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What is the name of the design pattern where you have a single-value, strongly typed property container?

Looking for the name of the design pattern by which you have a POJO with public final "properties" where the property acts as a holder/wrapper for a certain type of value and contains the getter/setter for that value as well as potentially some additional logic.
This differs from the "Property Container" design pattern where you have a single properties container which contains many types, as this only holds a single value and can thus enjoy the benefits of remaining strongly typed.
An example use:
public class User extends Entity<User> {
private static final Structure<User> STRUCTURE = Structure.of(User.class, User::new)
.addPrimaryKey("user_id", UUID).property((e) -> e.userID).setDefault(() -> UUID()).build()
.addIndex("username", VCHARS_50).property((e) -> e.username).build()
.addIndex("email", VCHARS_255).property((e) -> e.email).build()
.add("password", VCHARS_255).property((e) -> e.passwordHash).build()
.add("privacy_policy_accepted", EPOCH).property((e) -> e.ppAccepted).setDefault(() -> now()).build()
.add("tos_accepted", EPOCH).property((e) -> e.tosAccepted).setDefault(() -> now()).build()
.add("registration_date", EPOCH).property((e) -> e.registrationDate).setDefault(() -> now()).build()
.buildFor(Schema.MASTER);
public final Property<UUID> userID = new Property<>();
public final Property<String> username = new Property<>();
public final Property<String> email = new Property<>();
public final Property<String> passwordHash = new Property<>();
public final Property<Long> ppAccepted = new Property<>();
public final Property<Long> tosAccepted = new Property<>();
public final Property<Long> registrationDate = new Property<>();
public User() {
super(STRUCTURE);
}
public void hashAndSetPassword(String password) {
this.passwordHash.set(Argon2Factory.create(Argon2Types.ARGON2id).hash(3, 102800, 1, password.toCharArray()));
}
public boolean verifyPassword(String attempt) {
return Argon2Factory.create(Argon2Types.ARGON2id).verify(passwordHash.get(), attempt.toCharArray());
}
}
With each entity property using the following:
public class Property<T> {
private T currentValue;
public void set(T newValue) {
this.currentValue = newValue;
}
public T get() {
return this.currentValue;
}
#Override
public boolean equals(Object o) {
return Objects.equals(currentValue, o);
}
#Override
public int hashCode() {
return Objects.hashCode(currentValue);
}
#Override
public String toString() {
return String.valueOf(currentValue);
}
}
We can extend or modify this Properties class and make it do more useful stuff for us, like have it record an original value, provided on creation (pulled from a database) and allow it to self-report on whether the current value of the property differs from what it was originally. Useful for determining which columns need to be updated in a database.
Most notably, this eliminates the need to create getters and setters for every new property because the Property has that functionality already. Moreover, the getters/setters are able to be overridden per-property if additional logic is needed.
I naturally ended up using this design while aiming for a more broad goal of eliminating the use of reflection/annotation processors and other black magic from my web framework. However, I’m having difficulty finding it on the internet so that I might be able to research its potential deficiencies.

This kind of wrapper "variable" is used for Observable properties like StringProperty and such. Its primary use is to hold state and have change listeners, binding in general.
It is fruitfully used, like in JavaFX. And as you mentioned, in entity frameworks. But it definitely is stateful, non-functional, mutable.
A pattern name I cannot find, and I think the gang of 4 would haunt one, if calling this a pattern, other than State.

Credit to #Michael and #Kayaman for answering in the comments: This is not a known design pattern, contrary to my expectations.
In other words, there is not a name by which people generally know to refer to what I’m calling a "Property" nor the design I’m suggesting which assumes public getters and setters are desired and uses public final fields to expose a wrapper which provides them.
This is likely because, as Kayaman pointed out, it’s pretty heavy while being not terribly useful.

Coding style and organization

So I am currently making a airplane reservation system for a summer project to keep fresh with Java. With any reservation system its requiring a lot of classes and methods. Currently I'm working on importing the fleet.
My main method is acting like the chronological guide to my program.
public static void main(String[] args){
//start here
//accept passenger credentials
//place passenger in seat on plane
}
My question is a formatting problem. When I'm looking to start "making" my aircraft for my fleet. It goes a little like this.
//...
Airplane Boeing737 = new Airplane(seats[], nameOfAircraft);
This will put all values that i need to construct my airplane, obviously there are more variables for the airplane constructor.
My thought is to make a method in the Airplane class that will do this for me. but in order to do this i need to call a blank constructor for the other class (the one with my main method) to see it. I feel like this is horrible form for some reason. Is there a better way to do this?
Another thought as I'm posting is to modify the constructor to not accept any arguments and have that do everything in there. I feel like that's what I should be doing but I'm not 100% sure that would be the correct choice. I guess my overall question would be what are best practices in situations like this.

Use builder pattern, this will allow you:
dynamic way of building events
maintainable code (you can add more params when you want)
preserve integrity of the objects when created
Joshua Bloch's in Effective Java Chapter 1 Item 2 states:
Luckily, there is a third alternative that combines the safety of the telescoping
constructor pattern with the readability of the JavaBeans pattern. It is a form of the
Builder pattern. Instead of making the desired object directly,
the client calls a constructor (or static factory) with all of the required parameters and gets a builder object.
Modifying his example:
//Builder Pattern
public class Airplane {
private final int[] seats;
private final String name;
private final int maxSpeed;
private final int maxPassengers;
public static class Builder {
// Required parameters
private final int[] seats;
private final String name;
// Optional parameters - initialized to default values
private int maxSpeed = 1000;
private int maxPassengers = 150;
public Builder(int[] seats, String name) {
this.seats = seats;
this.name = name;
}
public Builder maxSpeed(int val) {
maxSpeed = val;
return this;
}
public Builder maxPassengers(int val) {
maxPassengers = val;
return this;
}
public Airplane build() {
return new Airplane(this);
}
}
private Airplane(Builder builder) {
seats = builder.seats;
name = builder.name;
maxSpeed = builder.maxSpeed;
maxPassengers = builder.maxPassengers;
}
}
Then you can create several different airplanes
public static void main(String[] args) {
// only mandatory params
Airplane boeing747 = new Airplane.Builder(new int[] {1,0,1}, "boeing747").build();
// just one param
Airplane boeing646 = new Airplane.Builder(new int[] {1,1,1}, "boeing646").maxPassengers(250).build();
// all params
Airplane fighter = new Airplane.Builder(new int[] {1,0,0}, "fighter_1").maxPassengers(3).maxSpeed(1600).build();
}

Forget the main method for now, you don't know if it will be a command line program, desktop app with a UI, web service or what. You don't know if it will be standalone or hosted in some framework or application server.
I would suggest starting with unit tests and drive the design of your domain model / business logic with TDD.
You don't want to see anything like Boeing737 hard coded like that. It will get its input from some other source, e.g. typed in, xml file, existing database, some other system.
You will then create instances of Airplane dynamically. You will pass something like a DTO from the UI or DB or XML parser to the constructor. There are other ways, look up Factory Pattern for example, but they tend to get overused IMHO.
You seem to be starting off in a way that doesn't match anything anyone does in the real world. Its hard to give any better advice.

Design patterns that can replace if statements

Our application is getting complex, it has mainly 3 flow and have to process based on one of the 3 type. Many of these functionalities overlap each other.
So currently code is fully of if-else statements, it is all messed up and not organised. How to make a pattern so that 3 flows are clearly separated from each other but making use of power of re-usability.
Please provide some thoughts, this is a MVC application, where we need to produce and consume web servicees using jaxb technology.
May be you can view the application as a single object as input on which different strategies needs to be implemented based on runtime value.

You did not specify what your if-else statements are doing. Say they filtering depending on some value.
If I understand your question correctly, you want to look at Factory Pattern.
This is a clean approach, easy to maintain and produces readable code. Adding or removing a Filter is also easy, Just remove the class and remove it from FilterFactory hashmap.
Create an Interface : Filter
public interface Filter {
void Filter();
}
Create a Factory which returns correct Filter according to your value. Instead of your if-else now you can just use the following :
Filter filter = FilterFactory.getFilter(value);
filter.filter();
One common way to write FilterFactory is using a HashMap inside it.
public class FilterFactory{
static HashMap<Integer, Filter> filterMap;
static{
filterMap = new HashMap<>();
filterMap.put(0,new Filter0());
...
}
// this function will change depending on your needs
public Filter getFilter(int value){
return filterMap.get(value);
}
}
Create your three(in your case) Filters like this: (With meaningful names though)
public class Filter0 implements Filter {
public void filter(){
//do something
}
}
NOTE: As you want to reuse some methods, create a FilterUtility class and make all your filters extend this class so that you can use all the functions without rewriting them.

Your question is very broad and almost impossible to answer without some description or overview of the structure of your application. However, I've been in a similar situation and this is the approach I took:
Replace conditions with Polymorphism where possible
it has mainly 3 flow and have to process based on this one of the 3
type. Many of these functionalities overlap each other.
You say your project has 3 main flows and that much of the code overlaps each other. This sounds to me like a strategy pattern:
You declare an interface that defines the tasks performed by a Flow.
public interface Flow{
public Data getData();
public Error validateData();
public void saveData();
public Error gotoNextStep();
}
You create an abstract class that provides implementation that is common to all 3 flows. (methods in this abstract class don't have to be final, but you definitely want to consider it carefully.)
public abstract class AbstractFlow{
private FlowManager flowManager
public AbstractFlow(FlowManager fm){
flowManager = fm;
}
public final void saveData(){
Data data = getData();
saveDataAsXMl(data);
}
public final Error gotoNextStep(){
Error error = validateData();
if(error != null){
return error;
}
saveData();
fm.gotoNextStep();
return null;
}
}
Finally, you create 3 concrete classes that extend from the abstract class and define concrete implementation for the given flow.
public class BankDetailsFlow extends AbstractFlow{
public BankDetailsData getData(){
BankDetailsData data = new BankDetailsData();
data.setSwiftCode(/*get swift code somehow*/);
return data;
}
public Error validateData(){
BankDetailsData data = getData();
return validate(data);
}
public void onFormSubmitted(){
Error error = gotoNextStep();
if(error != null){
handleError(error);
}
}
}

Lets take example, suppose you have model say "Data" [which has some attributes and getters,setters, optional methods].In context of Mobile application ,in particular Android application there can be two modes Off-line or On-line. If device is connected to network , data is sent to network else stored to local database of device.
In procedural way someone can , define two models as OnlineData,OfflineData and write code as[The code is not exact ,its just like pseudo code ]:
if(Connection.isConnected()){
OnlineData ond=new OnlineData();
ond.save();//save is called which stores data on server using HTTP.
}
else{
OfflineData ofd=new Onlinedata();
ofd.save();//save is called which stores data in local database
}
A good approach to implement this is using OOPS principles :
Program to interface not Implementation
Lets see How to DO THIS.
I am just writing code snippets that will be more effectively represent what I mean.The snippets are as follows:
public interface Model {
long save();//save method
//other methods .....
}
public class OnlineData extends Model {
//attributes
public long save(){
//on-line implementation of save method for Data model
}
//implementation of other methods.
}
public class OfflineData extends Model {
//attributes
public long save(){
//off-line implementation of save method for Data model
}
//implementation of other methods.
}
public class ObjectFactory{
public static Model getDataObject(){
if(Connection.isConnected())
return new OnlineData();
else
return new OfflineData();
}
}
and Here is code that your client class should use:
public class ClientClass{
public void someMethod(){
Model model=ObjectFactory.getDataObject();
model.save();// here polymorphism plays role...
}
}
Also this follows:
Single Responsibility Principle [SRP]
because On-line and Off-line are two different responsibilities which we can be able to integrate in Single save() using if-else statement.

After loong time I find opensource rule engine frameworks like "drools" is a great alternative to fit my requirement.

What is the difference between a Seam and a Mock?

Its being a few months since I am working with java legacy code, this are some of the things I am dealing with:
0% test coverage.
Huge functions in occasions I even saw some with more than 300 lines of code.
Lots of private methods and in occasions static methods.
Highly tight coupled code.
At the beginning I was very confused, I found difficult to use TDD in the legacy. After doing katas for weeks and practicing my unit testing and mocking skills, my fear has decreased and I feel a bit more confident. Recently I discovered a book called: working effectivelly with legacy, I didn't read it, I just had a look at the table of contents and I discovered something that is new for me, The Seams. Apparently this is very important when working in the legacy.
I think that this Seams could help me alot in breaking dependencies and make my code testeable so I can increase the code coverage and make my unit testing more precise.
But I have a lot of doubts:
Can somebody explain me the difference between a seam and a mock?
Do Seams, break TDD rules in what regards not touching production code, before is tested?
Could you show me some simple example that compares a Seam and a Mock?
Below I would like to paste an example I did today where I tried to break a dependency with the goal of making the code testeable and finally increasing test coverage. I would appreciate if you could comment a bit if you see some mistakes?
This is how the legacy code looked like at the beginning:
public class ABitOfLegacy
{
private String sampleTitle;
String output;
public void doSomeProcessing(HttpServletRequest request) {
String [] values = request.getParameterValues(sampleTitle);
if (values != null && values.length > 0)
{
output = sampleTitle + new Date().toString() + values[0];
}
}
}
If I just add a unit test that calls that method and asserts that variable output, has a certain value after the call,then I would be making a mistake, because I am not unit testing, I would be doing integration testing. So what I need to do, Is get rid of the dependency I have in the parameter. To do So, I replace the parameter with an interface:
public class ABitOfLegacy
{
private String sampleTitle;
String output;
public void doSomeProcessing(ParameterSource request) {
String [] values = request.getParameters(sampleTitle);
if (values != null && values.length > 0)
{
output = sampleTitle + new Date().toString() + values[0];
}
}
}
This is how the interface looks like:
public interface ParameterSource {
String[] getParameters(String name);
}
The next thing I do, is create my own implementation of that interface but I include the HttpServletRequest as a global variable and I implement the method of the interface using the method/s of HttpServletRequest:
public class HttpServletRequestParameterSource implements ParameterSource {
private HttpServletRequest request;
public HttpServletRequestParameterSource(HttpServletRequest request) {
this.request = request;
}
public String[] getParameters(String name) {
return request.getParameterValues(name);
}
}
Until this point, I think that all the modifications on the production code were safe.
Now I create the Seam in my test package. If I understood well, now I am able to safely change the behavoir of the Seam. This is how I do it:
public class FakeParameterSource implements ParameterSource {
public String[] values = {"ParamA","ParamB","ParamC"};
public String[] getParameters(String name) {
return values;
}
}
And the final step, would be to get support from the Seam, to test the original behavoir of the method.
import org.junit.Before;
import org.junit.Test;
import static org.junit.Assert.*;
import static org.mockito.Mockito.*;
import code.ABitOfLegacyRefactored;
import static org.hamcrest.Matchers.*;
public class ABitOfLegacySpecification {
private ABitOfLegacy aBitOfLegacy;
private String EMPTY = null;
#Before
public void initialize() {
aBitOfLegacy = new ABitOfLegacy();
}
#Test
public void
the_output_gets_populated_when_the_request_is_not_empty
() {
FakeParameterSource fakeParameterSource = new FakeParameterSource();
aBitOfLegacy.doSomeProcessing(fakeParameterSource);
assertThat(aBitOfLegacy.output,not(EMPTY));
}
#Test(expected=NullPointerException.class)
public void
should_throw_an_exception_if_the_request_is_null
() {
aBitOfLegacy.doSomeProcessing(null);
}
}
This will give me 100% test coverage.
I appreciate your thoughts:
Did I break the dependency correctly?
Are the unit tests missing something?
What could be done better?
Is this example good enough to help me understand the difference between a Seam and a Mock?
How could a mock help me here if I don't use the Seam?

A seam is a place in the code that you can insert a modification in behavior. You created a seam when you setup injection of your dependency.
One way to take advantage of a seam is to insert some sort of fake. Fake's can be hand-rolled, as in your example, or be created with a tool, like Mockito.
So, a mock is a type of fake, and a fake is often used by taking advantage of a Seam.
As for your tests and the way you broke the dependency, that's pretty much how I would have done it.

Seams
A seam is a place that allows you to modify the behavior without modifying the code.
In your example, the following is an example of an Object seam (if i'm not mistaken). It allows you to pass in a different object without having to change the code. hence it is a type of seam.
public void doSomeProcessing(ParameterSource request) {..}
By making the parameter an abstract type (instead of a concrete class), you have introduced a seam. The seam now allows you to modify the behavior of the method without editing its code - i.e. at the place of invokation, I can pass in a different object and make the method do something else.
Mocks
Now instead of creating your custom fake (creating a subtype of the interface), you could using a Mock framework to do something like this
Mocks also support asserting whether specific methods were called on it, argument matching and other nifty functionality to be consumed by tests. Less test code to maintain. Mocks are primarily used to assert that a specific call is being made to a dependency. In your example, you seem to be in need of a Stub, you just want to return a canned value.
Pardon my rusty JMock..
#Test
public void
the_output_does_not_get_populated_when_the_request_is_empty
() {
Mockery context = new Mockery();
final ParameterSource mockSource = context.mock(ParameterSource.class)
context.checking(new Expectations(){{
oneOf(mockSource).getParameters();
will(returnValue(new string[]{"ParamA","ParamB","ParamC"} );
}});
aBitOfLegacy.populate(mockSource);
assertThat(aBitOfLegacy.output,not(EMPTY));
}
in .Net
var mockSource = new Mock<ParameterSource>();
mockSource.Setup(src => src.GetParameters())
.Returns(new []{"ParamA","ParamB","ParamC"});

When would you use the Builder Pattern? [closed]

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What are some common, real world examples of using the Builder Pattern? What does it buy you? Why not just use a Factory Pattern?

Below are some reasons arguing for the use of the pattern and example code in Java, but it is an implementation of the Builder Pattern covered by the Gang of Four in Design Patterns. The reasons you would use it in Java are also applicable to other programming languages as well.
As Joshua Bloch states in Effective Java, 2nd Edition:
The builder pattern is a good choice when designing classes whose constructors or static factories would have more than a handful of parameters.
We've all at some point encountered a class with a list of constructors where each addition adds a new option parameter:
Pizza(int size) { ... }
Pizza(int size, boolean cheese) { ... }
Pizza(int size, boolean cheese, boolean pepperoni) { ... }
Pizza(int size, boolean cheese, boolean pepperoni, boolean bacon) { ... }
This is called the Telescoping Constructor Pattern. The problem with this pattern is that once constructors are 4 or 5 parameters long it becomes difficult to remember the required order of the parameters as well as what particular constructor you might want in a given situation.
One alternative you have to the Telescoping Constructor Pattern is the JavaBean Pattern where you call a constructor with the mandatory parameters and then call any optional setters after:
Pizza pizza = new Pizza(12);
pizza.setCheese(true);
pizza.setPepperoni(true);
pizza.setBacon(true);
The problem here is that because the object is created over several calls it may be in an inconsistent state partway through its construction. This also requires a lot of extra effort to ensure thread safety.
The better alternative is to use the Builder Pattern.
public class Pizza {
private int size;
private boolean cheese;
private boolean pepperoni;
private boolean bacon;
public static class Builder {
//required
private final int size;
//optional
private boolean cheese = false;
private boolean pepperoni = false;
private boolean bacon = false;
public Builder(int size) {
this.size = size;
}
public Builder cheese(boolean value) {
cheese = value;
return this;
}
public Builder pepperoni(boolean value) {
pepperoni = value;
return this;
}
public Builder bacon(boolean value) {
bacon = value;
return this;
}
public Pizza build() {
return new Pizza(this);
}
}
private Pizza(Builder builder) {
size = builder.size;
cheese = builder.cheese;
pepperoni = builder.pepperoni;
bacon = builder.bacon;
}
}
Note that Pizza is immutable and that parameter values are all in a single location. Because the Builder's setter methods return the Builder object they are able to be chained.
Pizza pizza = new Pizza.Builder(12)
.cheese(true)
.pepperoni(true)
.bacon(true)
.build();
This results in code that is easy to write and very easy to read and understand. In this example, the build method could be modified to check parameters after they have been copied from the builder to the Pizza object and throw an IllegalStateException if an invalid parameter value has been supplied. This pattern is flexible and it is easy to add more parameters to it in the future. It is really only useful if you are going to have more than 4 or 5 parameters for a constructor. That said, it might be worthwhile in the first place if you suspect you may be adding more parameters in the future.
I have borrowed heavily on this topic from the book Effective Java, 2nd Edition by Joshua Bloch. To learn more about this pattern and other effective Java practices I highly recommend it.

Consider a restaurant. The creation of "today's meal" is a factory pattern, because you tell the kitchen "get me today's meal" and the kitchen (factory) decides what object to generate, based on hidden criteria.
The builder appears if you order a custom pizza. In this case, the waiter tells the chef (builder) "I need a pizza; add cheese, onions and bacon to it!" Thus, the builder exposes the attributes the generated object should have, but hides how to set them.

The key difference between a builder and factory IMHO, is that a builder is useful when you need to do lots of things to build an object. For example imagine a DOM. You have to create plenty of nodes and attributes to get your final object. A factory is used when the factory can easily create the entire object within one method call.
One example of using a builder is a building an XML document, I've used this model when building HTML fragments for example I might have a Builder for building a specific type of table and it might have the following methods (parameters are not shown):
BuildOrderHeaderRow()
BuildLineItemSubHeaderRow()
BuildOrderRow()
BuildLineItemSubRow()
This builder would then spit out the HTML for me. This is much easier to read than walking through a large procedural method.
Check out Builder Pattern on Wikipedia.

.NET StringBuilder class is a great example of builder pattern. It is mostly used to create a string in a series of steps. The final result you get on doing ToString() is always a string but the creation of that string varies according to what functions in the StringBuilder class were used. To sum up, the basic idea is to build complex objects and hide the implementation details of how it is being built.

I always disliked the Builder pattern as something unwieldy, obtrusive and very often abused by less experienced programmers. Its a pattern which only makes sense if you need to assemble the object from some data which requires a post-initialisation step (i.e. once all the data is collected - do something with it). Instead, in 99% of the time builders are simply used to initialise the class members.
In such cases it is far better to simply declare withXyz(...) type setters inside the class and make them return a reference to itself.
Consider this:
public class Complex {
private String first;
private String second;
private String third;
public String getFirst(){
return first;
}
public void setFirst(String first){
this.first=first;
}
...
public Complex withFirst(String first){
this.first=first;
return this;
}
public Complex withSecond(String second){
this.second=second;
return this;
}
public Complex withThird(String third){
this.third=third;
return this;
}
}
Complex complex = new Complex()
.withFirst("first value")
.withSecond("second value")
.withThird("third value");
Now we have a neat single class that manages its own initialization and does pretty much the same job as the builder, except that its far more elegant.

For a multi-threaded problem, we needed a complex object to be built up for each thread. The object represented the data being processed, and could change depending on the user input.
Could we use a factory instead? Yes
Why didn't we? Builder makes more sense I guess.
Factories are used for creating different types of objects that are the same basic type (implement the same interface or base class).
Builders build the same type of object over and over, but the construction is dynamic so it can be changed at runtime.

You use it when you have lots of options to deal with. Think about things like jmock:
m.expects(once())
.method("testMethod")
.with(eq(1), eq(2))
.returns("someResponse");
It feels a lot more natural and is...possible.
There's also xml building, string building and many other things. Imagine if java.util.Map had put as a builder. You could do stuff like this:
Map<String, Integer> m = new HashMap<String, Integer>()
.put("a", 1)
.put("b", 2)
.put("c", 3);

While going through Microsoft MVC framework, I got a thought about builder pattern. I came across the pattern in the ControllerBuilder class. This class is to return the controller factory class, which is then used to build concrete controller.
Advantage I see in using builder pattern is that, you can create a factory of your own and plug it into the framework.
#Tetha, there can be a restaurant (Framework) run by Italian guy, that serves Pizza. In order to prepare pizza Italian guy (Object Builder) uses Owen (Factory) with a pizza base (base class).
Now Indian guy takes over the restaurant from Italian guy. Indian restaurant (Framework) servers dosa instead of pizza. In order to prepare dosa Indian guy (object builder) uses Frying Pan (Factory) with a Maida (base class)
If you look at scenario, food is different,way food is prepared is different, but in the same restaurant (under same framework). Restaurant should be build in such a way that it can support Chinese, Mexican or any cuisine. Object builder inside framework facilitates to plugin kind of cuisine you want. for example
class RestaurantObjectBuilder
{
IFactory _factory = new DefaultFoodFactory();
//This can be used when you want to plugin the
public void SetFoodFactory(IFactory customFactory)
{
_factory = customFactory;
}
public IFactory GetFoodFactory()
{
return _factory;
}
}

Building on the previous answers (pun intended), an excellent real-world example is Groovy's built in support for Builders.
Creating XML using Groovy's MarkupBuilder
Creating XML using Groovy's StreamingMarkupBuilder
Swing Builder
SwingXBuilder
See Builders in the Groovy Documentation

Another advantage of the builder is that if you have a Factory, there is still some coupling in you code, because for the Factory to work, it has to know all the objects it can possibly create. If you add another object that could be created, you will have to modify the factory class to include him. This happens in the Abstract Factory as well.
With the builder, on the other hand, you just have to create a new concrete builder for this new class. The director class will stay the same, because it receives the builder in the constructor.
Also, there are many flavors of builder. Kamikaze Mercenary`s gives another one.

/// <summary>
/// Builder
/// </summary>
public interface IWebRequestBuilder
{
IWebRequestBuilder BuildHost(string host);
IWebRequestBuilder BuildPort(int port);
IWebRequestBuilder BuildPath(string path);
IWebRequestBuilder BuildQuery(string query);
IWebRequestBuilder BuildScheme(string scheme);
IWebRequestBuilder BuildTimeout(int timeout);
WebRequest Build();
}
/// <summary>
/// ConcreteBuilder #1
/// </summary>
public class HttpWebRequestBuilder : IWebRequestBuilder
{
private string _host;
private string _path = string.Empty;
private string _query = string.Empty;
private string _scheme = "http";
private int _port = 80;
private int _timeout = -1;
public IWebRequestBuilder BuildHost(string host)
{
_host = host;
return this;
}
public IWebRequestBuilder BuildPort(int port)
{
_port = port;
return this;
}
public IWebRequestBuilder BuildPath(string path)
{
_path = path;
return this;
}
public IWebRequestBuilder BuildQuery(string query)
{
_query = query;
return this;
}
public IWebRequestBuilder BuildScheme(string scheme)
{
_scheme = scheme;
return this;
}
public IWebRequestBuilder BuildTimeout(int timeout)
{
_timeout = timeout;
return this;
}
protected virtual void BeforeBuild(HttpWebRequest httpWebRequest) {
}
public WebRequest Build()
{
var uri = _scheme + "://" + _host + ":" + _port + "/" + _path + "?" + _query;
var httpWebRequest = WebRequest.CreateHttp(uri);
httpWebRequest.Timeout = _timeout;
BeforeBuild(httpWebRequest);
return httpWebRequest;
}
}
/// <summary>
/// ConcreteBuilder #2
/// </summary>
public class ProxyHttpWebRequestBuilder : HttpWebRequestBuilder
{
private string _proxy = null;
public ProxyHttpWebRequestBuilder(string proxy)
{
_proxy = proxy;
}
protected override void BeforeBuild(HttpWebRequest httpWebRequest)
{
httpWebRequest.Proxy = new WebProxy(_proxy);
}
}
/// <summary>
/// Director
/// </summary>
public class SearchRequest
{
private IWebRequestBuilder _requestBuilder;
public SearchRequest(IWebRequestBuilder requestBuilder)
{
_requestBuilder = requestBuilder;
}
public WebRequest Construct(string searchQuery)
{
return _requestBuilder
.BuildHost("ajax.googleapis.com")
.BuildPort(80)
.BuildPath("ajax/services/search/web")
.BuildQuery("v=1.0&q=" + HttpUtility.UrlEncode(searchQuery))
.BuildScheme("http")
.BuildTimeout(-1)
.Build();
}
public string GetResults(string searchQuery) {
var request = Construct(searchQuery);
var resp = request.GetResponse();
using (StreamReader stream = new StreamReader(resp.GetResponseStream()))
{
return stream.ReadToEnd();
}
}
}
class Program
{
/// <summary>
/// Inside both requests the same SearchRequest.Construct(string) method is used.
/// But finally different HttpWebRequest objects are built.
/// </summary>
static void Main(string[] args)
{
var request1 = new SearchRequest(new HttpWebRequestBuilder());
var results1 = request1.GetResults("IBM");
Console.WriteLine(results1);
var request2 = new SearchRequest(new ProxyHttpWebRequestBuilder("localhost:80"));
var results2 = request2.GetResults("IBM");
Console.WriteLine(results2);
}
}

I used builder in home-grown messaging library. The library core was receiving data from the wire, collecting it with Builder instance, then, once Builder decided it've got everything it needed to create a Message instance, Builder.GetMessage() was constructing a message instance using the data collected from the wire.

When I wanted to use the standard XMLGregorianCalendar for my XML to object marshalling of DateTime in Java, I heard a lot of comments on how heavy weight and cumbersome it was to use it. I was trying to comtrol the XML fields in the xs:datetime structs to manage timezone, milliseconds, etc.
So I designed a utility to build an XMLGregorian calendar from a GregorianCalendar or java.util.Date.
Because of where I work I'm not allowed to share it online without legal, but here's an example of how a client uses it. It abstracts the details and filters some of the implementation of XMLGregorianCalendar that are less used for xs:datetime.
XMLGregorianCalendarBuilder builder = XMLGregorianCalendarBuilder.newInstance(jdkDate);
XMLGregorianCalendar xmlCalendar = builder.excludeMillis().excludeOffset().build();
Granted this pattern is more of a filter as it sets fields in the xmlCalendar as undefined so they are excluded, it still "builds" it. I've easily added other options to the builder to create an xs:date, and xs:time struct and also to manipulate timezone offsets when needed.
If you've ever seen code that creates and uses XMLGregorianCalendar, you would see how this made it much easier to manipulate.