NeilSys

Java – getClass().getResource() always returning null – IntelliJ Idea Fix

L J Arthur Neil — Thu, 17 May 2012 06:04:56 +0000

If you get the error like this and you are sure that you have set the absolute/relative path to the file correctly, then don’t look anywhere, just check your classpath and everything lies there. If you are using any IDE (Eclipse/IntelliJ ID) make sure you update the classpath in the buildpath or in the settings.

For IntelliJ Idea;

1. Press F4 (Right click on project -> open module settings)

2. On the left hand side, Find SDK’s option.

3. Click and find Classpath tab.

4. Update the classpath of your project here.

5. Now build and give a smile

Intellij Idea – Compiler internal error. Process terminated with exit code 3

L J Arthur Neil — Wed, 16 May 2012 16:59:09 +0000

Just increase the maximum heap size of the compiler(Setting->Compiler->Java Compiler)

That should solve it.

Hibernate’s HQL “inner join on” limitations

L J Arthur Neil — Fri, 20 Apr 2012 14:05:25 +0000

If you haven’t defined the association in the mapping file; then you can’t expect queries as follows will work as expected;

Query query = session.createQuery(“from Cat cat inner join Owner owner on cat.OwnerId = owner.Id where owner.Name=’Duke’”);

It seems that hibernate does not support arbitrary relationships between object being defined in the “on” clause.. You will get an error saying;

Caused by: org.hibernate.hql.ast.QuerySyntaxException: unexpected token: on near line 1, column xx

The solution to this is to use HQL with a cartesian product or cross join and do something like;

Query query = session.createQuery(“from Cat cat,Owner owner where cat.OwnerId = owner.Id and owner.Name=’Duke’”);

What is serialVersionUID?

L J Arthur Neil — Thu, 19 Apr 2012 14:02:42 +0000

Java platform allows us to create reusable objects in memory. However, all of those objects exist only as long as the Java virtual machine1 remains running. It would be nice if the objects we create could exist beyond the lifetime of the virtual machine, wouldn’t it? Well, with object serialization, you can flatten your objects and reuse them in powerful ways.

Object serialization is the process of saving an object’s state to a sequence of bytes, as well as the process of rebuilding those bytes into a live object at some future time. The Java Serialization API provides a standard mechanism for developers to handle object serialization. The API is small and easy to use, provided the classes and methods are understood.

The serialization runtime associates with each serializable class a version number, called a serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization. If the receiver has loaded a class for the object that has a different serialVersionUID than that of the corresponding sender’s class, then deserialization will result in an InvalidClassException. A serializable class can declare its own serialVersionUID explicitly by declaring a field named “serialVersionUID” that must be static, final, and of type long:

ANY-ACCESS-MODIFIER static final long serialVersionUID = 42L;

If a serializable class does not explicitly declare a serialVersionUID, then the serialization runtime will calculate a default serialVersionUID value for that class based on various aspects of the class, as described in the Java(TM) Object Serialization Specification. However, it is strongly recommended that all serializable classes explicitly declare serialVersionUID values, since the default serialVersionUID computation is highly sensitive to class details that may vary depending on compiler implementations, and can thus result in unexpected InvalidClassExceptions during deserialization. Therefore, to guarantee a consistent serialVersionUID value across different java compiler implementations, a serializable class must declare an explicit serialVersionUID value. It is also strongly advised that explicit serialVersionUID declarations use the private modifier where possible, since such declarations apply only to the immediately declaring class–serialVersionUID fields are not useful as inherited members.

Apache Axis2 Installation

L J Arthur Neil — Wed, 18 Apr 2012 13:56:38 +0000

Download Axis2 from http://axis.apache.org/axis2/java/core/download.cgi
Unzip the Axis2 Standard Binary Distribution into “C:\DevTools\axis2-1.3″
NOTE: Substitute the appropriate path to the current version of Axis2
Add the following system environment variables
AXIS2_HOME=C:\DevTools\axis2-1.3
Add the following to the PATH
%AXIS2_HOME%\bin;
[NOTE: You are doing all this so that you have access to the command line utilities like wsdl2java etc.]
Copy the axis2.war to the “C:\DevTools\Tomcat 5.5\webapps” directory
Browse to http://localhost/axis2/axis2-web/HappyAxis.jsp and verify that all needed components are installed
Copy any needed modules(http://axis.apache.org/axis2/java/core/modules/index.html) to “C:\DevTools\Tomcat 5.5\webapps\axis2\WEB-INF\modules”
Restart Tomcat

How to change username/password in TortoiseSVN

L J Arthur Neil — Wed, 18 Apr 2012 13:43:10 +0000

In TortiseSVN settings (right click on the icon and choose settings), open the Saved Data tab, and clear out the Authentication Data. The side effect is that it clears out all authentication data, and you will have to re-enter your own username/password.

Most Useful Keyboard Shortcuts for Intellij IDEA

L J Arthur Neil — Tue, 17 Apr 2012 13:34:08 +0000

Ctrl+B: Go to declaration. This will go to the declaration of whatever your cursor is over. Whether it be a variable, method, or class, Ctrl+B will take you to where it was declared.

Ctrl+N: Go to class

Ctrl+Shift+Backspace: Navigate to last edit location .It takes you to the location of the last thing you were editing. Keep pressing it to go back further in your editing history.

Ctrl+W: Expand selection. Ctrl+W smartly expands your selection. If your cursor is in the middle of a variable name it will select the variable name. Continue pressing Ctrl+W to expand your selection more and more. If you expand too far, you can press Ctrl+Shift+W to decrease your selection.

Ctrl+Shift+N: Go to file

Ctrl+Shift+I: Open quick definition lookup. It opens a popup that shows the definition of whatever your cursor is over. Press escape to close the popup.

Alt+Shift+Insert – Enable vertical selection of text. Use Alt+Shift+Insert again to disable it.

Ctrl+/: Comment/uncomment with line comment. Handy for quickly commenting out the current line or your current selection.

Ctrl+C or Ctrl+X (without a selection): Copy or Cut the current line. If you have nothing selected, it will copy or cut the whole line.

Importing .sql file to postgresql

L J Arthur Neil — Mon, 16 Apr 2012 13:28:34 +0000

You can use psql command line tool:

psql -h hostname -p port_number -U username databasename -f your_file.sql

psql: FATAL: Ident authentication failed for user

L J Arthur Neil — Sun, 15 Apr 2012 13:14:23 +0000

If you have done the new installation, make sure you accessing with the default user credentials. The default user name is ‘postgres’ and the password is the one you chose when you did the installation.

And now try creating your db and try to access. All should be well.

Go to C:\Program Files\PostgreSQL\9.1\bin

createddb -U postgres test

password:

psql -U postgres test

If you still face the issue;
open /data/pg_hba.conf

This file contains following information;

Which hosts are allowed to connect
How clients are authenticated
Which PostgreSQL user names they can use
Which databases they can access

You may want to add these lines to make it work.

local all all trust
host all 127.0.0.1/32 trust

For more info; Refer, http://www.postgresql.org/docs/8.3/static/auth-pg-hba-conf.html

Struts – HttpServletRequest – Get referrer

L J Arthur Neil — Tue, 13 Mar 2012 17:46:46 +0000

HttpServletRequest request = (HttpServletRequest) ActionContext.getContext().get(ServletActionContext.HTTP_REQUEST);

String referrer = request.getHeader(“referer”);