Highly Recommended Blog Post

I read the blog below a few days ago and I think it’s extremely good one.
It emphasize many points I believe in and constantly advocate to.

It was written by Simon Stewart.
I first saw it in Twitter. It was retweeted by Kent Beck.

Enjoy reading.



Spring Context with Properties, Collections and Maps

In this post I want to show how I added the XML context file to the Spring application.
The second aspect I will show will be the usage of the properties file for the external constants values.

All of the code is located at: https://github.com/eyalgo/request-validation (as previous posts).

I decided to do all the wiring using XML file and not annotation for several reasons:

  1. I am simulating a situation were the framework is not part of the codebase (it’s an external library) and it is not annotated by anything
  2. I want to emphasize the modularity of the system using several XML files (yes. I know it can be done using @Configuration)
  3. Although I know Spring, I still feel more comfortable having more control using the XML files
  4. For Spring newbies, I think they should start using XML configuration files and only when grasp the idea and technology, should start using annotation

About the modularization and how the sample app is constructed, I will expand in later post.

Let’s start with the properties file:
And here’s part of the properties file:

flag.external = EXTERNAL
flag.internal = INTERNAL
flag.even = EVEN
flag.odd = ODD


filter.external.name.max = 10
filter.external.name.min = 4

filter.internal.name.max = 6
filter.internal.name.min = 2

Properties File Location
We also need to tell Spring the location of our property file.
You can use PropertyPlaceholderConfigurer , or you can use the context element as shown here:

<context:property-placeholder location="classpath:spring/flow.properties" />

Simple Bean Example
This is the very basic example of how to create a bean

<bean id="evenIdFilter"

Using Simple Property
Suppose you want to add a property attribute to your bean.
I always use constructor injection, so I will use constructor-arg in the bean declaration.

<bean id="longNameExternalFilter"
    <constructor-arg value="${filter.external.name.max}" />

List Example
Suppose you have a class that gets a list (or set) of objects (either another bean class, or just Strings).
You can add it as a parameter in the constructor-arg, but I prefer to create the list outside the bean declaration and refer to it in the bean.
Here’s how:

<util:list id="defaultFilters">
  <ref bean="emptyNameFilter" />
  <ref bean="someOtherBean" />


<bean id="itemFiltersMapperByFlag"
   <constructor-arg ref="defaultFilters" />
   <constructor-arg ref="filtersByFlag" />

Collection of Values in the Properties File
What if I want to set a list (set) of values to pass a bean.
Not a list of beans as described above.
The in the properties file I will put:

And in bean:

<bean id="acceptedIdsValidation"
  <constructor-arg value="#{'${validation.acceptedIds}'.split(',')}" />

See how I used Spring Expression Language (SpEL)

Map Injection Example
Here’s a sample of an empty map creation:

<util:map id="validationsByFlag">

Here’s a map with some entries.
See how the keys are also set from the properties file.

<util:map id="filtersByFlag">
  <entry key="${flag.external}" value-ref="filtersForExternal" />
  <entry key="${flag.internal}" value-ref="filtersForInternal" />
  <entry key="${flag.even}" value-ref="filtersForEven" />
  <entry key="${flag.odd}" value-ref="filtersForOdd" />

In the map example above we have keys as Strings from the properties file.
The values are reference to other beans as described above.

The usage would be the same as for list:

<bean id="itemFiltersMapperByFlag"
   <constructor-arg ref="defaultFilters" />
   <constructor-arg ref="filtersByFlag" />

In this post I showed some basic examples of Spring configuration using XML and properties file.
I strongly believe that until the team is not fully understand the way Spring works, everyone should stick with this kind of configuration.
If you find that you start to get files, which are too big, then you may want to check your design. Annotations will just hide your poorly design system.

Spring and Maven Configuration

This is the first post of a series of posts demonstrating how we to use Spring in an application.
In the series I will show some howtos of technical aspects (context file, properties, etc.).
And I will also show some design aspects and test approach.

In this post I will simply show how to integrate Spring using Maven.

The basic dependency would be the context. Using Maven dependencies, spring-core will be in the project as well.


If we want to use annotation such as @Inject which comes from Java JSR, we’ll add the following dependency:


And in order to be able to test using Spring, here’s what we’ll need (in here, the scope is test):


You can see that I didn’t add spring-core as it comes with the context / test dependencies.

You can find the code at: https://github.com/eyalgo/request-validation

Some notes about the code.

I added the Spring code, context and the Spring’s Maven dependencies to the test environment.
This is on purpose.
I want to emphasize the separation of the validation-filter framework to the usage and wiring of an application.

In real life, you might have an external library that you’ll want to use it in a Spring injected application.
So the test environment in the code simulates the application and the src is the “external library”.

Request Validation and Filtering by Flags – Redesign and Refactoring

In the previous posts I started describing a validation / filtering framework we’re building.
While showing the code, I am trying to show clean code, test orientation and code evolution.
It has some agility in the process; We know the end requirements, but the exact details are evolving over time.

During the development we have changed the code to be more general as we saw some patterns in it.
The code evolved as the flow evolved as well.

The flow as we now understand it
Here’s a diagram of the flow we’ll implement

Request Sequence

Request Sequence

The Pattern
At each step of the sequence (validation, filtering, action), we recognized the same pattern:

  1. We have specific implementations (filters, validations)
  2. We have an engine that wraps up the specific implementations
  3. We need to map the implementations by flag, and upon request’s flags, select the appropriate implementations.
  4. We need to have a class that calls the mapper and then the engine

A diagram showing the pattern

The Pattern

The Pattern

Source Code
In order to show some of the evolution of the code, and how refactoring changed it, I added tags in GitHub after major changes.

Code Examples
Let’s see what came up from the mapper pattern.

public interface MapperByFlag<T> {
  List<T> getOperations(Request request);
public abstract class AbstractMapperByFlag<T> implements MapperByFlag<T> {
  private List<T> defaultOperations;
  private Map<String, List<T>> mapOfOperations;

  public AbstractMapperByFlag(List<T> defaultOperations, Map<String, List<T>> mapOfOperations) {
    this.defaultOperations = defaultOperations;
    this.mapOfOperations = mapOfOperations;

  public final List<T> getOperations(Request request) {
    Set<T> selectedFilters = Sets.newHashSet(defaultOperations);
    Set<String> flags = request.getFlags();
    for (String flag : flags) {
      if (mapOfOperations.containsKey(flag)) {
    return Lists.newArrayList(selectedFilters);
  public RequestValidationByFlagMapper(List<RequestValidation> defaultValidations,
    map<String, List<RequestValidation>> mapOfValidations) {
    super(defaultValidations, mapOfValidations);

  public ItemFiltersByFlagMapper(List<Filter> defaultFilters, Map<String, List<Filter>> mapOfFilters) {
    super(defaultFilters, mapOfFilters);

I created a test for the abstract class, to show the flow itself.
The tests of the implementations use Java Reflection to verify that the correct injected parameters are sent to the super.
I am showing the imports here as well. To have some reference for the static imports, mockito and hamcrest packages and classes.

import static org.hamcrest.Matchers.containsInAnyOrder;
import static org.junit.Assert.assertThat;
import static org.mockito.Mockito.when;

import java.util.List;
import java.util.Map;

import org.eyal.requestvalidation.model.Request;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mock;
import org.mockito.runners.MockitoJUnitRunner;

import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Lists;
import com.google.common.collect.Sets;

public class AbstractMapperByFlagTest {
	private final static String FLAG_1 = "flag 1";
	private final static String FLAG_2 = "flag 2";

	private Request request;

	private String defaultOperation1 = "defaultOperation1";
	private String defaultOperation2 = "defaultOperation2";
	private String mapOperation11 = "mapOperation11";
	private String mapOperation12 = "mapOperation12";
	private String mapOperation23 = "mapOperation23";

	private MapperByFlag<String> mapper;

	public void setup() {
		List<String> defaults = Lists.newArrayList(defaultOperation1, defaultOperation2);
		Map<String, List<String>> mapped = ImmutableMap.<String, List<String>> builder()
		        .put(FLAG_1, Lists.newArrayList(mapOperation11, mapOperation12))
		        .put(FLAG_2, Lists.newArrayList(mapOperation23, mapOperation11)).build();
		mapper = new AbstractMapperByFlag<String>(defaults, mapped) {

	public void whenRequestDoesNotHaveFlagsShouldReturnDefaultFiltersOnly() {
		when(request.getFlags()).thenReturn(Sets.<String> newHashSet());

		List<String> filters = mapper.getOperations(request);
		assertThat(filters, containsInAnyOrder(defaultOperation1, defaultOperation2));

	public void whenRequestHasFlagsNotInMappingShouldReturnDefaultFiltersOnly() {
		when(request.getFlags()).thenReturn(Sets.<String> newHashSet("un-mapped-flag"));
		List<String> filters = mapper.getOperations(request);
		assertThat(filters, containsInAnyOrder(defaultOperation1, defaultOperation2));
	public void whenRequestHasOneFlagShouldReturnWithDefaultAndMappedFilters() {
		when(request.getFlags()).thenReturn(Sets.<String> newHashSet(FLAG_1));
		List<String> filters = mapper.getOperations(request);
		assertThat(filters, containsInAnyOrder(mapOperation12, defaultOperation1, mapOperation11, defaultOperation2));
	public void whenRequestHasTwoFlagsShouldReturnWithDefaultAndMappedFiltersWithoutDuplications() {
		when(request.getFlags()).thenReturn(Sets.<String> newHashSet(FLAG_1, FLAG_2));
		List<String> filters = mapper.getOperations(request);
		assertThat(filters, containsInAnyOrder(mapOperation12, defaultOperation1, mapOperation11, defaultOperation2, mapOperation23));
public class RequestValidationByFlagMapperTest {

	private List<RequestValidation> defaultValidations;
	private Map<String, List<RequestValidation>> mapOfValidations;

	private RequestValidationByFlagMapper mapper;

	public void verifyParameters() throws NoSuchFieldException, SecurityException, IllegalArgumentException,
	        IllegalAccessException {
		Field defaultOperationsField = AbstractMapperByFlag.class.getDeclaredField("defaultOperations");
        List<RequestValidation> actualFilters = (List<RequestValidation>) defaultOperationsField.get(mapper);
		assertThat(actualFilters, sameInstance(defaultValidations));

		Field mapOfFiltersField = AbstractMapperByFlag.class.getDeclaredField("mapOfOperations");
		Map<String, List<RequestValidation>> actualMapOfFilters = (Map<String, List<RequestValidation>>) mapOfFiltersField.get(mapper);
		assertThat(actualMapOfFilters, sameInstance(mapOfValidations));

To Do
There are other classes that might be candidate for refactoring of some sort.
RequestFlowValidation and RequestFilter are similar.
RequestValidationsEngineImpl and FiltersEngine

To Do 2
Create a Matcher for the reflection part.

As always, all the code can be found at:

A Tag for this post: all-components-in

The infrastructure is almost done.
During this time we are also implementing actual classes for the flow (validations, filters, actions).
These are not covered in the posts, nor in GitHub.
The infrastructure will be wired to a service we have using Spring.
This will be explained in future posts.

Request Validation and Filtering by Flags – Filtering an Item

On a previous post, I introduced a system requirement of validating and filtering a request by setting flags on it.

Reference: Introduction

In this post I want to show the filtering system.

Here are general UML diagrams of the filtering components and sequence.

Filtering UML Diagram

General Components

public interface Item {
        String getName();
public interface Request {
        Set getFlags();
        List getItems();

Filter Mechanism (as described in the UML above)

public interface Filter extends Predicate {
	String errorMessage();

FilterEngine is a cool part, which takes several Filters and apply to each the items. Below you can see the code of it. Above, the sequence diagram shows how it’s done.

public class FiltersEngine {

	public FiltersEngine() {

	public ItemsFilterResponse applyFilters(List filters, List items) {
		List validItems = Lists.newLinkedList(items);
		List invalidItemInformations = Lists.newLinkedList();
		for (Filter validator : filters) {
			ItemsFilterResponse responseFromFilter = responseFromFilter(validItems, validator);
			validItems = responseFromFilter.getValidItems();

		return new ItemsFilterResponse(validItems, invalidItemInformations);

	private ItemsFilterResponse responseFromFilter(List items, Filter filter) {
		List validItems = Lists.newLinkedList();
		List invalidItemInformations = Lists.newLinkedList();
		for (Item item : items) {
			if (filter.apply(item)) {
			} else {
				invalidItemInformations.add(new InvalidItemInformation(item, filter.errorMessage()));
		return new ItemsFilterResponse(validItems, invalidItemInformations);

And of course, we need to test it:

public class FiltersEngineTest {
	private final static String MESSAGE_FOR_FILTER_1 = "FILTER - 1 - ERROR";
	private final static String MESSAGE_FOR_Filter_2 = "FILTER - 2 - ERROR";
	@Mock(name = "filter 1")
	private Filter singleFilter1;
	@Mock(name = "filter 2")
	private Filter singleFilter2;
	@Mock(name = "item 1")
	private Item item1;
	@Mock(name = "item 2")
	private Item item2;

	private FiltersEngine filtersEngine;

	public void setup() {



	public void verifyThatAllSingleFiltersAreCalledForValidItems() {

		ItemsFilterResponse response = filtersEngine.applyFilters(Lists.newArrayList(singleFilter1, singleFilter2),
				Lists.newArrayList(item1, item2));
		assertThat("expected no invalid", response.getInvalidItemsInformations(),
		assertThat(response.getValidItems(), containsInAnyOrder(item1, item2));

		verifyNoMoreInteractions(singleFilter1, singleFilter2);

	public void itemsFailIndifferentFiltersShouldGetOnlyFailures() {

		ItemsFilterResponse response = filtersEngine.applyFilters(Lists.newArrayList(singleFilter1, singleFilter2),
				Lists.newArrayList(item1, item2));
				containsInAnyOrder(matchInvalidInformation(new InvalidItemInformation(item1, MESSAGE_FOR_FILTER_1)),
						matchInvalidInformation(new InvalidItemInformation(item2, MESSAGE_FOR_Filter_2))));
		assertThat(response.getValidItems(), emptyCollectionOf(Item.class));

		verifyNoMoreInteractions(singleFilter1, singleFilter2);

	public void firstItemFailSecondItemSuccessShouldGetOneItemInEachList() {

		ItemsFilterResponse response = filtersEngine.applyFilters(Lists.newArrayList(singleFilter1, singleFilter2),
				Lists.newArrayList(item1, item2));
		assertThat(response.getInvalidItemsInformations(), contains(matchInvalidInformation(new InvalidItemInformation(item1,
		assertThat(response.getValidItems(), containsInAnyOrder(item2));

		verifyNoMoreInteractions(singleFilter1, singleFilter2);

	private static BaseMatcher matchInvalidInformation(InvalidItemInformation expected) {
		return new InvalidItemInformationMatcher(expected);

	private final static class InvalidItemInformationMatcher extends BaseMatcher {
		private InvalidItemInformation expected;

		private InvalidItemInformationMatcher(InvalidItemInformation expected) {
			this.expected = expected;

		public boolean matches(Object itemInformation) {
			InvalidItemInformation actual = (InvalidItemInformation) itemInformation;
			return actual.getName().equals(expected.getName())
					&& actual.getErrorMessage().equals(expected.getErrorMessage());

		public void describeTo(Description description) {

Some explanation about the test
You can see that I don’t care about the implementation of Filter. Actually, I don’t even have any implementation of it.
I also don’t have implementation of the Item nor the request.
You can see an example of how to create a BaseMatcher to be used with assertThat(…)

Try to see whether it is ‘clean’. Can you understand the story of the code? Can you tell what the code does by reading it line by line?

On the following post I will show how I applied the flag mapping to select the correct filters for a request.

You can find all the code in: https://github.com/eyalgo/request-validation

[Edit] Created tag Filtering_an_item before refactoring.

Request Validation and Filtering by Flags – Introduction


We are working on a service that should accept some kind of request.

The request has List of Items. In the response we need to tell the client whether the request is valid and also some information about each item: is it valid or not. If it’s valid, it will be persisted. If it’s not, it should be filtered out. So the response can have information of how many items are valid (and sent to be persisted) and list of information of the filtered out items.

The request has another metadata in it. It has collection (set) of flags. The filtering and validation is based on the flags of the request. So basically one request may be validated and filtered differently than the other, based on the flags of each request.

We might have general validations / filters that need to be applied to any request, whatever flags it has.

Request Validation and Filtering High level design


Flags Mapping

We’ll hold a mapping of flag-to-filters, and flag-to-validation.


Has flags and items.


Filter, Filter-Engine, Flags-Mapper

Development Approach

Bottom Up

We have a basic request already, as the service is up and running, but we don’t have any infrastructure for flags, flag-mapping, validation and filtering.

We’ll work bottom up; create the mechanism for filtering, enhance the request and then wire it up using Spring.


I’ll try to show the code using tests, and the development using some kind of TDD approach.

I am using eclipse’s EclEmma for coverage.


By looking at the code, you can see usage of JUnit, Mockito, Hamcrest, Google-Guava.

You can also see small classes, and interface development approach.

Source Code


Bitbucket vs. GitHub my Conclusion

When I first started blogging (not too long ago) I had to choose where to put the code I use as examples.
I already had GitHub and Bitbucket accounts, so I just needed to decide.

There are a lot of articles, blogs and question comparing the two options.
Below you can find some of them (Did some Googling…).

Initially I chose Bitbucket, but without a real particular reason.
Perhaps one reasons was working with Atlassian product, which I like as a company.
Another big advantage with Bitbucket is having the option of private repository.

However, GitHub is more popular; dzone lets you give your GitHub username, and I guess a user (profile) is more “searchable” there.
GitHub also has the gist feature, which is very helpful when writing code examples in a blog.

So for now, I decided to use both solutions.
Whenever I am working on a side project, which I don’t want to publicize, I will put it in Bitbucket as private repository.
But public repositories I will put in GitHub.
In the following days I will change the links of previous posts to direct to the GitHub location instead of Bitbucket.

Moving a Repository

If I am using two repositories hosts, I need to know how to move repositories from one location to another:

Bitbucket vs. GitHub Links