rednight

當(dāng)前，CORBA、DCOM、RMI等RPC中間件技術(shù)已廣泛應(yīng)用于各個(gè)領(lǐng)域。但是面對規(guī)模和復(fù)雜度都越來越高的分布式系統(tǒng)，這些技術(shù)也顯示出其局限性：（1）同步通信：客戶發(fā)出調(diào)用后，必須等待服務(wù)對象完成處理并返回結(jié)果后才能繼續(xù)執(zhí)行；（2）客戶和服務(wù)對象的生命周期緊密耦合：客戶進(jìn)程和服務(wù)對象進(jìn)程都必須正常運(yùn)行；如果由于服務(wù)對象崩潰或者網(wǎng)絡(luò)故障導(dǎo)致客戶的請求不可達(dá)，客戶會(huì)接收到異常；（3）點(diǎn)對點(diǎn)通信：客戶的一次調(diào)用只發(fā)送給某個(gè)單獨(dú)的目標(biāo)對象。
   面向消息的中間件（Message Oriented Middleware，MOM）較好的解決了以上問題。發(fā)送者將消息發(fā)送給消息服務(wù)器，消息服務(wù)器將消息存放在若干隊(duì)列中，在合適的時(shí)候再將消息轉(zhuǎn)發(fā)給接收者。這種模式下，發(fā)送和接收是異步的，發(fā)送者無需等待；二者的生命周期未必相同：發(fā)送消息的時(shí)候接收者不一定運(yùn)行，接收消息的時(shí)候發(fā)送者也不一定運(yùn)行；一對多通信：對于一個(gè)消息可以有多個(gè)接收者。
   已有的MOM系統(tǒng)包括IBM的MQSeries、Microsoft的MSMQ和BEA的MessageQ等。由于沒有一個(gè)通用的標(biāo)準(zhǔn)，這些系統(tǒng)很難實(shí)現(xiàn)互操作和無縫連接。Java Message Service（JMS）是SUN提出的旨在統(tǒng)一各種MOM系統(tǒng)接口的規(guī)范，它包含點(diǎn)對點(diǎn)（Point to Point，PTP）和發(fā)布/訂閱（Publish/Subscribe，pub/sub）兩種消息模型，提供可靠消息傳輸、事務(wù)和消息過濾等機(jī)制。

1.JMS
   JAVA 消息服務(wù)(JMS)定義了Java 中訪問消息中間件的接口。JMS 只是接口，并沒有給予實(shí)現(xiàn)，實(shí)現(xiàn)JMS 接口的消息中間件稱為JMS Provider，iLink實(shí)現(xiàn)了JMS接口，用戶可以通過使用JMS接口，在iLink中進(jìn)行JMS編程。 iLink支持JMS1.0.2版本。

2.JMS接口描述
   JMS 支持兩種消息類型PTP 和Pub/Sub，分別稱作：PTP Domain 和Pub/Sub Domain，這兩種接口都繼承統(tǒng)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 ：連接工廠，JMS 用它創(chuàng)建連接
   Connection ：JMS 客戶端到JMS Provider 的連接
   Destination ：消息的目的地
   Session： 一個(gè)發(fā)送或接收消息的線程
   MessageProducer： 由Session 對象創(chuàng)建的用來發(fā)送消息的對象
   MessageConsumer： 由Session 對象創(chuàng)建的用來接收消息的對象

3.JMS消息模型
JMS 消息由以下幾部分組成：消息頭，屬性，消息體。
  
3.1 消息頭(Header) - 消息頭包含消息的識別信息和路由信息，消息頭包含一些標(biāo)準(zhǔn)的屬性如：JMSDestination,JMSMessageID 等。

消息頭  由誰設(shè)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 客戶 JMSReplyTo 客戶 JMSType 客戶 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)
>

是由于某些文本編輯器（UltraEdit）存文本的時(shí)候產(chǎn)生的問題。可以使用text pad, word pad編輯XML格式的文件。

通過HTTP提交EDI請求,當(dāng)EDI處理時(shí)間超過了20分鐘后,就會(huì)看到在另一個(gè)weblogic server也接收到了這個(gè)EDI請求,重新處理這個(gè)報(bào)文.
如果報(bào)文處理時(shí)間更長,比如超過了50分鐘,就會(huì)發(fā)現(xiàn)這個(gè)報(bào)文被處理了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.


響應(yīng)等待時(shí)間參數(shù)WLIOTimeoutSecs (http://e-docs.bea.com/wls/docs81/plugins/plugin_params.html#1149781.
按照BEA 推薦的，這個(gè)值應(yīng)該設(shè)得大一些, 這個(gè)參數(shù)的缺省值為300s. 見下面：
<Location /EDIHandler>
         SetHandler weblogic-handler
         WebLogicCluster apc_app1wls1:7011,apc_app1wls2:7011
         KeepAliveEnabled ON
         WLIOTimeoutSecs 7200
</Location>

有時(shí)候使用的mq jar文件的版本不對給出現(xiàn)一些末名奇妙的問題,本文則是能接收消息但不能發(fā)送消息的一個(gè)問題.碰到這樣的問題一定要記得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"這樣的錯(cuò)誤信息,一定是應(yīng)用對一次http請求做了多次頁面跳轉(zhuǎn)或?qū)esponse對象做過close后,又去寫響應(yīng).

這個(gè)問題的根本原因由于響應(yīng)本次請求的Response對象的狀態(tài)是已提交狀態(tài)造成的, 它不允許響應(yīng)提交多次。

什么時(shí)候Response對象的狀態(tài)變成已提交狀態(tài)：當(dāng)你的應(yīng)用已經(jīng)實(shí)現(xiàn)了頁面跳轉(zhuǎn)邏輯。

通常原因：

1． 如果你使用了community的話， community的安全認(rèn)證和授權(quán)如果沒有通過，community內(nèi)部會(huì)進(jìn)行頁面跳轉(zhuǎn)。但你的應(yīng)用(對于workshop應(yīng)用的話，指的是action)又試圖進(jìn)行頁面跳轉(zhuǎn)，就會(huì)出現(xiàn)這樣的問題。


    /**

     * @jpf:action

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

     */

    protected Forward actionMethod()

{

    //如果已經(jīng)提交了響應(yīng)，你仍然試圖再次進(jìn)行頁面跳轉(zhuǎn)，即再次提交響應(yīng)，可能出現(xiàn)問題

    //通常可以加一個(gè)判斷

 

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

            return new Forward("success");

        } else {

            return null;

        }

    }

 

    protected void beforeAction() {

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

                CDConstants.CREATE_TERM_ACTION_NAME, ""));

      //這個(gè)調(diào)用可能實(shí)現(xiàn)了頁面跳轉(zhuǎn)，即提交響應(yīng)

}

 

注意JSP中實(shí)現(xiàn)頁面跳轉(zhuǎn)后，加return 語句防止繼續(xù)提交響應(yīng):

 

<%

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

                CDConstants.CREATE_TERM_ACTION_NAME, ""));

{

     //可能有實(shí)現(xiàn)頁面跳轉(zhuǎn)邏輯

    ……………forward();

        return;//記得加retrun.

    }

%>

 

2. .如果沒有使用community的話，下面情景也會(huì)出現(xiàn)這個(gè)問題

 

    /**

     * @jpf:action

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

     */

    protected Forward actionMethod()

 

//直接操作Response對象寫響應(yīng)

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

    …

/

   // 又執(zhí)行的頁面跳轉(zhuǎn)，也可能出現(xiàn)問題

        return new Forward("index");

    }

一個(gè)頁面流在第一次使用時(shí),內(nèi)部屬性currentpage并沒有指定頁面,所以避免在begin方法里使用return-to: current page用法.同時(shí)在用的時(shí)候注意頁面流的工作方式

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 創(chuàng)建一個(gè)多行的 tooltip ： ?

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

2) 創(chuàng)建需要顯示的信息的數(shù)組，即每行的信息為數(shù)組中的一個(gè)元素：
new String[] tooltipArray ; ?

3) 創(chuàng)建 tooltip, 第一個(gè)參數(shù)是上面創(chuàng)建的數(shù)組，第二個(gè)參數(shù)是顯示位置，必須是 SwingConstants.LEFT , RIGHT , or CENTER String tooltip = IlvToolTipManager.createMultiLineToolTipText(tooltipArray, SwingConstants.LEFT); ?

4) 設(shè)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();
??? }

?