Effective Java – Third edition​


Effective Java is always a good book to read and this latest edition is no different. Here is the Amazon link to get the book. Here are some code samples and presentation promoting the book. My quick code snippet from the book.

import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class StringManipLambda {
public static void main(String args[]){
 List stringArras= Arrays.asList("First","Second","third","fourth","fifth");

This is a simple code block, where we take a list of Strings and sort it based on its length. The book goes in depth of how to read this lambda expression and understand how it works.


Quickest way of getting an custom error message in Spring Boot 2.x

There are different ways to get a custom error message page in spring boot. The following solution worked for my web project. Here is the overview of the structure.

Pic Pic

To start with, if there is 404 error, then we want a custom error page showing up instead of the spring boot’s default page.
The first thing we are going handle is to suppress the boot framework’s error page. For this, we will go to the application properties and add the following line


As we are done with that, now let us implement the ErrorController interface. The thing to keep in mind is, we have the LOG entry that says what happened to the code base as we reached here. Here is the sample code.


public class ITContractErrorController implements ErrorController     {
    public static final Logger LOG = LoggerFactory.getLogger(ITContractErrorController.class);
    ErrorAttributes errorAttributes;
    public String handleError() {
        LOG.error("Sever error occured");
        return "/error/error.html";
public String getErrorPath() {
    return "error";

One other way that we can add the custom error message is using the Spring 2.x’s ConfigurableServletWebServerFactory implementation. We add this to the main method of the web module. Here is the sample code for this entry.


public class SkminfycontractorWebmoduleApplication {
    public ConfigurableServletWebServerFactory         containerCustomizer(){
        TomcatServletWebServerFactory factory = new     TomcatServletWebServerFactory();
        factory.addErrorPages(new ErrorPage(HttpStatus.NOT_FOUND,     "/error/error.html"));
        return factory;
    public static void main(String[] args) {
        SpringApplication.run(SkminfycontractorWebmoduleApplication.class, args);

One thing to remember is, when we implement the override with ConfigurableServeletFactory then Override that is ErrorController is gone.

There is a lot of best practice information laid out in spring documentation and other places. But none worked for my setup. I will update this entry if I find a more interesting solution.

Spring 5 and JUNIT.

Let us try to put together some JUNITs with Spring 5 injection. One of the most challenging things of integrating JUnit and Spring was the role of the IDE. It is important to keep an eye on that.
So here is the code we are going to look.

        @ContextConfiguration(classes = StreamsConfig.class)})
    public class StreamsFilterSampleTest {
      Logger LOG = getLogger(StreamsFilterSampleTest.class);
      StreamsFilterSample streamFilterStream;
      StreamstoListSample streamstoListSample;

      public void testStreamGroupBy() throws Exception {
        LOG.debug("Debugging method start ==> testStreamGroupBy " + "with parameter []");
        LOG.debug("Debugging method end ==> testStreamGroupBy " + "with parameter []");

We see the definition starts with Spring configuration initialization. The annotation

    @ContextConfiguration(classes = StreamsConfig.class)})

RunWith, we are annotating it to be Spring JUnit. The code block is getting initialized with configuration class of StreamConfig. Now let us take a look at the StreamConfig definition

    public class StreamsConfig {
    public static final Logger LOG = LoggerFactory.getLogger(StreamsConfig.class);
    StreamsFilterSample streamFilterStream;
      public StreamsConfig() {
        LOG.debug("Constructing Config");

We are autowiring an implementation class, StreamFilterSample. This is just a utility class and code goes something like this.

    public void streamGroupBy() {
    //3 apple, 2 banana, others 1
    List<Item> items = Arrays.asList(
        new Item(null, 10, new BigDecimal("20.00")),
        new Item("apple", 10, new BigDecimal("21.00")),
        new Item("apple", 10, new BigDecimal("22.00")),
        new Item("banana", 20, new BigDecimal("19.99")),
        new Item("orang", 10, new BigDecimal("29.99")),
        new Item("watermelon", 10, new BigDecimal("29.99")),
        new Item("papaya", 20, new BigDecimal("9.99")),
        new Item("apple", 10, new BigDecimal("9.99")),
        new Item("banana", 10, new BigDecimal("19.99")),
        new Item("apple", 20, new BigDecimal("9.99"))
    //group by price
    Map<BigDecimal, List<Item>> groupByPriceMap =
    Map<String, List<Item>> groupByNameMap =
        items.stream().filter(item -> item.getName() != null).collect(Collectors.groupingBy
    private static class Item {
    private String name;
    private int qty;
    private BigDecimal price;
    public Item(String name, int qty, BigDecimal price) {
      this.name = name;
      this.qty = qty;
      this.price = price;
    public Item(String name, BigDecimal price) {this.name = name;this.price = price;}
    public int getQty() {return qty;}
    public void setQty(int qty) {this.qty = qty;}
    public BigDecimal getPrice() {return price;}
    public void setPrice(BigDecimal price) {this.price = price;}
    public String getName() {return name;}
    public void setName(String name) {this.name = name;}

Now when we are running the JUnit, we have to make sure the @Test annotation is from the JUnit jar file. If you accidentally have the TestNG’s @Test annotation, it will not be able to understand the configuration that we have in the JUnit header. Finally, remember to make sure the IDE is not making anything goofy where it pulled a wrong Annotation class. Here is a useful Stackoverflow discussion on this.