Blog Archives
1 2 3

02: HTTP basics on headers, MIME types, & cookies for Java developers

Q1. What happens when you open up a browser and type a URL to request a Web page or RESTFul web service data? A1. HTTP is a stateless protocol on top of TCP (Transmission Control Protocol). 1) When the IP address is obtained, … Read more ›...



03: Identifying and fixing NonUniqueObjectException in Hibernate

NonUniqueObjectException is thrown when there is an object already associated with the session with the same id (primary key) (i.e. a duplicate). It is important to understand the concept of a “detached” object in Hibernate. This is one of the most common errors, understanding why and when this error is thrown will save you time in identifying and fixing this issue.

Read more ›



04: Identifying and fixing LazyInitializationException in Hibernate

LazyInitializationException is thrown when an object becomes detached, and if you try to access associated (i.e. proxied) object(s) of a detached object.

Q. What is a detached object in Hibernate?

When you close an individual Hibernate Session, the persistent objects you are working with are detached.

Read more ›



05: Debugging Hibernate & handling 4 common issues

#1. Enable Logging in your log4j.xml, log4j.properties, or myapp-logback.xml

In the log4j.properties file, you can enable Hibernate SQL logging as shown below

or in your log4j.xml or myapp-logback.xml as

You can then check your logs for the SQLs executed and the parameters passed. The example below shows 3 parameters passed to an update query

#2.

Read more ›



06: Debugging NoSuchBeanDefinitionException in Spring

#1. Adding the @Named annotation to the interface instead of the implementation Adding the @Named, @Component, @Repository, etc annotation on the interface as opposed to the implementation class. The code below can throw “NoSuchBeanDefinitionException” FIX: The @Named annotation is now in the implementation class. … Read more ›...



07: Debugging Spring Transaction Management

Never just trust that adding @Transactional annotation is going to create a transactional boundary for your service layer. EventRestController –> EventMergeProcesorImpl –> EventControlDAOImpl The @Transactional annotations added to “public” methods of the EventMergeProcesorImpl. Spring creates a proxy around the “EventMergeProcesorImpl”. … Read more ›...



15+ Apache Spark best practices, memory mgmt & performance tuning interview FAQs – Part-1

There are so many different ways to solve the big data problems at hand in Spark, but some approaches can impact on performance, and lead to performance and memory issues. Here are some best practices to keep in mind when writing Spark jobs. General Best Practices #1 Favor DataFrames over...



15+ Apache Spark best practices, memory mgmt & performance tuning interview FAQs – Part-2

This extends 15+ Apache Spark best practices, memory mgmt & performance tuning interview FAQs – Part-1, where best practices 1-6 were covered with examples & diagrams. #7 Use Spark UI: Running Spark jobs without inspecting the Spark UI is a definite NO. … Read more ›...



5 Ways to debug thread-safety issues in Java

Interviewers often judge your experience with debugging skills. For example, debugging jar hell issues, debugging SSL issues, debugging hibernate issues, debugging transaction management issues, etc. All these are covered in detail under the key areas “Key Area – Debug xxxx

How will you debug thread-safety issues in Java?

Read more ›



7 Java debugging interview questions & answers

Q1. How would you go about debugging thread-safety or concurrency issues? A1. #1: Manually reviewing the code for any obvious thread-safety issues. Good knowledge of multi-threading is required. #2: List all possible causes and add extensive log statements and write test cases to prove or disprove your theories. … Read...



Chrome Postman to test and debug RESTful Web Services

Step 1 You need to get the Postman extension for the Google chrome browser.

Step 2 Search and add POSTMAN.

Step 3 Once installed, open it from the Apps link.

chrome-appschrome-apps

Step 4 Set the TEST URL,

Read more ›



Debugging “NoSuchMethodError” in Java

The JAR hell issues also lead to exceptions like NoSuchMethodError or IllegalArgumentException. I have already discussed debugging JAR Hell issues. #1 Check the war file for any duplicate versions of the same jar The Maven’s transivie dependency might bring multiple versions of joda libraries like “ … Read more ›...



Debugging connection refused issues in Java with 9 tips

Possible reasons for “refused connections” 1) Client & Server are not connected by the LAN. For example, they can be in the different zones. 2) The Server might not be running. 3) The server might be listening on a different port or the server might have not started properly as...



1 2 3

800+ Java Q&As & tutorials

Top