Adds DI and SPI examples

spi/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xmlns="http://maven.apache.org/POM/4.0.0"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <parent>
+        <groupId>fr.gasser</groupId>
+        <artifactId>java-cookbook</artifactId>
+        <version>1.0-SNAPSHOT</version>
+    </parent>
+
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>spi</artifactId>
+
+</project>

spi/src/main/java/ovh/gasser/spi/CommandProvider.java

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+package ovh.gasser.spi;
+
+import ovh.gasser.spi.commands.Command;
+
+import java.util.Optional;
+import java.util.ServiceLoader;
+import java.util.stream.Stream;
+
+public class CommandProvider {
+    private static CommandProvider instance = new CommandProvider();
+
+    private final ServiceLoader<Command> loader;
+
+    private CommandProvider() {
+        loader = ServiceLoader.load(Command.class);
+    }
+
+    public static CommandProvider getInstance() {
+        return instance;
+    }
+
+    public Stream<Command> getCommands() {
+        return loader.stream().map(ServiceLoader.Provider::get);
+    }
+
+    public Optional<Command> getCommand(String commandId) {
+        return loader.stream()
+                .filter(commandProvider -> commandProvider.get().getId().equalsIgnoreCase(commandId))
+                .findFirst()
+                .map(ServiceLoader.Provider::get);
+    }
+}

spi/src/main/java/ovh/gasser/spi/Main.java

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+package ovh.gasser.spi;
+
+public class Main {
+    public static void main(String[] args) {
+        CommandProvider commandProvider = CommandProvider.getInstance();
+        // Execute all commands
+        commandProvider.getCommands()
+                .forEach(command -> System.out.println(command.execute("Hello")));
+
+        // Execute command with specific ID
+        String result = commandProvider.getCommand("reverse")
+                .map(command -> command.execute("Reverse command"))
+                .orElse("Unknown command");
+        System.out.println(result);
+    }
+}

spi/src/main/java/ovh/gasser/spi/commands/Command.java

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+package ovh.gasser.spi.commands;
+
+public interface Command {
+    String getId();
+
+    String execute(String input);
+}

spi/src/main/java/ovh/gasser/spi/commands/EchoCommand.java

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+package ovh.gasser.spi.commands;
+
+public class EchoCommand implements Command {
+
+    private static final String COMMAND_NAME = "echo";
+
+    public String getId() {
+        return COMMAND_NAME;
+    }
+
+    public String execute(String input) {
+        return input;
+    }
+}

spi/src/main/java/ovh/gasser/spi/commands/ReverseCommand.java

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+package ovh.gasser.spi.commands;
+
+public class ReverseCommand implements Command {
+
+    private static final String COMMAND_NAME = "reverse";
+
+    @Override
+    public String getId() {
+        return COMMAND_NAME;
+    }
+
+    @Override
+    public String execute(String input) {
+        return new StringBuilder(input).reverse().toString();
+    }
+}

spi/src/main/java/ovh/gasser/spi/commands/UpperCommand.java

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+package ovh.gasser.spi.commands;
+
+public class UpperCommand implements Command {
+
+    private static final String COMMAND_NAME = "upper";
+
+    @Override
+    public String getId() {
+        return COMMAND_NAME;
+    }
+
+    @Override
+    public String execute(String input) {
+        return input.toUpperCase();
+    }
+}

spi/src/main/resources/META-INF/services/ovh.gasser.spi.commands.Command

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+ovh.gasser.spi.commands.EchoCommand
+ovh.gasser.spi.commands.UpperCommand
+ovh.gasser.spi.commands.ReverseCommand