Wednesday, October 7, 2009
This works fine, however when we came to testing we couldn't seem to get Selenium to input text into the RichTextArea (iframe) component.
A number of websites (for example http://www.hietavirta.net/blog/item/2008/08/gwt-15-tree-and-richtextarea-testing-with-selenium) suggested something like "select the right frame with Selenium's selectFrame, type text to //html/body and finally select the top frame again."
However, this didn't work for us. We tried a combination of options for selecting the frame and then trying to select the body (or other elements) within the iframe, but all to no avail.
In the end, we didn't need to select the iframe/richtextarea separately first (and, indeed, this selecting didn't seem to work, even though the GWT "ensureDebugId" did correctly attach the id to the iframe element).
The final solution to get selenium to type into the RichTextArea was to include in our tests the code:
selenium.type("//*[@contentEditable='true'","This text is to be typed");
The first argument of the selenium.type command is a locator that finds the correct iframe (RichTextArea) element, based on the fact that GWT creates this element with a parameter indicating the content is editable. The second command is the text you want typed in your test.
Seems so simple here, but getting that to work took hours! We tried a bunch of much more "obvious" options to locate that element (including a bunch that other bloggers said worked), but in our case this was the only thing that we could find that did the job!!
So... now ya know what worked for us, too!
Tuesday, May 19, 2009
"java.sql.SQLException: Communication link failure" when using Hibernate, Tomcat and MySQL with Spring
Root Cause: java.sql.SQLException: Communication link failure: java.net.SocketException, underlying cause: Software caused connection abort: recv failed
Situation: When first deployed the application works fine. However, when the application is left running for a long time (eg > 8 hours) without any interactions, the connection to the MySQL database is lost and the web-app throws an exception. The full stacktrace of that exception is below, for those interested. I am using Tomcat 6.0.18 and MySQL 5.0.27-community-nt.
Aside: It is perhaps also worth noting that another computer with the same code-base does NOT throw this error - even though the MySQL time-out settings are the same. The main difference appears to be that the other computer is running Tomcat 6.0.14 and MySQL 5.0.18-nt so it is possible that these versions don't require the fix below - but I haven't confirmed that it isn't some other minor difference.
This is a fairly common problem, but a range of solutions presented elsewhere on the internet didn't fix my problem - and they aren't documented together anywhere I could find - so I'm recording some of these here, along with the one that finally worked for me.
How to test:
The first thing to note is that this is caused by MySQL closing down connections that are idle for a period of time. One fix is to just drastically increase the "Interactive timeout" and "Wait timeout" in the my.ini file that is read on startup in MySQL. Don't forget to restart MySQL each time you change these (and to stop Tomcat before restarting MySQL). A good way to test if this timeout is really your problem is to change these to a short value (eg 40) (that is, 40 seconds) and wait to see if the error occurs in a minute or so. That way you don't have to wait overnight to test whether changes fix your problem.
NB: Only one of these worked (or was deemed "acceptable") for my case - and that one is the last one, but I record them all here as I couldn't find one location with all these summarized.
1. One solution is to just increase the MySQL Timeout settings as described in the "testing" section above. However, while this fixed one application I was working on, in one (different) case I found that the error was occurring overnight even if I set this to a very large value (eg 604800 sec). In any case, just increasing this value isn't a great solution as you don't want the error to occur ever - so just stalling it for a week isn't great!
2. Another solution that I didn't like, but should mention, is to put a try/catch around the Java code that accesses the database. This isn't really a hibernate solution, but I thought I'd mention it. See the suggestions at the following URL if you want to try this. It's inelegant if you're using Hibernate, but might be good if you are doing your connections manually.
3. Another suggestion that I found on the web that didn't work - but might for similar problems - is to put the following into your hibernate config file:
4. A related suggestion is to add autoReconnect=true to jdbc URL. I did try this and it didn't work for me, but it might be worth considering.
5. Another suggestion was to set the C3P0 connection-pooling properties as follows:
<property name=“hibernate.c3p0.preferredTestQuery">select 1</property>
See https://www.hibernate.org/214.html for more details on C3PO config. This would set C3PO pooling values in the configuration - in particular setting the idle_test_period and timeout properties to be less than the values set for MySQL timeout (see 1 - I had the MySQL timeout set to 691200, so it was much longer). In fact, even before experiencing this problem I did actually already have these values set and yet the error still occurred! Still, this may be necessary /fix the problem for some people and I am still using these settings, above.
Aside: A similar set of properties for dbcp is given at https://forum.hibernate.org/viewtopic.php?f=1&t=933088&view=previous.
6. Solution (Actually worked for me): The final change that actually worked was to modify the Spring data-source to be:
lazy-init="default" autowire="default" dependency-check="default"
<property name="driverClass"> <value>com.mysql.jdbc.Driver</value> </property>
<property name="user"> <value>myUser</value></property>
<property name="autoCommitOnClose"> <value>true</value></property>
<property name="idleConnectionTestPeriod"><value>15</value> </property>
<property name="maxIdleTime"> <value>15</value> </property>
The key properties here are to set the idleConnectionTestPeriod and maxIdleTime to values that are less than the mySQL timeout values mentioned in (1) above. Setting these two new properties for the datasource in applicationContext-jdbc.xml file in my Spring config settings fixed the problem.
More StackTrace Info for Error:
org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.transaction.CannotCreateTransactionException: Could not open Hibernate Session for transaction; nested exception is org.hibernate.TransactionException: JDBC begin failed:
java.sql.SQLException: Communication link failure: java.net.SocketException, underlying cause: Software caused connection abort: recv failed** BEGIN NESTED EXCEPTION ** java.net.SocketExceptionMESSAGE: Software caused connection abort: recv failedSTACKTRACE:java.net.SocketException: Software caused connection abort: recv failed at java.net.SocketInputStream.socketRead0(Native Method) at java.net.SocketInputStream.read(Unknown Source) at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:1391) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:1538) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:1929) at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1167) at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1278) at com.mysql.jdbc.MysqlIO.sqlQuery(MysqlIO.java:1224) at com.mysql.jdbc.Connection.execSQL(Connection.java:2248) at com.mysql.jdbc.Connection.execSQL(Connection.java:2208) at com.mysql.jdbc.Connection.execSQL(Connection.java:2189) at com.mysql.jdbc.Connection.setAutoCommit(Connection.java:546) at com.mchange.v2.c3p0.impl.NewProxyConnection.setAutoCommit(NewProxyConnection.java:756) at org.hibernate.transaction.JDBCTransaction.begin(JDBCTransaction.java:63) at org.hibernate.impl.SessionImpl.beginTransaction(SessionImpl.java:1326) at org.springframework.orm.hibernate3.HibernateTransactionManager.doBegin(HibernateTransactionManager.java:496) at org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:322) at org.springframework.transaction.interceptor.TransactionAspectSupport.createTransactionIfNecessary(TransactionAspectSupport.java:255) at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:102) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:176) at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:210)
Wednesday, April 22, 2009
java.lang.UnsupportedClassVersionError: Bad version number in .class file
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
So my initial thought was "ok, a class is not loaded, but which one???".
Well - it turns out that this information would probably have led me down the wrong path anyway... and you don't need it (so don't get frustrated with whoever created that error message!).
The problem occurs, generally, when you compile a .java file with one version of JDK and then run the (compiled) .class with a different version of the Java Virtual Machine.
So... how was I doing this? Well - the .class file is being run within Tomcat and the .java file is being compiled by the preferred java compiler set in myEclipse. Ideally, these two versions would be the same - however they can be quite different. This won't be a problem AS LONG AS the Tomcat Java version (ie the Java running the .class files) is not an older version than the Java version used to compile the .class file from .java. It turns out that I had accidently set the Tomcat Java version to be an older one than the JAVA version being used to compile the code.
Tomcat Java Version is set by:
- MyEclipse Tomcat[*] -> Configure -> Jdk -> Tomcat JDK Name
MyEclipse Compiler Java Version is set by:
- Project-> Properties -> Java Compiler -> Compiler Compliance Level
- Window -> Preferences -> Java -> Installed JREs -> Selected JRE
So, all I had to do to fix this was to set both the Tomcat JDK Name and Selected JRE to jre1.6.0_05 and compiler compliance to 1.6 and I'd fixed the problem.
[*] or whichever Tomcat you are using...
Tuesday, February 17, 2009
I have the latest Flash player (and, indeed, did follow the link and upgrade it just to make sure). However, this kept occurring for a number of YouTube videoes I then tried to watch as a test.
A bit of investigation indicated a huge range of suggestions for how to fix this - everything from people claiming it is a bug with YouTube and "YouTube Engineers are working on it" through to those advising turning off various bits of your Internet Explorer security settings (such as any "Add blockers" etc) and deleting temporary internet files and cookies.
Given that these fixes didn't work for me - and I don't want to leave my browser in an unsafe state with popups etc, anyway - I changed all these settings back to their usual state.
SOLUTION (Well, almost!):
I did, however, come up with a way to watch the video.
Now, to be honest, I haven't actually fixed the problem - when I go to the original URL I get the same error message still - but, on the positive side, I can watch the YouTube video (which, after all was the point). To do this, you just need to modify the URL you are using slightly.
In this particular case (as embarrassing as this may be - I didn't choose this video), my friend wanted me to view the link:
This didn't (and still doesn't at the moment of writing this) work for me. However, if you modify the link to:
- remove the words "watch?"
- replace "=" with "/"
I obtain a new URL that does work:
So, the good news is this worked. The bad news is that had I known what the link was for I wouldn't have wasted the time :-) Ok - so maybe it isn't that bad?!?
Anyway, music taste aside, the good news is that this works on all the YouTube files I've tried so far. They're all giving me this same error message but, if I really wanted to, I could watch them by changing the URL manually...
So... it isn't a long term fix - but maybe this is a good start for others if the problem is with something at YouTube's end, or if you're just in a real hurry to watch that link you've been sent and don't wanna spend days re-installing Adobe products and Virus scanners!!!