[Book Review] ElasticSearch Server for fast scalable flexible search solution

ElasticSearch Server 

http://www.packtpub.com/elasticsearch-server-for-fast-scalable-flexible-search-solution/book

This is a good book for someone who wants understand and try out the latest search framework ElasticSearch built on top of Lucene. This claims to provide the best, flexible, distributed and enterprise Search Framework

It covers almost all the topic that is required

1. Introduction to Elastic Search
2. Understanding Shards, Nodes and cluster.
3. Indexing and Searching Techniques
4. Templates, Mapping
5. Different API's
6. Plugins.
7. etc.,

I would suggest this book for someone interested in ElasticSearch Server.

Java: Code to unquote string using Regex

str="\"hello\"" // or "'hello'"

public static unquote(String str)
{
        str = str.trim();
if (str.startsWith("'") && str.endsWith("'"))
{
    str = match(str, "(?<=').*(?=')");
}
else if (str.startsWith("\"") && str.endsWith("\""))
{
         str = match(str, "(?<=\").*(?=\")");
}
}

//matches the pattern
private static String match(final String string, final String regex)
{
final Pattern pattern = Pattern.compile(regex);
final Matcher matcher = pattern.matcher(string);
matcher.find();
return matcher.group(); 
}

[Shared Webinar] Getting Started with ElasticSearch

Click on the Below Image and fill in details to watch the Webinar

Quick Notes : Practical usage of collections

Different Types of Collections and when to Use them

Set

HashSet : 

• When you want unique set to objects. 
• Make sure equals and hashcode is implemented.
• This does not maintain the order of object addition. As the name says it is Hashed

TreeSet:

• You can have the list ordered the way you want, by passing in a comparator.
• Example: new TreeSet(String.CASE_INSENSITIVE_ORDER)
• It automatically orders the objects that you add accordingly

LinkedHashSet

• This gives us the flexibility of HashSet (uniqueness) and 
• also maintains the insertion-order of objects

Map

HashMap :

• Easier way of holding Key Value Pair
• Does not maintain the insertion-order (Hashed)

TreeMap:

• Sorted Map, Sorting of keys determined by the comparator in the constructor
• Quickly create a map of case insensitive keys as follows
  new TreeMap(String.CASE_INSENSITIVE_ORDER)
• Throws a NullPointerException if you use get without a null check.
  treemap.get(null), so better add a null check before invoking get()

LinkedHashMap:

• Extends HashMap. But, preserves of the insertion order

List:

ArrayList:

• Quicker way of maintaining a list of objects
• can add duplicate values.
• It is advisable to use this collection if we expect more number of gets() than add() or set()

LinkedList:

• Performs better when you have more additions and insertions than searching the list

Deleting Public Keys from GPG and RPM key rings

In order to delete the public keys from the key ring, we would require the key_id. The key_id can be idenfied using the below steps using the file where the public key is stored.

To get the Key Details

gpg --throw-keyids < [Key-File-Absolute Path]

pub  1021D/1689B887 2005-03-11 ABC Company 

sub  1048f/47E5X96D 2005-03-11  [expires: 2015-03-09]

To get the Key-ID from the keyfile

key_id=${gpg --throw-keyids < [Key-File-Absolute Path] | head -1 |  awk {'print $2'} |  cut -d '/' -f2 |  tr [A-Z] [a-z]}

1689B887

Delete from GPG keyring

gpg --delete-key  --yes $key_id

Delete from RPM keyring

rpm -e --allmatches gpg-pubkey-$key_id

Linux script to display tree structure of directory

ls -R | grep ":$" | sed -e 's/:$//' -e 's/[^-][^\/]*\//--/g' -e 's/^/   /' -e 's/-/|/'


Output from  a folder. This displays "ONLY" directories
 .
   |-resources
   |-src
   |---java
   |-target


(or)


yum install tree

tree -A
.
├── resources
├── src
│   ├── Hello.java
│   └── java
└── target

-A to be used if you use garbage chars as follows

.

âââ resources

âââ src

â   âââ Hello.java

â   âââ java

âââ target

Reference
http://ssteiner.wordpress.com/2009/05/12/quick-linux-tree-view-of-directory-contents/

Regex to find non-quoted string match

Created a below regex to  identify , that is not quoted. 

(,) (?=(?:[^\"]|\"[^\"]*'\")*$),

(,) 

    (?=   

           (?:                               # non capturing group

                 [^\"]|                     # string not quoted 

                 \"[^\"]*'\"           # string inside quotes

            )*$                            # many a times until end of string

     )

This has a an issue when you really run it with a lengthy string

positive lookahead  + alteration +  * + lengthy string  +  heap size crunch.

 JDK suggestion : http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=5050507

So the below regex will fetch you the 

(,)(?=(?:[^"]*"[^"]*")*[^"]*$)

(,)

   (?=                            # look ahead

       (?:                         # non capturing group, ignore string within group 

           [^"]*                 # group of non-quoted text  

           "[^"]*"               # followed by quoted quote + non quoted (*)+ quote  

        )*                        # this group can be 0 or many

    [^"]*                       # capturing group    (non quoted)

   $)                            # till end of string



Regex Tester Online: http://regexpal.com/


String used to Test 
(state "locked" OR state" not active" NOT state"pending or " OR state"running" AND state" and completed" OR state"error" OR state"warning") AND NOT hidden"true" AND NOT type"Background" AND NOT cycle"true" AND parent"null" AND test"asdfasdf asdfhasd fha sdfhas udfhuasdhfu asudfhasudfhuas fhuihas udfhuashd ufhasuidfhua shdfuas hduhuhasd fuhasdufhas duhuhu hasufhuasdhfdfsdfasdfsdasdsad7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777aasda777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777sd7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777as7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777d7end")