100+ System Design Interview Questions and Problems for Software Engineers
Java Revisited
by javin paul
4d ago
Hello guys, if you are preparing for System Design interviews then you may know that you have to prepare for theory questions as well as System design problems where you need to design a real world system like WhatsApp, YouTube or DropBox. Theory questions are mostly based upon System design basics and core concepts like Scalability, Caching, database sharding, load balancer, API gateway, security, proxies, messaging queues and software architecture, particularly Microservices. I have been sharing a lot of system design preparation material from last few years, in for example, in the past, I h ..read more
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How to POST JSON request from Linux to test RESTful Web Services? Example
Java Revisited
by javin paul
1w ago
Even though, Postman is a great tool and chrome plugin to test RESTful Web services for Java developers, I often find myself using "curl" or "cURL" command in Linux for testing RESTful Web Services, particularly Java web services built using Spring or Spring Boot framework. The curl command is easily available on most of Linux hosts and you just need to type a command to sent various types of HTTP requests to your application from Linux command line, as shown here. Though, many RESTful web developer and tester knows this trick, they mainly use GET request to access data from web service and&nb ..read more
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Top 20 Spring Framework Annotations Java Developers Should Know
Java Revisited
by javin paul
3w ago
Hello guys, annotations are quite important when working in modern Java application as almost all frameworks and libraries nowadays use annotations, including Spring Framework. There was time when we need to remember classes and methods to make effective use of JDK or any open source library but now we also need to remember annotations. For example, to use JUnit you must know about annotations like @Test, @BeforeEach, @AfterEach, @Disabled and so on. Similarly for Spring framework you need to know annotations like @Configuration, @Bean, @Component, @Service, @Value, @Autowired, @Repository, @Q ..read more
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4 Ways to take Heap dump in Tomcat and Java and 3 Tools to Analyse .hprof files
Java Revisited
by javin paul
1M ago
The heap dump is a great source of information on identifying memory related issues on Java application e.g. web and application servers like Tomcat, WebLogic, JBoss, WebSphere and IDEs like IntelliJIDEA and Eclipse. When you take heap dump all live objects of heap with their count and other details are written into a huge file (the .hprof file) for analysis. The name and location of heap dump file is provided by command you use to take the heap dump. There are many command line tools in JDK e.g. jmap and jcmd which can be used to take the heap dump in Java.  Java, Unix, Tibco RV and FIX ..read more
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10 Examples of @RequestMapping Annotation in Spring MVC and REST
Java Revisited
by javin paul
1M ago
The @RequestMapping annotation is one of the most important annotation of Spring MVC which provides mapping of HTTP requests to controller methods, I mean Java methods on Controller class for processing. If you wonder, how Spring handles a particular request and which method from controller class is called for a particular request, answer lies on @RequestMapping annotation. This annotation maps web request to methods on controller class. You can apply @RequestMapping on class or method level of your controller. This is a powerful annotation and give you a lot of option to sophistically map a w ..read more
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10 Things Beginners Should Know to Get Java Developer Job
Java Revisited
by javin paul
1M ago
Hello guys, if you are a beginner looking for a job as Java developer but not sure you should know then you have come to the right place. I get fresh computer engineers from colleges, interns, and new hires, so for the kids fresh out of school, here are some of the things I wish/hope they know. This is not just true for Computer science engineers and IT graduates but also to self-taught developers who have learned coding by themselves by following any YouTube video or joining an online course.  Java, Unix, Tibco RV and FIX Protocol Tutorial ..read more
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3 ways to solve java.lang.NoClassDefFoundError in Java J2EE
Java Revisited
by javin paul
1M ago
I know how frustrating is to see "Exception in thread "main" java.lang.NoClassDefFoundError" while running your Java application. This is one of the dreaded problem in Java  which is also a manifestation of NoClassDefFoundError in Java. I have seen it a couple of times and spent quite a lot of time initially to figure out what is wrong, which class is missing etc. The first mistake I did was mingling java.lang.ClassNotfoundException and NoClassDefFoundError, in reality, are totally different, and my second mistake was using the trial and error method to solve this java.lang.NoClassDe ..read more
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Top 10 Java map() and flatMap() Functional Programming Coding Problems with Solutions
Java Revisited
by javin paul
1M ago
Hello friends, in last a couple of years, I have seen an increase in coding problems where interviewer expect you to solve using functional programming concepts and particularly map() and flatMap(). They do this because they want to know whether you know about these methods or not and whether you can use them in real world scenarios like solving coding problems. I have been collecting such coding problems and today, I am ready with 10 such map and flatMap related coding questions which I am going to share with you. The beauty of these coding interview questions is that you can easily solve the ..read more
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Top 5 Websites to learn Microsoft Azure Cloud for FREE - Best of Lot
Java Revisited
by javin paul
1M ago
Hello guys, Cloud Computing is a great skill to learn in 2024 as more and more companies are moving to Cloud. and Azure is a cloud computing offered by the gain Microsoft for deploying your website or a web application as well as developing testing and managing your application with more than two hundred different services in eighteen categories ranging from computing to databases and others for IoT services. Java, Unix, Tibco RV and FIX Protocol Tutorial ..read more
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What is N+1 SELECT Problem in Hibernate? Strategies to avoid this?
Java Revisited
by javin paul
2M ago
In some cases while using Hibernate for object-relational mapping, you will encounter the N+ 1 select problem. That is, Hibernate will execute (n+1) queries to populate a list of records of size n, I mean 5 SELECT queries will be required to populate 4 records. This happens when each object contains reference of another object which needs to be populated. For example, suppose you have list of authors and you want to print out title of books written by each other. A naive ORM will first do a SELECT query to load all authors and then execute another N SELECT query to load book for each auth ..read more
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