In short, I have been playing with both Ruby and Rails3 and Git for the first time. Everything looks OK until I decided to restart rails server. Afterward, all rails related command (rails s, rails console and such) stopped working. Here’s the output from the command line. I put my ruby (which is 1.9.2. in c:\Ruby192)
Mac: lsof -i -P | grep -i “listen”
Note down the pid in order to kill it through activity monitor.
Sometime when I import or export Android application using eclipse, some cryptic null pointer error pops up. The error console will only prompt some kind of ‘Local Internal Error’ or something along that line despite there is no error in the application code. The full error trace can be seen below.
java.lang.NullPointerException at com.android.ide.eclipse.adt.internal.launch.AndroidLaunchController.launch(Unknown Source) at com.android.ide.eclipse.adt.internal.launch.LaunchConfigDelegate.doLaunch(Unknown Source) at com.android.ide.eclipse.adt.internal.launch.LaunchConfigDelegate.launch(Unknown Source) at org.eclipse.debug.internal.core.LaunchConfiguration.launch(LaunchConfiguration.java:853) at org.eclipse.debug.internal.core.LaunchConfiguration.launch(LaunchConfiguration.java:703) at org.eclipse.debug.internal.ui.DebugUIPlugin.buildAndLaunch(DebugUIPlugin.java:866) at org.eclipse.debug.internal.ui.DebugUIPlugin$8.run(DebugUIPlugin.java:1069) at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55)
My best hypothesis, the problem lies with the running ADV which contains corrupted app references. So what I recommend is to delete the ADV instance – yes delete and not stop – before making different ADV instance. It works… kinda
I have a very huge SQL table (5m entries and keep increasing) and want to select one row of entry at random. Typical method of using one SQL statement is apparently so slow. The typical method is by using the below statement by the way.
SELECT <column_name/*> FROM <table_name> ORDER BY RAND() LIMIT 1
while the above statement works fine on smaller table – generally 10000 records and below (depending on your processor speed), when its confronted with huge table, the statement just could not make it. Just to give you some imagination, I start using one of those statement and while waiting for the result, I can go to vending machine, grab a coke and come back, finish half a bottle of coke before stopping the process out of frustration.
After much tweaking and such, I realized that some statement are more size-conscious than the other. The trick is that using several statements which are less size-conscious to gather much needed parameter to assist statement that are more size conscious by increasing its … specifity (TODO: rephrase this paragraph)
I implement these principles using Java and the result can be seen below
public synchronized PhotoBean getRandomPhoto() throws DAOException {
Connection con = null;
try {
con = getConnection();
PreparedStatement pstmt1 = con
.prepareStatement("SELECT max(`id`) AS max_id FROM photos;");
ResultSet rs1 = pstmt1.executeQuery();
//this to to null-proof the logic
int max_id = 22101985;
int randomId = 22; // put some real ID just to make sure
while (rs1.next()) {
max_id = rs1.getInt("max_id");
}
Random randomGenerator = new Random();
randomId = randomGenerator.nextInt(max_id);
PreparedStatement pstmt2 = con
.prepareStatement("SELECT * FROM photos WHERE `id` >= ? ORDER BY `id` ASC LIMIT 1");
pstmt2.setInt(1, randomId);
ResultSet rs = pstmt2.executeQuery();
PhotoBean tmpPhoto = new PhotoBean();
while (rs.next()) {
tmpPhoto.setPhotoId(rs.getString("photo_id"));
//... more
}
//ps: you can use just one pstmt and it will be no problem as its executed separately but i am just too lazy
pstmt1.close();
pstmt2.close();
releaseConnection(con);
return tmpPhoto;
} catch (Exception e) {
//... more
}
Today, I discovered how easy it is to share my school’s Mac OS X (10.5.x) screen with another non-Mac OS computer. I know it is not a sophisticated or such but I’m posting it here as I know this might not be obvious to most Windows user or even Mac user who often live in their own world.
My first attempt to do this screen sharing thing is by following this super complex tutorial. http://howto.diveintomark.org/remote-mac/
The tutorial by Mark Pilgrim comes with videos and links and nice background music and such – making it looks highly reliable for beginner like me. It sounds like a very secure procedure, with explanation about SSH, man-in-the-middle and many more. However, this tutorial miss one crucial aspect regarding setting up fixed domain, tcp-forwarding and those ip related stuff that might confuse 99% of world population. Not to mention his tutorial only shows configuration for home internet with a particular ISP. The mac that I use for example was located behind CMU’s firewall and some other obstruction, making his tutorial to be only for geeks.
I could not set up the screen sharing capability through his tutorial. 
*swearing phase*
For some reason all the VNC client that I use, RealVNC, TightVNC, UltraVNC does not seems to work properly. The clients fails with message like: ”Server did not offer supported security type” (tightVNC), ”No matching security types” (realVNC), ”Incompatible Version” (UltraVNC).
Then I google this error message only to found out this very long tutorial on how to tweak Mac to accept screen sharing. The tutorial can be found in this forum:
http://forums.macrumors.com/showthread.php?t=380251
In short, the tutorial asks me to perform some kind of surgery to the mac machine which obviously I was not so keen of doing so.
*swearing phase*
Then Justin, one of my research mentor pointed out that for mac, there should be no additional set up other than setting up screen sharing. He suspects its a mac-windows uneasy relationship thing.
After few googling I stumble upon one of the forum post somewhere – I forgot from where but it basically said I need to set the password for screen sharing so that those windows based client can actually connect to the mac.
IT WORKS… wtf
Here is how.
Go to (top-left-apple)-> system preferences->sharing->tick screen sharing together with the users that can be allowed to screen share.
Go to system preferences and then Sharing
Click Computer Setting to set up the password for allowing screen share.
This is a quick and painless way to remove duplicate rows from a MySQL database table. It requires no programming or PHP coding whatsoever. Without further ado…
STEP 1
CREATE TABLE new_table as SELECT * FROM old_table WHERE 1 GROUP BY [column to remove duplicates by];
STEP 2
DROP TABLE old_table;
STEP 3
RENAME TABLE new_table TO old_table;
STEP 4
DO NOT FORGET TO RESET THE PRIMARY KEY AND FOREIGN KEY AGAIN
from
http://www.justin-cook.com/wp/2006/12/12/remove-duplicate-entries-rows-a-mysql-database-table/
If you have read my previous post, I was still struggling with Struts + Hibernate.
In any case, for some reason Tomcat gives this weird error message.
Server Tomcat v6.0 Server at localhost was unable to start within 45 seconds. If the server requires more time, try increasing the timeout in the server editor.
Pretty self explanatory except for the fact that the error never mention about where I need to open the config files.
I am looking into several files inside my eclipse without avail until one blog outline his quick and dirty method.
Solution: I’m not sure where the server editor is located, but changing the start-timeout=”45″ in workspace\.metadata\.plugins\org.eclipse.wst.server.core\server.xml would help, make sure restart eclipse after the change.
Neat
Got the solution from http://acodapella.blogspot.com/2009/12/server-tomcat-v60-server-at-localhost.html
You never believe what much configuration does it take to make Struts-Hibernate-Spring configuration run. I am currently following a very long tutorial outlined here http://www.scribd.com/doc/25244173/Java-Struts-Spring-Hibernate-Tutorial I got the tutorial from apache.org site – and pretty much a very promising one.
In short, the tutorial shows how to create web-app using hibernate and struts. The tutorial uses hibernate 3.3 core and annotation component. It is said that ‘If by the time you read this 3.5 has been released then you won’t need annotations as it is going to be’. I am using Hibernate 3.5 and noticing by page 56, the code does not works due to missing element and such.
Apparently, after much googling and code skimming, I have concluded that Hibernate 3.5 still required javax.persistence.jar
Solution: download Javax.persistence.jar and add it to lib.
Download the jar from here
Javax.persistence.jar
Continue with the tutorial
UPDATE:
No need to download the above files. Apparently that javax.persistence,jar do not have important class such as javax.persistence.Cacheable
I am looking for a newer version of javax.persistence.jar now
Let me know if you have
For some reason, I do whatever tutorial on Struts exception handling http://struts.apache.org/2.1.8.1/docs/exception-handling.html and yet the Struts giving me that obscure error message at package nodes.
It is said
The content of element type “package” must match “(result-types?,interceptors?,default-interceptor-ref?,default-
action-ref?,default-class-ref?,global-results?,global-exception-mappings?,action*)”.
I have no idea what is it until I see the tutorial mentions that I need to add two important nodes which I gladly copy pasted.
<global-exception-mappings>
<exception-mapping exception="org.apache.struts.register.exceptions.SecurityBreachException" result="securityerror" />
<exception-mapping exception="java.lang.Exception" result="error" />
</global-exception-mappings>
<global-results>
<result name="securityerror">/securityerror.jsp</result>
<result name="error">/error.jsp</result>
</global-results>
It took me 15 minutes to figure out that the tutorial gives me the wrong sequence of nodes. I need to do global-result before global-exception-mappings. Making the correct sequence to be:
<global-results>
<result name="securityerror">/securityerror.jsp</result>
<result name="error">/error.jsp</result>
</global-results>
<global-exception-mappings>
<exception-mapping exception="org.apache.struts.register.exceptions.SecurityBreachException" result="securityerror" />
<exception-mapping exception="java.lang.Exception" result="error" />
</global-exception-mappings>
and based on the above mentioned error notification and seeing the tutorial sample file, I could piece up the final struts.xml. In case you are lazy bum who do not want to download that extra 3.5 mb zip files and (assuming you follow the tutorial faithfully), the final struts.xml at the end of the day should be
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>
<constant name="struts.devMode" value="true" />
<constant name="struts.custom.i18n.resources" value="global" />
<package name="basicstruts2" extends="struts-default">
<!--
setup the default-stack exception mapping interceptor so that any
exceptions not caught by this application will be logged and then
handled by the global exception mapping
-->
<!--
You can configure the Struts 2 framework to log any uncaught
exceptions. To enable logging of the exceptions being handled by the
Struts 2 framework you must specify some parameter values in
struts.xml. If you examine the ExceptionMappingInterceptor class API
there are three parameter values you can set to enable logging
(logEnabled), the log level to use (logLevel), and the log category
(logCategory) to specify in the log message. To set these parameter
values for all actions that use a specific stack of interceptors in a
package include the following in struts.xml just after the opening
package node.
-->
<interceptors>
<interceptor-stack name="appDefault">
<interceptor-ref name="defaultStack">
<param name="exception.logEnabled">true</param>
<param name="exception.logLevel">ERROR</param>
</interceptor-ref>
</interceptor-stack>
</interceptors>
<default-interceptor-ref name="appDefault" />
<!--
To enable global exception handling you need to add two nodes to
struts.xml: global-exception-mapping and global-results. For example
examine struts.xml from the Exception Handling code download
(http://code.google.com/p/struts2-examples/downloads/list).
-->
<global-results>
<result name="error">/error.jsp</result>
<result name="securityerror">/securityerror.jsp</result>
</global-results>
<global-exception-mappings>
<exception-mapping
exception="org.apache.struts.register.exceptions.SecurityBreachException"
result="securityerror" />
<exception-mapping exception="java.lang.Exception"
result="error" />
</global-exception-mappings>
<action name="causesecurityexception" class="org.apache.struts.register.action.Register"
method="throwSecurityException">
<result>/register.jsp</result>
</action>
<action name="causeexception" class="org.apache.struts.register.action.Register"
method="throwException">
<result>/register.jsp</result>
</action>
<action name="causenullpointerexception" class="org.apache.struts.register.action.Register"
method="throwNullPointerException">
<result>/register.jsp</result>
</action>
<!--
If you need to handle an exception in a specific way for a certain
action you can use the exception-mapping node within the action node.
-->
<action name="actionspecificexception" class="org.apache.struts.register.action.Register"
method="throwSecurityException">
<exception-mapping
exception="org.apache.struts.register.exceptions.SecurityBreachException"
result="login" />
<result>/register.jsp</result>
<result name="login">/login.jsp</result>
</action>
<action name="index">
<result>/index.jsp</result>
</action>
<action name="hello"
class="org.apache.struts.helloworld.action.HelloWorldAction" method="execute">
<result name="success">/HelloWorld.jsp</result>
</action>
<action name="register" class="org.apache.struts.register.action.Register"
method="execute">
<result name="success">/thankyou.jsp</result>
<result name="input">/register.jsp</result>
</action>
<action name="registerInput" class="org.apache.struts.register.action.Register"
method="input">
<result name="input">/register.jsp</result>
</action>
</package>
</struts>
Often when I am doing coding on java, most changes I have made seldom appear instantly. To make it faster, the following steps (in order / combination) might be working.