Java Support Engineer Interview Questions and Answers

To fetch a value from application.properties file in Spring Boot, use @Value annotation or Environment object.

• Use @Value annotation to inject values directly into a field

• Use Environment object to access properties programmatically

• Example: @Value("${my.property}") private String myProperty;

• Example: @Autowired private Environment env; String propertyValue = env.getProperty("my.property");

You can change the data type of a column in SQL using the ALTER TABLE statement.

• Use the ALTER TABLE statement followed by the MODIFY COLUMN clause to change the data type of a column.

• Specify the new data type for the column after the MODIFY COLUMN clause.

• Make sure to handle any data conversion or potential data loss when changing the data type.

Front end communicates with the backend in Spring through HTTP requests using RESTful APIs.

• Front end sends HTTP requests to the backend server

• Backend server processes the requests and sends back HTTP responses

• Communication is typically done using RESTful APIs in Spring MVC

• Data is exchanged in JSON format between front end and backend

You can pull the pids of Java processes using command line tools like jps or ps.

• Use 'jps' command to list Java processes along with their pids.

• Use 'ps -ef | grep java' command to list all processes with 'java' in their name and find the pid.

• You can also use tools like VisualVM or JConsole to monitor and manage Java processes.

To create a Jar/war file, use the jar command in the terminal or an IDE like Eclipse.

• Use the jar command in the terminal to create a Jar file: jar cf jarFileName.jar file1 file2

• Use the jar command with 'war' option to create a War file: jar cf warFileName.war file1 file2

• In Eclipse, right-click on the project, go to Export > JAR file/WAR file, and follow the prompts

Use the put() method to replace a value in a HashMap.

• Use the put() method with the key of the value you want to replace

• Example: map.put(key, newValue);

To reduce heap memory usage in Java, you can optimize code, limit object creation, use data structures efficiently, and tune JVM settings.

• Optimize code by avoiding unnecessary object creation and using efficient algorithms

• Limit object creation by reusing objects, using object pooling, or implementing flyweight design pattern

• Use data structures efficiently by choosing the right data structure for the task at hand

• Tune JVM settings such as heap size, garbage collection algorithm...read more

Some annotations in Spring Boot are @RestController, @Autowired, @Component, @RequestMapping, @Service.

• @RestController - used to define RESTful web services.

• @Autowired - used for automatic dependency injection.

• @Component - marks a java class as a bean so that the component-scanning mechanism of Spring can pick it up and pull it into the application context.

• @RequestMapping - used to map web requests to specific handler classes or methods.

• @Service - used to indicate that a clas...read more