@Embeddable and @Embedded in Hibernate Annotation

Before jumping to @Embeddable and @Embedded annotation. Let me explain about hibernate different objects:

        Entity Object

o   Entity object are those object which can stand alone like Student or Professor and has its own database identity.

        Value Object

o   Objects which cannot stand alone like Address as you need to map address with some Entities like Student. It will belongs to an entity, and its persistent state is embedded in the table row of the owning entity

In short, always use @Embeddable for the value object and @Embedded with the entity class.

Let's understand it by a simple example:

We have one Address (Value object) and it is having attributes like city, state, zip code. Now we have two more different entity Student and Professor (Entity Object). Student or Professor can have Address attributes just by embedding the Address into its Entity.

The @Embedded annotation is used to specify the Address entity should be stored in the STUDENT table as a component.

@Embeddable annotation is used to specify the Address class will be used as a component. The Address class cannot have a primary key of its own, it uses the enclosing class primary key.

Download the source code of this example from Github.

You will see the output once you execute the Application class from source code

and will create the following tables in the database

Happy Coding..!!!

What is MappedSuperClass in hibernate ?

MapperSuperClass

·        A mapped superclass has no separate table defined for it.

·        Designates a class whose mapping information is applied to the entities that inherit from it. 

·        A class designated with the MappedSuperclass annotation can be mapped in the same way as an entity except that the mappings will apply only to its subclasses since no table exists for the mapped superclass itself. 

·        When applied to the subclasses the inherited mappings will apply in the context of the subclass tables. 

·        Mapping information may be overridden in such subclasses by using the AttributeOverride and AssociationOverride annotations or corresponding XML elements.

·        It avoids the code repetition like adding an id, version or timestamp fields in every Hibernate entity.

Example:

AbstractEntity.java class having MappedSuperClass but no Entity annotation.

User Class extends AbstractEntity class and will persisting user object, it will also persist Id and other details of mapped Class.

You can download the whole source code for Github.

After running the query, Attributes of AbstractEntity class will get created under 'USER' table.

Happy Coding...!!!

MongoDB basic Overview

Overview

• MongoDB is a cross-platform, documented oriented database and it is not based on schema like relational database.
• It uses dynamic schema and stores data in JSON format.
• It provides high performance, high availability, and easy scalability and it works on concept of collection and document.
• It is an open-source software.
• MongoDB is mainly written in C++, JavaScript and C.

Download

Please refer this link to setup MongoDB on your machine.

Terminology

·         Document

Document is similar to row/tuples in RDBMS, it is a set of key-value pairs and having dynamic schema i.e. the documents in the same collection do not need to have the same set of fields or structure and another document may hold different types of data.

·         Collection

It is the equivalent to a TABLE in RDBMS and do not enforce a schema. It exists within a single database and each document within a collection can have different schema.

·         Database

It is the equivalent to a DATABASE in RDBMS and a database can have zero or more collections.

Sample Document

{ "_id" : ObjectId("583c623e2226aa5f3b8e14f4"),

"title" : "MongoDB Basic Overview",

"by" : "http://waheedtechblog.in"

}

Where _id is the unique key for each document generated by MongoDB. Even we can provide unique key in MongoDB by specifying _id attribute while inserting data.

The generated unique key has specific format i.e. first 4 bytes are for the current timestamp, next 3 bytes are for machine id, next 2 bytes are for process id of MongoDB server and last 3 bytes are simple incremental VALUE. 

Advantages of MongoDB

· It is a schema less document

· No more complex joins

· Provides ACID properties at the document level as in the case of relational databases.

· Supports common authentication mechanisms, such as LDAP, AD, and certificates. Users can connect to MongoDB over SSL and the data can be encrypted.

· Enables horizontal scalability by using a technique called Sharding.

· Supports dynamic queries on documents using a document-based query language that's nearly as powerful as SQL.

· Conversion/mapping of application objects to database objects not needed.

· Cost effective solution as it improves flexibility and reduces cost on hardware and storage.

· Supports replica sets i.e. a failover mechanism is automatically handled. If the primary server goes down, the secondary server becomes the primary automatically, without any human intervention.

When to Use MongoDB Rather than MySQL or any Other RDBMS

· When your data is going to big and schema is not defined.

· When your data is location based

· When you expect a high load

· When you need to partition and shard your database.

· When you want to create, replica set (set of servers that act as Master-Slaves) 

Summary

MongoDB is great tool and can be very useful in creating applications like bug tracking, discussion forums, advertisements, and the like. However, Joins are not possible in MongoDB; It requires proper analysis before making a decision.

How to install and verify MongoDB on Windows 7 ?

Step by Step instructions:

1.      Download MongoDB

Check MongoDB msi from Official website and download Windows Server 2008 R2 64-bit and later version.

2.      Install MongoDB

Double click on downloaded MSI (mongodb-win32-x86_64-2008plus-ssl-3.2.11-signed.msi) file and follow the click on next button on wizard to complete the installation.

3.      Create Default Directory

MongoDB requires a data directory to store all data and its default data directory path is \data\db.

On Windows, By default it will always look for above directory under C:/ structure, Goto C: directory and create /data/db, So the full path of db folder will be C:\data\db

4.      Set environment variables

Set MongoDB location to system's environment variables and give path till bin folder.

5. 

5.      Start MongoDB

To start MongoDB server, Open cmd and type mongod, it will start the MongoDb server on port -27017.

6

6.      Verify MongoDB

Open cmd prompt and type mongo.exe

Additional Notes:

 1.      Configuration File

We can create a config file where we can add the custom path of data/db directory, Config file will be similar to properties file and add attributes in key/value pair.

##data path can be updated using dbpath

dbpath=E:\mongodb\data

##log file

logpath=E:\mongodb\log\mongo.log

Use mongod.exe –config E:/mongodb/mongo.config to load config file while starting mongodb2. 

2.      Start as a service

We can start mongoDB as a service, Adding MongoDB as Windows Service will start MongoDB automatically following each system restart. Install as Windows Service with --install.

E:\mongodb\bin> mongod --config E:\mongodb\mongo.config --install

To start MongoDB Service

net start MongoDB

To stop MongoDB Service

net stop MongoDB

To remove MongoDB Service

d:\mongodb\bin>mongod --remove

Thank you..!!!

How to extract Private key from keystore ?

There can be a situation where you want to extract private key from your keystore but it is not a straight forward as we think as It involves two steps i.e.

·         Extracting private key from keystore in PKCS#12 format

·         Converting it to .PEM file

Step1: Extracting in PKCS format

keytool -v -importkeystore -srckeystore KEYSTORE_NAME -srcalias CERTIFICATE_ALIAS -destkeystore FILE_NAME.p12 -deststoretype PKCS12

Eg: keytool -v -importkeystore -srckeystore keystore.jks -srcalias  application -destkeystore privatekey.p12 -deststoretype PKCS12

Note: If you don’t know the alias name of your certificate then you can display it:

keytool -list -v -keystore keystore.jks

Step2: Converting it into .PEM FILE

openssl pkcs12 -in privatekey.p12 -out private.pem

            

How to access Shibboleth as SP built in variables in your Application?

Most of the variables created by the SP are controlled by you, and correspond to mapped attributes. A few are built into the SP and can't be renamed.

Variable	Meaning
Shib-Application-ID	The applicationId property derived for the request.
Shib-Session-ID	The internal session key assigned to the session associated with the request.
Shib-Identity-Provider	The entityID of the IdP that authenticated the user associated with the request.
Shib-Authentication-Instant	The ISO timestamp provided by the IdP indicating the time of authentication.
Shib-Authentication-Method	The AuthenticationMethod or <AuthnContextClassRef> value supplied by the IdP, if any.
Shib-AuthnContext-Class	The AuthenticationMethod or <AuthnContextClassRef> value supplied by the IdP, if any.
Shib-AuthnContext-Decl	The <AuthnContextDeclRef> value supplied by the IdP, if any.

We can access all these variable as header in JAVA application.

Eg:

    request.getHeader("Shib-Identity-Provider")

   request.getHeader("Shib-Session-ID")

Reference:

https://wiki.shibboleth.net/confluence/display/SHIB2/NativeSPAttributeAccess

Attribute Authority, Command Line Interface (AACLI)

Today, I have encountered one interesting tool in Shibboleth IdP which will check the resolver, filters and also the metadata so that you can know exactly what will happen in any given situation without starting the IdP. J

As a developer, I would say it’s a great tool as you don’t have to restart your IdP again and again after every changes.

The name of the tool is (Attribute Authority, Command Line Interface) ACCLI which is located in the IDP_HOME/bin directory and is called aacli.sh or aacli.bat.

How it works?

Make sure, you have set IDP_HOME to your system environment variable.

To check what all attribute it will return for userId SysAdmin and Service Provider EntityId “https://domain.waheedtechblog.com/shibboleth”)

aacli.bat --configDir=C:\idp\conf\ --principal=SysAdmin --requester=https://domain1.com/Shibboleth

Please check here for detail information.