This post is motivated by ““Sorting a list or array of numbers by frequency of occurrences in Java”
Sorting a Map by Keys
Sorting a map by its keys is straightforward
|
1 2 3 |
SortedSet<String> keys = new TreeSet<String>(map.keySet()); |
Sorting a Map by its Values –
…
Q1. Can you write code to extract numbers from a given input text and return the sum of those numbers? Example: “1 some text 2 more text 4 more text 8” should return 15 as the sum. A The key steps are: 1. … Read more ›...
This extends 15 Spring Boot interview questions & answers. Spring Boot & Spring Cloud are used for building Microservices architecture. Q1. What is Spring Cloud? A1. Spring Boot is widely used to develop MicroServices. As many organisations deploy these services on the cloud like AWS, … Read more ›...
Messaging systems are used in enterprise applications for scalability. Here is some sample code that compliments JMS interview questions and answers. JMS configuration Step 1: Add the relevant dependency jars to the pom.xml file.
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 |
<properties> <spring.version>4.2.6.RELEASE</spring.version> <jms-api.version>2.0.1</jms-api.version> <mq-client.version>8.0.0.0</mq-client.version> </properties> <dependencies> <!-- Spring JMS --> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-jms</artifactId> <version>${spring.version}</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-test</artifactId> <version>${spring.version}</version> </dependency> <!-- JMS API --> <dependency> <groupId>javax.jms</groupId> <artifactId>javax.jms-api</artifactId> <version>${jms-api.version}</version> </dependency> <!-- Websphere MQ Implementation --> <dependency> <groupId>com.ibm.mq</groupId> <artifactId>allclient</artifactId> <version>${mq-client.version}</version> </dependency> </dependencies> |
Note that the “com.ibm.mq.allclient.jar” … Read more ›...
This is the continuation Spring JMS with Websphere MQ
Step 1: Write a listener class to receive the message by invoking the onMessage(Message message) method.
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 |
package com.myapp.service.impl; import javax.jms.Message; import javax.jms.MessageListener; import javax.jms.TextMessage; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.stereotype.Component; @Component //@Transactional public class MyAppListener implements MessageListener { private static Logger LOG = LoggerFactory.getLogger(MyAppListener.class); @Override public void onMessage(Message message) { LOG.info("Entered ..............."); if (message instanceof TextMessage) { try { String msg = ((TextMessage) message).getText(); LOG.debug("Message contents: {} ", msg); System.out.println(msg); } catch (Exception e) { LOG.error("Error processing the message"); } } } } |
Step 2 : Configure the Spring container and bootstrap the MyListener
…
Spring security pre-authentication scenario assumes that a valid authenticated user is available via either Single Sign On (SSO) applications like Siteminder, Tivoli, etc or a X509 certification based authentication. The Spring security in this scenario will only be used for authorization.
The example shown below retrieves the user name via the HTTP headers.
…
Example #1 Wiring JDBC Datasource
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 |
@Configuration @ImportResource("application.yml") public class AppConfig { @Autowired private Environment environment; @Bean public DriverManagerDataSource datasource() { DriverManagerDataSource ds = new DriverManagerDataSource(); ds.setDriverClassName(environment.getRequiredProperty("spring.datasource.driver-class-name")); ds.setUrl(environment.getRequiredProperty("spring.datasource.url")); ds.setUsername(environment.getRequiredProperty("spring.datasource.username")); ds.setPassword(environment.getRequiredProperty("spring.datasource.password")); return ds; } } |
application.yml where the datasource properties are read.
|
1 2 3 4 5 6 7 8 9 10 11 |
############ # Datasource properties ############ spring: datasource: driver-class-name: com.sybase.jdbc4.jdbc.SybDataSource url: jdbc:sybase:Tds:mydbhost:5700/my_db username: user password: pwd |
Example #2 Wiring JDBC Datasource with JNDI
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 |
@Configuration @ImportResource("application.yml") public class AppConfig { @Autowired private Environment environment; @Bean public DataSource dataSource() { final JndiDataSourceLookup jndiLookup = new JndiDataSourceLookup(); final String dataSourceJndi = environment.getRequiredProperty("spring.datasource.jndi"); return jndiLookup.getDataSource(dataSourceJndi); } } |
Example #3 Wiring JDBC Embedded Datasource for integration testing
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 |
@Configuration @ImportResource("application.yml") public class AppConfig { @Autowired private Environment environment; @Bean public DataSource dataSource() { final EmbeddedDatabaseBuilder builder = new EmbeddedDatabaseBuilder(); builder.setType(EmbeddedDatabaseType.HSQL); builder.addScript("classpath:hsqldb-oracle.sql"); builder.addDefaultScripts(); // defaults are schema.sql and data.sql return builder.build(); } } |
Example #4 Wiring up the JdbcTemplate by passing in the datasource
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 |
@Configuration @ImportResource("application.yml") public class AppConfig { @Autowired private Environment environment; @Bean public JdbcTemplate jdbcTemplate() { return new JdbcTemplate(datasource()); } @Bean public DataSource dataSource() { //...... } } |
Example #5 Wiring up a DAO...
Q1. Can you write an algorithm in Java to swap two variables? A1.
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 |
public class Swap { public static void main(String[ ] args) { int x = 5; int y = 6; //store 'x' in a temp variable int temp = x; x = y; y = temp; System.out.println("x=" + x + ",y=" + y); } } |
Q2. Can you write an algorithm to bubble sort the following array { 30, 12, 18, 0, -5, 72, 424 }?? … Read more ›...
#1: ConcurrentModificationException Getting a ConcurrentModificationException when trying to modify (i.e. adding or removing an item) a collection while iterating. The following code throws a ConcurrentModificationException.
|
1 2 3 4 5 6 7 |
List<T> list = getListOfItems(); for (Iterator<T> iter = list.iterator(); iter.hasNext(); ) { T obj = iter.next(); if (obj.someCondition()) { list.remove(0); // ConcurrentModificationException } } |
To avoid ConcurrentModificationException in a single-threaded environment, you can remove the object that you are working on with the iterator. … Read more ›...
Unlike Java 7, Java 8 has some significant changes. You can get familiarised with the the following simple working code. All you need is Java 8 installed on your machine.
#1: Interface can have static and default methods. This tries to solve the diamond (aka multiple inheriance) issue.
…
#1 One needs to get used to the transformation from imperative programming to functional programming. You like it or not, you will be using functional programming in Java 8, and interviewers are going to quiz you on functional programming. Fortunately, Java is not a fully functional programming language, … Read...
Q. Explain how you would get thread-safety issues due to non-atomic operations with a code example? A. The code snippets below demonstrate non-atomic operations producing incorrect results. The program below uses a “Counter” object, that is shared between three concurrent users (i.e. … Read more ›...
A stream is an infinite sequence of consumable elements (i.e a data structure) for the consumption of an operation or iteration. Any Collection can be exposed as a stream. The operations you perform on a stream can either be intermediate (map, filter, sorted, … Read more ›...
