Imagine there are 2 micro-services built using Spring-Boot and secured using Keycloak (OpenID + OAuth 2.0 compliant Authx Server).
from Pocket https://ift.tt/3ch0PyF
via IFTTT
7 Reasons Why JavaScript Async/Await Is Better Than Plain Promises (Tutorial)
Async/await was introduced in NodeJS 7.6 and is currently supported in all modern browsers. I believe it has been the single greatest addition to JS since 2017. If you are not convinced, here are a bunch of reasons with examples why you should adopt it immediately and never look back.
from Pocket https://ift.tt/2LNB5jo
via IFTTT
openCV – Android app
This a post from a guy that have just used openCV libraries directly on Android. Brilliant! Thank you for your post, Elvis Chidera
For those who doesn’t know what openCV is or what is it for, openCV is the most popular opensource library that allows you to manipulate images, like identifying objects and so on.
If you need that on your android app, take a look on this post.
Java 8 – Some of the new features
In this post, some of the new features of JAVA 8…
|
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 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 |
package pt.joaobrito.java8; import java.time.Duration; import java.time.Instant; import java.time.LocalDate; import java.time.Month; import java.time.Period; import java.util.ArrayList; import java.util.Arrays; import java.util.Comparator; import java.util.List; import java.util.Optional; public class Main { public static void main(String[] args) throws InterruptedException { // simple lambda example print("Hello Lambda", s -> s.length()); // another lambda example new Thread(() -> System.out.println("Hello Runnable")).start(); List<Person> people = new ArrayList<>(Arrays.asList( new Person("John Doe", LocalDate.of(1978, Month.JUNE, 14)), new Person("Jane Doe", LocalDate.of(1983, Month.FEBRUARY, 16)), new Person("Steven Smith", LocalDate.of(2008, Month.SEPTEMBER, 23)), new Person("Martin", LocalDate.of(2010, Month.NOVEMBER, 27)), new Person("Mike", LocalDate.of(2012, Month.NOVEMBER, 3)), new Person("Louis", LocalDate.of(2014, Month.NOVEMBER, 6)), new Person("Mary", LocalDate.of(2016, Month.FEBRUARY, 16)) )); System.out.println("---- All people sorted by name -----"); people.sort((p1, p2) -> p1.getName().compareTo(p2.getName())); people.forEach(p -> System.out.println(p.getName())); System.out.println("---- All people -----"); people = new ArrayList<>(Arrays.asList( new Person("John Doe", LocalDate.of(1978, Month.JUNE, 14)), new Person("Jane Doe", LocalDate.of(1983, Month.FEBRUARY, 16)), new Person("Steven Smith", LocalDate.of(2008, Month.SEPTEMBER, 23)), new Person("Martin", LocalDate.of(2010, Month.NOVEMBER, 27)), new Person("Mike", LocalDate.of(2012, Month.NOVEMBER, 3)), new Person("Louis", LocalDate.of(2014, Month.NOVEMBER, 6)), new Person("Mary", LocalDate.of(2016, Month.FEBRUARY, 16)) )); people.stream().map(Person::getName).forEach(System.out::println); // using method reference System.out.println("---- People older than 9 yrs -----"); people .stream() // convert to stream .filter(p -> Period.between(p.getDob(), LocalDate.now()).getYears() > 9) // get only the people thaht matches the given condition .map(Person::getName) // get a new stream with only the names => returns Stream<String> .forEach(System.out::println); // iterates the entire stream and prints out each element System.out.println("---- Remove items from list -----"); people.removeIf(i -> i.getAge() < 2); // remove if the given condition is true people. stream() .map(Person::getName) .sorted(Comparator.reverseOrder()) // order the list in reverse order .forEach(System.out::println); // calculate time between two dates LocalDate dob = LocalDate.of(1978, 6, 14); LocalDate now = LocalDate.now(); Period p = Period.between(dob, now); System.out.println("Priod of " + p.getYears() + " years; " + p.getMonths() + " months, " + p.getDays() + " days."); // calculate time between two instants Instant start = Instant.now(); Thread.sleep(1000); Instant end = Instant.now(); System.out.println("The time is... " + Duration.between(start, end).toMillis()); // Optional<T> Optional<String> opt = Optional.ofNullable("some string"); // not null value System.out.println(opt.orElse("or else")); opt.orElseThrow(UnsupportedOperationException::new); opt = Optional.ofNullable(null); // notice that here we pass a null value System.out.println(opt.orElse("or else")); opt.orElseThrow(UnsupportedOperationException::new); } public static void print(String s, MyLambda l) { System.out.println(l.getLength(s)); } } @FunctionalInterface interface MyLambda { int getLength(String s); } |
|
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 |
package pt.joaobrito.java8; import java.time.LocalDate; import java.time.Period; public class Person { private String name; private LocalDate dob; public Person(String name, LocalDate dob) { this.name = name; this.dob = dob; } public String getName() { return name; } public void setName(String name) { this.name = name; } public LocalDate getDob() { return dob; } public void setDob(LocalDate dob) { this.dob = dob; } public int getAge(){ return Period.between(dob, LocalDate.now()).getYears(); } } |
…and here are the results from running the file above
|
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 42 43 44 45 46 47 48 |
------------------------------------------------------------------------ Building Java8 0.0.1-SNAPSHOT ------------------------------------------------------------------------ --- exec-maven-plugin:1.2.1:exec (default-cli) @ Java8 --- 12 Hello Runnable ---- All people sorted by name ----- Jane Doe John Doe Louis Martin Mary Mike Steven Smith ---- All people ----- John Doe Jane Doe Steven Smith Martin Mike Louis Mary ---- People older than 9 yrs ----- John Doe Jane Doe ---- Remove items from list ----- Steven Smith Mike Mary Martin Louis John Doe Jane Doe Priod of 39 years; 9 months, 9 days. The time is... 1014 some string or else Exception in thread "main" java.lang.UnsupportedOperationException at java.util.Optional.orElseThrow(Optional.java:290) at pt.joaobrito.java8.Main.main(Main.java:83) ------------------------------------------------------------------------ BUILD FAILURE ------------------------------------------------------------------------ Total time: 1.649 s Finished at: 2018-03-23T00:07:33+00:00 Final Memory: 8M/309M ------------------------------------------------------------------------ |
Note that the build fails because we pass null to the Optional and we have a condition to throw an exception if null is passed to it (this is the reason why this line is the last statement of this example).
Thank you! 🙂
Design Pattern: Command and State together
In this article we will explain two JAVA design patterns:
Command and State.
In the main method we:
- first create the light object (aka receiver);
- then we check if the light is on or off;
- after that we create a light command passing to it the light we’ve just created;
- then we create a Remote Control and set the command into it;
- in the next step we press the button and we check the light state;
- finally, we repeat the process and check the light state again.
So lets start with the code:
Here we have the client class (the one that have the main 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 |
package pt.joaobrito.client; import pt.joaobrito.command.Command; import pt.joaobrito.command.LightCommand; import pt.joaobrito.command.invoker.RemoteControl; import pt.joaobrito.state.receiver.Light; /** * The client object */ public class Client { public static void main(String[] args) { // receiver Light light = new Light(); // prints to the console the current state of the light System.out.println("1st state - the light is " + (light.getCurrentState().isOn() ? "ON" : "OFF")); Command lightsCmd = new LightCommand(light); //invoker RemoteControl remoteControl = new RemoteControl(); remoteControl.setCommand(lightsCmd); //switch on remoteControl.pressButton(); System.out.println("2nd state - the light is " + (light.getCurrentState().isOn() ? "ON" : "OFF")); //switch off remoteControl.pressButton(); System.out.println("3rd state - the light is " + (light.getCurrentState().isOn() ? "ON" : "OFF")); } } |
The Command Design Pattern implementation
Here we define our Command interface
|
1 2 3 4 5 |
package pt.joaobrito.command; public interface Command { public void execute(); } |
This is the remote control class.
Note that in the pressButton method we actually execute the Command passed previously in the set method. Notice that this class has no knowledge at all about the receiver. Instead it just knows that it has a Command and how to interact with it.
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 |
package pt.joaobrito.command.invoker; import pt.joaobrito.command.Command; /** * Invoker */ public class RemoteControl { private Command command; public void setCommand(Command command) { this.command = command; } public void pressButton() { command.execute(); } } |
Here we have the concrete light command (the implementation of the Command interface). In the execute method we specify what the command really does: in this case with the help of the State Design Pattern we are simply saying to the light to go to the next state.
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 |
package pt.joaobrito.command; import pt.joaobrito.state.receiver.Light; /** * Concrete Command: light command */ public class LightCommand implements Command { //reference to the light private Light light; public LightCommand(Light light) { this.light = light; } public void execute() { light.switchToNextState(); } } |
The next section is the State Design Pattern part
This is the Light class. From the Command point of view this is the receiver and from the point of view of the state design pattern this is the object that keeps the current state of the light (also known as a wrapper that will be passed to the concrete states).
|
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 |
package pt.joaobrito.state.receiver; /** * This class is responsible to keep the state of the light */ public class Light { private State currentState; public Light() { // 1st state of light currentState = new LightOff(); } public State getCurrentState() { return currentState; } public void setState(State state) { currentState = state; } /** * light switch */ public void switchToNextState() { currentState.next(this); } } |
This is the state interface. Notice that here we have two methods that have to be implemented by the classes that implement the state interface.
|
1 2 3 4 5 6 |
package pt.joaobrito.state.receiver; public interface State { void next(Light wrapper); boolean isOn(); } |
The next class represents one of the possible state of the light (the concrete state that represents the ON state of the light)
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 |
package pt.joaobrito.state.receiver; /** * Receiver */ public class LightOn implements State{ @Override public void next(Light wrapper) { wrapper.setState(new LightOff()); } @Override public boolean isOn() { return true; } } |
This is the other possible state (the concrete state that represents the OFF state of the light)
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 |
package pt.joaobrito.state.receiver; /** * Receiver */ public class LightOff implements State{ @Override public void next(Light wrapper) { wrapper.setState(new LightOn()); } @Override public boolean isOn() { return false; } } |
And the results:
|
1 2 3 4 5 |
run: 1st state - the light is OFF 2nd state - the light is ON 3rd state - the light is OFF BUILD SUCCESSFUL (total time: 0 seconds) |
And that’s it. Feel free to comment.
Thank you!
Git Merge vs. Rebase: What’s the Diff?
Those who have eaten a chunk of wasabi thinking it was a chunk of avocado have learned the importance of distinguishing between two very similar things.
from Pocket https://ift.tt/2xIvCCd
via IFTTT
Working with nested Maps in JAVA
In this post I will show you a simple and easy way of working with JAVA Maps, more precisely, how to add an element (a.k.a value) to a multi nested maps:
|
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 |
public void addElementToMap(Map<Long, Map<String, Map<Short, List<SomeDto>>>> map, SomeDto dto) { // get the first inner map Map<String, Map<Short, List<SomeDto>>> someMap = map.get(dto.gePrimaryKey()); if(someMap == null){ someMap = new HashMap<>(); map.put(dto.gePrimaryKey(), someMap); } // get the second inner map Map<Short, List<SomeDto>> otherMap = someMap.get(dto.getSomeId()); if(otherMap == null){ otherMap = new HashMap<>(); someMap.put(dto.getSomeId(), otherMap); } // get the inner list List<SomeDto> someList = otherMap.get(dto.getOtherId()); if(someList == null){ someList = new ArrayList<>(); otherMap.put(dto.getOtherId()), someList); } // add dto to the list someList.add(dto); } |
That’s it. Simple, isn’t it? 😉
Source code: github
Git Workflow
Here is just an example (and suggestion) of git workflow best practices.
You can learn more about git here at Atlassian git tutorial website.
SQL JOINS
Builder Design Pattern
Here is the “usual” implementation of this design pattern.
|
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 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 |
package pt.joaobrito.builder; /** * This is the main class */ public class BuilderExample { public static void main(String[] args) { Vehicle v1 = new Client(new CarBuilder()).constructVehicle(); System.out.println(v1); Vehicle v2 = new Client(new BikeBuilder()).constructVehicle(); System.out.println(v2); Vehicle v3 = new Client(new CarBuilder()).constructVehicleWithoutWindowsOrSeats(); System.out.println(v3); Vehicle v4 = new Client(new BikeBuilder()).constructVehicleWithoutWindowsOrSeats(); System.out.println(v4); } } /** * The Client class has the responsability of building the vehicles */ class Client { private final VehicleBuilder vehicleBuilder; public Client(VehicleBuilder vehicleBuilder) { this.vehicleBuilder = vehicleBuilder; } /** * Builds a complete vehicle * @return a vehicle */ public Vehicle constructVehicle() { return vehicleBuilder.buildType().buildSeats().buildWindows().get(); } /** * Builds a vehicle without parts * @return a vehicle */ public Vehicle constructVehicleWithoutWindowsOrSeats() { return vehicleBuilder.buildType().get(); } } /** * This class is the abstract builder */ abstract class VehicleBuilder { protected Vehicle vehicle; public VehicleBuilder() { this.vehicle = new Vehicle(); } /** * Vehicle get method * @return the vehicle */ public Vehicle get() { return vehicle; } /** * The 3 following lines are the methods that must be implemented on the concrete builders * @return */ public abstract VehicleBuilder buildType(); public abstract VehicleBuilder buildSeats(); public abstract VehicleBuilder buildWindows(); } /** * This is a concrete builder for Bikes */ class BikeBuilder extends VehicleBuilder { @Override public VehicleBuilder buildType() { vehicle.setType("Bike"); return this; } @Override public VehicleBuilder buildWindows() { vehicle.setWindows(0); return this; } @Override public VehicleBuilder buildSeats() { vehicle.setSeats(2); return this; } } /** * This is the concrete builder for Cars */ class CarBuilder extends VehicleBuilder { @Override public VehicleBuilder buildType() { vehicle.setType("Car"); return this; } @Override public VehicleBuilder buildSeats() { vehicle.setSeats(5); return this; } @Override public VehicleBuilder buildWindows() { vehicle.setWindows(4); return this; } } /** * This is the vehicle class */ class Vehicle { private String type; private int seats; private int windows; public void setType(String type) { this.type = type; } public void setSeats(int seats) { this.seats = seats; } public void setWindows(int windows) { this.windows = windows; } /** * @return a printable vehicle */ @Override public String toString() { return "Vehicle[Type: " + type + "; Seats: " + seats + "; Windows: " + windows + "]"; } } |
The result is:
UML
