Feign + Eureka: UnknownHostException when Attempting to Invoke a Service


When attempting use Feign to invoke a service through Eureka, the following exception occurs:-

MY-HOST-NAME executing GET http://donkey-kong-service/throw/barrels/10
feign.RetryableException: MY-HOST-NAME executing GET http://donkey-kong-service/throw/barrels/10
	at feign.FeignException.errorExecuting(FeignException.java:84)
	at feign.SynchronousMethodHandler.executeAndDecode(SynchronousMethodHandler.java:113)
Caused by: java.net.UnknownHostException: MY-HOST-NAME
		at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184)


Go to the donkey-kong-service app and add the following line to the application.properties:-


Now, when Feign tries to invoke the service, the IP address will be used instead of the OS’ reported hostname.

Spring Boot: Restarting App using Dev Tools with IntelliJ IDEA

Spring Boot provides spring-boot-devtools module that allows the app to “smartly” restart whenever the files on the classpath have changed.

Because the rarely changed classes (ex: 3rd party JARs) are separated out into a different classloader from the app’s actively developed classes’ classloader, it allows Spring Boot to quickly restart the app compared to “cold start”.


First, add the following dependency:-



In IntelliJ IDEA:-

  • Click SHIFT twice to bring up the “Search History” dialog.
  • Select “Actions” tab.
  • Type “Registry” in the search box.
  • Select “Registry…”.

In the “Registry” dialog:-

  • Find “compiler.automake.allow.when.app.running” key.
  • Check the checkbox.
  • Close the dialog.

In IntelliJ IDEA “Preferences” dialog:-

  • Go to “Build, Execution, Deployment” » “Compiler”.
  • Check “Build project automatically”.
  • Close the dialog.

Finally, instead of running Maven goals to run the Spring Boot app, select the Application class (annotated with @SpringBootApplication) and run it from IntelliJ IDEA.

Anytime the app’s class files have changed, IntelliJ IDEA will compile the app, which will then trigger Spring Boot Dev Tools to restart the app.

Spring Boot: Connecting to IBM MQ over JMS using non-IBM JRE

There are several ways to connect to IBM MQ:-

  • com.ibm.mq.MQQueueManager
  • com.ibm.mq.jms.MQQueueConnectionFactory
  • com.ibm.msg.client.jms.JmsConnectionFactory

This article shows you how to connect with Spring’s JmsTemplate.


Typically, the MQ admin will provide the following connectivity info that allows you to connect to MQ:-

  • Queue manager name, ex: MY.QUEUE.MANAGER
  • Host name, ex: server.com
  • Port, ex: 1415
  • Channel name, ex: MY.SSL.CHANNEL
  • SSL Cipher Suite, ex: SSL_ECDHE_RSA_WITH_AES_128_GCM_SHA256
  • User, ex: user
  • Password, ex: password
  • Queue name, ex: MY.QUEUE


Add the following dependency:-

dependencies {
  compile 'com.ibm.mq:mq-jms-spring-boot-starter:2.1.1'


While the connectivity info can be hardcoded in Spring Boot’s application.properties, it’s probably more logical to use Spring @Configuration to dynamically set the values especially dealing with credential.

So, create a Spring configuration that looks something like this:-

// while all the value are hardcoded here for simplicity sake, you can inject
// sensitive values from DB, through <code>Environment</code>, etc.
class JmsConfig {
  // Adding @Primary will force Spring Boot to use this bean
  // instead of the one provided by the dependency 
  MQConfigurationProperties mqConfigurationProperties() {
    System.setProperty('javax.net.ssl.keyStore', '/path/to/keystore.jks')
    System.setProperty('javax.net.ssl.keyStorePassword', 'XXXXXXX')

    return new MQConfigurationProperties(
      queueManager: 'MY.QUEUE.MANAGER',
      channel: 'MY.SSL.CHANNEL',
      connName: 'server.com(1415)',
      user: 'user',
      password: 'password',
      userAuthenticationMQCSP: true,
      // If the provided SSL cipher suite begins with "SSL", 
      // replace it with "TLS" instead.
      // SSL_* is IBM JRE CipherSuite name.
      // TLS_* is Oracle JRE CipherSuite name. 
      sslCipherSuite: 'TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256',
      // true - if using IBM JRE
      // false - if using non-IBM JRE, ex: Oracle, OpenJDK, etc
      useIBMCipherMappings: false


Finally, to listen to the given queue, it is as easy as autowiring JmsTemplate and start using it.

JmsTemplate jmsTemplate


final Message message = jmsTemplate.receive('MY.QUEUE')
println message

Groovy/Java: Handling Byte Order Marks When Reading a File


Given a file with the following content:-


When reading the file:-

def inputStream = new FileInputStream('test.csv')
def value = inputStream.text.trim()

println "|${value}|"

… the following values are printed:-

| 10,20|

Even though the value is trimmed, there is still a leading space in front of text.

A further inspection reveals the leading space is not a regular space:-

// first character is not a space
assert value.charAt(0) != (char) ' '

// ASCII value: 65279 vs 32
assert (int) value.charAt(0) != (int) ((char) ' ').charValue()


Some editors prepend a special Unicode character called a byte order mark (BOM) to the file.

The simplest way to remove this special character is to leverage Apache Commons IO’s BOMInputStream:-

def inputStream = new BOMInputStream(new FileInputStream('test.csv'))
def value = inputStream.text.trim()

println "|${value}|"

… and now, the values are printed correctly:-


Spring Web: Encode ‘+’ Value Using UriComponentsBuilder


Given the following code…

final String url = UriComponentsBuilder.
        queryParam('var', '{var}').
        buildAndExpand('1 2+3').

When using Spring Web 4.3.18.RELEASE, the URL is properly encoded:-


However, when using version between 5.0.0.RELEASE and 5.0.7.RELEASE, the URL containing “+” value does not get encoded:-



There is a ticket opened regarding this breaking change.

To properly encode “+” value, use 5.0.8.RELEASE or later.

Then, ensure encode() is invoked before buildAndExpand(..):-

// Produces https://server?var=1%202%2B3
final String url = UriComponentsBuilder.
        queryParam('var', '{var}').
        buildAndExpand('1 2+3').

The above code can be further shorten to this:-

// Produces https://server?var=1%202%2B3
final String url = UriComponentsBuilder.
        queryParam('var', '{var}').
        build('1 2+3').