource, you should remember to use the following way to avoid memory leak.

Work Around: Subclass JList and invoke removeAll after painting is done:

       public class xxxList extends JList {

            private CellRendererPane renderer;

            private CellRendererPane getRenderer() {

                if (renderer == null) {

                    for (int i=0; i<getComponents().length; i++) {

                                          Component c  = getComponents()[i];

                        if (c instanceof CellRendererPane) {

                            renderer = (CellRendererPane)c;

                            break;

                        }

                    }

                }

                return renderer;

            }

            protected void paintComponent(Graphics g) {

                super.paintComponent(g);

                CellRendererPane renderer = getRenderer();

                if (renderer != null) {

                    renderer.removeAll();

                }

            }

Please note that in the state classes, if a method is supported by stateA and not supported by stateB. 
Then, in stateB, the method body will throw an exception (IllegalArgumentException) to indicate that coder call the wrong method in the wrong state.

Example, in VesselPlanView.java, public boolean addStowage(...).  This method is only meaningful to stowageView.

public boolean addStowage(IlvManager manager, List transformList, IlvGraphic stowage, String stadBayN,
                              boolean isSelect) {
        throw new IllegalArgumentException(
                "GrVessel::addStowage-->be sure the vessel at stowage view!");
    }


Hence, in PlanView, the method body will throw exception.

Just to share with you a better way to code.

使用 IlvToolTipManager 创建一个多行的 tooltip ：  

1) 首先需要注册 view (IlvManagerView)I
lvToolTipManager.registerView(view);  

2) 创建需要显示的信息的数组，即每行的信息为数组中的一个元素：
new String[] tooltipArray ;  

3) 创建 tooltip, 第一个参数是上面创建的数组，第二个参数是显示位置，必须是 SwingConstants.LEFT , RIGHT , or CENTER String tooltip = IlvToolTipManager.createMultiLineToolTipText(tooltipArray, SwingConstants.LEFT);  

4) 设置 tooltip ：
IlvGraphic.setToolTipText(tooltip);



public static String createMultiLineToolTipText(String as[], int i)
    {
        String s;
        switch(i)
        {
        case 2: // '\002'
            s = "left";
            break;

        case 4: // '\004'
            s = "right";
            break;

        case 0: // '\0'
            s = "center";
            break;

        case 1: // '\001'
        case 3: // '\003'
        default:
            throw new IllegalArgumentException("Alignment must be LEFT, RIGHT, or CENTER");
        }
        Font font = UIManager.getFont("ToolTip.font");
        StringBuffer stringbuffer = new StringBuffer("<p align=\"");
        stringbuffer.append(s);
        stringbuffer.append("\" style=\"font-family:");
        stringbuffer.append(font.getName());
        stringbuffer.append(";font-size:");
        stringbuffer.append(font.getSize());
        stringbuffer.append("pt\">");
        String s1 = stringbuffer.toString();
        StringBuffer stringbuffer1 = new StringBuffer("<html>");
        for(int j = 0; j < as.length; j++)
        {
            stringbuffer1.append(s1);
            stringbuffer1.append(as[j]);
            stringbuffer1.append("</p>");
        }

        stringbuffer1.append("</html>");
        return stringbuffer1.toString();
    }