Category Archives: Programming

Difference between java.home and JAVA_HOME

When setting up environments, one of the few things we have to do is set up environment variables. JAVA_HOME is the most common environment variable you have to set up, especially if doing Java development. So previously, I had asked this question about knowing the difference between java.home and JAVA_HOME on StackOverflow here.

Question

Basically, I was using System.getProperty("java.home") in my code and it would return difference value from what I had set for JAVA_HOME. I was wondering why the difference. This post is about the explanation of the difference between these two properties.

Answer

There are some contradictory answers about the difference. But what I found on my own is that java.home is a system variable created based on Java Runtime Environment (JRE). This is more like a system variable. JAVA_HOME is an environment variable, this is required when you install JDK. Java Development Kit(JDK) is an environment based software that an individual installs and this software needs Java Runtime Environment (JRE).  So JDK is a superset of JRE.

On any system, when you ask for JAVA_HOME environment variable, you generally get the path of your JDK installation. But since java.home is a system variable, the only way to find out that variable is through system properties. Also some machines have default Oracle installed JRE path and java.home might point to that path. You won’t be able to do any Java-based development if you do not have JAVA_HOME defined.

But the interesting fact is when you install JDK, it also installs JRE. But when you verify java.home , it doesn’t point to the same root path where JDK has been installed. One main reason for this, is that despite when you install JDK, JRE and JDK are two different products and many machines have default JRE installed.

Conclusion

In this post, I showed the difference between JAVA_HOME and java.home. Subscribe to my blog here.

References

  1. System Properties – Oracle Documentation

 

 

 

All about the skill of programming

Yes, this will be the post where we dissect the skill of programming. Recently I came across a lot of beginner’s questions from friends and families who want to get into programming. But also if I want to go back in time and want to give advice to 10 years younger me, what advice would I give? How would I approach programming skills differently compared to what I did?

Before I move forward, if you want to read design patterns, you can visit that link.

Why does programming matter?

Most of us are not born programmers or smart enough to gauge our ability to sit in front of a computer for hours and write something in a completely foreign language to mankind. Programming is definitely not foreign anymore, but there are still a lot of people in the world, who don’t know anything about how computers work. They want to use computers, but don’t care about how computers operate.

I will not cover how computers work in this topic, but want to remind everyone that when we designed computers back in 50s and 60s, one purpose was that it could help us to solve some of the complex problems we face. Computers have exceeded the expectations and there is a speculation that in near future, all mundane jobs will be replaced by artificial intelligence. Artificial intelligence is only possible when the programming continues to evolve and it has been. There are lot of curious people in our world and this mere mortal is one of them. For me, it was curiosity that drove towards computers and slowly i embraced the internals and ideas about computer. It was fascinating always. To answer the question, in short, to continually evolve as mankind, we need technology and technology is the fastest evolving paradigm which is majorly based on programming.

What’s your purpose for programming?

You don’t really need a purpose to program. I started with programming mundane algebraic functions . It was continuous improvement from that moment to solve some of the complex mathematics problems to engineering problems to real world business problems. Despite all that, there are lot of system level problems in computers that need attention. You can even choose a purpose of fun. Lot of programmers started programming for fun and built some of the coolest games. No purpose is still a purpose till the time you allocate certain time to improve your skill. It’s been 15 years from the time I have graduated from college, but I have not stopped programming and I am no where close to say that I am the best. You will never be the best, you will continually improve and that’s the aim you should have. Learn from all sources.

How to learn the skill of programming?

This is a broad topic. Learning how to learn itself covers lot of intricacies. How to learn programming. I will try to narrow down discussion about this in few steps

  1. Learn basic syntax, but not all of the syntax. You will learn this over the time.
  2. Learn programming principles, mostly object oriented principles.
  3. Find out common patterns and study them. In software engineering, we follow lot of design patterns and they get used all the time while designing any application.
  4. Find out common libraries in the language that you want to learn.
  5. If you are learning Java, definitely read Effective Java, Clean code and Refactoring.
  6. Try pair programming where you work with another programmer.
  7. Read, read and read lots of code – bad code to good code both.
  8. Fall in love with learning to program, process over results.
  9. If you take up a project, start with MVP (Minimum Viable Product), get feedback from peers/customers and then improve on the product you are building. While following this process, you will improve your programming as well. You will hit road blocks, that will challenge you to find out the solution on your own. Balance long term process (learning programming) with short term goals (projects that you will work on).
  10. If you work with senior programmers, get a feedback for your code.

Resources for programming

  1. Solve problems on HackerRank
  2. Free code camp – Freecodecamp
  3. Participate in hackathons
  4. Write blogs about your insights

Conclusion

In this post, I tried to simplify a process about how to learn programming, and how to improve the skill of programming. I hope this post helps all those who are on the fence about programming to take up programming.

Spring Boot Actuator

In this post, we will look at how we can use the spring boot actuator to add some metrics related endpoints in Spring Boot based microservice or application. Spring boot helps to monitor your production-ready application by offering a number of metrics related endpoints.

What do you need:

  • Java 8
  • Spring Boot
  • IntelliJ
  • Gradle

What are Spring boot actuator endpoints?

I will not be showing how to create a Spring boot REST in this article. You can refer my post to create a REST API based on Spring boot here.

As Spring documentation says – “Spring boot actuator let you monitor and interact with your application.” The endpoints that we will be discussing, are built in Spring Boot. Of course, the first question that comes to mind, is how do we activate these endpoints and what different endpoints are available there for what purposes.

How to activate actuator endpoints?

To activate these endpoints in a gradle-based project, we have to add the following dependency

dependencies {
  compile("org.springframework.boot:spring-boot-starter-actuator")
}

If you are using maven, this will be like below:

<dependencies>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-actuator</artifactId>
  </dependency>
</dependencies>

All the actuator endpoints are enabled by default.

  • auditevents – Audit events of your application
  • info– Displays information about your application – you can customize to show version information.
  • health – application’s health status
  • metrics – various metrics information of application
  • loggers – Displays and modifies configured loggers
  • logfile – Shows the contents of the log file
  • httptrace – Displays HTTP trace info for the last 100 HTTP request/response
  • env – Displays current environment information
  • flyway – Shows Flyway database migrations details
  • liquidbase – Shows details of liquibase database migrations
  • shutdown – Allows to shut down the application gracefully
  • mappings– Displays a list of all @RequestMapping paths
  • scheduledtasks – Displays the scheduled tasks in the application
  • threaddump – Performs a thread dump
  • headdump – Returns JVM head dump

Another way these endpoints can be enabled or disabled, is to add properties in application.properties as shown below:

management.endpoint.health.enabled=true

Running the spring boot application with actuator

Once we have added the required spring-boot-starter-actuator dependency, we can build our application. There is still one more change we need to add in our gradle build file to get application version information.

springBoot{
     buildInfo()
}

If you are using maven, this can be added as below:

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <executions>
        <execution>
            <goals>
                <goal>build-info</goal>
            </goals>
        </execution>
    </executions>
</plugin>

If you want to add some additional properties, add following properties in application.properties as below:

info.app.name = Reusable-Rest-Module
info.app.version = 0.1.0-SNAPSHOT
management.security.enabled=false

Now once you build the application and run it, this will give us following results:

Healthcheck metrics using Spring Boot Actuator

http://localhost:8080/health

Info Metrics using Spring Boot Actuator

http://localhost:8080/info

Logging metrics using Spring Boot Actuator

http://localhost:8080/loggers

Conclusion

In this post, we showed how we can use Spring Boot Actuator to get different metrics data for your spring boot based service.

 

Java Memory Management

One topic that I have always been curious, is java memory management. How JVM allocates the memory to different objects and frees up the memory when needed? In this post, I will talk about Java Heap Memory and Stack Memory. Heap and Stack are the memories that JVM allocates as per the application requirements.

Java Heap Space

The most basic question that arises during this discussion, is how do you define both of these memories. So I will start with Java Heap Space. When JVM starts, it creates Java Heap Space and it is used by the application till the time the application is running. Java runtime uses heap space to allocate memory to objects and JRE classes.

The heap size is adjusted according to when the application runs. When the heap gets full, garbage collection takes place. During garbage collection, objects that are not being used, get cleaned, in-process making space for new objects.

Java Stack Memory

Stack memory is like a RAM, used by an executing thread for method-specific values or operations. Most of the values or operations in the stack are short-lived. It can also contain references to objects that reside in heap.

Whenever a method is invoked, a block is allocated in the stack for a method to hold local variables. The block gets cleared once the method finishes execution.

From these earlier definitions, it is clear that Stack memory is smaller in size compared to heap space.

Stack Memory and Heap Space

Differences between Heap space and Stack memory

  1. Heap memory is used by the entire application while the stack is used by execution thread only.
  2. When an object is created, it is stored in heap space, while the reference for that object is stored in stack memory.
  3. Since stack memory is thread-specific, it can’t be accessed by multiple threads or other threads than the one thread that created it. Heap space is global.
  4. Heap space is available till the time application is running, stack memory is short-lived.
  5. JVM can throw errors if both memories are full or the application doesn’t have either of memory remaining to continue running the application. StackOverfFowError if JVM is out of stack memory. If the application stops running provided there is no memory to store objects, it will throw OutOfMemoryError: Java Heap Space Error.

Conclusion

In this post, I discussed the differences between Java heap space and stack memory as part of Java memory management.

References

  1. Stack vs Heap
  2. Understanding memory management

 

HTTP Security Headers – XFrame Options and Content Security Policies

Have you ever traced an HTTP request in a browser or fiddler? You must have seen these HTTP security headers in the request or response header?

X-Frame-Options SAMEORIGIN

OR

Content-Security-Policy:frame-ancestors 'none'

Do you know what are these headers about? In this post, I will show why we use these headers. These security headers often come up when you are rendering an application within iframes.  Conclusively, these headers are important if you are loading applications with an iframe inside the main iframe.

Why are these headers required?

These headers help in avoiding clickjacking attacks. You can read more about clickjacking here. To defend against clickjacking, we implement frame-breaking using two methods.

   1. X-Frame-Options –

This header is used in response header to indicate whether or not a browser can be allowed to render a web page in a <frame> or <iframe>.

Possible values for this header:

  1. DENY – The recommended value for X-Frame-Options and it prevents any domain to frame the content.
  2. SAMEORIGIN – This allows only the current site to frame the content.
  3. ALLOW-FROM URI – This allows the specified URI to frame the content.

   2. Content-Security-Policy –

Similarly, X-Frame-Options is used by the browser to allow to render a page in a frame or iframe, the same way Content-Security-Policy header is used. Accordingly, some browsers support X-Frame-Options and some Content-Security-Policy. Nevertheless, one key feature between these two headers (X-Frame-Options and Content-Security-Policy) is that Content-Security-Policy can allow the listing of multiple domains to load the content from.

Possible values for this header are:

  • Content-Security-Policy: frame-ancestors ‘none’ – This prevents any domain to render the content.
  • Content-Security-Policy: frame-ancestors ‘self’ – This only allows the current site to frame the content.
  • Option of Content-Security-Policy: frame-ancestors ‘self’, ‘*.betterjavacode.com’, ‘https://www.mytest.com’ – This allows the current site, any subdomain of betterjavacode.com or the web page at www.mytest.com to load the page. Single quotes are important here.

Spring-Security

Likewise, Spring-security offers a feature to enable the X-Frame-Options and Content-Security-Policy directive.

http.headers().frameOptions().disable();

http.headers().frameOptions().sameOrigin();

Conclusion

In conclusion, I showed why and how to use HTTP security headers X-Frame-Options and Content-Security-Policy. Hence, if you enjoyed this post, subscribe to my blog here. You can find more details about X-Frame-Options and Content-Security-Policy headers on this page.

References

  1. Clickjacking cheat sheet – Clickjacking
  2. Clickjacking – Clickjacking-2