Extend Oracle tablespace files

Sometimes you want to enlarge the tablespace file, when the size is not enough to handle transactions. This is the case when you get an error like:

ORA-01650: Unable to extend rollback segment RBS6
by %s in tablespace ROLLBACKSEGS

In this case, the rollback segment is not large enough to handle the database transaction. Now, you have to check if the autoextensible flag is set or if the datafile is too small.

First, find the correct database file of the rollback segment:

SELECT * FROM dba_rollback_segs;

Use the file ID from the result above to find the correct file on the file system:

SELECT * FROM dba_data_files;

Now enlarge the file:

ALTER DATABASE DATAFILE 'D:\ORACLE\ROLLBACKSEGS01.DBF'
RESIZE 1024m;

or set the autoextend to ON:

ALTER DATABASE DATAFILE 'C:\ORACLE\ROLLBACKSEGS01.DBF'
AUTOEXTEND ON NEXT 256m MAXSIZE 2048m;

Java 4 Ever

This is a really funny video about Java!

Sonar (Code Quality Management System)

Sonar is an open system to manage code quality. It monitors the 7 axes of code quality:

• Architecture & Design
  
• Comments
  
• Duplications
  
• Coding rules
  
• Unit tests
  
• Potential bugs
  
• Complexity
  

More info: http://www.sonarsource.org/

Setting response MIME-type in Java ServerFaces

To set the MIME-type in JSF, use the following code in your JSP-page:

<% response.setContentType("text/plain"); %>

In this example, the MIME-type is set to plain text. The browser will treat the page as plain text and will not render the page as a HTML-page.

Here is a list of common MIME-types.

Fixing ^M characters in VI

The new line in UNIX-like OS is represented differently than in Windows OS. When a Windows file is viewed in the VI editor, you can see ^M where the line ends. You can remove the ^M character by using the following VI regular expression command:

:%s/^V^M//g

The ^-sign means holding the CTRL-key while pressing the next character.

Getting client information in Java ServerFaces

I always log client information in JSF applications in debug mode. I use the following code in a managed bean to retrieve the IP-address, hostname and HTTP-headers from the browser.

// Get the request-object.
HttpServletRequest request = (HttpServletRequest)
(FacesContext.getCurrentInstance().
getExternalContext().getRequest());

// Get the header attributes. Use them to retrieve the actual
// values.
request.getHeaderNames();

// Get the IP-address of the client.
request.getRemoteAddr();

// Get the hostname of the client.
request.getRemoteHost();

MySQLs auto_increment in Oracle

MySQL has a reserved keyword "auto_increment" that can be used in the ID/primary key column of a new table. Whenever a new record is added to the table, this field will be automatically set to an unique incremented integer value.

In the Oracle database, this feature is missing. But we can simulate this feature using the SEQUENCE and TRIGGER functionality provided by Oracle.

A sequence is a sequential value stored in the database. It starts with an initial user supplied value, and can be incremented by an arbitrary value to a given maximum value. The statement to create a sequence for table ATABLE:

create sequence ATABLE_SEQ
minvalue 1
maxvalue 999999999999999999999999999
start with 1
increment by 1
cache 20;

Now, we want to hook up a trigger on an INSERT event of the table. Whenever a record is inserted into the table, the current value of the sequence is incremented and set in the primary key field of the inserted record.

create or replace trigger ATABLE_TRIG
before insert on ATABLE
for each row
begin
select atable_seq.nextval into :new.id from dual;
end;