How to create Remote Access Application on Salesforce?

Before I'll start with how to create Remote Access Application. First let me explain what is actually Remote Access Application.

What is Remote Access Application?

A remote access Application is an application external to salesforce that uses the Oauth protocol to verify both the salesforce user and the external data. All remote access applications have been integrated with salesforce, such that they can access a subset of your salesforce data once you explicitly grant each application permission.

How to create Remote Access Application?

To create an Remote application, You must have your developer account, If you don’t have it then You can create it from here.

Step to create your First Remote Access Application:

1. Login to salesforce.com then click Your Name |Create | Apps and click on “new” button. Check below screenshot :
   
     
   
   
   When you click on new button, you will see a page like this:
   
   
   
   
   

2. Enter the name of the Application. This is required.
3. Enter the specify Callback URL which is also required. It represents the URL that the user will be returned to after they approve access for the application. Mostly It uses HTTPS protocol.
4. Enter your Contact Email. Contact Email is required.
5. Now Save the Remote Access Application.

Once you saved the application you will get the generated consumer key and consumer secret as shown below:

Note : Later, If you change the name of the application, the consumer key and consumer secret are not regenerated. It will be same as it was generated on the first time.
 
Congratulation!!! You have created your first Remote Access Application.

What is Maven repository ?

Maven Repository :

A repository is a place where all the project jars, library jar, plugins or any other project specific artifacts are stored and can be used by Maven easily.

There are three types of repository :

•  local
• central
• remote 

Local Repository :

The maven local repository is a local folder that is used to store all your project’s dependencies (plugin jars and other files which are downloaded by Maven). In simple, when you build a Maven project, all dependency files will be stored in your Maven local repository.

The default name of the Maven's local repository is .m2.

Central Repository

Maven central repository is repository provided by Maven community. It contains a large number of commonly used libraries.

When you build a Maven’s project, Maven will check your pom.xml file, to identify which dependency to download. First, Maven will get the dependency from your local repository, if not found, then get it from the default Maven central repository – http://repo1.maven.org/maven2/

This repository is managed by Maven community, required to be configured and it requires internet access to be searched.

Remote Repository

Sometime, Maven does not find a mentioned dependency in central repository as well then it stopped build process and output error message to console. To prevent such situation, Maven provides concept of Remote Repository which is developer's own custom repository containing required libraries or other project jars.

For example, using below mentioned POM.xml,Maven will download dependency (not available in central repository) from Remote Repositories mentioned in the same pom.xml.

<repositories>
<repository>
<id>JBoss repository</id>
<url>http://repository.jboss.org/nexus/content/groups/public/</url>
</repository>
</repositories>

Maven Dependency Search Sequence :

When we execute Maven build commands, Maven starts looking for dependency libraries in the following sequence:

Step 1 - Search dependency in local repository, if not found, move to step 2 else exit.
Step 2 - Search dependency in central repository, if not found, move to step 3 else exit.
Step 3 - Search dependency in remote repository or repositories, if not found then it is prompt error message else exit.

how to install MAVEN on linux

What is MAVEN ?

Read here : http://maven.apache.org/

Here are the steps to download and install Maven on linux :

Step 1 : Download the latest binary from the http://maven.apache.org/download.cgi.

             apache-maven-3.0.4-bin.tar.gz

Step 2 : Untar it using tar command.

              tar -zxvf /usr/local/apache-maven-3.0.4-bin.tar.gz

Step 3: Add Maven binary Path to the System Path i,e add in .bash_profile path

          $ cd $HOME
          $ vi ~/.bash_profile

Set PATH and M2_HOME as follows

M2_HOME=/usr/local/apache_maven-3.0.4
PATH=PATH=$PATH:$HOME/bin:/usr/local/apache_maven-3.0.4/bin

save the file by pressing esc : wq button

Note: Don't delete the previous PATH, Just append the M2_HOME path after :

Now save and close the file then logout and login back to see the effects, To confirm where the installation has done properly or not, check :

mvn --version

you will see following ouput :

Apache Maven 3.0.4 (r1232337; 2012-01-17 00:44:56-0800)
Maven home: /usr/local/apache-maven-3.0.4
Java version: 1.7.0_10, vendor: Oracle Corporation
Java home: /usr/local/jdk1.7.0_10/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "linux", version: "2.6.18-92.el5", arch: "amd64", family: "unix"

Congratulation... you are done here  :)

How ExceptionHandler return JSON in spring MVC

I am working on one project where client/server response is in JSON format. It is easy to send object in JSON format but what if some exception occured and you want to send the Exception also in JSON format ?
After n number of trial. I finally able to do the above task. 

Step 1 : Add following annotation "AnnotationMethodHandlerExceptionResolver" in your <CONTROLLER>-servlet.xml file.

<!-- JSON format support for Exception -->
    <bean id="methodHandlerExceptionResolver"
        class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver">
        <property name="messageConverters">
            <list>
                <ref bean="jacksonMessageConverter" />
            </list>
        </property>
    </bean>
    <bean id="jacksonMessageConverter"
        class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter"></bean>

Step 2: Make sure you have added jackson jars into your classpath.

Step 3: In controller class :

    @RequestMapping(value="/test", method = RequestMethod.GET)
    @ResponseBody
    public String toTest() throws MxlServiceException {
   try {
      int i = 10/0; // it will throw exception which will be caught by handleException(...)
  }catch (Exception e) {
    throw e;
   }
             return "hello";
 }

then catch them both by writing an exception handler that looks like this:

@ExceptionHandler({ Exception.class })
  @ResponseBody
    public ErrorResponse handleException(Exception ex,
            HttpServletRequest request, HttpServletResponse response) {
             response.setStatus(HttpServletResponse.SC_BAD_REQUEST);
        ErrorResponse errorResponse = new ErrorResponse();
        errorResponse.setMessage(ex.getMessage());
        return errorResponse;
    }

Output:

{"message": "your_message"}


Feel free to comment :)

What is Hibernate Caching?

In a typical application, you perform lot of operations like instantiate objects, load object from the database and so on. Sometime in multiuser application you may face a situation in handling multiple call of databases.

Hibernate offers caching functionality which is designed to reduces the amount of necessary database access. This is a very powerful feature if used correctly. It increases your application performance and works between your application and the database as it avoids the number of database hit as many as possible.

Hibernate Cache Types :

Hibernate uses different types of caches. Each type of cache is used for different purposes. Let us first have a look at this cache types.

• First level cache

• Second level cache

• Query level cache

1. First level cache :

First-level cache is the session cache and is always Associates with the Session object. Hibernate uses this cache by default. The Session object keeps an object under its own cache before committing to the database. Here, it processes one transaction after another one, means wont process one transaction many times. Mainly it reduces the number of SQL queries it needs to generate within a given transaction. That is instead of updating after every modification done in the transaction, it updates the transaction only at the end of the transaction.

2. Second level cache :

Second-level cache is an optional cache and is always associates with the Session Factory object. The second-level cache can be configured on a per-class and per-collection basis and mainly responsible for caching objects across sessions. While running the transactions, in between it loads the objects at the Session Factory level, so that those objects will available to the entire application, don’t bounds to single user. Since the objects are already loaded in the cache, whenever an object is returned by the query, at that time no need to go for a database transaction. In this way the second level cache works.

Hibernate supports four open-source cache implementations named EHCache (Easy Hibernate Cache), OSCache (Open Symphony Cache), Swarm Cache, and JBoss Tree Cache.

Each cache has different performance, memory use, and configuration possibilities.
  

S.N.	Cache Name	Description
1	EHCache	It can cache in memory or on disk and clustered caching and it supports the optional Hibernate query result cache.
2	OSCache	Supports caching to memory and disk in a single JVM, with a rich set of expiration policies and query cache support.
3	warmCache	A cluster cache based on JGroups. It uses clustered invalidation but doesn't support the Hibernate query cache
4	JBoss Cache	A fully transactional replicated clustered cache also based on the JGroups multicast library. It supports replication or invalidation, synchronous or asynchronous communication, and optimistic and pessimistic locking. The Hibernate query cache is supported

3. Query level cache :

Hibernate also implements a cache for query resultsets that integrates closely with the second-level cache. This is an optional feature and requires two additional physical cache regions that hold the cached query results and the timestamps when a table was last updated. This is only useful for queries that are run frequently with the same parameters.

Useful java Keytool Command

Generate a Java keystore and key pair :

keytool -genkey -alias mycert -keyalg RSA -keystore keystore.jks -keysize 1024

Generate a keystore and self-signed certificate :

 keytool -genkey -keyalg RSA -alias selfsigned -keystore keystore.jks -storepass password -validity 360 -keysize 2048

keytool command to view certificate details from keyStore :

keytool -list -v -keystore keystore.jks

Check a particular keystore entry using an alias:

keytool -list -v -keystore keystore.jks -alias mydomain

keytool command option is -printcert which prints details of a certificate stored in .cer file :

keytool -printcert -file test.cer

Export a certificate from a keystore:

keytool -export -alias mydomain -file mydomain.crt -keystore keystore.jks

 keytool -export -alias mydomain -keypass keypass -keystore keystore.jks -storepass jkspass -rfc -file keytool_crt.pem

Note: "keytool -export" command uses DER format by default. The "-rfc" option is to change it to PEM (RFC 1421) format.

How to install mod_jk.so on Cent OS

The Basics - What is mod_jk?

The mod_jk connector is an Apache HTTPD module that allows HTTPD to communicate with Apache Tomcat instances over the AJP protocol.

Steps:

1. Download the latest apache connector from http://tomcat.apache.org/download-connectors.cgi.
2. Untar the download by
         tar zxvf <filename>
3. Goto native directory of connector
         cd <connector dir>/native/
4. Run the buildconf.sh scripts
       ./buildconf.sh
Note: If you get any issue like "autocong" not installed then install following things:
       yum install autoconf
       yum install libtool
5. You need "httpd-devel" tools to build it. So make sure you have already installed it by
         yum list installed | grep httpd-devel    else install it "yum install httpd-devel"
6. From the native directory Run
      ./configure --with-apxs=/usr/sbin/apxs
      make
 

Congrats!! Now you can see the mod_jk.so module under your native directory.